We present results for continuous-wave second-harmonic generation of 532 nm
light in an external cavity locked using a spatial mode interference techn
ique. This technique does not require frequency modulation and thus yields
a clean second-harmonic spectrum devoid of modulation sidebands. The perfor
mance is compared with the same system controlled by Pound-Drever-Hall lock
ing. Both techniques achieved the same maximum output power with comparable
stability which is predominantly limited by fluctuations in the pump power
and the nonlinear crystal temperature.