Phase fluctuations in a parametric light source operating inside a laser resonator

A theoretical analysis is given of phase fluctuations in a parametric light source consisting of a nonlinear crystal operating inside die resonator of the pumping laser ("internal parametric light source"). It is shown that an exponential instability of phase fluctuations may arise in such an internal source. The condition of stability of the phase fluctuations is determined. The minimum possible width of the emission line of an internal parametric source is calculated in the stability range of phase fluctuations. It is shown that the optimization of an internal parametric source in respect of its output power results in strong broadening of the emission line.