Tunable Lasers Handbook

7 Optical Parametric Oscillators 343

10. TUNING

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

(60)

Using this relation, the tuning rate can be approximated by

~ OAk/()O

~---0 = - OAk/O~

(61)

for angular tuning and

~---T =- ~Ak/~)-----~

(62)

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,

~)Ak_2rt(1

Oni

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,