Investigation of the characteristics of the intensity noise of singly resonant active second-harmonic generation

We derive analytical expressions for the quantum-noise spectra of a singly resonant active frequency-doubling laser with single-frequency operation by using a linearized input–output method. For operation of a practical solid-state laser, we analyze separately the contributions of the various noise sources to the final spectrum. The change in resonance in the spectrum from an overdamped- (at higher μ) to an underdamped- (at smaller μ) driven second-order oscillator where μ is the nonlinear coupling coefficient, was experimentally observed with a diode-pumped Nd:YVO4+KTP single-frequency-doubling laser. The experimental result is in good agreement with the theoretical expectation.