Abstract

A recently developed technique,¹ three-beam phase-modulated nonlinear spectroscopy, provides signals linear in the third-order susceptibility [χ⁽³⁾]. Selection of the relative phase offset of the two orthogonal, linearly polarized pump waves (derived from a single linearly polarized wave propagated through an electro-optic modulator) allows measurement of either the real or the imaginary part of chi-three. The relative phase offset is controlled by the voltage applied to the EO modulator, and application of a sinusoidal voltage modulation allows for low-noise signal recovery. The probe wave is linearly polarized along one of the pump field directions, and the signal wave is produced with a polarization orthogonal to the input probe field. The signal is detected by heterodyning with the input probe after passing through a Glan polarizing prism, set at 45° to the field directions of the two waves. The power in both the transmitted and reflected beams from the polarizing prism is detected by two matched photodiodes, and the electrical outputs from these are combined in a 180° power adder.

© 1984 Optical Society of America