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Filtered Rayleigh Scattering for Pressure Measurement Applications

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A model of filtered Rayleigh scattering (FRS) sensitivity for air is developed and presented over the gas temperature range of 300–750 K for an iodine vapor cell and laser wavelength around 532 nm with the objective of developing a method of the direct imaging of pressure fields. Temperature, pressure, and velocity sensitivities are modeled with respect to the following experimental parameters: cell vapor pressure, laser frequency, and observation angle. Temperature insensitivity is discussed and experimentally demonstrated with good agreement between 300 and 750 K, and simultaneous pressure sensitivity is demonstrated with a nanosecond laser spark-generated blast wave between 2 and 10  μs after formation. Modeling shows conditions for which the FRS signal sensitivity to temperature is significantly reduced, leaving only sensitivity to pressure. In addition, FRS signal measurements show the ability to further correct for velocity effects by taking advantage of the laser spark symmetry. Experiments using a hot jet flow and nanosecond laser spark blast wave are conducted to help validate the modeling predictions. A strategy is described with parameters of the experimental configuration to reproduce the modeling conditions for pressure sensitivity and reduced temperature/velocity sensitivity.