MesaPhotonics VideoFROG FROGscan, User Manual

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Chapter 5. Maximizing the Intensity of the Signal Beam
09/07/2018 Vs 003 FROGSCAN USER’S MANUAL Page 39
5.1 Optimizing the Crystal Tilt
1. Ensure that your LASER has the same horizontal polarization as the crystal. If the crystal cut angle
corresponds to the Theta angle for a particular wavelength, the crystal will be vertical. When the
crystal cut angle corresponds to the phase matching angle for the input wavelength. For example, for
800 nm, BBO’s phase matching angle is 29.2 degrees. If the crystal is cut at that angle, and the
wavelength is 800 nm, the crystal will be vertical when properly phase matched. If the Theta angle
differs from the crystal cut angle, the crystal tilt must be tilted by the difference of the two angles plus
the internal refraction of the crystal.
2. Follow steps 1 to 3 above.
3. In instruments without the crystal autotilt control, change the crystal tilt by tilting the crystal cartridge
manually until the SHG signal is maximized. Follow the instructions below to unlock the crystal
cartridge.
Remove the crystal bars as described in
Section 2.2.
Manually hold the Crystal Mount in place while
the Adjustment nut is loosened or tightened.
Loosen the Adjustment nut, then tilt the crystal
by hand until it is approximately vertical.
Secure in place with the Locking Screw by
turning the knurled head 90 degrees
.
A:
Locking screw to secure the crystal tilt in
vertical position. Disengage to tilt crystal.
B: Adjustment nut: loosen to adjust the tilt
angle; tighten to secure in place.
4. In FROG instruments with automated crystal tilt function, adjust the crystal using the Crystal Tilt
functions in the Left Control Panel and as described in Section 3.4.1.
6. Once the optimal crystal tilt was determined, optimize the spatial overlap of the beams in the crystal
by adjusting the Overlap Mirror. Use the provided 64 ball head driver to adjust the 5/64 hex sockets
on the back of the Mirrors until the signal is maximized in the VideoFROGscan Setup and Alignment
spectrogram.
5. Click on the “LED” again to restore the time spacing to the previous value.
PROTECT YOURSELF AND OTHERS AGAINST REFLECTIONS FROM THE SHG
CRYSTAL WHEN TILTING THE CRYSTAL
A
B