Method and system for compact, multi-pass pulsed laser amplifier

1. A laser amplifier comprising:

an input aperture operable to receive laser radiation having a first polarization state;

a polarizer disposed along an optical path, the polarizer having a transmission axis aligned with the first polarization state;

a Pockels cell disposed along the optical path and operable to receive light transmitted through the polarizer;

an optical gain element disposed along the optical path;

a polarization rotation device disposed along the optical path and operable to rotate the polarization of light from the first polarization state to a second polarization state orthogonal to the first polarization state;

a second polarizer disposed along the optical path, the second polarizer having a transmission axis aligned with the first polarization state;

an optical loop operable to receive light reflected from the second polarizer and to direct light to impinge on the first polarizer; and

an output aperture disposed along the optical path.

2. The laser amplifier of claim 1 wherein the optical gain element is positioned between the Pockels cell and the second polarizer.

3. The laser amplifier of claim 1 further comprising an second optical gain element disposed along the optical path.

4. The laser amplifier of claim 1 wherein the optical loop comprises:

a first mirror;

a relay telescope; and

a second mirror.

5. The laser amplifier of claim 1 further comprising a harmonic converter operable to receive light from the output aperture.

6. The laser amplifier of claim 1 wherein the polarization rotation device comprises a Faraday rotator.

7. The laser amplifier of claim 1 further comprising a near-field spatial filter disposed along the optical loop.

8. The laser amplifier of claim 7 wherein the near-field spatial filter comprises a volume Bragg grating.

9. A method of operating an optical amplifier, the method comprising:

directing optical radiation having a first polarization state along an optical path;

transmitting the optical radiation through a first polarizer having a polarization axis aligned with the first polarization state;

transmitting the optical radiation through a Pockels cell, wherein no substantial change in the first polarization state of the optical radiation results from transmitting the optical radiation through the Pockels cell;

amplifying the optical radiation;

rotating the polarization state of the optical radiation from the first polarization state to a second polarization state orthogonal to the first polarization state;

reflecting the optical radiation from a second polarizer having a transmission axis aligned with the first polarization state;

rotating the polarization state of the optical radiation from the second polarization state to the first polarization state using the Pockels cell;

amplifying the optical radiation;

rotating the polarization state of the optical radiation from the first polarization state to the second polarization state;

reflecting the optical radiation from the second polarizer;

amplifying the optical radiation;

rotating the polarization state of the optical radiation from the second polarization state to the first polarization state; and

transmitting the optical radiation through the second polarizer.

10. The method of claim 9 wherein rotating the polarization state of the optical radiation from the first polarization state to a second polarization state orthogonal to the first polarization state comprises use of a Faraday rotator.

11. The method of claim 9 wherein amplifying the optical radiation comprises:

amplifying the optical radiation in a first optical gain element;

thereafter rotating the polarization state of the optical radiation; and

amplifying the optical radiation in a second optical gain element.

12. The method of claim 9 further comprising spatially filtering the optical radiation using a relay telescope.

13. The method of claim 9 further comprising spatially filtering the optical radiation using a near-field spatial filter.

14. The method of claim 9 further comprising transmitting the optical radiation through the Pockels cell, wherein no substantial change in the second polarization state of the optical radiation results from transmitting the optical radiation through the Pockels cell prior to amplifying the optical radiation a third time.

15. A laser amplifier comprising:

an input aperture operable to receive laser radiation having a first polarization;

an output aperture coupled to the input aperture by an optical path;

a polarizer disposed along an optical path, wherein a transmission axis of the polarizer is aligned with the first polarization;

an optical switch disposed along the optical path, wherein the optical switch is operable to pass the laser radiation when operated in a first state and to reflect the laser radiation when operated in a second state;

an optical gain element disposed along the optical path; and

a polarization rotation device disposed along the optical path.

16. The laser amplifier of claim 15 wherein the optical switch comprises a Pockels cell and a second polarizer aligned with a second polarization orthogonal to the first polarization.

17. The laser amplifier of claim 16 wherein the Pockels cell is off in the first state and the Pockels cell is on in the second state.

18. The laser amplifier of claim 15 further comprising a second optical gain element disposed along the optical path.

19. The laser amplifier of claim 15 wherein the polarization rotation device comprises a Faraday rotator.

20. The laser amplifier of claim 15 further comprising a beam expanding telescope optically coupled to the input aperture.

21. The laser amplifier of claim 15 further comprising a near-field spatial filter disposed along the optical path.

22. The laser amplifier of claim 15 further comprising a relay telescope disposed along the optical path.

23. A method of amplifying optical radiation, the method comprising:

transmitting the optical radiation through a first polarizer;

amplifying the optical radiation;

injecting the optical radiation into a closed loop;

determining that the optical radiation is to be maintained in the closed loop;

activating an optical switch;

amplifying the optical radiation;

injecting the optical radiation into the closed loop;

determining that the optical radiation is not to be maintained in the closed loop;

deactivating the optical switch;

amplifying the optical radiation; and

transmitting the optical radiation through an output aperture.

24. The method of claim 23 wherein the optical radiation has a first polarization state and the first polarizer has a transmission axis aligned with the first polarization state.

25. The method of claim 24 wherein injecting the optical radiation into the closed loop comprises reflecting the optical radiation off a second polarizer having a transmission axis aligned with the first polarization state.

26. The method of claim 23 wherein the closed loop comprises a relay telescope.

27. The method of claim 23 wherein the closed loop comprises a near-field spatial filter.

28. The method of claim 23 wherein activating the optical switch comprises applying a bias voltage to a Pockels cell.

29. The method of claim 23 wherein deactivating the optical switch comprises operating a Pockels cell in a state such that no substantial change in a polarization state of the optical radiation results from transmitting the optical radiation through the Pockels cell.

30. The method of claim 23 further comprising transmitting the optical radiation through a second polarizer prior to transmitting the optical radiation through the output aperture.