Laser-Excited Rotation–Vibration Raman Scattering in Ultra-Small Gas Samples*

The focused beam of an argon–ion laser was used as a light source for Raman-scattering experiments in gases. Photoelectric recording of rotation–vibration Raman spectra has been observed from about 1011 gas molecules in the focal region of the laser beam. The focusing geometry used to illuminate the gas samples is discussed and the important parameters of the optical system for collecting the Raman-scattered light from the small volumes are considered. The pulse-counting detection system is described and the new experimental results are presented.