Optical Third Harmonic Generation by Molecular Vibration

Abstract

A theoretical consideration of nearly resonant interaction between the infrared radiation and the anharmonic molecular vibration has been developed to evaluate an efficiency of third harmonic generation in the infrared by molecules. By using the spectroscopically measured molecular constants in the Morse function, the nonlinear susceptibilities for second and third harmonic generation are derived. The problem is treated both classically and quantum mechanically. It is found that the spectroscopic stability holds for the nonlinear susceptibility. Non-resonant interactions which usually occur in solids are also discussed briefly.
A gas of molecules with random orientations cannot produce optical second harmonics. However, each molecule has the nonlinear susceptibility of second harmonic generation by its molecular vibration and it is found that the Miller’s rule also holds for the molecular susceptibility.