Wavelength-Agile Rayleigh Scattering by use of an Atomic Vapor Cell

Abstract

A wavelength-agile technique using an atomic vapor cell is developed and applied to the measurement of Rayleigh scattering. The atomic vapor cell displays a steep change in refractive index as a function of wavelength, thereby creating a wavelength scan over a narrow spectral range. This scan can be utilized for high resolution spectral measurements. For example, a short pulse duration laser was input into the cell and the resulting wavelength-agile scan was used to resolve a single iodine absorption feature. These measurements revealed that the atomic vapor cell distorts the input pulse shape and therefore this technique must be used with care. A wavelength-agile scan of the Rayleigh scattering spectrum was created using the atomic vapor cell; the resolved Rayleigh scattering spectrum can be compared to theory to obtain the temperature, pressure, and velocity of the scattering medium. The overall goal of this research was to direct light scattered by the gas in a vortex tube into the atomic vapor cell in order to create a wavelength-agile Rayleigh scattering spectrum. The temperature, pressure, and velocity at the scattering location would be resolved from the results of this time-of-flight technique. In this research only the scattering in a fiber was measured due to experimental difficulties. The results of this measurement indicate that this wavelength-agile Rayleigh scattering technique is difficult. Rayleigh scattering is extremely weak and therefore difficult to measure while the atomic vapor cell distorts the light passing through it.