  This paper presents a detailed numerical study of the effect of focusing on
the conversion efficiency of low-loss singly-resonant parametric oscillators
with collinear focusing of pump and signal. Results are given for the maximal
pump depletion and for pump power levels required for various amounts of
depletion, as functions of pump and signal confocal parameters, for kI/kP=0.33
and 0.50. It is found that the ratio of pump depletion to maximal depletion as
a function of the ratio of pump power to threshold power agrees with the
plane-wave prediction to within 5%, for a wide range of focusing conditions.
The observed trends are explained as resulting from intensity and phase
dependent mechanisms.
