Nice to see this miniaturization of photoacoustic spectroscopy - something I've done a bit of in the past. It is an underappreciated technique. Ordinarily one

Nice to see this miniaturization of photoacoustic spectroscopy - something I've done a bit of in the past. It is an underappreciated technique. Ordinarily one measures the difference in optical throughput with and without a sample. If it is a weak absorber, it is a difference between two large numbers. PAS is zero background. No absorption, no pressure wave, no signal. Any absorption stands out clearly against that zero background.