Raman amplification spectroscopy using mode-locked lasers

Abstract

The theory necessary for an understanding of the Raman amplification process is reviewed in order to accentuate the factors which are of significance in designing an instrument to take advantage of the sensitivity potentially available with the techniques of inverse-Raman or Raman-gain spectroscopy. The dependence of the signal intensity on the product powers of the pump-and-probe lasers leads to a need for pulsed rather than continuous-wave lasers, while the requirements for a low noise level accompanying the signal dictate the need for a rapid-pulse system capable of being utilized with fast lock-in amplifiers. These requirements are most suitably met by synchronously pumped mode-locked and/or cavity-dumped dye lasers. The detailed design of systems combining either two synchronously pumped mode-locked dye laser are described and compared. Following a discussion of the factors influencing the signal-to-noise ratio attainable, representative spectra are presented which reflect the quality of the spectra attainable with this newly developed technique.