Frequency dependence in a liquid's complex refractive index measured with infrared spectroradiometry

A laboratory measurement of wavelength dependence in the real n(lambda) and the imaginary k(lambda) parts of a liquid's complex refractive index is presented. A known heat flow through the liquid-gas interface is generated while a high-resolution infrared radiance spectrum is taken simultaneously. Wavelength variations of the absorption coefficient allow the emerging radiation to sense subsurface temperature gradients. This technique is valid only at intervals at which the absorption coefficient is sufficiently low to allow subsurface temperatures to be measured. Knowledge of a liquid's thermal conductivity, specific heat, and light transmission speed is required. Measurement error depends on radiance measurement error and the minimization of atmospheric parameters.