RAMAN SPECTROSCOPY USING A GAS LASER.

Author Institution: Ministry of Aviation, Royal Radar Establishment St. Andrews Road, Great MalvernMeasurements of first and second order Raman scattering in a solid provide useful information about the phonon spectron. The first order spectrum is due to the creation or destruction of single phonons at the center of the zone, and it identifies the optic phonons at the zone center unambiguously. The second order spectrum is due to processes involving pairs of phonons of equal or equal and opposite wave vector. It provides information which is complimentary to that obtained from two-phonon infrared absorption and is directly related to the two-phonon density of states. The gas laser is ideally suited to Raman spectroscopy. We have recently made successful measurements of Raman spectra using a helium-neon gas laser. The method used is to place the sample in an external resonator built into the laser resonator and then to record the spectrum photographically. A description will be given of the techniques used and this will be illustrated by results obtained on GaP and $CaF_{2}$ which have been measured over a wide range of temperatures