7 Optical Parametric Oscillators 343
Tuning of the optical parametric oscillator can be handled using the same
techniques as described in the chapter on solid-state lasers (Chapter 6; see also
Chapter 2). However, significant differences do exist that can be attributed to the
difference in the operating principles of the two devices. Some of these differ-
ences are manifest in the coarse tuning available with phase matching of the
optical parametric oscillator and in the time-varying instanteous gain, which has
to be taken into account if injection seeding is to be utilized. However, because
many of the tuning and line narrowing elements are discussed in Chapter 6, they
will not be discussed here. Rather, the tuning aspects unique to the optical para-
metric oscillator will be emphasized.
Coarse tuning of the optical parametric oscillator can be accomplished using
either angular or temperature tuning. In fact, any effect that causes a differential
change in the refractive indices at the pump, signal, and idler wavelengths could
be used to effect tuning. For example, tuning could be achieved using an applied
pressure through the stress optic effect. However, to date, only angular or tem-
perature tuning has received wide application. To calculate the tuning rate, the
partial derivatives of the phase mismatch can be used. According to a theorem in
partial differential calculus,
Ox I-OY l Oz l =-1
Using this relation, the tuning rate can be approximated by
~ OAk/()O
~---0 = - OAk/O~
for angular tuning and
~---T =- ~Ak/~)-----~
for temperature tuning. To evaluate the derivatives of Ak with respect to the direc-
tion of propagation and temperature, the results of Sec. 4 can be used. Thus,
1 ~n2 1 ()n3)
c)--O- ~l ~)0 ~2 c)0 ~3 (90 (63)
in general. Of course, the partial derivative with respect to angle for ordinary
waves is zero in uniaxial crystals. For temperature tuning,

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