Influence of phase mismatching in a nonlinear crystal and in air on intracavity frequency conversion of ultrashort pulses

A theoretical analysis is made of intracavity second harmonic generation of ultrashort laser pulses under conditions of active modulation for the cavity (resonator) losses. An allowance is made of the changes in the phases of the light waves at the fundamental and second-harmonic frequencies in a nonlinear crystal and in air. It is shown that both linear and nonlinear changes in the phases of the light waves during the interaction process have a strong influence on the time characteristics and on the efficiency of second harmonic generation: the shape of the pulses of the fundamental-frequency wave becomes strongly distorted and a complex time structure is formed in the case of the second harmonic pulses. The solution of the problem makes it possible to find the conditions under which minimal distortions occur in the shape of the pulses of the converted radiation but the conversion efficiency remains maximal.