Page 380 - Tunable Lasers Handbook

340 Norman P. Barnes
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c 8.0 -
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v 6.0 -
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50 52 54 56 58
Angle (degrees)
FIGURE 2 1 Phase-matching curve for ZnGeP, for a 2.10-pm pump.

A device tunable across the visible region of the spectrum was produced by
using ADP as the nonlinear crystal [SI. A frequency-quadrupled Nd:YAG laser,
yielding about 1.0 mJ/pulse at 0.266 pm, was utilized as the pump. Gains were
high enough with this configuration that external mirrors were not necessary to
obtain significant conversion. With the 50-mm ADP crystal oriented normal to
the pump beam, an average power conversion of the pump to the outputs in the
visible region of the spectrum was as high as 0.25. Temperature tuning the crys-
tal from 50 to 105°C allowed the region from 0.42 to 0.73 pm to be covered.
A cw optical parametric oscillator tunable in the red region of the spectrum,
from 0.680 to 0.705 pm, was demonstrated using an Ar ion laser operating at
0.5145 pm in conjunction with a 16.5-mm LiNbO, crystal [52]. To avoid opti-
cally induced refractive index inhomogeneities, the crystal was operated at ele-
vated temperatures, nominally 240°C. A threshold of 410 mW was possible. At
2.8 times threshold, 1.5 mW of output power was available even though the out-
put mirror only had a transmission of approximately 0.0004.
An optical parametric oscillator tunable in the mid-infrared region was
obtained by using a Nd:YAG laser directly as the pump and a LiNbO, crystal
[56]. Operation in this region of the spectrum is more difficult because the gain