On certain regularities of the response of a medium upon generation of the triple frequency of a few-period laser pulse in the case of its passage through an optically thin nonlinear layer

The response of a medium at the triple frequency under the action of few-period laser pulses is considered within the framework of the thin-optical-layer approximation for the case where the triple frequency is close to the natural frequency of the linear oscillator. It is shown that a bistable dependence of the polarization amplitudes on the external action amplitude simultaneously appears at both the natural frequency and the frequency of the external action. This allows one, in particular, to reveal the presence of bistability of the regime of third harmonic generation in a physical experiment by using the transmitted radiation of the acting pulse. A decrease in the duration of the pulse incident on the medium leads to an increase in the hysteresis loops. The effect of the absolute phase of a short pulse on the spectral composition of the response of the medium is studied. For pulses of medium duration, in addition to the resonant response of the medium, the presence of the dynamic response of the medium at the triple frequency was revealed, despite a detuning of the latter from the resonance. The presence of this frequency in the spectrum of the response of the medium results in the dependence of the resonant response of the medium on the absolute phase even for a sufficiently long pulse containing tens oscillations of the electric field strength under the pulse envelope. To obtain the dynamics of the spectral lines from the results of computer simulation, the Fourier-Gabor method is used, the applicability of which is demonstrated by the comparison of the results obtained on its basis with the corresponding analytical dependences.