Optical heterodyne detection for cavity ring-down spectroscopy

摘要

A cavity ring-down system for performing cavity ring-down spectroscopy (CRDS) using optical heterodyne detection of a ring-down wave ERD during a ring-down phase or a ring-up wave ERU during a ring up phase. The system sends a local oscillator wave ELO and a signal wave ESIGNAL to the cavity, preferably a ring resonator, and derives an interference signal from the combined local oscillator wave ELO and the ring-down wave ERD (or ring-up wave ERU). The local oscillator wave ELO has a first polarization and the ring-down wave ERD has a second polarization different from the first polarization. The system has a combining arrangement for combining or overlapping local oscillator wave ELO and the ring-down wave ERD at a photodetector, which receives the interference signal and generates a heterodyne current IH therefrom. Frequency and phase differences between the waves are adjustable.