Knowledge Bank

CW frequency modulation (FM) spectroscopy is a technique capable of providing quantum limited sensitivity and laser limited resolution. By pulsed amplification of CW laser radiation in a hi-fi dye amplifier followed by nonlinear frequency mixing the benefits of FM spectroscopy can be extended throughout UV and IR $regions1$. By cascading three capillary dye cells pumped by a 20 ns injection seeded Nd:YAG, we obtain pulse energies in excess of 1 mJ $(at17000cm-1)$. This light is then mixed with the 3rd harmonic of the Nd:YAG resulting in radiation at $45000cm-1$. The outlined procedure produces tunable pulsed UV radiation with essentially transform limited bandwidth (<70 MHz FWHM) while preserving the sideband phase relationships of the original FMed laser which is crucial to the sensitivity of the technique. This radiation is then used to study the change in the acetylene $A~1Au\leftarrow X~1\Sigma +g$ absorption spectrum in the presence of a large electric field.