Tsunami - Beckman Institute Laser Resource Center

Tsunami
The oscilloscope display should now show two pulse trains with a fixed
delay. The pulse trains are now synchronized, but are probably not -
overlapped in time.
6. Verify the time between the pulse trains can be varied by using the
coarse TIMING control on the LTC Tsunami laser.
The timing control provides up to 2 ns of adjustment. If the pulses are
more than 2 ns apart, change the length of the cable between the
Model 3930 and the Model 3932 (30 cm of cable corresponds to
about 1 ns of delay). Do not modify the cables between the LTC laser
head and its Model 3955! When the cable length is optimized,
activate the sweep generator (press the TIMING button) on the Model
3930 and observe the pulses from the LTC Tsunami sweeping back
and forth over those from the mode-locked laser.
To overlap the pulses more precisely in time, focus the two laser
output beams in a nonlinear crystal such as BBO.* As you sweep the
phase-matching angle of the BBO crystal, a frequency-doubled signal
should be observed from each laser. Set the crystal for an intermediate
angle to observe the sum frequency mixed signal from both lasers. By
activating the sweep generator, the crystal can be easily phasematched
for observation of this sum frequency mixed signal. It will
be modulated at the 10 Hz sweep period. Once the sum frequency
mixed signal is observed, deactivate the sweep generator and use the
coarselfine TIM 1 NG controls to optimize this signal.
A cross-correlation of the two pulses can be generated by displaying
the sum frequency mixed signal on a photodetector and activating the
sweep generator. Alternatively, the cross-correlation signal can be
observed by sending the spatial and temporally overlapped beams into
an autocorrelator such as the Model 409. Figure 8-9 shows a typical
cross-correlation trace for a ps LTC Tsunami lasers and a second
mode-locked ps laser, each having 1.5 ps pulse widths.
- +
* The nonlinear crystal must be cut such that it canfrequency-double the output of each
lasel: Verify this by temporarily placing a white card at the output of the crystal and
changing the phase-matching angle of the crystal while watching the laser output on the
card.