Modification of a Commercial Argon Ion Laser for Enhancement of Gas Phase Raman Scattering
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.
KeywordsLaser Cavity Lasing Action Plane Mirror Laser Head Spherical Mirror
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- 5.Using a computer program written by J. F. Young, W. W. Hansen Laboratories of Physics, Stanford University, M. L. Report No. 1803, November 1969 (unpublished).Google Scholar
- 6.Although the Eirewster’s angle itself is not critical, skewness of the two angle faces with respect to the polarization vector will cause high cavity losses.Google Scholar
- 7.A method for reducing the strong Rayleigh line in the spectrometer by making the polarization vector parallel to the spectrometer axis is described in Reference 4. This is useful when viewing depolarized (e.g., rotational) Raman scattering close to the exciting line. Note that this method should not be used for examining strongly polarized Raman lines.Google Scholar
- 8.The reader may be interested in the cleaning techniques described by S. Levy and R. H. Wright, Jr., Rev. Sci. Instr. 42, 1737 (1971).Google Scholar