SUMMARY

Research into hypersonics and other high enthalpy gas flows is necessary to develop the next generation of mission-critical vehicles and understand complex flow dynamics behind shock waves. In particular, characterizing the optical properties of high temperature gases is critical to model various types of signal distortion that are observed when information travels through hypersonic flowfields. While models exist, experimentally measuring these optic properties becomes important to provide validation databases. Challenges that come with measuring high temperature environments include limitations on the diagnostic. Two novel interferometric diagnostics are developed in this work to address the limitations of current techniques. The first is a hybrid interferometer that combines a narrowband source with a broadband source. This diagnostic is tested in a shock tube at Georgia Tech to characterize the capabilities, then used at the free-piston High Temperature Shock Tube (HST) at Sandia National Laboratories. Using the reflected shock, we generate temperatures between 6000 and 7800~K and measure the GD coefficient at moderate to high pressure. The data taken here are the first known values that show clear temperature dependence in accordance with the high temperature gas models. Following the high temperature measurements, a second multi-wavelength interferometer is designed to address some limitations of the hybrid method. This diagnostic is also tested at the Georgia Tech shock tube for two wavelength combinations across the visible regime. Results show that this technique provides more capabilities than the hybrid diagnostics with similar uncertainty and resolution. Overall, the development of these diagnostics provides the necessary tools to make accurate validation measurements of high temperature optical properties.