Milli-Hertz Surface Spectroscopy

Abstract:

A technique that has been repeatedly employed in high resolution light scattering experiments is that of light beating, or heterodyne, spectroscopy. By detecting the beating signal between the scattered light and a 'local oscillator' derived from the same laser source, one can obtain ultrahigh spectral resolution, independent of the random fluctuations of the light source. We reported earlier of a novel Fourier transform heterodyne spectroscopy (FTHS) technique with high resolution which is simpler and more direct than the conventional heterodyne technique; we have since improved our resolution ten-thousand fold to the 20-Hz range. We applied this technique first to study nonequilibrium phenomena at liquid-vapor interfaces. The ultrahigh resolution also enables one to observe the very small Doppler shift of a light beam reflected from a growing silicon crystal.