Raman spectroscopy with a single-frequency, high-power, broad-area laser diode

A high-power, broad-area laser diode was used as an incident light source i n a Raman spectrometer. The laser was forced to lase in a very narrow frequ ency range (less than or equal to 400 MHz) by the use of a Metcalf-Littman arrangement. All side bands and light-emitting diode (LED) modes were suppr essed; their intensities are lower than the noise of recorded rotational sp ectra, The incident wavelength was tuned to coincide with the D-1 transitio n of Rb-85. Due to this choice, the elastically scattered light (Rayleigh c omponent) can be eliminated by a Rb cell in front of the spectrometer, The usefulness of this arrangement is demonstrated for CO2, N-2, and air. Becau se of the suppression of the dominating Rayleigh intensity, this setup is i deally suited for a Fourier transform Raman spectrometer.