CW cavity ring-down spectroscopy (CRDS) with a semiconductor optical amplifier as intensity modulator

We summarized both advantages and disadvantages of different light modulators used in cw-CRDS experiments. For the first time, we introduce the use of a semiconductor optical amplifier (SOA) as light modulator in cw-CRDS. A direct comparison of the sensitivity realized on the same instrument using an SOA as modulator with use of an acousto-optic modulator (AOM) has been made. It is found that the SOA has larger extinction ratio (∼81 dB) than the AOM. For our instrument, with single-shot initial signal-to-noise ratio of 1400:1, these two modulators are found giving equivalent sensitivity.