|Numéro de publication||USRE42184 E1|
|Type de publication||Octroi|
|Numéro de demande||US 11/805,862|
|Date de publication||1 mars 2011|
|Date de dépôt||23 mai 2007|
|Date de priorité||25 nov. 1998|
|État de paiement des frais||Payé|
|Autre référence de publication||US6897999|
|Numéro de publication||11805862, 805862, US RE42184 E1, US RE42184E1, US-E1-RE42184, USRE42184 E1, USRE42184E1|
|Inventeurs||Michael Bass, Jason Eichenholz, Alexandra Rapaport|
|Cessionnaire d'origine||Research Foundation Of The University Of Central Florida, Inc.|
|Exporter la citation||BiBTeX, EndNote, RefMan|
|Citations de brevets (39), Citations hors brevets (1), Classifications (17), Événements juridiques (2)|
|Liens externes: USPTO, Cession USPTO, Espacenet|
This invention claims the benefit of priority to U.S. Provisional Application 60/342,578 filed Dec. 26, 2001, and this invention is a Continuation-In-Part of U.S. application Ser. No. 09/976,921 filed Oct. 12, 2001 now U.S. Pat. No. 6,501,590, which is a Divisional Application of U.S. application Ser. No. 09/448,657 filed Nov. 24, 1999, now U.S. Pat. No. 6,327,074, which claims priority to U.S. Provisional Application 60/109,837 filed by the same subject inventors and assignee as the subject invention on Nov. 25, 1998, and this invention is a Continuation-In-Part of U.S. application Ser. No. 09/919,131 filed Jul. 31, 2001 now U.S. Pat. No. 6,654,161, and U.S. application Ser. No. 09/919,130 filed Jul. 31, 2001 now U.S. Pat. No. 6,844,387, and this invention was partially funded under U.S. Army Contract DAAD199910220.
This invention relates to displays, and in particular to methods and apparatus for forming an optically written projection display encompassing two dimensional single, dual color and three coloured, green and blue) color displays that uses near infrared laser beams that are simultaneously split and modulated and directed at particles in display mediums, wherein the emitted colors have high limit efficiencies.
Two dimensional and three dimensional displays are well known to be made monochromatic displays. However, monochromatic does not offer the detail such as shown using red, green and blue colors.
Displays using liquid crystals have been proposed of generating color displays. See for example, U.S. Pat. Nos. 5,359,345 and 5,724,062 to Hunter. However, these patents require arranging individual pixels in rows and corresponding columns, column 4, lines 36-39. The devices described can be expensive and complicated to manufacture, can have a narrow angular view ranges with low brightness.
Additional display systems have been proposed with similar problems to those described above. See for example, U.S. Pat. No. 4,791,415 to Takahashi; U.S. Pat. No. 4,871,231 to Garcia, Jr.; U.S. Pat. No. 5,184,114 to Brown; U.S. Pat. No. 5,192,946 to Thompson et al.; and U.S. Pat. No. 5,317,348 to Knize.
Several patents have been proposed for panel displays using two-frequency upconversion fluorescence. See for example, U.S. Pat. Nos. 5,684,621; 5,764,403; 5,914,807; 5,943,160; and 5,956,172 all to Downing. The Downing '403 patent appears to be the most relevant to the subject invention. Downing '403 is primarily concerned with embodiments where the use different layers for red, green and blue emitters, abstract,
The first objective of the present invention is to provide an inexpensive methods and systems for forming two dimensional and three dimensional displays.
The second object of this invention is to provide methods and systems for uniformly dispersing micron sized particles in a transparent host media for two and three dimensional displays.
The third object of this invention is to provide a two and three dimensional display media methods and systems using dye doped plastics uniformly dispersed in a plastic transparent host media.
The fourth object of this invention is to provide for optically written projection display methods and systems that can directly write an entire image at one time without having to form an image one pixel at a time or one line at a time.
The fifth object of this invention is to provide methods and systems for creating large screen direct view displays such as movie screen, television screen, HDTV(high definition television) and computer monitor displays, using rare earth doped crystals.
The sixth object of this invention is to provide methods and systems for projecting near IR(infrared) laser light to a display using single devices that include both modulators and scanners.
The seventh object of this invention is to provide a single laser source such as a laser diode to efficiently excite two colors with the same pump wavelength.
The eigth object of this invention is to provide a single laser source such as a laser diode to efficiently excite three colors with the same pump wavelength.
The invention covers uniformly dispersing particles of approximately 0.5 microns to approximately 50 microns in appropriate places in a transparent host display medium. The appropriate places are the locations of the pixels that will produce the desired color emission when illuminated by the corresponding exciting laser. The particles can be dye doped plastics, rare earth doped crystals, and the like, in display mediums such as plastic, acrylic plastic, and glass. The first preferred embodiment includes up to three lasers each emitting a laser beam at a different wavelength elected to excite specific groups of particles in the laser beam illuminated areas of the display medium. There are three different particulate types, with selected amounts of each uniformly dispersed in the appropriate places in the display medium. One particle type when excited by a first laser beam emits a red visible fluorescence, a second particle type when excited by the second laser beam emits a green visible fluorescence, and a third particle type when excited by the third laser beam emits a blue visible fluorescence. The two dimensional display does not require a matched index of refraction between the particles and the display medium.
A second embodiment is for a three dimensional display having up to six laser beams, each being emitted at a different wavelength. Similar to the first embodiment, the display medium has a substantially uniform dispersement of red, green and blue particles therethrough. A pair of laser beams is directed so that the beams intersect at a specific location in the display medium. One pair of intersecting beams that excites a first particle type that then emits red fluorescence, another intersecting pair with a second particulate type emits green fluorescence, and a third pair of intersecting beams with a third particulate type emits blue fluorescence. The three dimensional display requires a matched index of refraction between the particles and the display medium.
Optically written projection display(OWPD) embodiments are also disclosed, which can be more efficient electrically and cost less to manufacture than CRT(cathode ray terminals) and conventional projection televisions, by using novel combinations with scanners and modulators allowing for the simultaneous splitting and modulating of generated beams in addition to designs employing electro-optic and acousto optic modulators and scanners, The additional modifications allow for applications for high end projection televisions such as HDTV(high definition television) and movie screen applications that do not use raster type scanning techniques.
The display mediums for OWPD can include transmissive displays where light is directed through panels which either block or transmit incoming light to create an image. Additionally, the display medium can be a reflective display where light is reflected of a surface such as a mirror, and the like. This light is then imaged and projected onto the viewing screen. In reflective projectors, the television image is formed by driving a small, pixilated, reflective chip such as the Texas Instruments Digital Light Projector(DLP) with a selected electrical input from the video signal. The viewed image can be formed by reflection off the chip, and through a projection lens to the display screen. The light can be modulated when the light hits regions of the mirror in the “on” state and reflects off of the mirror and through the projection lens to the screen. When the light hits regions of the mirror in the “off” state, the mirror will reflect the light away from the screen to an absorber.
The novel OWPD embodiments can include splitting and modulating devices that include: spatial light modulators (SLMs), micro electro mechanical systems(MEMS), liquid crystal displays(LCDs), digital micromirror devices (DMDs), digital light projectors(DLPs), grating light valves (GLVs), liquid crystal on silicon(LCOS) devices, polysilicon LCDs, ferro electric crystals(FECs), electron beam written spatial light modulators(E-beam SLMs), and electrically switchable Bragg gratings(ESBGs).
The light sources for the optically written projection displays can be a single laser diode for monochromatic displays, and can include up to three diodes for displays of red, green, and blue. The displayed image can be formed from reflecting three laser sources each having different wavelengths off the modulator,(or through it in a transmissive modulator), to each of the three different types of particles in the display medium. Infrared light can be absorbed by the particles in the pixels in the display. The particles in the pixels become excited and can emit visible radiation. Specifically, blue light can be efficiently generated by Yb,Tm:YLF(yttrium lithium fluoride) when pumped with diode laser light having a wavelength of approximately 958 to approximately 959 nm, green visible light can be efficiently generated by Yb,Er:NYF(sodium yttrium fluoride) when pumped with diode laser light having a wavelength of approximately 976 nm, and red visible light can be efficiently generated by Yb,Er:KYF(potassium yttrium fluoride) or Yb, Ef:YF3 when pumped with diode laser light having a wavelength of approximately 973.5 nm to approximately 976 nm.
Single laser sources operating at one wavelength can generate at least one color(for example, Red) having a limit efficiency of at least approximately 7%. A single laser source pumping at approximately 976 nm can cause Green and Red color emissions having a limit efficiency of at least approximately 4%, or three color(Green, Red, Blue) emissions having a limit efficiency of at least approximately 2%.
Further objects and advantages of this invention will be apparent from the following detailed descriptions of a presently preferred embodiments that are illustrated schematically in the accompanying drawings.
Before explaining the disclosed embodiments of the present invention in detail it is to be understood that the invention is not limited in its applications to the details of the particular arrangements shown since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation.
Modulators 20, 60 and 100 can be electro optic modulators by Lasermetrics, Co., an acousto-optic modulator by Newport Electro Optical Systems, or a direct drive to the power supply of the diode laser that can modulate the current to the laser diode and therefore modulate the laser power. The modulators 20, 60 and 100 control the intensity(power) or on and off states of the light emitted from lasers 10, 50, 90, respectively.
Scanners 30, 70 and 110 are used to control the direction of the light from the laser sources 10, 50, 90 to be incident at any location in the display medium 170. Scanners 30, 70 and 110 can be chosen from rotating mirrors, galvanometer mounted mirrors such as those sold by Cambridge Technology, rotating prism scanner sold by Speed Ring Co. or MEMs based scanner such as those sold by Analog Devices, Microvision, and the like. Alternatively, Scanners 30, 70 and 110 can be acousto-optic scanners manufactured by Newport Electro Optical Systems, a Binary, liquid crystal based scanners, and the like.
Optics 40, 80 and 120 are optics such as lens, and the like, that can focus the laser light into the specific location within the display medium 170. Optics can help achieve the selected display resolution(e.g., number of resolvable display points per unit length along either the height or width of the display).
130, 140 and 150 refer to the modulated, scanned and focused beams of light from their respective laser source, modulator, scanner and optics that are directed towards selected locations in display medium 160.
Display medium 160(shown and described in greater detail in reference to
A preferred embodiment of one of the most inexpensive materials to manufacturer and produce for the particles 162, 164, 166 are dye doped plastics, such as dye doped plastic polymethylmethacrylate(pmma). The dyes can be colored dyes such as rhodmaine B, and rhodaime 6G, and the like. Table 1 which will be described later gives examples of dyes.
Alternative particles 162, 164, 166 that are not as inexpensive to manufacture and produce as dye doped pmma include rare earth doped crystals, transition metal doped crystals, rare earth doped glasses, combinations thereof, and the like.
Rare earth doped crystals offer the most efficient two photon up converters. In particular the host crystal sodium yttrium fluoride(NaYF4) doped with rare earth family emitting ions has been tested by the subject inventors. For example, doping the host crystal with Er(erbium) can produce green, doping the host crystal with Tm(thulium) can produce blue, doping with Ho(holmium) can produce either or both red and green, and doping with Pr(praesodymium) can produce red, green, &/Or blue emissions. Adding co-dopant such as Yb(ytterbium) to the doped crystals can be done to improve the efficiency. Next the host crystal containing the emitting ions(doped rare earth materials) is placed into a liquid state of pmma and thoroughly mixed into the pmma until the particles are substantially uniformly mixed throughout the pmma.
The Particles 162, 164, 166 can be conventionally ground up and sieved. The novel sized particles are individually sized in the range of approximately 0.5 microns to approximately 50 microns. This sizing is to maximize absorption of pump light and consequently, the emission.
The display medium 161 is transparent and can be formed from materials such as pmma, acrylic plastic, epoxy, glass, and the like. The overall size of the display medium can range from less than 1 centimeters square to a few meters square or more. The particles 162, 164 and 166 are mixed in the display medium 161 while the latter is in a liquid type state, until the particles are substantially uniformly dispersed throughout the display medium 161, which later hardens over time. All the particles 162, 164 and 166 can be of uniform size within the range of approximately 0.5 microns to approximately 50 microns when the display medium 161 applications call for uniform emissions of red, green and blue. Additionally, each of the particles 162, 164 and 166 can be variably sized within the range of approximately 0.5 microns to approximately 50 microns as would be needed for specific applications where more of one color is needed for the display itself.
The entire display volume 161 can contain particles 162, 164, 166 that make up between the ranges of approximately 1/10% to approximately 99.9% of the overall volume of the display medium 161.
Each pixel is sized to contain selected amounts of particles 162, 164, and 166. For example, if a pixel is considered to have a diameter of D, and if the number of particles is n, then the dimension of each particle is less than or equal to D divided by the square root of n. The area of a single particle would be equal to D squared divided by n. For a pixel having a diameter of 500 microns by 500 microns, and the display is 1 micron thick, the pixel area would be 25,000 microns and if each particle size were approximately 1 micron by 1 micron, there could be as many as approximately 25,000 particles. Where an embodiment of the display would have substantially equal numbers of red, green and blue emitters there would be approximately 8333 particles of each type. The example, changes if the display &/or the particle size &/or the pixel size changes.
For a 2 dimensional display all the pixels must contain a substantially equal number and distribution of particles 162, 164, 166 throughout the display.
A two dimensional display using the subject invention does not have to have a matching index between the particles 162, 164, 166 and the display medium 161 itself. For a matching index between the display medium 161 and the particles 162, 164, 166, visible light can be observed from both sides of the display medium 161. Such a display would be substantially transparent to other light from other sources that the viewer would want to see. If there is an unmatched index between the display medium 161 and the particles 162, 164, 166, visible light to the observer 200 would appear to be scattered.
Thus, for a two dimensional display having a matching index, the particles 162, 164, 166 can be dye doped pmma and the display medium 161 can be pmma. Additionally, for a two dimensional display having an unmatching index, the particles 162, 164, 166 can be dye doped pmma, and the display medium 161 can be formed from glass.
Unlike the two dimensional displays, for a three dimensional display there must be substantial index matching between the transparent host display medium material and the particles because for a three dimensional display the observer must be able to see into the three dimensional display from all angles. Thus, dye doped plastic pmma particles substantially uniformly dispersed in a pmma display medium would work for a three dimensional display. However, dye doped plastic pmma particles inside a lead glass display medium would not work for three dimensional displays since dye doped plastic pmma particles have a low index of refraction while the lead glass has a high index of refraction.
Three dimensional display media sizes can range from small sizes of approximately 5.0 cm on a side, to medium sizes of approximately 25 cm on a side, to large of approximately 1 meter on a side.
For a display media of approximately 25 cm on a side, and 500 voxels in each linear dimension a voxel can be approximately 500 micrometers in diameter. If the crystallites are approximately 10 micrometers in diameter and doped to approximately 1% of the volume then there will be approximately 400 each of red, green and blue emitters per voxel.
Experimentation was conducted and will now be described.
Two-photon absorption experiments were performed using either a Q-switched neodymium-doped yttrium aluminum garnet (Nd3+: YAG) laser, or a Q-switched chromium-doped lithium strontium aluminum fluoride (Cr3+: LiSAF) laser, or both depending on the peak absorption wavelength of the dye studied. Visible emission was detected through a monochromator by a type I photomultiplier. The pump pulses were monitored by fast PIN photo-diodes having approximately 0.5 ns response times.
In order to demonstrate the absorption of two photons of the same wavelength in the dye solutions and in the dye-doped polymers, we needed to prove the dependence of the visible emission intensity on the square of the intensity of the pump. The necessary proof in both liquid solutions and dye-doped polymers was obtained by varying the peak pump intensity and monitoring the resulting peak intensity of the signal. Calibrated neutral density filters were placed in the pump beam in these experiments. Data obtained from such measurements for a solution of 5×10−4 M rhodamine pumped by the Q-switched Nd3+:YAG laser are shown in FIG. 6A and demonstrated the square-law relationship. Additional confirmation was obtained since our detection system was fast enough to show that the signal wave form (e.g., the visible light intensity as a function of time) follows exactly the square of the pump pulse wave form. This type of data for the same dye solution is given in FIG. 6B. It is clear that the visible emission observed is due to two-photon absorption of the single pump source.
Two-photon absorption of a single infrared pump wavelength was observed in several of the dye-doped polymers (see Table 1). Some of the samples showed very strong visible emission and some much weaker. These plastics were designed for use in advertising displays and were not optimized for the present study. As a result, quantitative measurement of the emitted light was deferred until improved materials are received. In Table 1, the blue CYRO plastics 6122-8 and 6141-8 are seen to have produced no visible emission under excitation at approximately 850 nm. However, these two samples emitted quite well in the blue when excited with the Cr3+:LiSAF laser tuned to approximately 800 nm (their absorption coefficient at approximately 400 nm is approximately 20 cm−1). As a result, visible emission by dye-doped polymers of blue, green, yellow, and red light was obtained.
Experiments to show the absorption of two photons of two different infrared wavelengths in the dye solutions were conducted using both the Nd: YAG and Cr: LiSAF lasers. The use of a Stanford Research System model DG 535 pulse generator to Q switch both lasers resulted in very little interpulse jitter.
It should be noted that in some dye solutions with too small a Stokes shift, overlap between the absorption and emission regions causes the color of the observed visible emission to depend on the location of the emitting site within the sample. Thus, a solution that emits yellow light near the surface appears to emit a more reddish color when excited in the center of the sample. To reduce this effect, dye solutions with large Stokes shift (such as obtained in solutions of coumarin dyes) will be more attractive candidates for 3D display applications.
The experiments reported show that dyes in liquid and polymeric solutions can be excited to emit visible light by simultaneous absorption of two different infrared light sources. Since the region of overlap of two such beams can be moved around within the volume of such a medium, the visible emissions can be made to trace out a three-dimensional image. The result would be a real-time, three-dimensional display.
Some of the properties that an appropriately chosen dye should exhibit have already been identified. It should present a large Stokes shift and a narrow absorption band. It should also have a high coefficient of nonlinear absorption as well as high quantum efficiency. However, more research remains to be done to optimize the dye and the host material. The samples studied showed that laser damage was an issue with the laser pulse energies used in the demonstration. Attention should be given to make polymers free of scattering. The use of mode-locked diode lasers should enable the intensities necessary for effective nonlinear excitation of dye-doped media.
Liquid display media could be difficult to handle and possibly dangerous. On the other hand, with proper dye and polymer chemistry, polymers that efficiently emit visible light under the demonstrated excitation can be developed. Such dye-doped polymers will likely be able to serve as one-color displays. When dye/polymer combinations are more fully developed capable of blue, green, and red emission (see Table 1) three-color displays are possible. Since it is likely that unwanted intermolecular interactions will occur if all three dyes were placed in the same host, we suggest that the doped polymers could be powdered and then dispersed in a clear passive host polymer. In this model, the concentration of each emitting particulate should be such that there are many in each volume element of the display. As a result, each volume element could emit any desired color. Note that a polymer containing the dispersed particles could be prepared in sheet form and used as a two-dimensional display with single-wavelength excitation sources for each color. The LISA plastics were supplied by CYRO Industries, CT.
at 532 nm
near 425 nm
TABLE 1 is a list of dye-doped polymers tested and their properties. The visually observed emission strength is indicated by no asterisks for no emission to three for strong emission. The nonlinear emission was observed either with a 1064 nm Nd:YAG laser focused to about 100 MW/cm2 with the sample or a 850 nm Cr:LiSAF laser focused to 30 MW/cm2.
The invention has many applications. Military such as the Army can be used for terrain map presentation and analysis, visualization and prototyping for design and manufacturing, battlefield awareness and war fighter visualization of the battlefield. Other military and civilian applications are the need for 3D color displays in air traffic control. Medical applications can be used to help train physicians and healthcare providers. Training on medical models of body organs and skeletal structure would allow medical persons to be able to train on images of their patients before and while caring for them.
Optically Written Displays
Beam shaper lens 320 is intended to represent a group of one or more elements. The light is then directed using lenses, mirrors or prisms towards the spatial light modulator (SLM) 330, which will be described later in greater detail. Spatial light modulator (SLM) 330 can include but is not limited to an array of pixel generating elements that emit or reflect light of the display screen towards the projection lens. The SLM 330 modulates light and forms an image by turning the pixel-generating elements “on” or “off”. This spatial light modulator 330 breaks the light image up into an array of M×N pixels where M and N can be any integer greater than 1. Depending on the type and selection of the spatial light modulator 330, the laser light will either be reflected off of or transmitted through the spatial light modulator towards the projection lens optics 350. Since the laser light is quasi-monochromatic and can also be polarized, a large number of different types of spatial light modulators 340 can be utilized in this invention. One example of a SLM is a DMD (digital micro-mirror device) by Texas Instruments (as described for example in U.S. Pat. No. 6,317,171 which is incorporated by reference). A DMD is an electromechanical device, whose pixel-generating elements form an array of thousands of tiny tilting mirrors. The DMD is mounted on top of a control circuitry, which provides individually addressable electrostatic forces, which can cause each mirror to selectively tilt. Laser light incident on the mirror array is reflected in one direction by the “on” state mirrors and in the other direction by mirrors in the “off” state. The pattern and timing of “on” versus “off” forms an image. Inmost applications, the light from the DMD mirrors in the “on” state is directed by a projection lens optics 350 to a screen 360. DMD arrays can have over 2 million individual mirrors in one device, sufficient for generating HDTV or UXGA displays.
An example of a one dimensional SLM (where M is 1) is a grating light valve (GLV) by Silicon Light Machines. The GLV architecture consists of a linear array of pixels oriented along a vertical column of image data. Once per image refresh, this linear array is optically scanned across the screen to produce a complete two-dimensional image. Therefore, the use of a GLV or any 1-dimensional spatial light modulator in this invention would also require the use of an additional one dimensional scanner to for a two-dimensional image.
Another SLM 330 that can be used with the subject invention can be a Silicon Light Machines Grating Light Valve(GLV), such as those described in U.S. Pat. No. 5,982,553 which is incorporated by reference. The GLV chip can consist of tiny reflective ribbons mounted over a silicon chip, where each ribbon is approximately 100 fentometers long, approximately 100 nanometers wide and approximately 3 fentometers thick. The ribbons can be suspended over the chip with a small airgap in between. When a voltage is applied to the chip below the ribbon, the ribbon moves toward the chip by a fraction of the wavelength of the illuminating light. The deformed ribbons can form a diffraction grating and the various orders of light can be combined to form the pixel of an image.
The Different types of Spatial Light Modulators 330 can include:
The projection lens optics 350 can be a combination of optical surfaces and materials, which image the spatial light modulator(SLM) 330 onto the upconversion display screen 360. Lens optics 350 for projecting the light from a spatial light modulator 330 are well-known in the optical art and can require a combination of one or more spherical, aspheric, toroidal, cylindrical (spherical and aspherical), micro-optic, and diffractive optical elements. Since the laser light in this embodiment is quasi-monochromatic, the projection lens optics 350 can be simplified and can even be a single element since the projection lens optics 350 does not need to compensate for chromatic aberration as in typical Red, Green, Blue (RGB) display projection systems. Additionally the anti-reflective coating for both the projection optics 350 and beam shaper lens optics 320 can be simplified due to the ability to use less expensive anti-reflective coating such as a “V coating” or single layer coatings.
The up conversion screen 360 used in
Red(R), Green(G) and Blue(B) Efficiencies
Data from experimentation has shown that blue light can be efficiently generated by Yb,Tm:YLF(yttrium lithium fluoride) when pumped with diode laser light having a wavelength of approximately 958 to approximately 959 mm, green visible light can be efficiently generated by Yb,Er:NYF(sodium yttrium fluoride) when pumped with diode laser light having a wavelength of approximately 976 mm, and red visible light can be efficiently generated by Yb,Er:KYF(potassium yttrium fluoride) when pumped with diode laser light having a wavelength of approximately 973.5 nm.
The definitions and units discussed in this section are as follows:
2. Excitation Spectra
3. Current cw Efficiency Values for a Fixed Spot Size
The inventors used a calibrated spectroradiometer with an integrating sphere to measure the visible emitted power for the different materials. The diode laser used was a approximately 500-mW 976 nm single emitter for the Green and the Red emitters, and an approximately 1-W 959 nm diode laser for the Blue emitter.
The efficiencies were measured by reflection and a metallic mirror which was used behind the sample in order to collect all the visible light emitted. The size of the excited spot was determined by the divergence of our diode laser, the focus lengths of our collimating lenses, the physical dimensions of our integrating sphere, and the final focusing through the cabochon. We estimate the emitting spot to be approximately 1 mm in diameter.
The graphs of
As to the efficiency with respect to absorbed power the inventors have recorded the unabsorbed IR power measured by the integrating sphere. We estimate that the limit efficiency measured with respect to absorbed power would be between approximately 10 and approximately 15% for the 3 colors(Green, Red, and Blue).
4. Efficiency vs. Average Power For Several Excitation Durations & Fixed Spot Size
In order to check the effect of pulse duration on the efficiency of pumping, we used a mechanical chopper(which continuously cuts light) rotating at approximately 30 Hz with variable slit sizes. The duration of pumping was measured using a fast oscilloscope and a photodiode at the sample location. The average power was measured for various neutral density filters and for each slit size.
We measured the brightness obtained from an approximately 500 micron spot. For the green and red emitters, we used our fiber coupled approximately 968 nm diode laser array capable of delivering approximately 5 to approximately 6 W of cw radiation. The quantity plotted on the vertical axis in the graphs in
For the Green and Red, the increase in maximum efficiency is not significant when pulse pumping. However, the above graphs show that one reaches higher efficiencies for smaller pump powers when pumping with a short, intense pulse. For the blue, the change is quite significant, and we gain a factor of at least approximately 3 in maximum efficiency when pumping with a short pulse without even reaching saturation of the efficiency.
Table 2 is a summary table of the limit efficiency of the RGB upconverters:
Limit efficiency when
pumped cw at 976 nm
Output W/incident W
efficiency for pulse
pumping at 976 nm
Output W/incident W
Limit efficiency when
pumped cw at 959 nm
Output W/incident W
efficiency for pulse
pumping at 959 nm
Output W/incident W
The top row is the limit efficiency when the materials in the various columns are pumped at a continuous wave(cw) at approximately 976 nm, with values for both: output power(W) divided by incident pumped power(W); and for lumens(Lm) per Watt(W).
The second row is an estimated limit efficiency for pulse pumping at approximately 976 nm, with values for both; output power(W) divided by incident pumped power(W); and for lumens(Lm) per Watt(W).
The third row is the limit efficiency when the materials in the various columns are pumped at a continuous wave(cw) at approximately 959 nm, with values for both: output power(W) divided by incident pumped power(W); and for lumens(Lm) per Watt(W).
The fourth row is the estimated limit efficiency when the materials in the various columns for pulse pumping at approximately 959 nm, with values for both: output power (W) divided by incident pumped power(W); and for lumens (Lm) per Watt(W).
As demonstrated in Table 2, a single laser source pumped at approximately 976 nm can cause emissions of three colors(Green, Red, and Blue) having an efficiency of at least 2% for all three colors.
Additionally, a single laser source pumped at approximately 976 nm can cause emissions of at least two colors (Green and Red) having an efficiency of at least approximately 4% for the two colors.
Table 2 further demonstrates that Red emissions can have an efficiency of at least approximately 7% when being pulse pumped by laser source at approximately 976 nm.
Additionally, Table 2 demonstrates blue emissions can have an efficiency of at least 4.5% when being pulse pumped by a laser source at approximately 959 nm.
While the invention has been described, disclosed, illustrated and shown in various terms of certain embodiments or modifications which it has presumed in practice, the scope of the invention is not intended to be, nor should it be deemed to be, limited thereby and such other modifications or embodiments as may be suggested by the teachings herein arc particularly reserved especially as they fall within the breadth and scope of the claims here appended.
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|1||Kaminskii, Alexander A.; Laser Crystals, Springer Series in Optical Sciences, v. 14, 1981, pp. 170-311.|
|Classification aux États-Unis||359/326, 365/151, 501/126, 501/904, 501/123|
|Classification internationale||G11C13/04, G02F1/35, G02F2/02, C09K11/02, C09K11/77|
|Classification coopérative||Y10S501/904, C09K11/02, C09K11/7773, G03B21/2033, G03B21/60|
|Classification européenne||C09K11/02, C09K11/77S4B|
|5 juil. 2011||CC||Certificate of correction|
|4 oct. 2012||FPAY||Fee payment|
Year of fee payment: 8