WO1992003186A1

WO1992003186A1 - Laser focus adjustment system

Info

Publication number: WO1992003186A1
Application number: PCT/US1991/005647
Authority: WO
Inventors: William D. Fountain
Original assignee: Phoenix Laser Systems, Inc.
Priority date: 1990-08-13
Filing date: 1991-08-08
Publication date: 1992-03-05
Also published as: CN1059654A; AU8432491A

Abstract

A laser beam delivery system has an improved focus adjustment for controlling the depth at which the beam focusses in the target. An objective lens (24) remains stationary with respect to the target (26), and focus depth is controlled by adjusting the separation between a pair of positive and negative lenses (46, 48) which are positioned a distance behind the objective lens at least one additional optical path (34) is folded onto the laser beam path upstream of the objective lens. Thus, the surgical laser axis and at least one further axis on which analysis, target imaging and other functions are performed are joined together upstream of the objective lens. In this way, the laser beam may be focussed to given depth in the target, without interrupting optics along the partially colinear axis. Also, the objective lens assembly, which may be quite massive, is not relied upon for quick-response focussing during a surgical procedure.

Description

LASER FOCUS ADJUSTMENT SYSTEM

S P E C I F I C A T I O N

Background of the Invention

The invention relates to lasers and laser beam delivery systems, and in particular the invention is concerned with the focussing of a laser beam in a laser surgery system, such as for ophthalmic surgery.

In laser delivery systems, particularly those intended for laser surgery on target tissue placed in front of the front element, which is usually an objective lens assembly, parallel laser beam light typically approaches the objective lens assembly from the rear. This parallel light beam is focussed by the objective, to a prescribed focal plane in front of the objective.

In most such systems prior to this invention, the control of the depth at which the beam is focussed, or the "Z" distance or position of beam focus, was controlled by Z- direction movement of the objective.

One problem with this form of focus depth adjustment is that the objective lens assembly often must be somewhat massive, and fast response of the objective lens assembly to dynamic changes in the needed position of beam focus was difficult. An- xample of focus control is the need of the surgeon/user of the system to control focus depth for manipulating the point of focus in the tissue, as in ophthalmic surgery; when the surgeon/user's control is indirect, by means of a computer that effects direct control, fast-response changes in focussing depth (as well as in X and Y position) must be made. To accomplish these fast-tracking adjustments via the objective lens would require a simplified, lightweight objective which could be subjected to very high acceleration. In many cases this is impractical at best.

Another problem with use of the objective or Z-axis adjustment of beam focus position occurs in the case of a system which is split into several optical axes or paths, with the several paths sharing the same objective lens assembly. In such a system beam splitters typically are used for several different diagnostic and analysis devices, such as imaging devices for enabling a surgeon to control the procedure while viewing the tissue in one or several modes. Target illumination light and target-tracking functions may be folded in from a further axis or axes. If in such a multi-optical axis system the common objective lens is being adjusted in position for the purpose of moving the focus depth of the laser beam, as by the surgeon moving the point of focus to different depths, activities and data along the other split-off axes are also affected. For accuracy of data on some of these axes it might be required to compensate for each such movement of the objective lens. ^•

It is therefore desirable in many circumstances that the objective lens assembly be kept stationary with respect to the target in order not to disrupt the optics of the paths other than the laser beam's path. This is a general object of the present invention described below.

Summary of the Invention

In accordance with the present invention, a laser beam delivery system particularly for surgical applications has an efficient and improved focus adjustment for controlling the depth at which the beam focusses on or in the target. The focus adjustment system also has advantageous application to industrial processes.

In the apparatus of the invention an objective lens assembly at the front of the delivery system remains stationary with respect to the target, and focus depth is controlled by adjusting the separation between a pair of positive and negative lenses which are positioned a distance behind the objective lens along the laser beam delivery axis. Beam splitters are located between the objective lens and the pair of focus adjustment lenses, and at least one additional optical path may be folded onto the laser beam path upstream of the objective lens, without passing through the pair of positive and negative lenses. Thus, the laser axis and at least one further axis on which analysis, target imaging and/or other functions may be performed are joined together upstream of the objective lens, but downstream of the focussing lenses.

In this way, the laser beam may be manipulated as to the depth at which it is focussed at the target, without interrupting optics along the partially collinear analysis and imaging axis. As a further advantage, the objective lens assembly, which may be quite massive, may not be relied upon for quick-response focussing during a surgical procedure which may require such responses.

In a preferred embodiment of the invention, the treatment laser beam approaching the pair of focussing lenses is nominally parallel, i.e. a parallel beam or very close to parallel. The beam is made to diverge by the first, negative or concave lens, then brought back to parallel or near- parallel by the second, positive or convex lens. In this "normal" position the system focusses at a nominal or starting position on the target (e.g. the surface of the cornea in eye surgery) , after passing through the objective lens assembly. When the two lenses are brought closer together the exiting beam from the convex lens becomes slightly divergent (or more divergent) and this has the effect of moving the focal point deeper at the target.

The pair of positive and negative lenses used in the system of the invention has not been unknown in other fields. In some viewing devices a pair of such lenses have been used as part of a so-called zoom system. However, in this invention the optical use of the lens pair is somewhat different and it is particularly advantageous in simplifying and increasing the efficiency and reliability of a medical laser delivery system.

It is therefore among the objects of the present invention to address problems associated with Z-movement of an objective lens or objective lens assembly for focussing of a laser beam in^'a medical laser beam delivery system, and to produce a simplified beam delivery system of higher reliability and greater efficiency. These and other objects, advantages and features of the invention will be apparent from the following description of a preferred embodiment, considered along with the accompanying drawings.

Description of the Drawings

Figure 1 is a schematic overall system view showing one example of a surgical laser beam delivery system which may utilize the improvements embodied in the present invention.

Figures 2 and 3 are simplified schematic views showing a portion of the system of Figure 1, and illustrating an adjustment in the separation distance between a positive and negative lens in an optical path of the system, in order to effect a change in the depth at which laser beam focus is located.

Description of Preferred Embodiments

In the drawings, Figure 1 shows a laser beam delivery system generally identified by the reference number 10. The system 10 includes a laser source 12 producing a laser beam schematically indicated at 14. The beam 14 passes through various beam delivery optics which may include, for example, a beam expander 16, a mirror 18 (which may be a turning mirror) , beam splitters 20 and 22 and an objective lens assembly 24. As indicated in Figure 1, in a principal embodiment the depth focussing system of the invention is used in conjunction with ophthalmic surgery, and thus in

Figure 1 the beam is shown as converging to a focal point 26 at the corneal surface of the patient's eye 28. It should be understood, however, that the focus adjustment system described herein will find advantageous uses in other laser surgical processes and also in non-surgical industrial processes involving lasers.

In the beam delivery system 10 shown in Figure 1 the laser beam 14 follows an optical path or beam axis identified as 30 in the drawing. Another, separate optical path or axis is indicated at 32 and is folded onto the optical path 30 of the laser beam by the beam splitter indicated at 20. The drawing also shows a further optical path or axis 34 which is folded onto the path 32 at a downstream location by a further beam splitter 36. The axis 32 is thus partially collinear with the beam axis 30, in the portion between the beam splitter 20 and the target or focal point 26. The other optical axis 34 is similarly collinear, having been joined with the optical axis 32.

As discussed above, the optical axis 32, may be used for target tracking and the optical axis 34 may be used for imaging of the target. The instruments and optical devices 38, 40 and 42 shown as examples in Figure 1 may produce for the surgeon or user a series of selectable and separately adjustable images for analysis of the target (such as the eye 28) or for otherwise gaining information used in making decisions regarding the surgery procedure to be undertaken or for monitoring the progress of the surgery as it progresses.

The optical paths or axes 32 and 34, although sharing some of the optics of the laser axis 30 such as the objective lens assembly 24 and the mirror 22, are for different purposes and handle different light rays from the system. They reflect light back toward the imaging instruments thus providing information for the surgeon/user. They may comprise viewing, tracking, and analysis channels which in many procedures will be desirable to adjust separately from the adjustments in focussing depth of the laser beam 14 itself. As the point of laser beam focus on the target is moved in the operating procedure, which may be by an automatic, programmed laser beam steering system, it often is not desired that those systems move along with the movements of the beam focal point.

Therefore, it is desirable that the objective lens assembly 24 not be relied upon for simultaneous adjustments in Z-axis or focus depth for both the treatment laser beam and the non-treatment channels, at least not solely. The objective 24 can be moved for other purposes, such as movement of the patient's eye 28 along the Z-axis, whereupon the position of the objective 24 can be adjusted to follow this movement of the patient. This will affect both the viewing channels (and tracking and analysis channels) and the laser beam delivery, in order to maintain a constant relationship between the eye and the objective 24.

However, the manipulations of the depth at which the focal point 26 occurs on or in the eye 28 (or workpiece, in an industrial operation) should be controlled separately, so as not to affect the viewing channels as discussed above.

In accordance with the invention, Z-axis or focus depth adjustment is accomplished by a lens pair 44, including a first, negative or concave lens 46 and a second, positive or convex lens 48. As is known in some so-called zoom systems, the separation distance between the negative and positive lenses 46 and 48 will affect the degree of convergence or divergence of the beam exiting the downstream or convex lens 48. The closer the lens pair, the greater the divergence of the emerging exit beam, and thus the deeper the focus point will occur after passing through the objective 24.

Thus, it can be seen from Figure l that the use of the lens pair 44 enables the laser beam delivery optics along the beam axis 30 to focus the operating or treatment laser beam 14 independently of and without affecting the imaging optics along the imaging axes 32 and 34.

Figures 2 and 3 are schematic views showing the principle of operation of the focussing system just described.

Figure 2 shows components of the system at and near the objective lens assembly 24. The laser beam 14 enters the first, concave lens 46 of the lens pair 44, is refracted to be divergent as indicated in Figure 2, and then is refracted back to near-parallel collimated condition downstream of the convex lens 48. Figure 2 is intended to show a "normal" or "home" position of the lens pair 44, wherein parallel or close to parallel light is reflected off the beam splitter and off the mirror 22, whereupon it is focussed by the objective 24 to a desired focus depth, i.e. at the focal point 26 as shown. Again, although the drawings show the system in conjunction with a laser beam for eye surgery, it should be understood that the item 28 can be a workpiece in an industrial process.

It should also be understood that the emerging beam from the second, convex lens 48 need not be parallel or even essentially parallel in this "normal" position. The arrangement illustrated and described is preferred because it makes the optics somewhat simpler with respect to other functions of the objective lens assembly 24, as relates to the non-treatment axes 32 and 34.

Figure 3 illustrates that, as the concave lens 46 is moved closer to the convex lens 48, e.g. via a movable stage device 50, the beam 14 between the two lenses, although it diverges at the same angle, passes through the convex lens 48 with, its extremal rays closer to the axis 30. Thus, the convex lens has less effect in converging the beam, or in bringing it back toward collimation, and thus the beam will emerge still diverging somewhat in the configuration shown in Figure 3. This of course causes the beam to be brought to a focal point 26a farther from the objective and hence deeper into the target 28.

As is known in optics, such as in zoom optics as discussed earlier, in order for the two lenses of the lens pair 44 to receive a collimated beam and also dispatch a collimated beam, their separation distance should be equal to the unsigned focal length (f₂) of the convex lens 48, less the unsigned focal length (fi) of the concave lens 46. This is indicated schematically in Figure 2.

It will be clear to the artisan that, while the discussion above describes the preferred embodiment, other embodiments can be realized using the principles of the invention. For example, the order of the positive and negative lenses can be reversed, or a more complex ensemble of lens elements can replace the two elements described herein, or the positive lens, rather than the negative lens, can be the lens that is repositioned, or any combination of the preceding implementations can be used. A pari of positive lenses can be used. Also, reflective elements (curved mirrors) can be used instead of refractive elements.

The above described preferred embodiment is intended to illustrate the principles of the invention, but not to limit its scope. Other embodiments and variations to this preferred embodiment w^τill be apparent to those skilled in the art and may be made without departing from the spirit and scope of the invention as defined in the following claims.

I CLAIM:

Claims

1. In a surgical laser beam delivery system having a laser source and optical path means for delivering a laser beam from the laser source to a target and including a front or objective lens assembly at the downstream end of the optical path means, a focus control apparatus for adjusting the depth or Z distance from the objective lens assembly at which the laser beam is focussed at target tissue, comprising, a plurality of lenses on the optical path means, movable stage means associated with the pair of lenses for adjusting at least one separation distance among the lenses, so as to adjust the degree of divergence or convergence of the laser beam downstream of the plurality of lenses, as it approaches the objective lens assembly, and focus control means under the control of the surgeon/user, for adjusting the movable stage means and said separation distance, to control the depth in front of the objective lens assembly at which the laser beam is brought to a focus.

2. Apparatus according to claim 1, wherein the laser beam delivery system further includes analytic devices for obtaining information optically obtained from the target tissue, and a second optical path means associated with the analytic devices, said second optical path means being partially coextensive with the first optical path means and passing through, the objective lens assembly, with beam splitter means at a point of juncture of the first and second optical path means, whereby op-ical information conducted along the second optical path means to the analytic devices is not affected by focus depth adjustment accomplished by the plurality of lenses in the first optical path means.

3. Apparatus according to claim 1, wherein the plurality of lenses comprises a pair of lenses including a negative or concave lens and a positive or convex lens, separated by said separation distance.

4. Apparatus according to claim 3, wherein the negative lens is upstream of the positive lens on the optical path means.

5. Apparatus according to claim 4, wherein the negative lens is connected to the movable stage means.