Sensitive nonlinear optical spectroscopy

摘要

Saturation spectroscopy involving synchronous phase-sensitive detection and measurement of the intensity of the output when one of the input beams is chopped has a drawback that scattered light and fluorescence from the sample will also be chopped and produce a large background signal. According to the present invention, the direction of propagation of one of the input beams is modulated. This causes the direction of propagation of the output to be similarly modulated while producing only a negligible effect on the background radiation from scattering and fluorescence.