Bench testing of a heterodyne CO2 laser dispersion interferometer for high temporal resolution plasma density measurements

Aheterodyne detection scheme is combined with a 10.59 μm CO2 laserdispersioninterferometer for the first time to allow large bandwidthmeasurements in the 10-100 MHz range. The approach employed utilizes a 40 MHz acousto-optic cell operating on the frequency doubled CO2 beam which is obtained using a high 2nd harmonic conversion efficiency orientation patterned gallium arsenide crystal. Themeasured standard deviation of the line integratedelectron density equivalent phase resolution obtained with digital phase demodulation technique, is 4 × 1017 m−2. Air flow was found to significantly affect the baseline of the phase signal, which an optical table cover was able to reduce considerably. Theheterodynedispersioninterferometer (DI) approach is found to be robustly insensitive to motion, withmeasured phase shifts below baseline drifts even in the presence of several centimeters of retroreflector induced path length variations. Plasma induceddispersion was simulated with a wedged ZnSe plate and themeasured DI phase shifts are consistent with expectations.

Source: Review of Scientific Instruments - December 8, 2016 Category: Physics Authors: T. Akiyama, M. A. Van Zeeland, R. L. Boivin, T. N. Carlstrom, J. A. Chavez, C. M. Muscatello, R. C. O ’Neill, J. Vasquez, M. Watkins, W. Martin, A. Colio, D. K. Finkenthal, D. L. Brower, J. Chen, W. X. Ding and M. Perry Source Type: research