Optical measurements of gas temperatures in atmospheric pressure RF cold plasmas

Rotational temperatures can be estimated directly from the ratios between peaks in the ultra violet (UV) band of OH molecular spectra. With a relatively poor spectral resolution of approximately 0.4 nm, ratios between two broad band peaks near 308 and 309 nm are identified to be sensitive to the gas temperatures in the range of 350∼1000 K. In cold radio frequency (RF) generated atmospheric plasmas, rotational temperatures of molecules are measured to be in a relatively low temperature range of 400∼700 K. These temperatures are confirmed to be in good agreement with gas temperatures measured by thermocouples. This simple emission spectroscopy can be used to monitor gas temperatures in cold atmospheric plasmas without any expensive spectrometer.