A pulsed laser source using stimulated Raman scattering and difference frequency mixing: Remote sensing of methane in air

Abstract

Mid-infrared radiation at 3.43 μm is generated by difference frequency mixing a 1.064 μm Nd:YAG laser with a methane gas Raman shifted Nd:YAG (1.064 μm) laser at 1.54 μm in KTiOAsO₄(KTA). Using this pulsed (7 ns), moderate energy (1 mJ) source we demonstrate the optical detection of methane in air and measure an absorption coefficient of 1.2cm⁻¹ atm⁻¹. Additional source characteristics include an intrinsic wavelength stability defined by the methane Raman vibrational frequency and a moderate linewidth (1.5 cm⁻¹).