US20070106285A1 - Laser scanner - Google Patents

Abstract

A laser scanner is disclosed. The laser scanner comprises a laser source, a first optical element, and a focusing element. The first optical element is adapted to move along the optical axis of light from the laser source. The focusing element receives laser light from the first optical element and is adapted to move orthogonally to the optical axis. Optionally, the focusing element may include multiple focusing lenses. A first focusing lens may be adapted to move along a first axis which is orthogonal to the optical axis. A second focusing lens may be adapted to move along a second axis which is orthogonal to the optical axis and to the first axis. The laser scanner may also include a second optical element which receives light from the focusing element and is adapted to effectively increase the focal length of the focusing element without increasing its f number.

Description

BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The field of the present invention is laser scanners, particularly laser scanners that may be employed for ophthalmic laser surgery.
• 2. Background
• Laser scanners for ophthalmic laser surgery generally utilize a pair of scanning mirrors to angularly deflect and scan the laser beam. Typically two scanning mirrors are employed, each scanning the laser along one of two orthogonal axes. A focusing objective, whether one lens or several lenses, images the laser beam onto a focal plane of the optical system. The focal point of the laser beam is thus scanned in two dimensions (x and y) within the focal plane of the optical system. Scanning along the third dimension, i.e., moving the focal plane along the optical axis (z-axis), may be achieved by moving the focusing objective, or one or more lenses within the focusing objective, along the optical axis.
• The optical systems used to focus ophthalmic surgical lasers are generally quite complex. Such optical systems are typically required to have diffraction limited performance with a high numerical aperture (NA) and to scan the laser beam over an extended range. The moving mirrors that are typically used in such systems create significant design constraints because significantly high field angles are used during the scanning process, thus requiring optical correction for aberrations such as astigmatism, coma, and other higher order aberrations. In addition, since the beam is scanned angularly, off-axis aberrations of the objective are typically generated and require correction.
• The optics required to correct the aberrations created in such laser scanners of the prior art tend to add to the weight and cost of the overall optical system. The overall cost added to such systems may be in the range of tens of thousands of dollars or more. The overall weight of laser scanners, with corrected optics, can be in the range of five kilograms or more. Such heavy systems are extremely difficult to manually position over a patient's eye. To compensate, motorized gantries are frequently employed to move the optics into position with the eye in a “docking” procedure. To assure patient safety during “docking”, and to prevent inadvertent movement of the motorized gantry, special safety electronics are included as part of such scanning systems. These additional electronics further increase the complexity and cost of the scanning system.
SUMMARY OF THE INVENTION
• The present invention is directed towards a laser scanner. The laser scanner comprises a laser source and optics for scanning the focal point in three dimensions. The optics include optical elements for scanning the laser beam along three orthogonal axes and an optical element which extends the focal plane of the optics away from the focusing lens(es).
• In a first separate aspect of the invention, a first optical element and a focusing element are included as part of the optics of the laser scanner. This first optical element is adapted to move along an optical axis of light from the laser source. The focusing element is adapted to move orthogonally to the optical axis. The focal plane depth of the optics may be adjusted through movement the first optical element. Further, the focusing element may include two focusing lenses, each adapted to move along two orthogonal axes, these axes also being orthogonal to the optical axis.
• In a second separate aspect of the invention, an optical element within the optics of the laser scanner is adapted to effectively increase the focal length of an included focusing element without increasing the f number of the focusing element. Preferably, the refractive index of this optical element is greater than one.
• In a third separate aspect of the invention, the laser scanner is incorporated into a system adapted for ophthalmic laser surgery and includes a mirror optically disposed between the focusing element and the eye on which the surgical procedure is conducted. This mirror is adapted to pass light from the laser source and to reflect visible light. The surgical system also includes a view port optically coupled to the mirror to receive the reflected visible light from the mirror. This view port optionally allows an attending surgeon to directly view the ophthalmic surgical laser procedure as it occurs. If desired, magnification optics may be included as part of the view port to facilitate viewing of the surgical procedure.
• In a fourth separate aspect of the invention, the focal point of the laser is scanned in a manner which helps minimize the time needed to scan an entire area. The focal point is scanned along substantially linear path. During the scan along the path, an oscillatory motion is introduced to the scan path in a direction which is orthogonal to the path. In larger scan patterns, this technique may be employed for any linear or substantially linear segment of the scan pattern.
• In a fifth separate aspect of the invention, any of the foregoing aspects may be employed in combination.
• Accordingly, the present invention provides an improved laser scanner. Other objects and advantages will appear hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
• In the drawings, wherein like reference numerals refer to similar components:
• FIG. 1 schematically illustrates a laser scanner;
• FIG. 2 illustrates the laser scanner ofFIG. 1 and how movement of various optical elements enable scanning of the focal point in three dimensions;
• FIG. 3 illustrates a first focal point scan pattern which may be advantageously realized using the laser scanner ofFIG. 1;
• FIG. 4 illustrates a second focal point scan pattern which may be advantageously realized using the laser scanner ofFIG. 1; and
• FIG. 5 illustrates a raster scan in accordance with the prior art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• Turning in detail to the drawings,FIG. 1 illustrates a laser scanner11 which may advantageously be used for ophthalmic laser surgery. The laser scanner11 includes alaser source13 and optics15 for directing light from the laser source toward an eye17, along with a view port19 which enables the physician a view of the eye17 as surgery proceeds. Thelaser source13 may be of any type, but for purposes of ophthalmic laser surgery, thelaser source13 is preferably capable of generating a pulsed laser beam. One such laser source is described in U.S. Pat. No. 4,764,930, the disclosure of which is incorporated herein by reference. Further, the pulsed laser beam preferably has a pulse duration which is as long as a few nanoseconds or as short as a few femtoseconds.
• Light emitted from thelaser source13 passes through the movable z-axis scanning lens21, the collimating lens23, the two movable focusinglenses25,27, themirror29, the block ofrefractive material31, and theapplanation lens33 to afocal point35 which is on or within the cornea of the eye17. Unlike much of the prior art relating to laser scanners, the laser scanner11 ofFIG. 1 does not include any scanning mirrors. As such, light from the laser source is always on-axis as it passes through each optical element. Having an on-axis laser beam greatly reduces or eliminates the need to correct off-axis aberrations, astigmatism, and coma. Elimination of the need for corrective optics in turn reduces the overall weight of the laser scanner, thus making it possible to perform a manual “docking” procedure instead of requiring complex automation to perform the “docking” procedure. This also leads directly to a significant reduction in costs for such laser scanners, and particularly ophthalmic laser surgical equipment which incorporates such laser scanners.
• While two focusinglenses25,27 are shown, a single movable focusing lens, or alternatively more than two focusing lenses, may be used. Regardless of how many lenses are used as the focusing objective, light from thelaser source13 is preferably focused to less than a 5 μm spot size.
• Themirror29 is transparent to the wavelength of light from thelaser source13, but reflective to light at visible wavelengths. This permits an image of the eye on which a procedure is being performed to be reflected by themirror29, toward the view port19. The view port19 includes amirror37 which directs the image toward magnification lenses39,41. Because themirror29 extracts the image of the eye17 at a point between the eye17 and the objective of the laser scanner optics, the amount of magnification required for the view port19 is drastically reduced as compared to laser scanner systems of the prior art. While themirror29 is shown as a separate optical element from the block ofrefractive material31, it may be incorporated into the block ofrefractive material31 as a mirrored internal surface or as an interface between two pieces of refractive material, which together form the block of refractive material.
• The block ofrefractive material31 is included after the focusing objective of the laser scanner optics, i.e., the focusinglenses25,27, to effectively extend the focal length of the focusinglenses25,27. This is accomplished by using a block of refractive material with a refractive index which is greater than the refractive index of air. With the block ofrefractive material31 in place, the actual focal length of the combined focusing lenses can be made relatively short, say on the order of 20 mm, without actually increasing the f number of the focusing lenses. By having focusing lenses with short focal lengths, the need to correct chromatic aberrations, which often arise from focusing optics with long focal lengths, is greatly reduced or eliminated. The effective focal length of the focusinglenses25,27, with therefractive material31 in place, can be significantly lengthened. This facilitates focusing light from the surgical laser on or in the patient's eye from the end of the scanner.
• Theapplanation lens33 is included to facilitate use of the laser scanner11 as part of a ophthalmic laser surgery system. The function of theapplanation lens33 is described in U.S. Pat. No. 5,549,632, the disclosure of which is incorporated herein by reference. Other than as a basic block of refractive material disposed between thelaser source13 and the eye17, theapplanation lens33 is not actively employed in to scan light from the laser across or within the cornea.
• Turning toFIG. 2, the z-axis scanning lens21 is movable along the optical axis43 of the laser beam. Movement of this z-axis scanning lens21 may be achieved by a drive mechanism (not shown), which may be of any type known to those skilled in the art, including galvanometers, stepper motors, rotational motors with lead-screw driven linear stages, linear motors, voice coil type linear actuators, piezo actuators, ultrasonic piezo ceramic motors, DC servo motors, and the like. The drive mechanism also preferably includes a feedback loop so that associated control electronics (not shown) can determine the position of the z-axis scanning lens21 and control the movement thereof. By placing control of the z-axis scanning in a lens which is optically disposed outside of and before the focusing objective, finer control of the z-axis position of thefocal point35 is possible. In the prior art, the z-axis position of the focal point is typically controlled by z-axis movement of the focusing objective itself, giving rise to a 1:1 ratio between movement of the focusing objective and movement of the focal point. In contrast, using the configuration disclosed herein, ratios of 10:1, 100:1, 1000:1, or greater are possible.
• Similarly, the first focusinglens25 is moveable along the y-axis, and the second focusing lens27 is movable along the x-axis. Movement of these two lenses may be accomplished and controlled in the same manner as movement and control of the z-axis scanning lens21. Movement of each of these two focusinglenses25,27 along their respective axes results in scanning of thefocal point35 along those axes within the focal plane. Each of the focusinglenses25,27 are shown displaced along the x- and y-axes inFIG. 2, resulting in thefocal point35 being scanned to an off-axis position within the focal plane. In the event that a single focusing lens is employed, the single lens would be movable within the plane defined by the x- and y-axes, thereby permitting the focal point to be scanned across the entire focal plane.
• Use of the described laser scanner within an ophthalmic laser surgery system and in conjunction with a computer to control the position and motion of the z-axis scanning lens and the two focusing lenses, permits fine control over the laser scanner so that the scanable focal point may be used to create surgical cuts on or within the cornea of the eye.
• FIG. 3 illustrates a scan pattern which includes linear motion along one axis (the “fast axis”) and small amplitude, high frequency oscillations along the second, orthogonal axis (the “slow axis”). This type of scan pattern may be employed to effectively increase the coverage area of the laser scanner without requiring an increase in scan speed along the fast axis. Moreover, it may be employed during any essentially linear motion of the laser scanner, regardless of the actual scan direction. For a given linear speed, the effective coverage area is increased by approximately four times. The oscillatory motion along the slow axis may be achieved through the scanner motor(s) which drive the x-axis and/or y-axis scanning lens(es), or alternatively, it may be achieved by additional scanner motor(s) which superimpose the oscillatory motion on onto the linear motion of the scanning lens(es).
• FIG. 4 shows how the oscillatory motion described above may be advantageously employed to increase the effective coverage area for each linear pass along the fast axis as compared to a common raster pattern, which is illustrated inFIG. 5. By reducing the number of passes necessary to scan the same area, the time needed to scan an entire area may be significantly reduced.
• Thus, an improved laser scanner is disclosed. While embodiments of this invention have been shown and described, it will be apparent to those skilled in the art that many more modifications are possible without departing from the inventive concepts herein. Particularly, light from the laser source is shown passing directly from one optical element to the next. The particular configuration of mirrors and lenses described herein, however, is merely illustrative of the optics underlying the laser scanner. Alternative embodiments, which may include additional or different optical elements to accommodate a desired mechanical or optical configuration, are possible. The invention, therefore, is not to be restricted except in the spirit of the following claims.

Claims (31)

1. A laser scanner comprising:

a laser source;

a first optical element adapted to move along an optical axis of light from the laser source;

a focusing element receiving laser light from the first optical element, wherein the focusing element is adapted to move orthogonally to the optical axis; and

a second optical element receiving laser light from the focusing element, wherein the second optical element is adapted to effectively increase a focal length of the focusing element without increasing the f number of the focusing element.

2. The laser scanner ofclaim 1 further comprising a collimating lens optically disposed between the first optical element and the focusing element.

3. The laser scanner ofclaim 1, wherein the focusing element comprises a first focusing lens adapted to move along a first axis, the first axis being orthogonal to the optical axis.

4. The laser scanner ofclaim 3, wherein the focusing element further comprises a second focusing lens adapted to move along a second axis, the second axis being orthogonal to the first axis and to the optical axis.

5. The laser scanner ofclaim 1, wherein the second optical element has a refractive index which is greater than one.

6. The laser scanner ofclaim 1 further comprising a mirror optically disposed between the focusing element and the second optical element, the mirror being adapted to pass light from the laser source and to reflect visible light.

7. A laser scanner comprising:

a laser source;

a scanning lens adapted to move along an optical axis of light from the laser source;

first and second focusing lenses receiving laser light from the scanning lens, wherein the first focusing lens is adapted to move along a first axis, the first axis being orthogonal to the optical axis, and the second focusing lens is adapted to move along a second axis, the second axis being orthogonal to the first axis and to the optical axis; and

an optical element receiving laser light from the focusing lenses, wherein the optical element has a refractive index which is greater than one.

8. The laser scanner ofclaim 7 further comprising a collimating lens optically disposed between the scanning lens and the first focusing lens.

9. A laser scanner comprising:

a laser source;

a scanning lens adapted to move along an optical axis of light from the laser source;

a collimating lens receiving laser light from the scanning lens;

first and second focusing lenses receiving laser light from the collimating lens, wherein the first focusing lens is adapted to move along a first axis, the first axis being orthogonal to the optical axis, and the second focusing lens is adapted to move along a second axis, the second axis being orthogonal to the first axis and to the optical axis;

an block of refractive material receiving laser light from the focusing lenses; and

a mirror optically disposed between the focusing element and the block of refractive material, the mirror being adapted to pass light from the laser source and to reflect visible light.

10. A method of scanning light from a laser source, the method comprising:

directing light from the laser source through an optical system to a focal point, the optical system comprising, in optical alignment, a scanning lens, a focusing element, and an optical element, wherein the optical element is adapted to effectively increase a focal length of the focusing element without increasing the f number of the focusing element;

moving the scanning lens along a z-axis to adjust a depth of the focal point along the z-axis; and

moving the focusing element in a plane orthogonal to the z-axis to adjust a position of the focal point relative to the z-axis.

11. The method ofclaim 10, wherein the focusing element comprises first and second focusing lenses.

12. The method ofclaim 11, wherein moving the focusing element includes moving the first focusing lens along a first axis, the first axis being orthogonal to the z-axis.

13. The method ofclaim 12, wherein moving the focusing element includes moving the second focusing lens along a second axis, the second axis being orthogonal to the z-axis and to the first axis.

14. The method ofclaim 10, wherein the optical element has a refractive index which is greater than one.

15. A method of scanning light from a laser source, the method comprising:

directing light from the laser source through an optical system to a focal point, the optical system comprising, in optical alignment, a scanning lens, a collimating lens, first and second focusing lenses, and an optical element, wherein the optical element has a refractive index which is greater than one;

moving the scanning lens along a z-axis to adjust a depth of the focal point along the z-axis;

moving the first focusing lens along a first axis to adjust a position of the focal point relative to the z-axis, the first axis being orthogonal to the z-axis; and

moving the second focusing lens along a second axis to further adjust a position of the focal point relative to the z-axis, the second axis being orthogonal to the z-axis and to the first axis.

16. A laser scanner system for ophthalmic laser surgery, the system comprising:

a laser source;

optics adapted to direct light from the laser source toward an eye, the optics comprising:

a first optical element adapted to move along an optical axis of light from the laser source;

a focusing element receiving laser light from the first optical element, wherein the focusing element is adapted to move orthogonally to the optical axis;

a second optical element receiving laser light from the focusing element, wherein the second optical element is adapted to effectively increase a focal length of the focusing element without increasing the f number of the focusing element;

a mirror optically disposed between the focusing element and the second optical element, the mirror being adapted to pass light from the laser source and to reflect visible light; and

a view port optically coupled to the mirror to receive the reflected visible light.

17. The system ofclaim 16, wherein the optics further comprises a collimating lens optically disposed between the first optical element and the focusing element.

18. The system ofclaim 16, wherein the focusing element comprises a first focusing lens adapted to move along a first axis, the first axis being orthogonal to the optical axis.

19. The system ofclaim 18, wherein the focusing element further comprises a second focusing lens adapted to move along a second axis, the second axis being orthogonal to the first axis and to the optical axis.

20. The system ofclaim 16, wherein the second optical element has a refractive index which is greater than one.

21. The system ofclaim 16, wherein the mirror is adapted to reflect an image of the eye.

22. The system ofclaim 16, wherein the view port comprises one or more magnifying lenses.

23. A laser scanner system for ophthalmic laser surgery, the system comprising:

a laser source;

optics adapted to direct light from the laser source toward an eye, the optics comprising:

a scanning lens adapted to move along an optical axis of light from the laser source;

first and second focusing lenses receiving laser light from the scanning lens, wherein the first focusing lens is adapted to move along a first axis, the first axis being orthogonal to the optical axis, and the second focusing lens is adapted to move along a second axis, the second axis being orthogonal to the first axis and to the optical axis;

an optical element receiving laser light from the focusing lenses, the optical element having a refractive index which is greater than one; and

a mirror optically disposed between the first and second focusing lenses and the optical element, the mirror being adapted to pass light from the laser source and to reflect an image of the eye; and

a view port optically coupled to the mirror to receive the image of the eye.

24. The system ofclaim 23 wherein the optics further comprises a collimating lens optically disposed between the first optical element and the first and second focusing lenses.

25. The system ofclaim 23, wherein the view port comprises one or more magnifying lenses.

26. A method of scanning a focal point of a laser during ophthalmic surgery, the method comprising:

scanning the focal point in a first direction, the first direction being substantially linear; and

simultaneously introducing an oscillatory motion to the scanned focal point, the oscillatory motion being in a second direction orthogonal to the first direction.

27. The method ofclaim 26, wherein scanning the focal point includes scanning the focal point in the first direction for a predetermined distance, and wherein the oscillatory motion has a period not greater than the predetermined distance.

28. The method ofclaim 26, wherein scanning the focal point includes scanning the focal point in the first direction for a predetermined distance, and wherein the oscillatory motion has an amplitude substantially less than the predetermined distance.

29. A method of scanning a focal point of a laser during ophthalmic surgery, the method comprising:

scanning the focal point in a predetermined scan pattern, the scan pattern having at least one substantially linear segment; and

introducing an oscillatory motion into the scan pattern during one or more of the linear segments.

30. The method ofclaim 29, wherein the oscillatory motion has a period not greater than the linear segment.

31. The method ofclaim 29, wherein the oscillatory motion has an amplitude substantially less than the linear segment.

Images