Tsunami Mode-Locked Ti:sapphire Laser
11-4
Pump laser is not warmed up. Refer to pump laser instruction manual for required warm-up time.
Tsunami is not optimized. Adjust M
1
and M
10
as described in Chapter 6, “Alignment: Cavity Alignment.”
If these adjustments fail to restore output, refer to the next cause below.
Optics are dirty. Inspect the optics for dirt or contamination. If dirty, clean the optics using the
cleaning procedure in Chapter 9, “Maintenance.” If an optic is dirty, an IR
viewer will show unusual scatter.
System is not properly aligned. Check that the pump beam is centered on M
2
and M
3
(the side facing the
Ti:Sapphire rod). Avoid parallax error.
Check for beam centering on mirrors M
1
through M
5
, prisms, AOM and OC.
Check for the location of the cavity beam on M
6
through M
9
(M
8
should be a
mirror image of M
7
).
SF-10 prism (G0360-000 (apex ∼60° 42’)) use in systems without the Blue
set, a must for X-long systems.
At 800 nm, the beam should be centered on M
7
and M
8
.
LaFn28 Prism (G0383-000 (apex ~ 59° 15’)) used in Blue, Broadband and
USP options.
At 800 nm, the beam should be
3
/4 of the way toward PR
2
/Pr
3
assembly.
Improper phase adjustment. Adjust the fine PHASE control on the Model 3955 for the highest signal. If
unsuccessful, refer to Chapter 6, “Alignment: Coarse Phase Adjustment...”
for details.
Improper pump power (too high
or too low).
Lower the pump power in 5% increments from the recommended setting.
Raise the pump power in 5% increments from the recommended setting.
Improper dispersion in the cav-
ity.
Femto configuration:
Verify beam position on Pr
1
/Pr
4
according to Table 6-4. Turn the Pr
2
/Pr
3
micrometer counterclockwise until there is an abrupt change in power (Pr
2
/
Pr
3
are moved away from the beam path). Turn the Pr
2
/Pr
3
assembly clock-
wise and watch for signs of mode locking (i.e., spectral spread of the wave-
length using a CCD camera behind a monochromator.
Pico configuration:
Adjust the GTI POSITION and fine PHASE controls while watching the
autocorrelation signal for pulses. Refer the Chapter 6, “Alignment: Mode
Locking” for details.
AOM is misaligned in the cav-
ity.
With the beam already centered on M
5
and M
10
, center the AOM substrate
on the beam. Refer to Chapter 6, “Alignment: Aligning the
A/O Modulator
(AOM)” for details.
Photodiode pc board is not
properly aligned.
Refer to Chapter 6, “Alignment: Aligning the Photodiode PC Board” for
details.
Cavity frequency is near or on
an AOM resonance frequency
(femto configuration only).
The cavity frequency of the system approaches the AOM resonance fre-
quency as the wavelength approaches the edges of the tuning range. At
this point, the amount of prism adjustment in the cavity is limited by the cav-
ity frequency closing in on the AOM resonance frequency. Together with
optic conversion from one set to another, it becomes necessary to alter the
cavity length in order to avoid running into this problem. Occasionally, it is
necessary to move the femto M
4
bracket to avoid this problem.
Symptom: Laser will not mode lock
Possible Causes Corrective Action
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