Abstract

A simple but highly effective method for enhancement of spontaneous Raman scattering from gases is described. It employs a multimode blue laser diode that receives feedback from a near-concentric bidirectional multipass cavity in such a way as to generate a circulating power on the order of 100 W for a sample volume of $ 10\,\,{{\rm mm}^3} $. The feedback, provided via a volume Bragg grating, reduces the laser bandwidth to $ 4\,\,{{\rm cm}^{ - 1}} $. Spectra of spontaneous Raman scattering from ambient atmospheric air, detected collinearly with the pump, were recorded with a limit of detection below 1 ppm. The performance of the setup is further illustrated through detection of acetone, methane, and isotopic carbon dioxide in breath.

© 2019 Optical Society of America

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