Birefringent lens for laser beam delivery

1. An ophthalmic laser system, comprising:

a laser engine configured to generate a beam of femtosecond laser pulses;

a laser scanner configured to scan each laser pulse of the beam in three dimensions according to a scan pattern;

a compound lens comprising a glass lens and at least one birefringent lens, the compound lens arranged to receive the scanned beam and configured to split each laser pulse of the scanned beam into an ordinary pulse and an extraordinary pulse, thereby producing an ordinary beam comprising ordinary pulses and an extraordinary beam comprising extraordinary pulses,

wherein a particular ordinary pulse and a particular extraordinary pulse split from a particular laser pulse are spatially separated in depth along an optical axis of the compound lens, by a distance greater than or equal to 5 μm, and temporally separated by a delay greater than or equal to a pulse duration of the femtosecond laser pulses; and

an objective configured to focus the ordinary beam and the extraordinary beam within an ophthalmic target.

2. The system of claim 1 , wherein the scan pattern comprises a spiral scan pattern.

3. The system of claim 1 , wherein the birefringent lens comprises a birefringent crystal.

4. The system of claim 3 , further comprising:

a rotation lens mount coupled to the birefringent lens; and

wherein the birefringent lens is rotatable to adjust a relative energy content of the ordinary beam and the extraordinary beam.

5. The system of claim 4 , wherein the birefringent lens is configured such that:

rotating the birefringent lens to a first position causes the relative energy content between the ordinary beam and the extraordinary beam to be equally distributed; and

rotating the birefringent lens to a second position causes at least 95% of the relative energy to be distributed to the ordinary beam and no more than 5% of the relative energy to be distributed to the extraordinary beam.

6. The system of claim 4 , further comprising a laser controller configured to:

generate a scan pattern based on a rotation position of the birefringent lens; and

control the scanner to scan the beam according to the generated scan pattern.

7. The system of claim 3 , further comprising:

a rotation mount coupled to a halfwave plate positioned before the scanner and the birefringent lens; and

wherein the halfwave plate is rotatable to change an orientation of polarization of the scanned beam and thereby adjust the relative energy content of the ordinary beam and the extraordinary beam.

8. The system of claim 7 , wherein the halfwave plate is configured such that:

rotating the halfwave plate to a first position causes the relative energy content between the ordinary beam and the extraordinary beam to be equally distributed; and

rotating the halfwave plate to a second position causes at least 95% of the relative energy to be distributed to the ordinary beam and no more than 5% of the relative energy to be distributed to the extraordinary beam.

9. The system of claim 3 , wherein:

the spatial separation in depth of the ordinary and extraordinary pulses along the optical axis is in the range of 5-100 μm; and

the delay temporally separating the ordinary and extraordinary pulses is in the range of 100-10,000 femtoseconds.

10. The system of claim 3 , wherein the laser engine is configured to generate the beam of femtosecond laser pulses with a pulse energy sufficient to cause photodisruption in an ophthalmic target at focus spots of the ordinary beam and the extraordinary beam.

11. The system of claim 10 , wherein the compound lens is configured so that the spatial and temporal separation between the particular ordinary pulse and particular extraordinary pulse is sufficient to cause a photodisruption at a first depth in the ophthalmic target before causing photodisruption at a second depth in the ophthalmic target, wherein the first depth is greater than the second depth relative to an external surface of the ophthalmic target.

12. The system of claim 3 , wherein the birefringent lens comprises at least one of calcite (CaCO 3 ), ytrium orthovanadate (YVO 4 ), lithium niobate (LiNbO 3 ), or barium borate (BaB 2 O 4 ).

13. A method of performing ophthalmic surgery, comprising:

generating a beam of femtosecond laser pulses;

scanning each laser pulse of the generated beam in three dimensions according to a scan pattern;

splitting, with a compound lens comprising a glass lens and at least one birefringent lens, each laser pulse of the scanned beam into an ordinary pulse and an extraordinary pulse, thereby generating an ordinary beam comprising ordinary pulses and an extraordinary beam comprising extraordinary pulses;

wherein a particular ordinary pulse and a particular extraordinary pulse resulting from splitting a particular laser pulse are spatially separated in depth, along an optical axis of the compound lens, by a distance greater than or equal to 5 μm, and temporally separated by a delay greater than or equal to a pulse duration of the laser pulse; and

delivering the ordinary beam and the extraordinary beam into an ophthalmic target according to the scan pattern such that the particular extraordinary pulse causes photodisruption at a first depth in the target tissue before the particular ordinary pulse causes photodisruption at a second depth in the target tissue, wherein the first depth is greater than the second depth relative to an external surface of the ophthalmic target.

14. The method of claim 13 , wherein the scan pattern comprises a spiral scan pattern.

15. The method of claim 13 , wherein the birefringent lens comprises a birefringent crystal.

16. The method of claim 15 , further comprising:

rotating the birefringent lens or a polarization of the generated beam to adjust a relative energy content of the ordinary beam and the extraordinary beam.

17. The method of claim 16 , further comprising:

rotating the birefringent lens or the polarization of the generated beam to a ϕ=45° polarization to equally distribute the relative energy content between the ordinary beam and the extraordinary beam prior to a cataract procedure.

18. The method of claim 16 , further comprising:

rotating the birefringent lens or the polarization of the generated beam to a ϕ=0° polarization to distribute at least 95% of the relative energy to the ordinary beam and no more than 5% of the relative energy to the extraordinary beam prior to a corneal procedure.

19. The method of claim 16 , further comprising:

generating the scan pattern based on a rotation position of the birefringent lens; and

controlling a scanner to scan the beam according to the generated scan pattern, wherein the scan pattern comprises a spiral scan pattern.

20. The method of claim 15 , wherein:

the spatial separation in depth of the ordinary and extraordinary pulses along the optical axis is in the range of 5 μm-100 μm; and

the delay temporally separating the particular ordinary and extraordinary pulses is in the range of 100-10,000 femtoseconds.