Continuum Surelite EX 10, Руководство по эксплуатации и обслуживанию

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Appendix A: PIV Operation and Maintenance
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PIV Optical description
Figure 56 shows the PIV optical layout. Two 1064 nm fundamental Nd:YAG laser beams
are first combined on a common optical axis and passed through a single doubling crystal.
532 nm dichroic separation optics then provide two green output pulses.
The beam from laser A defines this common optical axis. Horizontally polarized, it passes
directly through the beam merger, a dielectric polarizer (11), which combines this beam with
the second laser’s output.
The beam from laser B is also horizontally polarized; it passes through half wave plate (9)
external to the cavity changing fundamental output of laser B to vertical polarization so that
the dielectric polarizer (11) reflects the beam into the horizontally polarized beam path. The
two mirrors (10a & b) optimize the overlap. The
λ
/4 plate (3) then gives both beams circular
polarization. Because they now have circular polarization, the doubling crystal (12) converts
them equally to their second harmonic. A pair of dichroics (13a and b) now strips the
unconverted 1064 nm light and steers the vertically 532 nm second harmonic pulses towards
the PIV experiment.
Figure 56 PIV optical layout
HEAD A
HEAD B
a
b
L
EGEND
1. HR mirror
2. Pockels cell
3.
λ
/4 plate
4. Dielectric polarizer
5. Head
6. Gaussian mirror output coupler
7. Compensator
8. Shaping lenses
9.
λ
/2 plate
10. 45° mirror, 1064 nm
11. Polarizer, 199-0055
12. SHG (second harmonic generator) crystal, in
a sealed oven
13. 45° mirror, 532 nm
Second harmonic generation
In the doubling process, two 1,064 nm photons enter the KDP crystal collinear and with
the same (circular) polarization. They combine into a single photon, provided that the
resulting photon conserves both energy and momentum. A combined photon with
doubled frequency satisfies energy conservation. Angular momentum conservation gives
the doubled photon a different (horizontal) polarization. Linear momentum conservation
requires the combined photon to have the same velocity as the incoming photon pair. In