Second harmonic generation

1. A second harmonic generator, comprising:

a second harmonic crystal to receive, at a first point in time, a fundamental optical beam and output, at a second point in time, a residual fundamental optical beam; and

a combiner to combine, at a third point in time, the fundamental optical beam with the residual fundamental optical beam,

the second harmonic crystal being coupled to the combiner and being further to generate, at a fourth point in time, a second harmonic optical beam from the fundamental optical beam and the residual fundamental optical beam,

wherein, upon generation of the second harmonic optical beam, the residual fundamental optical beam is to exit the second harmonic generator.

2. The second harmonic generator of claim 1 , wherein the fundamental optical beam is in a first polarization and the residual fundamental optical beam is in a second polarization,

wherein the second polarization is orthogonal to the first polarization, and

wherein the second harmonic crystal is to perform Type-II phase matching.

3. The second harmonic generator of claim 1 , wherein the fundamental optical beam is in a first polarization and the residual fundamental optical beam is in a second polarization,

wherein the second polarization is orthogonal to the first polarization, and

wherein the combiner is a polarizing combiner to combine the fundamental optical beam and the residual fundamental optical beam.

4. The second harmonic generator of claim 1 , wherein the fundamental optical beam is to be incident on an input optical face of the second harmonic crystal at a first angle, and the residual fundamental optical beam is to be incident on the input optical face of the second harmonic crystal at a second angle,

wherein the first angle is different from the second angle, and

wherein the second harmonic crystal is to perform non-collinear phasematching.

5. The second harmonic generator of claim 4 , wherein the second harmonic crystal is to perform either Type-I phasematching or Type-II phasematching.

6. The second harmonic generator of claim 4 , wherein the second harmonic crystal is to perform non-critical phasematching.

7. The second harmonic generator of claim 1 , wherein the fundamental optical beam is to be incident on an input optical face of the second harmonic crystal at a first angle, and the residual fundamental optical beam is to be incident on the input optical face of the second harmonic crystal at a second angle,

wherein the first angle is different from the second angle, and

wherein the combiner is an angular combiner to steer at least the residual fundamental optical beam such that the residual fundamental optical beam is incident on the input optical face of the second harmonic crystal at the second angle.

8. The second harmonic generator of claim 1 , wherein the fundamental optical beam, the residual fundamental optical beam, or the second harmonic optical beam is to enter or exit the second harmonic crystal at approximately a Brewster angle.

9. The second harmonic generator of claim 1 , wherein a loop round-trip time, associated with the second harmonic generator, is approximately equal to or a multiple of a pulse separation time of a laser source of the fundamental optical beam,

wherein a pulse length, associated with the laser source, is shorter than the loop round-trip time.

10. The second harmonic generator of claim 1 , wherein a loop round-trip time, associated with the second harmonic generator, is approximately equal to or a multiple of a laser source round-trip time of a laser source of the fundamental optical beam,

wherein the laser source operates in a multi-longitudinal mode, and

wherein the laser source is a continuous wave laser, or a pulse length, associated with the laser source, is longer than the loop round-trip time.

11. A method, comprising:

propagating, by a second harmonic generator and at a first point in time, a fundamental optical beam through a second harmonic crystal to output, at a second point in time, a residual fundamental optical beam; and

propagating, by a second harmonic generator and at a third point in time, the fundamental optical beam and the residual fundamental optical beam through the second harmonic crystal to generate a second harmonic optical beam from the fundamental optical beam and the residual fundamental optical beam,

wherein, upon generation of the second harmonic optical beam, the residual fundamental optical beam is to exit the second harmonic crystal at a fourth point in time.

12. The method of claim 11 , wherein the fundamental optical beam is in a first polarization and the residual fundamental optical beam is in a second polarization,

wherein the second polarization is orthogonal to the first polarization.

13. The method of claim 12 , further comprising rotating the residual fundamental optical beam from the first polarization to the second polarization.

14. The method of claim 11 , wherein the fundamental optical beam is to be incident on the second harmonic crystal at a first angle, and the residual fundamental optical beam is to be incident on the second harmonic crystal at a second angle,

wherein the first angle is different from the second angle.

15. The method of claim 11 , wherein the second harmonic crystal is to perform either Type-I phasematching or Type-II phasematching.

16. The method of claim 11 , wherein the second harmonic crystal is to perform non-critical phasematching.

17. The method of claim 11 , wherein the fundamental optical beam, the residual fundamental optical beam, or the second harmonic optical beam is to enter or exit the second harmonic crystal at approximately a Brewster angle.

18. The method of claim 11 , wherein a surface of the second harmonic crystal is coated with an anti-reflection coating.

19. A laser, comprising:

a second harmonic crystal to receive, at a first point in time, a fundamental optical beam and output, at a second point in time, a residual fundamental optical beam; and

a combiner to combine, at a third point in time, the fundamental optical beam with the residual fundamental optical beam;

the second harmonic crystal to generate, at a fourth point in time, a second harmonic optical beam from the fundamental optical beam and the residual fundamental optical beam,

wherein, upon generation of the second harmonic optical beam, the residual fundamental optical beam is to exit the second harmonic crystal; and

one or more optical components to direct the residual fundamental optical beam to the combiner.

20. The laser of claim 19 , wherein the second harmonic crystal is to perform at least one of:

Type-I phasematching;

Type-II phasematching;

non-collinear phasematching; or

non-critical phasematching.