A theory is developed of four-photon parametric frequency conversion in gases under two-photon resonance conditions. A study is made of the polarization characteristics of the process and of the conditions under which the conversion efficiency has its maximum value.
A theoretical analysis is made of the process of parametric up-conversion of the frequency of an infrared signal involving two-photon resonance of a pump field whose spectrum is considerably wider than the widths of the atomic transition lines. It is shown that the maximum steady-state efficiency of conversion in a wideband field is only slightly different from the maximum efficiency of conversion in a regular and monochromatic field. A dynamic improvement in the conversion efficiency is possible under transient interaction conditions.
Six-photon parametric up-conversion under conditions of two-, three-, and four-photon resonance of a constant nonmonochromatic pump field is analyzed allowing for population migration, transient response of the medium, Stark shift of the levels, and width of the frequency spectrum of the the pump field. It is found that in the steady-state conversion regime, the maximum average conversion efficiency in the four-photon resonance case differs only negligibly from the maximum conversion efficiency in a monochromatic field, whereas in the two-photon and three-photon resonance cases it is higher than the maximum efficiency in a monochromatic pump field. An analysis is made of the influence of optically induced relaxation on the average conversion efficiency under conditions of pulsed excitation of two-, three-, and four-photon resonances.
Four-photon parametric up-conversion of a weak infrared signal under conditions of two-photon resonance of a constant nonmonochromatic pump field is analyzed allowing for population migration, transient response of the medium, Stark shift of the levels, and width of the pump frequency spectrum. It is found that under steady-state conversion conditions in a nonmonochromatic pump field, it is possible to achieve an average conversion efficiency differing only negligibly from the maximum conversion efficiency in a monochromatic pump field. An analysis is made of the influence of optically induced relaxation on the average conversion efficiency in the transient regime. Numerical estimates are made of the transition parameters for an alkali metal vapor in a frequency-degenerate pump field exciting a two-photon transition.
An analysis is made of the frequency addition processes in the case of a two-frequency double resonance involving vibrational-rotational transitions and their potential applications in nonlinear spectroscopy. A study is made of the influence of the saturation effect and of the frequency detuning from one- and two-photon resonances on the conversion processes and estimates are obtained for a specific molecular gas. It is shown that in the case of two-frequency interaction under double resonance conditions the efficiency of conversion of a probe wave into a wave at the signal frequency increases at least several hundred times, compared with the case of the one-frequency interaction.