Doppler Width Limited Near-Infrared Raman Spectrometer

Abstract

A new ultra high resolution spontaneous Raman spectrometer with a single mode tunable laser diode as an excitation source and a 0.275 m, f/#4 spectrograph is presented. The spectrometer is expanded by an atomic vapor (Rb) absorption filter. One of the rubidium resonance lines serves as the frequency marker by absorbing selected Raman lines during the frequency scan of the excitation laser. High resolution was achieved while preserving the speed of the spectrometer. The extended spectrometer's capability was tested by differentiating overlapping Raman lines from molecular hydrogen isotopomers: H2, D2, and HD. Experiments were carried out at 300 K and pressures near 104 Pa. Spectral lines separated by approximately 10 Ghz (0.3 cm−1) can be resolved with this instrument with data collection times of minutes.