Page 350 - Tunable Lasers Handbook

310 Norman P. Barnes

one will be presented [15]. Measurement of the acceptance angle can be per-
formed using parametric amplifier experiments. Amplifier experiments can be
used directly since the interacting wavelengths are fixed in these experiments. In
parametric oscillator experiments, changing the angle at which the nonlinear
crystal is oriented will tend to change the wavelength. As such, a measurement
of the parametric oscillator output as a function of the orientation of the nonlin-
ear crystal is likely to produce a tuning curve rather than a measurement of the
acceptance angle. Data on the parametric amplifier presented here are for an
AgGaSe, parametric amplifier pumped by a Ho:YAG laser. In this case, the
AgGaSe, is =20 mm in length and oriented at 48" to the direction of propaga-
tion. A 5.39-pm HeNe laser is being amplified. Measured amplification as a
function of the angular orientation of the crystal is shown in Fig. 7. Also shown
is the predicted relative amplification as a function of the orientation of the cvs-
tal. To obtain the predicted relative amplification versus angle a relation of the
form sinh'[(rl)z - (AX1/2)2]/[(r1)2 - (Ak1/2)1] is used since the low-gain approxi-
mation is not valid in this case. Results of this experiment, as well as many oth-
ers cited in the literature, tend to confirm the validity of this analysis.
The spectral bandwidth of the nonlinear interaction will be determined
much like the acceptance angle in some respects. For optical parametric oscilla-
tors, the pump wavelength is usually fixed. However, as the signal wavelength
varies, the idler wavelength can vary in order to satisfy conservation of energy
or vice versa. Thus, a variation in one of these wavelengths will produce a com-

AgGaSep 0

c
.-
a,
0 0.6 -

0

I
-0.015 -0.005 0.005 0.015
Crystal angle (radians)
FIGURE 7 Measured acceptance angle.