Alignment
6-41
1. Use a photodiode or autocorrelator to see if the Tsunami is creating
short output pulses.
Look for a short output pulse (80 fs or 2 ps, depending on laser config-
uration) when the mode locker is enabled (the ENABLE lamp is illumi-
nated on the STATUS panel of the Model 3955 electronics).
If short pulses are present, the laser is aligned and properly mode-
locked, and you are done. If the pulses are broader than specified for
your configuration, proceed.
2. Remove the cover (4 screws) from the Model 3955 electronics module.
3. Set the fine PHASE control to its center of rotation (the center bar of
the PHASE indicator will be lit).
4. Locate the large, white, coarse control knob on the pc board and note
its current setting in case you wish to return to it later.
5. Turn the coarse control knob until an autocorrelation signal appears on
the oscilloscope, then adjust for maximum signal.
This action matches the phase of the mode locker electronics to the
actual pulse.
6. Tune the modulator for short pulses.
Refer to “Aligning the A/O Modulator (AOM)” earlier in this chapter.
7. Test for proper modelocking.
Refer to “Test for Proper Modelocking” earlier in this chapter for
information on verifying stable mode-locked operation. Note: if you
are running in the long wavelength range, block the incoming pump
beam instead of opening the laser head to perform this test. Removing
the cover introduces water vapor into the cavity (which can severely
compromise performance in this range), and it can take some time
before the purge is again effective. Refer to “System Start-up” in
Chapter 7.
8. Replace the cover and screws. Do not leave the cover off!
This completes the coarse phase adjustment.
Removing the cover exposes you to high voltage and current circuits.
Do not attempt repairs or alterations other than for those expressly out-
lined in these instructions. Otherwise, you may be harmed or the unit
damaged. Such damage is not covered by your warranty.
Danger!
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