SHOT-NOISE-LIMITED DETECTION IN FM SPECTROSCOPY BY OPTICAL NULLING OF RESIDUAL AMPLITUDE MODULATION.

Abstract

Summary form only given. Frequency-modulation (FM) techniques have been widely recognized as a valuable tool in high resolution high-sensitivity laser spectroscopy. In practice, perfect phase modulation is difficult to achieve, and the laser beam emerging from the electro-optic modulator (EOM) exhibits residual amplitude modulation (RAM) even when no sample is present. The authors present evidence that the main contribution to this RAM is caused by the EOM crystal acting as a Fabry-Perot etalon filled with a dielectricum which is characterized by a modulated index of refraction. With this model the RF frequency and phase behavior of this RAM contribution are correctly accounted for.