Page 379 - Tunable Lasers Handbook

7 Optical Parametric OsciI/atois 33

2.0 -
l.E -

56 60 64 68 72
Angle (degrees)
FIGURE 20 Phase-matching curve for CdSe for a 2.10-ym pump.

ranged from 0.98 to 1.16 pm. With 0.3 W of pump power, the available power at
both the signal and idler wavelengths was estimated at 0.003 W, yielding an effi-
ciency of 0.01. Later. by using a cw Ar ion laser for a pump laser, a threshold as
low as 2.0 mW was achieved. A power output of about 0.0015 W was achieved
at about 2.8 times threshold. While a continuous pump was employed, the output
consisted of a series of pulses with pulse lengths ranging from 0.1 to 1.0 ins in
length [52].
More efficient operation in the near infrared was obtained by two
researchers both using LiNbO, as the nonlinear crystal. In one case. a frequency-
doubled Nd:glass laser was used as the pump source [53], and the other used a
Q-switched Cr:A1,03 laser [54]. In the first case; a threshold of z.bout 5.0 kW
was required for -a 8.Q-mm crystal length. At twice threshold, a peak output
power of 1.8 kW was achieved yielding an efficiency of 0.18. In the second case
a threshold of 65 kW was achieved in a doubly resonant arrangement with a
9.35-mm crystal length. With the doubly resonant arrangement, 0.22 of the peak
pump poweir was converted to the signal at 1.04 pm. On the other hand, with a
singly resonant arrangement. only 0.06 of the peak pump power was converted
to the signal. Although the efficiencies reported in these experiments are impres-
sive, the output energy of these devices is in the millijoule range or less.