Service and Repair
11-7
Electronics phase shifts
because the electronics
cover(s) is/are off.
Verify that the top covers of the electronics are on. This is especially important on
a broad picosecond pulse system.
Poor beam mode profile. With the beam directed to far field (e.g., displayed on a wall), adjust M
2
to obtain
a solid, slightly elliptical mode with high contrast. There should be no spikes on
the outer edges of the beam profile.
The pump laser is unstable. Refer to the pump laser manual for troubleshooting.
Symptom: Laser is mode locked but has noisy >2 ps pulses with side lobes or baseline noise (ps
configuration only)
Possible Causes Corrective Action
Improper phase adjust-
ment.
Adjust the fine PHASE control on the Model 3955 electronics module. If this is
unsuccessful, refer to Chapter 6, “Alignment: Coarse Phase Adjustment...” for
details on making further adjustments.
Improper dispersion in the
cavity (ps configuration
only)
Adjust the GTI position and fine phase while watching the autocorrelation signal
for pulses. Refer to Chapter 6, “Alignment: Mode Locking,” for more 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.
M
2
is too close to the
Ti:sapphire rod.
Move M
2
away from the Ti:sapphire rod in increments of 1/4 turns. Reiterate
these adjustments to phase, GTI position and pump power to eliminate the sat-
ellite pulses.
Symptom: Pulses are broad with low power
Possible Causes Corrective Action
Improper phase adjust-
ment.
Adjust the fine PHASE control on the Model 3955 electronics module. If this is
unsuccessful, refer to Chapter 6, “Alignment: Coarse Phase Adjustment...” for
details on making further adjustments.
Improper dispersion in the
cavity (ps configuration
only)
Adjust the GTI position and fine phase while watching the autocorrelation signal
for pulses. Refer to Chapter 6, “Alignment: Mode Locking,” for more details.
Pump power is too low. Raise the pump power in 5% increments from the recommended setting.
Wavelength on or near
water or oxygen absorp-
tion lines.
Consult Chapter 7, “Operation,” Figure 7-1 for the location of water and oxygen
absorption. Purge when necessary.
The bi-fi is misaligned (or
other mishaps).
There is dirt in the beam path of the bi-fi and/or the GTI. Clean.
The wrong order is present as a result of mis-orienting the bi-fi.
The Bi-fi assembly is not at
Brewster’s angle to the
beam.
The beam is not centered on the GTI.
Changing from a 2-plate to a 3-plate bi-fi requires a correction to the Brewster’s
angle.
Note the tick marks on the bi-fi Brewster’s angle adjustment bracket, then
loosen the bracket lockdown screw and rotate the bracket 1.5 marks toward the
input bezel.
Reverse the direction of rotation when going back to the 2-plate bi-fi.
The wrong bi-fi is installed. Consult Chapter 10, “Options and Accessories,” Table 10-10, for the appropriate
bi-fi for the installed optic set.
Symptom: Poor Long-term Stability
Possible Causes Corrective Action
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