Cavity ringdown spectroscopy with widely tunable swept-frequency lasers

The paper reports an efficient way to record a single cavity ringdown (CRD) spectroscopy data point per FSR in real time, by measuring the time interval for the CRD decay to drop from one preset level to another. Registering a data point for each build-up and decay event, without logging the full CRD waveform at each laser frequency, imposes much less demand on digitizer memory depth and data processing. Data-acquisition schemes of this type are able to generate characteristic spectroscopic signatures for key gas-sensing applications, such as security screening for airborne chemical agents.