Development and experimental results of a synthetic dispersion interferometer for air dispersion measurement

We present the latest advancements in our Synthetic Dispersion Interferometer (SDI), focusing on the experimental setup, robustness, and sensitivity enhancements. SDI is a modification of traditional dispersion interferometry. It utilizes a two-color, two-arm setup with digital in-phase and quadrature (IQ) demodulation. This enables the precise measurement of dispersion changes in transparent media. Similar devices have been presented by J. Irby[1] and D.-G. Lee[2] for line integrated electron density measurements. Our research aims to adapt the SDI approach for static pressure measurement in aviation[3]. The system is based on a continuous wave diode-pumped solid-state (DPSS) laser and features an acousto-optic modulator (AOM) for heterodyne detection. The subsequent IQ-demodulation is implemented on a field-programmable gate array (FPGA) which allows for real-time, continuous measurement at MHz bandwidth. Our work will detail the operational principles of SDI, recent experimental results and comparative analyses, emphasizing how our findings can be applied to dispersion interferometry, such as line integrated electron density measurements in plasma physics. We will present our findings on how the AOM material choice, phasor modulation, IQ-fitting and phase front matching can be utilized to increase the robustness and accuracy of the SDI. [1] J. Irby et. al., Rev. Sci. Instrum. 70, 699 (1999) [2] D.-G. Lee et al., 2024 Nucl. Fusion 64 016024 [3] H. Uittenbosch et al., Opt. Express 31, 6356-6369 (2023)