Page 381 - Tunable Lasers Handbook

7 Optical Parametric Oscillators 341

10.0 \
12.0
11.0:

2 9.0 -
h -
a
c
0.0 -
0
b 7.0 -
.-
E
v 6.0 -
5
0)
-
$ 5.0 -
a
z 4a -
3.0 - -
2.0 -

22 24 26 20 30
Angle (degrees)
a
FIGURE 22 Phase-matching curve for T1:.4sSe; .. 2.10-ym pump.
for
coefficient is inversely proportional to the product of the signal and idler wave-
lengths. To help compensate for the low gain, a 50-mm-long crystal was used.
Using angle tuning. the spectral range from 1.1 to 4.5 pm could be covered. The
threshold was 4.0 mJ when the oscillator was operating near 1.7 ym. An energy
conversion efficiency of 0.15 was reported.
Optical parametric oscillation further into the mid-infrared region was POS-
sible by using a CdSe crystal. Initially, a Nd:YAG laser operating at 1.83 pm was
used as the pump [57]. Later, a HF laser, operating around 2.87 ym was used for a
pump [%I. In the former case, threshold for a 21-mm crystal length was observed
to be between 0.55 and 0.77 liW. A power conversion efficiency of 0.40 was
inferred by measuring the depletion of the transmitted pump. In the latter case,
threshold for a 28-mm crystal length was found to be 2.25 kW. At about twice
threshold, a signal power of 0.8 kW was observed that indicated a power efficiency
of 0.15. By employing angle tuning, a signal was generated over the range from
4.3 to J.5 pm. Corresponding to this. the idler was tuned between S.l 10 8.3 pm.
Optical jparametric oscillator operation can be enhanced by utilizing a mode-
locked pump [59]. For one set of experiments, a mode-locked Nd:glass laser.
operating at- 1.058 ym. was amplified to produce an output of 0.55 J. By using an