Spontaneous Raman scattering at trace gas concentrations with a pressurized external multipass cavity

A setup is described with which the spontaneous Raman scattering rate from pressurized gas samples is greatly enhanced inside a near-concentric optical cavity. The pump source is a high power multimode semiconductor laser diode that receives optical feedback from the cavity by way of a volume Bragg grating, resulting in a linewidth of 80 pm and circulating power close to 100 W. Under pressurization (up to 8 bar) a limit of detection below 100 parts-per-billion was obtained for gaseous hydrogen, measured in ambient air and in breath. Furthermore, isotopic trace detection is demonstrated by headspace measurements of semiheavy water.

Automated summary

The setup utilizes a high power multimode semiconductor laser diode and an optical cavity to greatly enhance the spontaneous Raman scattering rate from pressurized gas samples, achieving a detection limit below 100 parts-per-billion for gaseous hydrogen. Isotopic trace detection is also demonstrated through headspace measurements of semiheavy water.