Detection of Molecular Hydrogen by Stimulated Raman Emission

Abstract

Molecular hydrogen is a very difficult molecule to detect in a noninvasive manner. The molecule has no dipole moment. Excitation of its first electronic excited state requires light in the vacuum ultraviolet region, ~110 nm. Hydrogen has been shown to produce spontaneous Raman emission at pressures as low as 550 Torr, but the process occurs with a low quantum efficiency, and efficient collection of the emissions is difficult. Lower partial pressures of hydrogen can be detected with coherent anti-Stokes Raman spectroscopy (CARS), but the experimental apparatus can be prohibitively expensive.