Modification of a Commercial Argon Ion Laser for Enhancement of Gas Phase Raman Scattering

Abstract

Although the availability of high-powered argon ion lasers has significantly reduced the difficulty of obtaining Raman spectra of gases, nevertheless there are still many cases where enhancement of the scattered light from weakly scattering samples is required. One particular example is in the study of vibrationally excited molecules produced thermally1 and in an electrical discharge.2, 3 Because the concentration of excited species is not very high, standard methods of laser excitation do not provide sufficiently intense Raman spectra. In this note, the application of intracavity excitation using a commercial laser (Coherent Radiation Laboratory, model 52A) is described. The resultant signal enhancement is much superior to that obtained with other techniques which excite the sample outside the cavity (e.g., a multiple pass device). Although spectra have been obtained by intracavity excitation4 with a laboratory-built laser, an ordinary commercial laser can also be modified for such use at a cost of less than $1000. The modification described below outlines the minimum requirements of the apparatus and the techniques used for alignment. We feel the information in this report will help other Raman spectroscopists to take advantage of intracavity sampling.