Devices and methods for separating layers of materials having different ablation thresholds

1. A method for performing photoablation along an interface between a first material and a second material, with the first material having a higher energy ablation threshold and the second material having a lower energy ablation threshold, the method comprising the steps of:

selecting a beam geometry, a beam energy, and a pulse duration to create a pulsed laser beam having a beam energy density, with the beam energy density being less than the higher energy ablation threshold and greater than or equal to the lower energy ablation threshold;

focusing the laser beam to a focal point;

locating the focal point in the first material near the interface where no photoablation response is obtained; and

advancing the focal point toward the second material until a photoablation response is obtained in the second material adjacent the interface.

2. A method as recited in claim 1 further comprising the steps of:

scanning the laser beam along the interface; and

sequentially repeating said locating step and said advancing step to photoablate another portion of the second material adjacent the interface.

3. A method as recited in claim 2 wherein the first material and the second material are part of the cornea and wherein the scanning and repeating steps are performed until a periphery for a flap is formed, the method further comprising the steps of:

incising the cornea between the anterior surface of the cornea and the periphery to form an edge, with the flap being bounded by the edge; and

separating the first material and the second material along the periphery.

4. A method as recited in claim 3 wherein said separating step is performed by mechanically peeling the first material and the second material from one another at the periphery.

5. A method as recited in claim 2 further comprising the steps of:

withdrawing the focal point toward the first material until no photoablation response is obtained; and

selectively repeating said advancing and withdrawing steps until the portion of the second material adjacent the interface and nearest the focal point is photoablated.

6. A method as recited in claim 2 wherein the second material extends from the interface to a boundary, and wherein the locating step is accomplished by:

situating the focal point in the first material or second material;

sensing whether any second material is photoablated in response thereto;

identifying that the focal point is in the first material when said sensing step senses no second material is photoablated;

resituating the focal point away from the boundary of the second material when said sensing step senses that second material is photoablated; and

repeating said sensing, identifying and resituating steps until the focal point is identified as being in the first material.

7. A method as recited in claim 2 further comprising the steps of:

determining whether the photoablated material is adjacent the interface when said detecting step detects that second material is photoablated;

adjusting the focal point away from the second material to an energy density greater than the lower energy density threshold when said determining step indicates that the photoablated material is not adjacent the interface; and

repeating said determining and adjusting steps until the photoablated material is determined as being adjacent the interface.

8. A method as recited in claim 2 wherein the locating step to find the interface is accomplished by employing a device selected from a group comprising a confocal microscope and an optical coherence tomography.

9. A method as recited in claim 1 wherein the laser beam passes through the first material before reaching the interface.

10. A method as recited in claim 1 wherein the laser beam passes through the second material before reaching the interface.

11. A method as recited in claim 1 wherein the first material is a corneal tissue and the second material is a corneal tissue.

12. A method as recited in claim 11 wherein the first material is Bowman's membrane and the second material is the epithelium.

13. A method for performing photoablation along an interface between a first material and a second material, the method comprising the steps of:

identifying a higher energy ablation threshold of the first material and a lower energy ablation threshold of the second material;

generating a pulsed laser beam having a beam energy density that is less than the higher energy ablation threshold and greater than or equal to the lower energy ablation threshold;

focusing the laser beam to a focal point;

locating the focal point in the first material near the interface where no photoablation response is obtained; and

advancing the focal point toward the second material until a photoablation response is obtained in the second material adjacent the interface,

repeating said locating and advancing steps to photoablate further portions of the second material adjacent the interface.

14. A method as recited in claim 13 wherein the pulsed laser beam has the beam density at a focal point and has a minimum ablation beam density equal to the lower energy ablation threshold, and wherein said directing step is accomplished by:

placing the minimum ablation beam density in the first material; and

advancing the minimum ablation beam density toward the interface until the minimum ablation beam density reaches and photoablates the second material.

15. A method as recited in claim 14 wherein the advancing step is accomplished by:

moving the focal point toward the interface; and/or

increasing the beam energy density.