Technique for locking a second-harmonic generation cavity with an electro-optic active nonlinear crystal

A new technique for generating an error signal for locking a second-harmoni c generation (SHG) enhancement cavity is presented. The calculations are de veloped within a linear system framework treated with a Laplace transform. The error-signal generation is based on FM sidebands, but it differs from t he Pound-Drever-Hall technique by performing the modulation on the (assumed ) electro-optic active nonlinear crystal in the cavity. This new technique for generating the error signal has some advantages over the former one in that (i) the shape of the error signal is independent of the relative phase of the rf signal between the photodiode and the local oscillator; Gi) it p rovides a handy, high-bandwidth actuator to improve the cavity lock, which can improve the average SHG power; and (iii) it decreases cost and complexi ty by not requiring an external electro-optical modulator. The specific cas e of SHG in KNbO3 is treated as an example of the feasibility of the techni que. (C) 2001 Optical Society of America.