Tsunami - Beckman Institute Laser Resource Center

Service and Repair
Symptom: Low output power (cont.)
Possible Causes
Corrective Action
Tsunami is not optimized. Refer to chapter 7, "Operation: Optimizing Laser Output."
Cavity focus mirror alignments
are not optimized.
Do not move the translation positions of M2 and M3 after initial alignment. If
they have been moved, refer to chapter 6, "Alignment: Cavity Alignment."
Cavity Optics
alignment.
are Out Of
Pump focus mirror Pp is
out of position.
Rod position is not optimized.
Chiller is not on.
Adjust MI and Ml0 as described in chapter 6, "Alignment: Cavity Alignment.''
Unless the position of P2 was moved since installation, this adjustment should not
be necessary. Adjust P2 as described in chapter 6, "Alignment: Cavity Alignment."
Adjust the rod position as described in chapter 6, "Alignment: Cavity Alignment."
Turn on the chiller.
Symptom: Laser will not mode lock
Possible Causes
Pump laser is not
warmed up.
Tsunami is not optimized.
Poor beam mode profile.
Improper phase adjustment.
Wavelength on or near
water or oxygen absorption
lines.
Possible Feedback
Corrective Action
Refer to pump laser instruction manual for required warm-up time.
Refer to chapter 7, "Operation: Optimizing Laser Output."
With the beam directed to far field (e.g., displayed on a wall), adjust M2 to
obtain a solid, slightly elliptical mode with high contrast. There should be no
spikes on the outer edges of the beam profile.
Press the STATUS mode locker enable button on the Model 3955. lncrease
the gain on the autocorrelator and angle-tune the doubling crystal to search for
the autocorrelator signal. Adjust the fine PHASE control for the highest signal,
then adjust the GTI POSITION control to obtain the pulse. If there is no noticeable
change in the autocorrelator signal, center the PHASE LED display using
the PHASE fine control. Increase the autocorrelator signal by adjusting the
coarse phase control inside the Model 3955 (refer to "Coarse Phase Adjustment
..." in chapter 6). Test for proper mode locking (refer to "Test for Proper
Mode Locking" in chapter 6). Lower the pump power and repeat the above if a
pulse still does not appear.
Refer to Figure 7-1 to see if your operating wavelength is on or near the
absorption region. If so, purging is necessary. Note that more intense absorption
lines require larger quantities of purge gas for longer periods of time. For
operation near 900 to 980 nm, a purge rate of >0.17 m3/hr (6 SCFH) for >4
hours is essential for problem-free mode locking.
Feedback occurs when a reflection from a flat surface (such as a mirror, fiber,
or the plano surface of a lens) enters the laser cavity. Feedback radiation of a
few mW may disrupt mode locking. To test for possible feedback, set up a fast
photodiode (or the Model 409 autocorrelator) to monitor the Tsunami pulse
using a beam splitter between the Tsunami and the suspected feedback
source. If stable pulse operation is obtained after blocking the beam to the
suspected source, you have a feedback problem. Try realigning the suspected
device to the Tsunami laser. If this does not work, try installing a Faraday or
other isolator in your optical system. When selecting an isolator, be sure it can
accommodate the Tsunami wavelength tuning range.