Imaging Temporal Variation of Metastable Helium Distribution using Ghost Imaging Absorption Spectroscopy

We are developing ghost imaging absorption spectroscopy by integrating computational ghost imaging (CGI) with plasma absorption spectroscopy. Random structured light is generated using a digital micromirror device (DMD) as a probe beam for absorption spectroscopy. The structured light absorbed by the plasma is focused on a photodiode, and the integrated intensity is measured. In the ghost imaging method, the correlation between the output of this photodiode and the structured light provides an image of the absorber. Obtaining images requires time, as correlations must be calculated using tens of thousands of differently structured light patterns. However, as no camera is used, image measurements can be made with photodiode time resolution for repetitive phenomena. We plan to use this measurement method to visualize the response of atoms to fluctuations in recombining plasmas. This study applies the method to pulsed discharging helicon wave plasmas to image the time variation of metastable helium atom density with high temporal resolution. We will report on the details of this measurement method and the time evolution of metastable atoms in the helicon wave plasma.