Abstract
A simple and universal technique for performing optical feedback cavity enhanced absorption spectroscopy with a linear Fabry-Pérot cavity is presented. We demonstrate through both theoretical analysis and experiment that a diode laser can be sequentially stabilized to a series of cavity modes without any influence from the direct reflection if the feedback phase is appropriately controlled. With robust handling of the feedback phase and help from balanced detection, a detection limit of 1.3 × 10(-9) cm(-1) was achieved in an integration time of 30 s. The spectrometer performance enabled precision monitoring of atmospheric methane (CH(4)) concentrations over a time period of 72 h.