Oscillator-amplifier drive laser with seed protection for an EUV light source

1. A device comprising:

an oscillator producing a light output on a beam path;

a target material for interaction with light on the beam path at an irradiation site;

a beam delay on said beam path the beam delay having a beam folding optical arrangement; and

a switch positioned along said beam path and interposed between said oscillator and said beam delay; the switch closable to divert at least a portion of light on said beam path from said beam path, said switch having close time, t 1 and said beam path having a length, L 1 , along the path from the switch to the irradiation site; with t 1 <cL 1 , where c is the speed of light on said path, to protect said oscillator.

2. A device as recited in claim 1 wherein the switch is an acousto-optic modulation (AOM) switch.

3. A device as recited in claim 1 further comprising an amplifier positioned on the beam path.

4. A device as recited in claim 1 wherein said switch has a close time, t 1 , in the range of 300-500 ns.

5. A device as recited in claim 1 wherein said oscillator is a first oscillator generating a main pulse seed output and said device further comprises a second oscillator generating a pre-pulse seed output.

6. A device as recited in claim 1 wherein said beam delay has a length in the range of 80 to 120 meters.

7. A device as recited in claim 1 further comprising an optical isolator positioned on the beam path.

8. A device as recited in claim 7 wherein the optical isolator comprises a polarization discriminating optic and a phase retarding optic.

9. A device comprising:

an oscillator producing a light output on a beam path, the oscillator having an output coupler;

an amplifier positioned on the beam path;

a target material droplet traveling at a speed, v, for interaction with focused light having a beam waist diameter, D, on the beam path at an irradiation site, the droplet having a pre-seed interaction time, T, in the waist, with T=D/2v;

a beam delay on said beam path, the beam delay having a beam folding optical arrangement, said beam path having a length, l, along the path from the output coupler to the irradiation site; with 2cl>T, where c is the speed of light on said path, to reduce oscillation between said output coupler and said droplet.

10. A device recited in claim 9 wherein said droplet speed, v, is in the range of 50 to 100 meters per second and said beam waist diameter is in the range of 80 to 120 μm.

11. A device as recited in claim 9 further comprising an optical isolator positioned on the beam path.

12. A device as recited in claim 9 wherein said beam delay has a length in the range of 60 to 140 meters.

13. A device as recited in claim 9 further comprising a lens to focus light on said beam path to a waist having beam waist diameter, D.

14. A device as recited in claim 9 wherein said oscillator is a first oscillator generating a pre-pulse seed output and said device further comprises a second oscillator generating a main pulse seed output.

15. A device as recited in claim 14 wherein said amplifier has a one-pass, main pulse gain in the range of 1×10 5 to 1×10 7 .

16. A device comprising:

an optical amplifier,

a pre-pulse seed laser,

a main pulse seed laser; and

a beam combiner for directing the pre-pulse output and the main pulse output on a common beam path through the optical amplifier;

a first switch interposed between the pre-pulse seed laser and the beam combiner; and

a second switch interposed between the main pulse seed laser and the beam combiner.

17. A device as recited in claim 16 wherein said first and second switches each comprise an acousto-optic modulation (AOM) switch.

18. A device as recited in claim 16 further comprising an optical isolator positioned on the beam path between the optical amplifier and beam combiner.

19. A device as recited in claim 16 wherein said beam combiner is a partially reflective optic.

20. A device as recited in claim 16 wherein said beam combiner comprises a dichroic beam combiner.