In-situ detection of plasma emission using in-vacuum active optical sensor

Signal detection of plasma provides us information of internal underlying processes in plasma-enhanced active gas phase. Typical examples of plasma probing have been based on Langmuir-probe current-voltage analysis and optical emission spectroscopy, where passive metal tips in plasma chambers or optical sensors through vacuum windows contribute to data acquisition, respectively. To enhance signal-to-noise ratio and data accuracy, here we propose in-vacuum installation of a sensor device which includes a sensor head with photo-diode array, a one-chip data processor, and a wireless communication module. As shown in Ref. [1], we installed the sensor just 10-mm apart from plasma emissive region in Ar at 100 Pa, raw Red/Green/Blue signals being converted into digital data, and the data transfer via wireless communication between vacuum-air interface was successfully performed. Through the measurement procedure, the functions of the module electronic devices were invariant, all of which were popular and available without special demands. This result opens new possibilities for plasma diagnostics in which many sensors work simultaneously in a vacuum chamber. [1] O. Sakai, T. Kitagawa, K. Sakurai, G. Itami, S. Miyagi, K. Noborio and K. Taguchi, Sci. Rep. 11, 1364 (2021).