Surface erosion using lasers

• US 4,941,093 A
• Filed: 09/09/1986
• Issued: 07/10/1990
• Est. Priority Date: 09/12/1985
• Status: Expired due to Term

• Current Assignee: Summit Technologies LLC (Summit Global Group, LLC)
• Original Assignee: Summit Technologies LLC (Summit Global Group, LLC)
• Inventors: Welford, Walter T., Ness, Karen M. M., Raven, Anthony L., Marshall, John
• Primary Examiner(s): Smith, Jerry
• Assistant Examiner(s): BUI, KIM T
• Application Number:
  US06/905,156
• Time in Patent Office: 1,400 Days
• Field of Search: 364/413, 364/413.01, 128/303.1, 219/121 L, 219/121 LP, 219/121 LG, 219/121 LN, 219/121 LR, 219/121.61, 606/3-6
• US Class Current: 606/5
• CPC Class Codes: A61B 2017/00119 alarm; indicating an abnormal situation
• CPC Class Codes: A61B 2017/306 holding by means of suction
• CPC Class Codes: A61F 2009/00844 Feedback systems
• CPC Class Codes: A61F 2009/00872 Cornea
• CPC Class Codes: A61F 2009/00882 based on topography
• CPC Class Codes: A61F 9/00804 Refractive treatments
• CPC Class Codes: A61F 9/00817 Beam shaping with masks
• CPC Class Codes: B23K 26/0622 by shaping pulses
• CPC Class Codes: B23K 26/0648 comprising lenses
• CPC Class Codes: B23K 26/0652 comprising prisms
• CPC Class Codes: G02B 5/001 Axicons, waxicons, reflaxicons

Abstract

Laser apparatus for eroding a surface comprises means to select and control the shape and size of the area irradiated by each pulse of laser energy without varying the energy density of the beam. By varying the size of the irradiated area between pulses, some regions of the surface may be eroded more than others and so the surface may be reprofiled. The method and apparatus are suitable, inter alia, for removing corneal ulcers and reprofiling the cornea to remove refractive errors and also for reprofiling optical elements. In one embodiment the beam from the laser enters an optical system housed in an articulated arm and terminating in an eyepiece having a suction cup for attachment to an eye. The optical system includes a beam forming arrangement to correct an asymmetric beam cross-section, a first relay telescope, a beam dimensional control system and a second relay telescope. The beam dimension control system has a stop with a shaped window or a shaped stop portion and movable axially along a converging or diverging beam portion. An alternative beam dimension control system has a stop with a shaped window and positioned between coupled zoom systems. Mirrors, adjustable slits and refractive systems may also be used. The laser is preferably an ArF Excimer laser. The apparatus may include a measurement device to measure the surface profile, and a feedback control system to control the laser operation in accordance with the measured and desired profiles.

Claims

1. A laser system for eroding a surface, said laser system comprising:

laser means for generating pulses of laser light along a beam path at an energy level, such that the pulses can be absorbed at a surface to induce photoablation;

support means for aligning a surface relative to the laser means; and

beam dimension control means disposed along said laser beam path, including optical means for optically varying an area on the surface to which the pulses of laser energy are delivered while maintaining a substantially constant energy per unit area during each pulse.

2. A laser system according to claim 1 and further comprising optical beam-shaping means for varying the shape of the area of the surface to which the pulses are delivered.

3. A laser system according to claim 1 in which the laser means generates from about 1 to about 500 pulses per second.

4. A laser system according to claim 1 in which said control means further comprises beam-shaping means for receiving a laser beam provided by said laser means and for shaping the beam by passage through an aperture, the beam-shaping means being disposed about an optical axis of the laser beam, such that movement along the optical axis varies the cross-sectional area of the beam which passes through the aperture.

5. A laser system according to claim 4 which further comprises a focusing means for focusing an image of the aperture of the beam-shaping means onto the surface to be eroded.

6. A method of eroding a surface by laser energy, said method comprising the steps of:

aligning a surface with a laser means, which is operable to deliver a beam of photoablative pulses of laser energy along a path to the surface;

adjusting the size of the area on the surface to which the pulses are delivered; and

operating a beam dimension control means disposed along said path for optically controlling said beam to deliver pulses of laser energy of variable cross-sectional area to the surface while maintaining a substantially constant energy per unit area during each pulse.

7. A method according to claim 6 in which the shape of the area on the surface to which the pulses are delivered is adjusted in a controlled manner thereby selecting the shape of the area eroded by the pulses.

8. A method according to claim 6 in which the size of the area to be eroded by said pulses is varied in a controlled manner during said step of operating the laser.

9. A method according to claim 6 in which following said step of adjusting the size of the area to be eroded, the size of said area to be eroded is maintained substantially constant during said step of operating the laser.

10. A laser system for eroding and thereby shaping or reprofiling a surface, said laser system comprising:

support means for aligning a surface to be eroded relative to an optical axis (or vice versa),

a beam delivery system for relaying energy from a laser light source onto the surface along said optical axis,

a laser light source, power supply and an associated control circuit for generating pulses of laser energy for application to the surface; and

beam dimension control means disposed along said optical axis, including optical means for optically controlling the area over which the pulses of laser energy are applied to the surface while maintaining a substantially constant energy per unit area during each pulse, thereby causing greater or lesser ablation of selected regions of the surface.

11. A laser system according to claim 10 for use when the said surface is the surface of an optical element and further comprising:

a measuring device for measuring a parameter which is a function of surface shape of the optical element;

means for receiving an input defining a desired value for the parameter;

comparison means for comparing the measured value of the parameter with the desired value and deriving therefrom a feedback signal; and

control signal generating circuit means for generating control signals for the laser from the feedback signal obtained from the comparison means, the control signals serving inter alia, to determine the area of the surface to which the laser pulses are applied thereby obtaining the desired value of the parameter of the optical element.

12. A laser system according to claim 10 in which the energy density of the laser pulses applied to the surface is above the threshold value for ablation of corneal tissue and not substantially higher than the saturation level for ablation of corneal tissue.

13. A laser system according to claim 10 in which said beam delivery system comprises a straight-sided-concave optical element for causing beam portions to diverge, leaving an intervening area of reduced beam intensity.

14. A laser system according to claim 10 in which said means for controlling the area comprises an optical stop with first and second zoom systems to the upstream and downstream thereof, said zoom systems being coupled for simultaneous adjustment.

15. A method of eroding a surface of an object, said method comprising the steps of:

aligning a surface of an object with a laser source which is operable to deliver pulses of laser energy to the surface,

pulsing the laser source along a path so that light therefrom falls on the surface of the object, and

controlling the light from the laser with a beam dimension control means disposed along said path so as to optically vary the area over which the light is incident during the emission of a plurality of pulses, thereby selectively exposing areas of the surface to a greater or lesser extent while maintaining a substantially constant energy per unit are during each pulse, and thereby obtaining a desired erosion profile of the surface.

16. A method according to claim 15 in which the laser wavelength is selected so that the laser energy incident on the surface of the object is absorbed by the material forming the surface, so that there is little or no energy remaining to penetrate and affect the material below the surface.

17. A method according to claim 15 in which pulses of energy are directed towards selected overlapping regions of the surface, so that, over a period of time, different regions of the surface are exposed to different quantities of energy from the laser source, so as to produce differential erosion of the surface.

18. A method according to claim 15 in which the energy density of the laser pulses falling on the surface is greater than the threshold for ablation but not substantially greater than the saturation level for ablation of the material of the object.

19. A method according to claim 15 and comprising the further step of inducing a flow of gas over the surface during the erosion process to remove debris arising from the interaction of the laser beam with the surface.

20. A method according to claim 19 in which the gas is nitrogen.

21. A method of eroding an area of a cornea of an eye said method comprising the steps of:

fixing an eye relative to laser means operable to deliver a beam of photoablative pulses of laser energy along a path to the surface of the cornea;

varying the area on the surface of the cornea to which the pulses are delivered in a controlled manner; and

operating a beam dimension control means disposed along said path for optically controlling said beam to deliver pulses of laser to the varied areas of the surface while maintaining a substantially constant energy per unit area during each pulse.

22. A method of removing corneal ulcers comprising steps of:

fixing an eye relative to laser means operable to deliver a beam of photoablative pulses of laser energy along a path to the surface of the cornea;

varying the area on the surface of the cornea to which the pulses are delivered in a controlled manner so as to expose the corneal ulcer; and

operating a beam dimension control means disposed along said path for optically controlling said beam to deliver pulses of laser energy of variable cross-sectional area to the ulcer while maintaining a substantially constant energy per unit area during each pulse.

23. A method of preparing a bed for a corneal transplant in which corneal material is removed by erosion using a method comprising the steps of:

fixing an eye relative to the laser means to deliver a beam of photoablative pulses of laser energy along a path to the surface of the cornea;

varying the area on the surface of the cornea to which the pulses are delivered in a controlled manner so as to expose a corneal transplant bed; and

operating a beam dimension control means disposed along said path for optically controlling said beam to deliver pulses of laser energy of variable cross-sectional area to the transplant bed while maintaining a substantially constant energy per unit area during each pulse.

24. A method of preparing a donor implant for a corneal transplant in which the implant is obtained from a donor cornea by eroding the surrounding area of the donor cornea by a method comprising the steps of:

fixing an eye relative to laser means to deliver a beam of photoablative pulses of laser energy along a path to the surface of the cornea;

varying the area on the surface of the cornea to which the pulses are delivered in a controlled manner so as to expose a region surrounding a donor cornea; and

operating a beam dimension control means disposed along said path for optically controlling said beam to deliver pulses of laser energy of variable cross-sectional area to the surrounding region while maintaining a substantially constant energy per unit area during each pulse.

25. A method of correcting ocular disorders by reprofiling a corneal surface of an eye, the method comprising the steps of:

aligning a cornea of an eye with a laser which, in use, generates a beam of laser light capable of photoablating corneal tissue;

pulsing the laser source so that light therefrom propagates along a path and falls intermittently on the surface of the cornea to induce photoablation of a thin surface layer of the cornea within an area of exposure during each pulse;

controlling the light with a beam dimension control means disposed along said path from the laser to optically vary said area of exposure while maintaining a substantially constant energy per unit area during each pulse, whereby a reprofiled corneal surface is obtained as a result of variations in the total energy delivered to selected regions of corneal surface.

26. The method of claim 25 wherein the step of aligning the cornea with the laser further comprises immobilizing the eye by vacuum clamping.

27. The method of claim 25 wherein the step of pulsing the laser source to induce photoablation further comprises delivering ultraviolet light to the surface of the cornea.

28. The method of claim 27 wherein the step of delivering ultraviolet light to the surface of the cornea further comprises delivering ultraviolet light at a wavelength of about 193 nanometers.

29. The method of claim 25 wherein the step of pulsing the laser source to induce photoablation of the cornea further comprises delivering laser light at an energy level ranging from about 0.1 to about 1.0 Joules/cm².

30. The method of claim 25 wherein the step of controlling the light from the laser further comprises varying the area of exposure to obtain a general flattening of the surface of the cornea and thereby decrease the refractive power of the eye.

31. The method of claim 25 wherein the step of controlling the light from the laser further comprises varying the area of exposure to increase the curvature of the cornea and thereby increase the refractive power of the eye.

32. The method of claim 25 wherein the step of controlling the light from the laser further comprises varying a non-circular area of exposure to correct astigmatisms.

33. The method of claim 25 wherein the method further comprises the step of periodically measuring the curvature of the corneal surface while the area of exposure is being varied and comparing the measured curvature values with expected values in order to provide a feedback-based control of said laser.

34. The method of claim 25 wherein the method further comprises employing a microprocessor which is initially input with a final shape desired, which is also input with measured data as to the extent of reprofiling achieved after a first area is exposed to photoablative light and which outputs control signals which control subsequent exposures.

35. A corneal reprofiling system for modifying the surface of a cornea of an eye, the system comprising:

a laser means generating a beam of pulses of laser light along a path at an energy level, such that the light pulses can be absorbed in a thin surface layer of a cornea of an eye to induce photoablation;

a support means for aligning an eye relative to the laser means; and

a beam dimension control means disposed along the path, including a beam-forming optical means for optically varying a area over which the laser light is incident while maintaining a substantially constant energy per unit area during each pulse.

36. The system of claim 35 wherein the laser means generates pulses of ultraviolet laser light at a wavelength of about 193 nanometers.

37. The system of claim 36 wherein the laser means generates pulses of laser light at an energy level ranging from about 1.0 Joules/cm².

38. The system of claim 35 wherein the support means for aligning an eye relative to the laser means further comprises a vacuum clamp capable of immobilizing an eye.

39. The system of claim 35 wherein the beam-forming optical means further comprises a composite zoom lens arrangement.

40. The system of claim 35 wherein the beam-forming optical means further comprises complementary conical lenses.

41. The system of claim 35 wherein the beam-forming optical means further comprises complementary mirrored surfaces.

42. The system of claim 35 wherein the system further comprises a feedback monitoring means for inspecting the surface which is being exposed to the laser light and for generating control signals to the laser means in response to said inspection of the surface.

43. The system of claim 35 wherein the system further comprises a microprocessor which is initially input with a final shape desired, which also input during the procedure with measured data as to the extent of reprofiling so far achieved, and which outputs control signals which control at least the laser means.

44. The system of claim 35 wherein the system further comprises means for introducing a gaseous flow over the corneal surface during the ablation process to remove debris.