The Bench Test of a High Temporal Resolution HCN Interferometry for Atmospheric Pressure Air Plasmas

A heterodyne interferometer operating at the frequency f= 0.89 THz has been designed for measuring electron density of atmospheric pressure air plasmas. The system is configured as a Mach-Zehnder type interferometer and the bench test has been finished with He-Ne laser. The interferometer light source is hydrogen cyanide (HCN) laser with wavelength of 337 μm, which the power is up to 100 mW. The intermediate frequency, shifted by 500 kHz, is generated by the Doppler shift with a high speed rotating grating (HSRG), which is installed in a vacuum vessel. The frequency shift is one order higher than the conventional rotating grating. With this novel technology, to measure the electron density profile and high frequency density fluctuation simultaneously in plasmas becomes possible with a single far-infrared laser source.