Tempest Nd:YAG Laser Operator’s Manual
40
The third harmonic generator (THG) crystal may be used to provide UV
radiation at 355 nm. The third harmonic generation process is Type I in BBO,
created with horizontally polarized fundamental and second harmonic light. A
half wave plate for the second harmonic is mounted on the input to the THG
housing. The third harmonic output is vertically polarized. The THG housing
may be installed by the end user. THG generation requires that the SHG crystal
has been installed and is aligned. Third harmonic energy (355 nm) energy may
be optimized for only one laser head. Installation is described below.
1) Remove the laser head harmonic housing (front) cover.
2) Install the third harmonic generator using the last set of alignment
pins and screw holes just before the dichroic mirror set next to the
exit aperture. Insure that the harmonic generator housing is installed
such that it is against the second alignment pin.
3) Remove the 532 nm dichroic mirror set closest to the exit aperture
and install the 355 nm dichroic mirror set using the same alignment
pins and screw holes.
4) Adjust the wave plate on the second harmonic generator housing to
maximize the 355 nm energy, figure 4-5. This adjustment maximizes
355 nm energy for only one laser head.
5) Adjust the external screw on the THG housing to optimize the crystal
angle, maximizing 355 nm energy. The crystal angle may be
adjusted using a trim pot adjustment tool. Only one laser head will
be optimized for 355 nm energy.
6) Reinstall the laser head harmonic generator housing (front) cover.
The fourth harmonic generator is used to produce ultraviolet radiation at 266 nm
by doubling the second harmonic output in BBO. A half wave plate for the
second harmonic is mounted on the input to the fourth harmonic housing. The
fourth harmonic output is vertically polarized. Fourth harmonic generation
(4HG) requires that the SHG crystal has been installed and is aligned. Fourth
harmonic generation may be optimized for both laser heads. Use the following
procedure to install the fourth harmonic generator.
1) Remove the laser head harmonic housing (front) cover.
2) Install the fourth harmonic generator using the last set of alignment
pins and screw holes closest to the dichroic mirror set next to the exit
aperture. Insure that the harmonic generator housing is installed such
that it is against the second alignment pin.
Third
Harmonic
Installation
Fourth
Harmonic
Installation
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