Page 353 - Tunable Lasers Handbook

7 Optical Parametric OsciiIators 3 13
For TEM,, mode pump beams, the divergence internal to the nonlinear crystal is

Using this for the beam divergence and evaluating the partial derivatives, the
magnitude of this effect can be estimated.
Experimental results appear in agreement with this analysis of the spectral
bandwidth. The spectral bandwidths of parametric oscillators have been deter-
mined experimentally for several situations [ 17.181. In one instance, a Nd:YAG
pump laser was utilized with a LiNbO, parametric oscillator. In this study, the
wavelength control exerted by the nonlinear crystal was compared with wave-
length control exerted by other wavelength control elements such as gratings and
etalons. In the other instance, an Er:YLF laser was used to pump an AgGaSe,
optical parametric oscillator. In this study the effects of the pump divergence on
the spectral bandwidth are compared with the effects of the pump spectral band-
width and the spectral bandwidth of the nonlinear interaction. Results are shown
in Fig. 8. 11 is of interest that in both cases the spectral bandwidth is significantly
increased by the pump beam divergence.
An allowable variation of the temperature can also be defined in a similar
manner by expanding the phase-matching condition as a function of tempera-
ture. Expanding the phase mismatch as a function of the temperature T yields

FIGURE 8 Measured spectral bandwidth