Tsunami Mode-Locked Ti-sapphire Laser
6-24
2. Set up an autocorrelator to measure the Tsunami output pulse width.
To measure pulses, use a Spectra-Physics Model 409-08 autocorrelator
(or equivalent). Avoid saturating the autocorrelator. Subtle adjustments
to the phase-matching angle of the nonlinear crystal will be required to
obtain an optimum autocorrelation signal. Refer to the autocorrelator
manual for setup and operation instructions.
3. Open the pump and Tsunami shutters and adjust the pump laser until
your Tsunami achieves the output power specified in the appropriate
table at the end of Chapter 3.
4. Test for proper modelocking.
Too much bandwidth can make it difficult for the regenerative mode-
lock loop to acquire modelocking from CW operation. In addition,
operating at wavelengths at or near water and oxygen absorption lines
would be either difficult or impossible without sufficient cavity purg-
ing (see Figure 3-11).
a. Temporarily disable the regenerative modelock RF loop (push the
STATUS button on the Model 3955 front panel).
b. Close and reopen the pump laser shutter to take the system off
modelocking.
c. Adjust the fine PHASE control so that only the bottom bar of the
PHASE LED bar graph glows.
d. Enable the regenerative modelock RF loop (push the STATUS but-
ton again).
e. Adjust the fine PHASE control slowly to find the position on the
PHASE LED bar graph where modelocking occurs.
f. Turn the PHASE knob to set the PHASE LED to the top bar. Repeat
the last four steps to find the other LED position for initiating
modelocking.
g. Adjust the fine PHASE control to center the LED position between
these two limits.
h. Repeat Steps a, band d above. If the phase adjustment is correct,
the system will return to modelocked status within a second.
After proper purging, the system should modelock over the entire tun-
ing range within a second or two if the fine
PHASE control is tested as
described above. However, as cavity length changes as a function of
wavelength (except when the cavity frequency is locked to a constant
when the Lok-to-Clock option is used), the fine phase setting changes
as well. Provided that the cavity frequency throughout the entire tun-
ing range is within the frequency limit of the AOM, the fine
PHASE
LED
position goes upwards as the wavelength increases for non Lok-to-
Clock systems.
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