Plasma diagnostics of a DC glow discharge using Tuneable Diode Laser Absorption Spectroscopy

摘要

The behaviour of plasmas is influenced by thermodynamicquantities such as gas and electron temperatures and their correspondingnumber densities. For applications such as thin-filmdeposition, material synthesis, sputter coating, spark plugs, andspacecraft thrusters that depend upon plasma processes it is ofpractical interest to quantify these physical properties in orderto optimise their performance and efficiency. In this work, timeresolvedtuneable diode laser absorption spectroscopy (TDLAS)is used to characterise an Argon glow discharge in a Dynavacpulsed DC sputter coater. This is achieved by currentscanning a vertical-cavity surface-emitting laser (VCSEL) at aknown neutral Argon transition wavelength of 794.8 nm thatcorresponds to an energy level transition from the 3s~23p~54smetastable state to the excited upper state 3s~23p~54p [4]. Thepressure and current conditions of the sputter coater are keptconstant at 11 Pa and 24mA respectively during the experiment.A Doppler-broadened absorption profile is assumed from whichboth time-resolved temperature and number density are calculated.It was found that the plasma temperature is constant towithin measurement uncertainty for a given duty cycle, whilethe number density variation over a cycle follows the voltagecharacteristics of the device.