This thesis describes the application of a novel Fourier transform
heterodyne spectroscopy technique with an ultrahigh resolution of 200 mHz
to the study of capillary waves at liquid-vapor interfaces. The apparatus uses
a frequency-shifted local oscillator to separate signals from counter-
propagating capillary waves of identical frequency. The main beam and local
oscillator are aligned in such a way as to select capillary waves of a given,
continuously adjustable frequency.
This capability to separate counter-propagating waves was used to study
the spectral asymmetry of light scattered from capillary waves at a
nonequilibrium water surface in the presence of a temperature gradient. The
observed asymmetries agree, in sign and order of magnitude, with the one
predicted by linearized fluctuating hydrodynamics.
This apparatus was also used to measure the spatial damping
coefficients of capillary waves at a clean water surface and a water surface
covered with a monolayer of pentadecanoic acid. For these measurements a
double-beam heterodyne technique, which requires no calibration or
deconvolution of instrumental functions, was used. The spatial damping
coefficient of a clean water is in good agreement with the hydrodynamics
theory. A sharp maximum in the spatial damping was observed at the end of
the coexistence region of two phases of the pentadecanoic acid monolayer.
Research area description 
