Theory of light fluctuation filtering in two-photon absorption process by multiple second harmonic generation. I. Basic equations. Classical description

摘要

Multiple second harmonic generation in which the generated second harmonic radiation is filtered out at each stage is studied in this paper. Both classical and quantum equations describing this process are derived, and it is shown that multiple second harmonic generation in thin nonlinear plates acts in the same way as the two-photon absorption process. A closed classical solution for stochastic photon number is found and, for chaotic input radiation, the mean photon number and the mean quadratic fluctuation (variance) of the integrated intensity in the fundamental radiation are calculated. It is shown that the variance of the intensity systematically decreases in the course of the process and, thus, the statistical distribution of the fundamental radiation approaches the coherent state from the point of view of classical theory.