WO2006090356A1

WO2006090356A1 - Add-on laser gated imaging device for associating with an optical assembly

Info

Publication number: WO2006090356A1
Application number: PCT/IL2005/001257
Authority: WO
Inventors: Eyal Zohar; Ofer David
Original assignee: Elbit Systems Ltd.
Priority date: 2005-02-23
Filing date: 2005-11-24
Publication date: 2006-08-31

Abstract

System for producing a target image of a target, according to target light beams received from the target through an optical assembly, the system being optically coupled with the optical assembly, the system including an adapter for mechanically and optically coupling the system with an eyepiece of the optical assembly, a first laser source for illuminating the target by laser pulses, a gated light intensifier optically coupled with the optical assembly by the adapter, a controller electrically coupled with the first laser source and with the gated light intensifier, and a relay lens assembly located between the adapter and the gated light intensifier, the controller controlling the pulsed operation of the first laser source, and enabling the gated light intensifier to intensify substantially exclusively, reflections of the laser pulses from the target, which correspond to a range between a front portion and a rear portion of the target, about the location of the target relative to the system, the relay lens assembly projecting the target image on the gated light intensifier.

Description

ADD-ON LASER GATED IMAGING DEVICE FOR ASSOCIATING WITH

AN OPTICAL ASSEMBLY

FIELD OF THE DISCLOSED TECHNIQUE The disclosed technique relates to optical observation systems in general, and to a method and system for imaging using the principle of gated imaging, in particular.

BACKGROUND OF THE DISCLOSED TECHNIQUE Target detection and identification using an imaging system that includes a camera having a long focal lens is known in the art. Long focal lenses have limited light collecting capability due to volume, weight and cost constraints. During poor visibility conditions, the low intensity of the background light results in low quality image resolution. The camera cannot produce an image with an adequate signal-to-noise ratio, to exploit the total resolution capability of the camera and discern fine details of the target for identification purposes. Therefore, when imaging during night or poor visibility conditions, such cameras require an auxiliary light source to illuminate the target and improve the quality of the captured image (i.e., operating in an active mode). The auxiliary light source may be a laser device capable of producing a light beam that is parallel to the line-of-sight (LOS) of the camera, and that illuminates the field-of-view (FOV) of the camera or a part thereof. Television systems utilize such illumination for adequate imaging. The active mode of operation can include a radar detection system operating in the infrared (IR) region. Operation in the passive mode are also known in the art (i.e., gated intensification of the ambient light). In the passive mode either a charge-coupled device (CCD) or a forward looking infrared radiometer (FLIR) is utilized. An inherent problem in optical observation systems is the effect of inclement weather conditions such as humidity, haze, fog, mist, smoke, or rain. Particles or substances in the atmosphere may be associated with certain weather conditions, for example haze resulting from aerosols in the air. These atmospheric substances may obstruct the area between the observation system and the target to be observed. A similar situation may result when the observation system operates in other media, such as underwater, due to the influence of scattering in the water or the air above. In an observation system integrated with a laser device for target illumination (i.e., operation in the active mode), the interference of substances in the medium between the system and the target can cause backscatter of the laser beam. The backscatter of the laser beam results in "self-blinding" of the camera, which reduces the contrast of the target relative to the background. The same type of problem exists in an optical observation system which attempts to produce an image of an object located behind a semi-reflective surface (e.g., glazing) in a building. The glazing reflects part of the transmitted laser beam toward the camera, thereby blinding the camera. In this case, the camera is unable to produce the desired image. In dark conditions, contrast reduction significantly lowers the achievable range of target or object detection and identification or imaging, with respect to the attainable detection and identification range in daylight conditions.

In order to reduce the influence of atmospheric substances or a semi-reflective surface between the observation system and the target, the imaging sensor may be synchronized with respect to the time that the reflected energy from the laser illuminated target is due to be received in the optical assembly of the photodetector. In particular, a laser generates short light pulses at a certain frequency. The imaging sensor is activated at the same frequency, but with a time delay that is related to the frequency. When the laser beam is conveyed toward the target, the receiving assembly of the imaging sensor is deactivated. The laser beam impinges the target, and illuminates the target and the surrounding area. A small part of the laser light is reflected back toward the camera, which is activated as this reflected light reaches the camera. Laser light which reflects off of atmospheric substances relatively close to the camera (relative to the distance between the camera and the target) will reach the receiving assembly of the camera while the camera is still deactivated. Therefore, this light will not be received by the camera and will not affect the contrast of the image. However, reflex light from the target and its nearby surroundings will reach the camera after the camera has been switched to the "on" state, and so light from the target will be fully collected by the camera.

The camera switches from the "off" state to the "on" state in a synchronized manner with the time required for the pulse to travel to the target and return. After the light reflected from the target has been received and stored, the camera reverts to the "off" state, and the system awaits transmission of the following laser pulse. This cycle is repeated at a rate established in accordance with the range from the camera to the target, the speed of light, and the inherent limitations of the laser device and the camera. This technique is known as gated imaging to minimize back-scatter.

US Patent 5,408,541 issued to Sewell and entitled "Method and System for Recognizing Targets at Long Ranges", is directed to a method and system for recognizing targets at ranges near or equal to ranges at which they are initially detected. A detect sensor, such as a radar system or thermal imaging sensor, detects a target relative to a sensor platform. The detect sensor determines a set of range parameters, such as target coordinates from the sensor platform to the target. The detect sensor transfers the set of range parameters to a laser-aided image recognition sensor (LAIRS). LAIRS uses the set of range parameters to orient the system to the angular location of the target. A laser source illuminates the area associated with the range parameters with an imaging laser pulse to generate reflected energy from the target. A gated television sensor receives the reflected energy from the illuminated target, and highly magnifies and images the reflected energy. The image is then recognized by either using an automatic target recognition system, displaying the image for operator recognition, or both.

It is noted that Sewell requires preliminary range measurement.

Before the laser source illuminates the target, the laser source directs a low power measurement laser pulse toward the target to measure the range between the system and the target. The range sets a gating signal for the gated television sensor. The gated television sensor is gated to turn on only when energy is reflected from the target. However, the measuring line to the target of the laser ranger must be parallel, in a very accurate manner, to the LOS of the observation system. Light intensifiers are also known in the art. US Patent No.

6,836,059 B2 issued to Smith and entitled "Image lntensifier and Electron Multiplier Therefore", is directed to an image intensifier for night vision applications. The image intensifier includes a photo-cathode, an electron bombarded device (EBD), and a sensor. The photo-cathode receives light beams from an object. The EBD is located between the photo-cathode and the sensor. The photo-cathode includes a first input surface and an output surface. The EBD includes a doped semiconductor structure, and a blocking structure. The doped semiconductor structure includes a second input surface and an emission surface opposite the second input surface. A first doped region is in contact with the second input surface and a second doped region is in contact with emission surface.

The output surface is activated to a negative electron affinity state. Emission areas of the emission surface are activated to a negative electron affinity state. The first doped region inhibits recombination of electrons at the second input surface, by increasing the number of electrons at the second input surface. The second doped region directs the increased number of electrons toward the emission areas. The photo-cathode converts the photons of an image of an object into free electrons, the EBD increases the number of free electrons, the sensor senses the increased number of free electrons, and the display displays the intensified image of the object.

SUMMARY OF THE DISCLOSED TECHNIQUE

It is an object of the disclosed technique to provide a novel system for gated light intensified imaging using active illumination. In accordance with the disclosed technique, there is thus provided a system for producing a target image of a target, according to target light beams received from the target through an optical assembly, the system being optically coupled with the optical assembly. The system includes an adapter for mechanically and optically coupling the system with an eyepiece of the optical assembly, and a first laser source for illuminating the target by laser pulses.

The system further includes a gated light intensifier optically coupled with the optical assembly by the adapter, a controller electrically coupled with the first laser source and with the gated light intensifier, and a relay lens assembly located between the adapter and the gated light intensifier. The controller controls the pulsed operation of the first laser source, and enables the gated light intensifier to intensify substantially exclusively, reflections of the laser pulses from the target, which correspond to a range between a front portion and a rear portion of the target, about the location of the target relative to the system. The relay lens assembly projects the target image on the gated light intensifier.

In accordance with another aspect of the disclosed technique, there is thus provided a system for producing a target image of a target, according to target light beams received from the target. The system is optically coupled with an optical assembly. The system is located between the target and the optical assembly, in close proximity to the optical assembly. The system includes a first laser source for illuminating the target by laser pulses, a gated light intensifier optically coupled with the optical assembly, a controller electrically coupled with the first laser source and with the gated light intensifier, and a relay lens assembly located between the gated light intensifier and the optical assembly. The controller controls the pulsed operation of the first laser source, and enables the gated light intensifier to intensify substantially exclusively, reflections of the laser pulses from the target, which correspond to a range between a front portion and a rear portion of the target, about the location of the target relative to the system. The relay lens assembly projects the intensified target image on the optical assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed technique will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which: Figure 1 is a schematic illustration of a gated light intensifying module, constructed and operative according to an embodiment of the disclosed technique;

Figure 2A is an elaborated schematic illustration of the gated light intensifying module of Figure 1 ; Figure 2B is a schematic illustration of a system mounted on a rifle, for producing an intensified image of an object, constructed and operative according to another embodiment of the disclosed technique;

Figure 3 is an elaborated schematic illustration of a gated light intensifying module similar to the gated light intensifying module of Figure 1 , and constructed and operative according to a further embodiment of the disclosed technique;

Figure 4 is a graph depicting gated imaging as a function of time;

Figure 5 is a typical sensitivity graph depicting sensitivity of the gated light intensifier of Figure 2A, as a function of the range between the gated light intensifier and a target area;

Figure 6 is a graph depicting timing adjustment relating to the pulse width of a laser beam;

Figure 7 is a graph depicting the observation capability of the gated light intensifying module of Figure 2A, with the timing technique depicted in Figure 6;

Figure 8 is a graph depicting a specific instant in time in relation to the scenario depicted in Figure 7;

Figure 9 is a graph depicting a specific instant in time after than the instant depicted in Figure 8; Figure 10 is a sensitivity graph in accordance with the timing technique depicted in Figure 6;

Figure 11 is a sensitivity graph in accordance with the Long Pulse Gated Imaging (LPGI) timing technique; Figure 12 is a schematic illustration of a gated light intensifying module, constructed and operative according to another embodiment of the disclosed technique; and

Figure 13 is a schematic illustration of a system mounted on a rifle, for producing an intensified image of an object, constructed and operative according to a further embodiment of the disclosed technique.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The disclosed technique overcomes the disadvantages of the prior art by providing a gated light intensifying module, which can be assembled on an existing optical assembly (e.g., a telescope of a rifle), as an add-on component, and without requiring modifications to the optical assembly or the rifle. A gating controller operates a laser source to emit a beam of light toward a target, over a predetermined illumination period of time, and then the gating controller operates a gated light intensifier to intensify light which is reflected from the target and received in a predetermined intensification time period. Both the illumination time period and the intensification time period are determined according to the distances between the gating controller, the laser source (e.g., if both these units are not located at the same place) and the targeting range (i.e., the range in which targets are sought for). The disclosed technique is described herein with reference to laser light pulses, however any suitable pulsed emission of electromagnetic radiation may be applied, including light in the visible and non-visible spectrum, X-ray, ultraviolet (UV), near and far infrared (IR), radar, microwave, radio frequency (RF) and the like, all with respect to the sensitivity of the gated light (i.e., electromagnetic radiation) intensifier employed. Also other pulse sources of energy may be applied, including acoustic waves, ultrasound, and various particles (other than photons) emission, and the like.

Accordingly, the disclosed technique provides for manipulation of the sensitivity or image gain as a function of field depth, by changing the width of the transmitted laser pulses, changing the state of the gated light intensifier in a manner related to the distance to the target, synchronization of the gated light intensifier to the pulse timing, and other factors. The disclosed technique allows for dynamic imaging or other information gathering in real-time. The system provides detection and identification of potential military targets in combat situations. Reference is now made to Figures 1 , 2A, 2B and 3. Figure 1 is a schematic illustration of a gated light intensifying module, generally referenced 100, constructed and operative according to an embodiment of the disclosed technique. Figure 2A is an elaborated schematic illustration of the gated light intensifying module of Figure 1. Figure 2B is a schematic illustration of a system mounted on a rifle, generally referenced 228, for producing an intensified image of an object, constructed and operative according to another embodiment of the disclosed technique. Figure 3 is an elaborated schematic illustration of a gated light intensifying module similar to the gated light intensifying module of Figure 1 , generally referenced 112, and constructed and operative according to a further embodiment of the disclosed technique.

With reference to Figure 1 , gated light intensifying module 100 includes a laser source 102 and a gated light intensifier 104. Laser source 102 generates a laser beam 106 in form of pulses. Laser source 102 conveys laser beam 106 toward a target 108. Laser beam 106 illuminates target 108.

With reference to Figure 2A, gated light intensifying module 100 includes a relay lens assembly 118, a gated light intensifier 122, a viewing device 124, a user interface 126, a power source 128, a controller 132, a symbol injection unit 134, laser sources 136 and 138, a light detector 142, a reflector 144, beam combiner 146, beam splitter 148, collimators 186 and 188, and a band-pass filter 238. Gated light intensifying module 100 is assembled on an optical assembly 156 (e.g., an aiming scope) of a device (e.g., a rifle - not shown), by an adapter 116. Adapter 116 serves to mechanically and optically couple gated light intensifying module 100, with an eyepiece (not shown) of optical assembly 156, and mechanically with the rifle. Adapter 116 further serves to optically couple gated light intensifier 122 with optical assembly 156. Power source 128 provides electric power to gated light intensifier 122, controller 132, and to laser sources 136 and 138. Beam combiner 146 is located between target 108 and optical assembly 156. Adapter 116 is located between optical assembly 156 and relay lens assembly 118. In general, band-pass filter 238 is located in front of gated light intensifier 122. In the example set forth in Figure 2A, band-pass filter 238 is located between relay lens assembly 118 and gated light intensifier 122. Gated light intensifier 122 is located between band-pass filter 238 and viewing device 124.

Target 108, beam combiner 146, optical assembly 156, adapter 116, relay lens assembly 118, band-pass filter 238, gated light intensifier 122, and viewing device 124, are optically coupled together. Symbol injection unit 134 is optically coupled with optical assembly 156 through reflector 144 and beam combiner 146. Controller 132 is electrically coupled with gated light intensifier 122, user interface 126, symbol injection unit 134, laser sources 136 and 138, and with light detector 142. All components of gated light intensifying module 100 are packed together in an enclosure (not shown).

Alternatively, the optical components of gated light intensifying module 100, such as relay lens assembly 118, band-pass filter 238, gated light intensifier 122, viewing device 124, symbol injection unit 134, laser sources 136 and 138, light detector 142, reflector 144, beam combiner 146, beam splitter 148, and collimators 186 and 188 are packed in a first enclosure attached to optical assembly 156 on the top of the rifle, by adapter 116. In this case, the electronic components of gated light intensifying module 100, such as power source 128 and controller 132 are packed in a second enclosure attached to the rifle below optical assembly 156.

Band-pass filter 238 admits light within the range of wavelengths of laser source 136, while blocking light within substantially all other wavelengths. In this manner, band-pass filter 238 prevents blooming in the intensified image (i.e., intensified target image) of target 108, as viewed by a user (not shown). Band-pass filter 238 is a module which can be detached from gated light intensifying module 100, by the user, and replaced when needed. For example, if the user uses gated light intensifying module 100 in a substantially bright environment, then the user can leave band-pass filter 238 in place, in order to prevent blooming in the intensified image of target 136, or by other light sources in the environment, such as street lights or headlights of approaching vehicles. On the other hand, the user can remove band-pass filter 238 in a dim environment (e.g., a desert), in order to view a sufficiently bright intensified image of target 108, in the available ambient light condition. Alternatively, band-pass filter 238 can be switchable, electronically turned on and off by controller 132. Controller 132 determines whether to enable or disable band-pass filter 238, according to an output of a light detector (not shown) coupled with the controller. Controller 132 determines whether to enable or disable laser source 136 according to the output of the light detector (e.g., the controller disables laser source 136, when the light detector detects a substantially high intensity ambient light). This is provided in order to prevent damage to gated light intensifier 122. Further alternatively, band-pass filter 238 can be an integral part of gated light intensifier 122. Optical assembly 156 receives incoming light and modifies the incoming light, for example by magnifying an image (not shown) of a distant target 108. On a rifle which includes only the optical assembly (i.e., without the gated light intensifying module), the optical assembly is constructed to project the image of the target, at a focal point suitable to be viewed by an eye of the user. In order to operate gated light intensifying module 100 as an add-on device, it is necessary to move the focal point (not shown) of the image produced by optical assembly 156, to an object plane (not shown) of gated light intensifier 122. Relay lens assembly 118 includes a plurality of optical components, in order to project the image produced by optical assembly 156, on gated light intensifier 122. Gated light intensifier 122 converts the light beams received from relay lens assembly 118, to electrons and projects these electrons onto a fluorescent screen (not shown). The electrons excite a fluorescent substance of the fluorescent screen, forming an intensified image (not shown), representing target 108. One or more eyes 158 of a user (not shown) observes the intensified image through viewing device 124. Viewing device 124 is a single eyepiece which provides the intensified image to only one of the eyes 158. Alternatively, viewing device 124 is a pair of binoculars which provides the intensified image to both eyes 158. Further alternatively, viewing device 124 is a charge-coupled device (CCD). Light detector 142 is a device which produces an electric output, according to the flux of photons entering light detector 142. The electric output is proportional to the flux of the photons. Light detector 142 can be an avalanche photo diode (APD), and the like. Controller 132 controls laser source 136 to emit a light beam

164A toward target 108, through collimator 186, over an illumination time period. Gated light intensifier 122 receives a light beam 164B as a reflection of light beam 164A from target 108. Controller 132 further controls gated light intensifier 122 to intensify light beam 164B, over an intensification time period.

The user can control the operation of each of laser sources 136 and 138, to emit laser pulses 164A and 168A, respectively, at a selected power level, via user interface 126. The user can for example, lower the power level of each of laser pulses 164A and 168A, in order to zoom-in on a distant target. This provision reduces the probability of being detected by a rival. The user can also reduce the beamwidth of each of laser pulses 164A and 168A, thereby making possible to view a substantially distant target, while consuming substantially the same electric power as in the case of a substantially close target. Relay lens assembly 118 projects light beam 164B on gated light intensifier 122. Gated light intensifier 122 is operative to intensify light beam 164B, only at selected intensification time periods. Controller 132 can control the electronic operation of gated light intensifier 122, by enabling or disabling electron excitation within gated light intensifier 122.

Alternatively, gated light intensifying module 100 includes a gated light valve (not shown) located in front of the gated light intensifier. In this case, the controller controls the activation of the gated light valve, instead of electronically controlling the operation of the gated light intensifier. The controller controls the operation of the gated light valve, thereby admitting or blocking the light beam which travels toward the gated light intensifier.

Gated light intensifier 122 may be in one of two states. During the "on" state, gated light intensifier 122 receives incoming light, whereas during the "off" state gated light intensifier 122 does not receive incoming light. In particular, gated light intensifier 122 is open during the "on" state and closed during the "off" state. The term "activated" is used herein to refer to gated light intensifier 122 being in the "on" state, whereas the term "deactivated" is used herein to refer to gated light intensifier 122 being in the "off" state. Gated light intensifier 122 can be operative within a predetermined range of wavelengths, for example, at wavelengths between 400 nm and 950 nm (i.e., near infra red).

It is noted that optical assembly 156 provides an already aligned image at the entrance of gated light intensifying module 100, which in turn, intensifies that image for the user. Accordingly, a preliminary alignment of optical assembly 156 with a rifle (i.e., bore-sighting) is sufficient, and therefore no re-alignment is necessary when gated light intensifying module 100 is assembled onto optical assembly 156.

An aperture number of a typical rifle scope, (i.e., the ratio of the focal length of a lens and the effective diameter of the lens), is generally very high, which produces a lot of image noise and decreases the signal-to-noise ratio of images provided by optical assembly 156 to gated light intensifying module 100. With reference to Figure 2B, system 228 includes a gated light intensifying module 230, an adapter 232, an optical assembly 234 and a light collecting optical assembly 236. Adapter 232 is coupled with gated light intensifying module 230 and with optical assembly 234. Light 5 collecting optical assembly 236 is mounted in front of optical assembly 234, as an add-on device. Gated light intensifying module 230, adapter 232 and optical assembly 234 are similar to gated light intensifying module 100 (Figure 2A), adapter 116 and optical assembly 156, respectively, as described herein above. o Light collecting optical assembly 236 has an objective with a diameter greater than the diameter of the objective of optical assembly 234 and an ocular having a diameter similar to that of the objective of optical assembly 234. Accordingly, light collecting optical assembly 236 collects more light than optical assembly 234 and directs it to optical 5 assembly 234, thereby decreasing the effective aperture number of optical assembly 234 and increasing signal-to-noise ratio of the image at the exit of optical assembly 234.

Atmospheric substances, such as humidity, haze, fog, mist, smoke, rain, airborne particles, and the like, represented by a zone 114 o (Figure 1), exist in the surrounding area of gated light intensifying module 100. Backscatter from the area in the immediate proximity to gated light intensifying module 100 has a more significant influence than backscatter from a further distanced area due to obvious geometrical relations. For example, an interfering particle relatively close to gated light intensifying 5 module 100 will reflect back a larger portion of laser beam 106 than a similar particle located relatively further away from gated light intensifying module 100.

Accordingly, the area proximate to gated light intensifying module 100 from which avoidance of backscattering is desirable, can be 0 defined with an approximate range "R_min". Target 108 is not expected to be located within range R_mj_n and therefore the removal of the influences of atmospheric or other interfering substances in this range from the captured image is desirable. Such atmospheric substances can also be present beyond R_min, but their removal is both problematic and of less significance. These atmospheric substances interfere with laser beam 106 on its way to illuminating target 108, and with laser beam 110 reflected from target 108.

Gated light intensifier 122 is deactivated for the duration of time that laser beam 106 has propagated entirely a distance R_min toward target 108, including the return path from distance R_min. Range "R_mj_n" is the minimum range for which gated light intensifier 122 is deactivated. The distance between gated light intensifying module 100 and target 108 is designated range "RMAX"-

Laser source 136 transmits light beam 164A toward target 108, and optical assembly 156 receives light beam 164B, which is a reflection of light beam 164A from target 108, through beam combiner 146. Controller 132 controls the operation of symbol injection unit 134 to emit a light beam 166A respective of a symbol (not shown). Light beam 166A reflects from reflector 144 toward beam combiner 146, and beam combiner 146 combines the reflection of light beam 166A with light beam 164B to produce a combined light beam 166B, and directs combined light beam 166B toward optical assembly 156. Gated light intensifier 122 intensifies light beam 166B and produces an image of the symbol, against the intensified image of target 108.

Laser source 138 emits a laser pulse 168A toward target 108, through beam splitter 148 and collimator 188. A light beam 168B which is a reflection of laser pulse 168A from target 108, reflects from beam splitter 148 as a light beam 168C and enters light detector 142. In response to light beam 168C, light detector 142 provides controller 132 an electric output, thereby enabling controller 132 to determine the range of target 108 from gated light intensifying module 100. Controller 132 can control the operation of symbol injection unit 134 to produce a visual representation of this range, to be observed by one or more eyes 158 together with the intensified image of target 108.

It is noted that beam splitter 148 is not a mandatory component of gated light intensifying module 100. In this case, laser source 138 can direct laser pulses toward the target in a first optical channel, and the light detector can detect the reflections of these laser pulses from the target, in a second optical channel.

The user can communicate with controller 132 via user interface 126. Use interface 126 can be a tactile device, audio device, haptic device, and the like. The user can adjust for example, the gain and duty cycle of gated light intensifier 122, the intensity of light beam 164A produced by laser source 136, activation of laser source 136, activation of gated light intensifying module 100, selecting the range at which the user desires to view targets, and the like. Power source 128 can be for example, a primary battery, secondary battery, fuel cell, power supply, and the like. Viewing device 124 can include a mechanism (not shown) to provide diopter adjustment for one or more eyes 158. Gated light intensifying module 100 can further include a safety mechanism (not shown), coupled with the controller, in order to prevent operation of the laser sources, in case the gated light intensifying module is not properly assembled onto the optical assembly and the firearm. The controller allows both laser sources to operate, if the safety mechanism indicates that the gated light intensifying module is properly assembled, and prevents the operation of the laser sources, otherwise.

Gated light intensifying module 100 can further include another light detector (not shown) coupled with the controller. This light detector detects the intensity of the ambient light. If the light detector detects that the intensity of the ambient light is greater than a predetermined threshold, then the controller disables the gated light intensifier, in order to prevent damage to the gated light intensifier. It is noted that the magnification power of gated light intensifying module 100 is substantially equal to one. Hence, there is no need to make any optical adjustment to optical assembly 156, after coupling gated light intensifying module 100 with optical assembly 156. With reference to Figure 3, gated light intensifying module 112 includes a relay lens assembly 172, a gated light intensifier 174, a viewing device 176, a user interface 178, a power source 182, a controller 194, a symbol injection unit 196, laser sources 198 and 202, a light detector 204, a reflector 206, beam splitters 208, and 214, a beam combiner 212, and a band-pass filter 240. Relay lens assembly 172, gated light intensifier 174, viewing device 176, user interface 178, power source 182, controller 194, symbol injection unit 196, light detector 204, and band-pass filter 240, are similar to relay lens assembly 118 (Figure 2A), gated light intensifier 122, viewing device 124, user interface 126, power source 128, controller 132, symbol injection unit 134, light detector 142, and to band-pass filter 238, respectively. Laser sources 198 and 202 are similar to laser sources 136 and 138, respectively.

Beam splitter 214 is optically located between an optical assembly 216 and relay lens assembly 172. Laser source 198 emits a light beam 218A which reflects from beam splitter 214 as a light beam 218B toward a target 222. Target 222 reflects light beam 218B as a light beam 218C toward optical assembly 216. Light beam 218C travels through optical assembly 216, an adapter 224 and relay lens assembly 172, to be intensified by gated light intensifier 174 and to be observed by one or more eyes 226 through viewing device 176, in the same path as that of light beam 218B.

Reference is further made to Figure 4, which is a graph, generally designated 120, depicting gated imaging as a function of time. In graph 120, a laser pulse (not shown) is transmitted at a time t₀. The duration of the laser pulse, or the pulse width of the laser beam, is designated T|_aser; and extends between time t₀ and time ^. It is noted that the description herein refers to a "square" pulse, for the sake of simplification and clarity. It is noted that such description is equally applicable to a general pulse pattern, in which threshold values define the effective beginning, duration and end of the pulse, rendering its analysis analogous. The gated light intensifier, such as gated light intensifier 122 (Figure 2A) or gated light intensifier 174 (Figure 3), is initially in the "off" state for as long as the laser pulse is emitted, between time t₀ and time t-i

\ I laser) ^■

The gated light intensifier is further maintained in the "off" state between time t-_t and time X₂, (i.e., Δt_min), and remains in the "off" state so as not to receive reflections of the entire laser pulse (including the end portion of the pulse) from objects located within a range R_min from a gated light intensifying module (e.g., gated light intensifying module 100 - Figure 2A or gated light intensifying module 112 - Figure 3). At time X₂, the gated light intensifier is activated and begins receiving reflections. The reflections from objects located immediately after range R_mj_n from the gated light intensifying module are received from photons at the rear end of the transmitted pulses which have impinged on these objects. The front portion of the transmitted pulses is wasted for objects located immediately in front of range R_mj_n. At time t₃, the gated light intensifier first receives reflections from the entire width of the pulses.

The range of objects, for which the entire width of the pulse is first received, is designated "R₀". Thus the time span between time X₂ and time t₃ is equal to T|_aser. The gated light intensifier remains in the "on" state until time t₅. At time t₄, the gated light intensifier still receives the full reflection of the pulses from objects located up to a range depicted R₁. Reflections from objects beyond this range reflect less and less portion of the laser pulse. The tail portion of the reflected pulse is cut off to a greater extent, as the light intensifier gates from its "on" state to its "off state, the further away such objects are located beyond R₀ up to a maximal range R_maxi beyond which no reflections are received at all, due to the deactivation of the light intensifier into its "off" state. At time t₅, corresponding to receiving reflections from objects at R_max, the gated light intensifier receives reflections only from photons at the very front end of pulses whose tails are just prior to passing range R-|. Thus the time span between time t₄ and time t₅ is equal to T|_aser.

Reference is now made to Figure 5, which is a typical sensitivity graph, generally designated 130, depicting sensitivity of the gated light intensifier of Figure 2A₁ as a function of the range between the gated light intensifier and a target area. The vertical axis represents sensitivity of the gated light intensifier. The horizontal axis represents the range between the gated light intensifier and the target. The term "sensitivity", referred to in this context relates to the gain or responsiveness of the gated light intensifier in proportion to the number of reflected photons actually reaching the gated light intensifier when it is active, and not to any variation in the performance of the gated light intensifier, per se, which has nothing to do with the range from which light is reflected (ignoring attenuation due to geometrical and atmospheric considerations, for sake of simplifying).

In graph 130, from range R_min up to range R₀ the sensitivity of the gated light intensifier gradually increases to a maximum level. This region encompasses mainly atmospheric sources that cause interference and self-blinding in the gated light intensifier and so a high sensitivity here is undesired. The gated light intensifier initially encounters the photons at the very front end of the transmitted laser pulse, then the photons in the middle of the pulse and finally the photons at the very end of the pulse. But the "on" state of the gated light intensifier "misses" most of the front portion of the pulses reflected from objects just beyond R_mj_n, incrementally includes more and more of the pulse as its reflection is from further ranges, until all of the pulse is received for objects at R₀. Thus, the duration of the incline in graph 130 is equivalent to the width of the laser pulse T|_aser. The gated light intensifier remains at maximum sensitivity between range R₀ and range Ri. This is the region where targets are most likely located and so a high sensitivity is desirable. The sensitivity of the gated light intensifier gradually decreases to a negligible level beyond range R₁. In particular, for objects located immediately after range R₁, the gated light intensifier begins to miss the photons at the very front end of the laser pulse, then for further ranges misses also the photons in the middle of the pulse, and finally toward objects at R_max, the photons at the very end of the pulse until no photons are received. The duration of the decline in graph 130 is equivalent to the width of the laser pulse T|_aser. A particular sensitivity as a function of range may be obtained by gated light intensifying module 100 (Figure 1) by application of several techniques, either individually or in various combinations. These techniques will now be discussed.

Reference is now made to Figure 6, which is a graph, generally designated 140, depicting timing adjustment relating to the pulse width of a laser beam. The technique relates to the time gated light intensifier 122 (Figure 2A) is activated with respect to the pulse width of laser beam 106. The vertical axis represents sensitivity, and the horizontal axis represents time. Range "R₀" is the range from which full reflections first arrived at gated light intensifier 122 while it is activated, where reflections are the end result of the whole span of the pulse width passing in its entirety over a target located at range R₀ from gated light intensifier 122. Range R_min is the range up to which the full reflections from a target at this range will encounter gated light intensifier 122 in the "off" state. Range R_max is the range of the field for which reflections, or any portion thereof, can still be obtained, i.e. the maximum range for which the sensitivity of gated light intensifier 122 is high enough for detection. The pulse width of laser beam 106 is designated T|_aser- Time "T_off" is the time during which gated light intensifier 122 is deactivated, immediately after transmitting laser pulse 106. Time "T_off" may be determined in accordance with the range from which reflections are not desired (R_mj_n), thereby preventing reflections from atmospheric substances and the "self-blinding" effect. In particular, T_off may be determined as twice this range divided by the speed of light in the medium (c), as this is the time span it takes the last photon of the laser pulse to reach the farthest point in the range R_min and reflect back to gated light intensifier 122. It may be desirable to lengthen the duration of time the senor unit is deactivated by the duration of pulse width of the laser beam, to ensure that no backscattered reflections from the area up to R_min are received in gated

2x R light intensifier 122, and so: T_off = —+T_laier .

Time "T_0n" is the time during which gated light intensifier 122 is activated and receives reflections from target 108 (Figure 1). Time "T_0n" may be determined in accordance with the entire distance the "last" photon of the pulse scans up to R₀ and back to the gated light intensifier 122. Since gated light intensifier 122 is activated at time 2xR_mj_n/c this last photon is already distanced 2xR_min from gated light intensifier 122 and it propagates a distance R₀-2xR_min until target 108, and a further distance R₀ back to gated light intensifier 122; the range sums up to 2x(R₀-R_mj_n) and the time it takes to scan this range results in twice this range divided by

the speed of light: T_0n = ^{2 x}(^R° ^{~ R}™ϊ .

C

It is noted that the aforementioned calculations serve to substantially define the time variables. The final values for these variables can be further refined or customized in accordance with certain factors related to gated light intensifying module 100. Such refinement or customization will be elaborated upon henceforth, and may consider, for example, accounting for specific environmental conditions, the speed of the vehicle (if gated light intensifying module 100 is mounted to a vehicle), the specific characteristics of targets expected to be located at certain ranges, changing the form of laser pulse 106, and the like. Reference is now made to Figure 7, which is a graph, generally designated 150, depicting the observation capability of the gated light intensifying module of Figure 2A, with the timing technique depicted in

Figure 6. The vertical axis represents sensitivity, and the horizontal axis represents distance.

Gated light intensifier 122 is "blind" up to range R_min. In particular, there are no reflections generated by laser pulse 106 from objects located in the region immediately beyond gated light intensifying module 100 up to range R_min. This is due to the fact that laser pulse 106 propagates throughout path R_min while gated light intensifying module 100 was blind to reflections generated by laser pulse 106 colliding with any object throughout this range, gated light intensifier 122 having been deactivated during this period. Thus, R_min is the minimum range for which reflections, in their entirety, may encounter gated light intensifier 122 in the "off" state.

An element 152 is an object to be detected, located somewhere beyond range R_min. An element 154 is an object to be detected, located further away, slightly below range R₀.

To understand how sensitivity as a function of range is achieved, it is helpful to examine how reflections are received from objects located at the range between R_min and R₀.

Reference is now made to Figure 8, which is a graph, generally designated 160, depicting a specific instant in time in relation to the scenario depicted in Figure 7. In particular, graph 160 depicts the specific instant at which a laser pulse 162 has just completed passing element 152 and continues advancing. The vertical axis represents sensitivity, and the horizontal axis represents distance.

Reflections from element 152 may be received the moment gated light intensifier 122 is activated, even before the entire pulse width of laser pulse 162 has passed element 152. Therefore, plenty of time is provided for gated light intensifier 122 to receive reflections that can be intensified from object 154, but only limited intensifying time is provided for reflections from the closer element 152.

Gated light intensifier 122 may be activated just a short time before the last portion of the pulse energy is reflected from element 152 (as long as laser beam 106 remains on element 152). This portion is proportional to the small distance between R_min and element 152. Immediately afterwards, pulse energy is also reflected continuously from element 154 (now being passed by advancing laser pulse 162) also in proportion to the greater distance between R_min and element 154. Consequently, the total energy received by gated light intensifier

122 as a result of reflections from element 152 is relative to the duration of time during which laser pulse 162 fully passes element 152, and still manages to reflect to gated light intensifier 122, while gated light intensifier 122 is in the "on" state. Reference is now made to Figure 9, which is a graph, generally designated 170, depicting a specific instant in time after than the instant depicted in Figure 8. In particular, graph 170 depicts the specific instant at which laser pulse 162 has just completed passing element 154 and continues advancing. The vertical axis represents sensitivity, and the horizontal axis represents distance.

At this instant, reflections from element 152 may be received by gated light intensifier 122 (as long as laser beam 106 remains incident on element 154), and no longer receives reflections from element 152 (as laser pulse 162 has already passed element 152). Consequently, the reflection intensity absorbed from element

154, located near range R₀, may be substantially greater than the reflection intensity absorbed from element 152. This is because the received reflection intensity is determined according to the period during which gated light intensifier 122 is activated while the element is reflecting thereto. This means that laser pulse 162 may remain incident on element 154 for a longer time than on element 152, during a period that gated light intensifier is activated (i.e., receives reflections). In such a case, gated light intensifier 122 receives more energy from an object near the optimal range R₀ than from an object closer to gated light intensifying module 100. Reference is now made to Figure 10, which is a sensitivity graph, generally designated 180, in accordance with the timing technique depicted in Figure 6. The vertical axis represents sensitivity, and the horizontal axis represents distance. It is noted that graph 180 may not be ideal, because laser pulse

106 may also illuminate elements located beyond range R_max, as laser beam 106 gradually fades away, although there may be no need to illuminate such elements. Furthermore, graph 180 may not be ideal because the sensitivity remains constant between the first optimum range R₀ and the last optimum range R₁, while further attenuation exists within the range span R₁-R₀. It is possible to reduce the sensitivity of gated light intensifying module 100 for receiving reflections originating from beyond range R₀ by other techniques. Such techniques include changing the form or shape of laser beam 106, changing the time that gated light intensifier 122 is activated, and changing the width of laser pulse 106. These techniques are now discussed.

Reference is now made to Figure 11 , which is a sensitivity graph, generally designated 184, in accordance with the Long Pulse Gated Imaging (LPGI) timing technique. In the LPGI timing technique, the pulse width of the laser beam

(Ti_aser) is set to the difference between the time required for the laser beam to traverse the path from the system to the minimal target distance and back (2-R_min/c) and the time the last photon reflects back from the target at R₁. This time is also equivalent to the duration of time for which the gated light intensifier is activated (T_0n)- Thus, both T|_aser and T_0n are given by the relation: ^2χ(^R™* ^~R™^ ; where c is the speed of light. It is noted that LPGI

C may be considered a particular example of the timing techniques depicted in graphs 140, 150, 160, 170 and 180, in which

For example, if target 108 (Figure 2A) is located at a farthest distance of R₁=25km away from gated light intensifying module 100, and if

R_min is equal to 3km, then T_0n and T|_aSer will substantially equal:

2 x (25km -3km) _{Λ Λ r n} - = 146.7 //sec . c

From the instant that laser beam 106 is transmitted, gated light intensifier 122 operates in LPGI mode. To eliminate backscattered light without loss of contrast while maintaining a high quality image of target and background, it is sufficient to switch gated light intensifier 122 to the "off" state when the reflected beam has traversed approximately 6 km (3 km each way to and from range R_mj_n). It is noted that it may be desirable to lengthen time T_off by the pulse width of the laser beam (T|_aser), to ensure that no backscattered reflections from the area up to R_min are received by

2xR gated light intensifier 122. Therefore, the actual time T_off is: —+T_hser .

C

In the particular case of LGPI, 7W= — ^-^ — — , and so T_off may be

C

2x R simplified to: — . c

According to another aspect of the disclosed technique, the gated light intensifying module is mounted in front of an existing optical assembly of a rifle (i.e., day scope), as an add-on module. This arrangement provides night vision to a conventional rifle, and provides an even greater visibility range than a gated light intensifying module mounted behind the optical assembly (as shown in Figure 2A). Furthermore, in case the magnification of the gated light intensifying module is one, the optical parameters and characteristics of the optical assembly remain intact, and it is not necessary to recalibrate the optical assembly.

Reference is now made to Figures 12 and 13. Figure 12 is a schematic illustration of a gated light intensifying module, generally referenced 260, constructed and operative according to another embodiment of the disclosed technique. Figure 13 is a schematic illustration of a system mounted on a rifle, generally referenced 330, for producing an intensified image of an object, constructed and operative according to a further embodiment of the disclosed technique. With reference to Figure 12, gated light intensifying module 260 includes an objective lens 262, a gated light intensifier 264, a relay lens assembly 266, a band-pass filter 268, a user interface 270, a power source 272, a controller 274, a symbol injection unit 276, laser sources 278 and 280, collimators 282 and 284, a light detector 286, beam splitter 288, beam combiner 290, and a reflector 292. Gated light intensifier 264, user interface 270, power source 272, controller 274, symbol injection unit 276, light detector 286, reflector 292, relay lens assembly 266, and band-pass filter 268, are similar to gated light intensifier 122 (Figure 2A), user interface 126, power source 128, controller 132, symbol injection unit 134, light detector 142, reflector 144, relay lens assembly 118, and band-pass filter 238, respectively, as described herein above.

Laser sources 278 and 280 are similar to laser sources 136 and 138 (Figure 2A), respectively, as described herein above. Collimators 282 and 284 are similar to collimators 186 and 188, respectively. Beam splitter 288 and beam combiner 290 are similar to beam splitter 148 and beam combiner 146, respectively.

Beam combiner 290 is located between a target 298 and objective lens 262. Band-pass filter 268 is located between objective lens 262 and gated light intensifier 264. Gated light intensifier 264 is located between band-pass filter 268 and relay lens assembly 266. Relay lens assembly 266 is located between gated light intensifier 264 and optical assembly 294. Relay lens assembly 266 is optically coupled with an objective lens (not shown) of optical assembly 294. Target 298, beam combiner 290, objective lens 262, band-pass filter 268, gated light intensifier 264, relay lens assembly 266, and optical assembly 294 are optically coupled together. Gated light intensifying module 260 is located between optical assembly 294 and target 298, at a distance close to optical assembly 294, compared to the distance between gated light intensifying module 260 and target 298 (i.e., in close proximity to optical assembly 294). Gated light intensifying module 260 is firmly attached to a device

(e.g., a rifle - not shown), as an add-on module, in the front of an optical assembly 294 (e.g., a day scope, a telescope) of the rifle, for example, to a rail (not shown) of the rifle, or directly coupled with optical assembly 294. Optical assembly 294 is similar to optical assembly 156 (Figure 2A), as described herein above. Controller 274 is electrically coupled with gated light intensifier 264, user interface 270, power source 272, symbol injection unit 276, laser sources 278 and 280, and with light detector 286. Symbol injection unit 276 is optically coupled with objective lens 262, through reflector 292 and beam combiner 290. All components of gated light intensifying module 260 are packed together in an enclosure (not shown), similar to the manner which gated light intensifying module 100 (Figure 2A) is packed, as described herein above.

Objective lens 262 receives incoming light from target 298, and transmits this incoming light to gated light intensifier 264, through band-pass filter 268. Gated light intensifier 264 produces an intensified image (not shown) of target 298, according to the incoming light received from band-pass filter 268. Relay lens assembly 266 projects the intensified image on the object plane (not shown) of the objective lens of optical assembly 294. Optical assembly 294 delivers the intensified image toward the eyes 300 of a user (not shown). With reference to Figure 13, system 330 includes a gated light intensifying module 332, an optical assembly 334, and a light collecting optical assembly 336. Light collecting optical assembly 336 is mounted in front of gated light intensifying module 332, as an add-on device. Gated light intensifying module 332, and optical assembly 334 are similar to gated light intensifying module 260 (Figure 12), and optical assembly 294, respectively, as described herein above. Light collecting optical assembly 336 is similar to light collecting optical assembly 236 (Figure 2B), as described herein above. Controller 274 controls laser source 278 to emit a light beam

302A toward target 298, through collimator 282, over an illumination time period. Gated light intensifier 264 receives a light beam 302B as a reflection of light beam 302A from target 298, through beam combiner 290, objective lens 262, and band-pass filter 268. Controller 274 controls the operation of symbol injection unit 276 to emit a light beam 304A respective of a symbol (not shown). Light beam 304A reflects from reflector 292 toward beam combiner 290, and beam combiner 290 produces a combined light beam 304B by combining the reflection of light beam 304A with light beam 302B, and directs combined light beam 304B toward objective lens 262. Gated light intensifier 264 intensifies light beam 304B which is received through objective lens 262 and band-pass filter 268, and gated light intensifier 264 produces an image of the symbol, against the intensified image of target 298.

Laser source 280 emits a light beam 306A toward target 298, through beam splitter 288 and collimator 284. A light beam 306B which is a reflection of light beam 306A from target 298, reflects from beam splitter 288 as a light beam 306C and enters light detector 286. In response to light beam 306C, light detector 286 provides controller 274 an electric output, thereby enabling controller 274 to determine the range of target 298 from gated light intensifying module 260. Controller 274 can control the operation of symbol injection unit 276 to produce a visual representation of this range, to be observed by one or more eyes 300 together with the intensified image of target 298.

Gated light intensifying module 260 can include a gated light valve (not shown) located in front of the gated light intensifier, as described herein above in connection with Figure 2A. In this case, the controller controls the activation of the gated light valve, instead of electronically controlling the operation of the gated light intensifier. Gated light intensifying module 260 can further include a safety mechanism (not shown), coupled with the controller, which is operative as described herein above in connection with Figure 2A. Gated light intensifying module 260 can further include another light detector (not shown) coupled with the controller, as described herein above in connection with Figure 2A, to detect the intensity of the ambient light.

It is noted that the magnification power of gated light intensifying module 260 is substantially equal to one. Hence, there in no need to make any optical adjustment to optical assembly 294, after coupling gated light intensifying module 260 with optical assembly 294.

It will be appreciated by persons skilled in the art that the disclosed technique is not limited to what has been particularly shown and described hereinabove. Rather the scope of the disclosed technique is defined only by the claims, which follow.

Claims

1. System for producing a target image of a target, according to target light beams received from the target through an optical assembly, the system being optically coupled with the optical assembly, the system comprising: an adapter for mechanically and optically coupling said system with an eyepiece of said optical assembly; a first laser source for illuminating said target by laser pulses; a gated light intensifier optically coupled with said optical assembly by said adapter; a controller electrically coupled with said first laser source and with said gated light intensifier, said controller controlling the pulsed operation of said first laser source, and enabling said gated light intensifier to intensify substantially exclusively, reflections of said laser pulses from said target, which correspond to a range between a front portion and a rear portion of said target, about the location of said target relative to said system; and a relay lens assembly located between said adapter and said gated light intensifier, said relay lens assembly projecting said target image on said gated light intensifier.

2. The system according to claim 1 , wherein said optical assembly is a telescope firmly attached to a firearm.

3. The system according to claim 1 , being firmly attached to a firearm, said optical assembly being firmly attached to said firearm.

4. The system according to claim 1 , further comprising a band-pass filter located in front of said gated light intensifier, said band-pass filter admitting light within a range of wavelengths respective of said first laser source, and substantially blocking light within undesirable ranges of wavelengths.

5. The system according to claim 1 , further comprising a viewing device optically coupled with said gated light intensifier, said viewing device directing an intensified target image of said target, to at least one eye of a user.

6. The system according to claim 5, wherein said viewing device is selected from the list consisting of: single eyepiece dedicated to one eye of said user; pair of binoculars dedicated to both eyes of said user; and charge-coupled device.

7. The system according to claim 1 , further comprising a safety mechanism coupled with said controller, said safety mechanism detecting the assembly state of said system on said optical assembly, wherein said controller enables at least said first laser source, when said safety mechanism indicates that said system is properly assembled on said optical assembly, and wherein said controller disables at least said first laser source, when said safety mechanism indicates that said system is improperly assembled on said optical assembly.

8. The system according to claim 1 , further comprising a light detector coupled with said controller, said light detector detecting the intensity of the ambient light, wherein said controller controls the operation of said gated light intensifier, according to said intensity as detected by said light detector.

9. The system according to claim 1 , further comprising a band-pass filter located between said relay lens assembly and said gated light intensifier, said band-pass filter admitting light within a range of wavelengths respective of said first laser source, and substantially blocking light within substantially all other ranges of wavelengths.

10. The system according to claim 1 , further comprising a power source coupled with said controller, said power source providing electric power to said controller, said gated light intensifier, and to said first laser source.

11. The system according to claim 10, wherein said power source is selected from the list consisting of: primary battery; secondary battery; power supply; and fuel cell.

12. The system according to claim 1 , further comprising a collimator located in front of said first laser source, said collimator collimating said laser pulses.

13. The system according to claim 1 , further comprising a user interface coupled with said controller, said user interface enabling a user to enter at least one parameter to said controller.

14. The system according to claim 13, wherein said at least one parameter is selected from the list consisting of: gain of said gated light intensifier; duty cycle of said gated light intensifier; intensity of said laser pulses; activation of said first laser source; activation of said system; power level of said laser pulses; beamwidth of said laser pulses; and target viewing range.

15. The system according to claim 13, wherein said user interface is selected from the list consisting of: tactile; audio; and haptic.

16. The system according to claim 1 , further comprising: a symbol injection unit electrically coupled with and controlled by said controller, so as to produce symbol light beams respective of a symbol; and a beam combiner optically coupled with said optical assembly and with said symbol injection unit, said beam combiner directing said symbol light beams toward said gated light intensifier, while maintaining light which arrives at said optical assembly, and which is directed toward said gated light intensifier, substantially unaffected.

17. The system according to claim 16, further comprising a reflector optically coupled with said beam combiner and with said symbol injection unit, said reflector reflecting said symbol light beams toward said beam combiner.

18. The system according to claim 1 , further comprising: a second laser source electrically coupled with and controlled by said controller, for directing a laser pulse toward said target; and a light detector electrically coupled with said controller, said light detector receiving a reflection of said laser pulse from said target, to enable said controller to determine said range according to a temporal interval between a first point in time at which said second laser source directs said laser pulse toward said target, and a second point in time at which said light detector detects said reflection of said laser pulse.

19. The system according to claim 18, further comprising a beam splitter located between said second laser source and said target, said beam splitter being optically coupled with said light detector, said beam splitter transmitting said laser pulse there through, and further reflecting said reflection of said laser pulse from said target, toward said light detector.

20. The system according to claim 18, further comprising a collimator located in front of said second laser source, said collimator collimating said laser pulse.

21. The system according to claim 18, wherein said light detector is an avalanche photo diode.

22. The system according to claim 1 , further comprising a viewing device located between said gated light intensifier and at least one eye of a user, said viewing device enabling said at least one eye to view an intensified target image produced by said gated light intensifier.

23. The system according to claim 1 , further comprising a beam splitter located between said optical assembly and said relay lens assembly, said beam splitter reflecting said laser pulses from said first laser source toward said target, through said optical assembly, said beam splitter transmitting said reflections of said laser pulses from said target, toward said relay lens assembly.

24. The system according to claim 1 , further comprising a light collecting optical assembly mounted in front of said optical assembly, said light collecting optical assembly directing collected light to said optical assembly.

25. The system according to claim 1 , further comprising a gated light valve optically coupled with said gated light intensifier and electrically coupled with said controller, said controller controlling the operation of said gated light valve, to control the arrival of said reflections of said laser pulses at said gated light intensifier.

26. System for producing a target image of a target, according to target light beams received from the target, the system being optically coupled with an optical assembly, the system being located between the target and the optical assembly, in close proximity to the optical assembly, the system comprising: a first laser source for illuminating said target by laser pulses; a gated light intensifier optically coupled with said optical assembly; a controller electrically coupled with said first laser source and with said gated light intensifier, said controller controlling the pulsed operation of said first laser source, and enabling said gated light intensifier to intensify substantially exclusively, reflections of said laser pulses from said target, which correspond to a range between a front portion and a rear portion of said target, about the location of said target relative to said system; and a relay lens assembly located between said gated light intensifier and said optical assembly, said relay lens assembly projecting said intensified target image on said optical assembly.

27. The system according to claim 26, wherein said optical assembly is a telescope firmly attached to a firearm.

28. The system according to claim 26, being firmly attached to a firearm, said optical assembly being firmly attached to said firearm.

29. The system according to claim 26, further comprising a band-pass filter located in front of said gated light intensifier, said band-pass filter admitting light within a range of wavelengths respective of said first laser source, and substantially blocking light within undesirable ranges of wavelengths.

30. The system according to claim 26, further comprising a safety mechanism coupled with said controller, said safety mechanism detecting the assembly state of said system on said optical assembly, wherein said controller enables at least said first laser source, when said safety mechanism indicates that said system is properly assembled on said optical assembly, and wherein said controller disables at least said first laser source, when said safety mechanism indicates that said system is improperly assembled on said optical assembly.

31. The system according to claim 26, further comprising a light detector coupled with said controller, said light detector detecting the intensity of the ambient light, wherein said controller controls the pulsed operation of said gated light intensifier, according to said intensity as detected by said light detector.

32. The system according to claim 26, further comprising a power source coupled with said controller, said power source providing electric power to said controller, said gated light intensifier, and to said first laser source.

33. The system according to claim 32, wherein said power source is selected from the list consisting of: primary battery; secondary battery; power supply; and fuel cell.

34. The system according to claim 26, further comprising a collimator located in front of said first laser source, said collimator collimating said laser pulses.

35. The system according to claim 26, further comprising a user interface coupled with said controller, said user interface enabling a user to enter at least one parameter to said controller.

36. The system according to claim 35, wherein said at least one parameter is selected from the list consisting of: gain of said gated light intensifier; duty cycle of said gated light intensifier; intensity of said laser pulses; activation of said first laser source; activation of said system; power level of said laser pulses; beamwidth of said laser pulses; and target viewing range.

37. The system according to claim 35, wherein said user interface is selected from the list consisting of: tactile; audio; and haptic.

38. The system according to claim 26, further comprising: a symbol injection unit electrically coupled with and controlled by said controller, so as to produce symbol light beams respective of a symbol; and a beam combiner optically coupled with said optical assembly and with said symbol injection unit, said beam combiner directing said symbol light beams toward said gated light intensifier, while maintaining light which arrives at said gated light intensifier, substantially unaffected.

39. The system according to claim 38, further comprising a reflector optically coupled with said beam combiner and with said symbol injection unit, said reflector reflecting said symbol light beams toward said beam combiner.

40. The system according to claim 26, further comprising: a second laser source electrically coupled with and controlled by said controller, for directing a laser pulse toward said target; and a light detector electrically coupled with said controller, said light detector receiving a reflection of said laser pulse from said target, to enable said controller to determine said range according to a temporal interval between a first point in time at which said second laser source directs said laser pulse toward said target, and a second point in time at which said light detector detects said reflection of said laser pulse.

41. The system according to claim 40, further comprising a collimator located in front of said second laser source, said collimator collimating said laser pulse.

42. The system according to claim 40, wherein said light detector is an avalanche photo diode.

43. The system according to claim 26, further comprising a light collecting optical assembly mounted in front of said gated light intensifier, said light collecting optical assembly directing collected light to said gated light intensifier.

44. The system according to claim 26, further comprising a gated light valve optically coupled with said gated light intensifier and electrically coupled with said controller, said controller controlling the operation of said gated light valve, to control the arrival of said reflections of said laser pulses at said gated light intensifier.

45. System for producing a target image of a target, according to any of claims 1-44 substantially as described hereinabove.

46. System for producing a target image of a target, according to any of claims 1-44 substantially as illustrated in any of the drawings.