A Nomarski Interferometer for Electron Density Measurement in Atmospheric Pressure Plasma

Although it is more frequently applied in low-pressure or laser-induced plasma, interferometry has been used successfully to characterize atmospheric pressure plasmas [1]. We present the design of an interferometer for pulsed measurements of electron density in an atmospheric pressure plasma jet. Motivated by the setup simplicity and relatively low sensitivity to vibration, we employ a Nomarski (single-beam) interferometer. Since the phase shift is expected to be very small (1-100 microradians), we use lock-in detection with narrow bandwidth to recover the signal. At the first stage of development, we will send a continuous laser beam through an atmospheric plasma jet with modulating electron density at 10 to 20 kHz. We will present progress to date and details of the experiment setup.

References

[1] Choi, J. Y., Takano, N., Urabe, K., & Tachibana, K. (2009). Measurement of electron density in atmospheric pressure small-scale plasmas using CO2-laser heterodyne interferometry. Plasma Sources Science and Technology, 18(035013). https://doi.org/10.1088/0963-0252/18/3/035013