Optical absorption spectrometry using Laser amplitude modulation

We present a new technique for cavity enhanced optical absorption spectrometry, employing a radio-frequency amplitude modulated laser to interrogate an optical cavity. It is capable of sensing molecular absorption at the fundamental laser shot noise limit, and is able to perform quantum noise limited gas sensing at atmospheric pressure. We implement this technique, for the first time, in a free space cavity, and demonstrate that the demodulated error signal can be used to measure losses in a resonator.