Tsunami - Beckman Institute Laser Resource Center

Laser Description
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AOM
OC
n
Fast
Photodiode
\
\\ Beam Output
'\ Splitter Brewster
Window
Window
Model 3955
AOM Driver Electronics
Motorized
Pump
H R Beam Dump Optional
Model 3930
Lok-to-Clock Electronics
Figure 3-4: Beam Path for Tsunami Model 39506 Picosecond Configuration.
A10 Modulator (AOM)
Wavelength Tuning Characteristics
However, astigmatism still exists within the laser rod. Therefore, the pump
beam must also be astigmatic for efficient coupling between the pump and
intracavity beam. A concave focusing mirror used at the proper angle induces
astigmatism in the pump beam that matches that of the Tsunami
cavity mode. The result is a laser with high conversion efficiency and good
beam quality.
The Tsunami acousto-optic modulator (AOM) ensures an 82 MHz nominal
mode-locked operation at laser start-up. It also allows the laser to operate
for extended periods without the dropouts or shut-downs associated with
standard passive mode-locking systems. The AOM is at Brewster's angle
and is driven by a regeneratively-derived rf signal.
Because the Ti:sapphire rod is birefringent, unintempted tuning is
achieved when the c-axis of the rod is aligned coplanar with the polarization
of the electric field within the cavity. Since the Ti:sapphire rod and
the birefringent filter plates or prism surfaces represent a total of ten
Brewster's angle surfaces, the polarization within the cavity is largely determined
by the orientation of these surfaces. Furthermore, cavity losses
are minimized and tuning is optimized when all these surfaces are accurately
aligned at Brewster's angle. The Tsunami laser uses a proprietary
Ti:sapphire rod holder that orients the rod surfaces at Brewster's angle and
allows the c-axis of the rod to be aligned coplanar to the electric field vector.
This technique compensates for unavoidable errors in rod orientation
that occur when the rod is cut and polished.