Two-dimensional temperature measurements in laser-induced air plasma

Simultaneous measurements using two Intensified Charge-Coupled Device (ICCD) cameras with two bandpass filters on laser-induced air plasma have facilitated the illustration of a two-dimensional temperature distribution within the plasma. In each pixel, the intensity captured by the ICCD cameras could replace the intensity measurements using a spectrometer in the two-line ratio method for temperature measurement. The plasma was produced by a 532 nm pulse from a Q-switched neodymium-doped yttrium aluminum garnet laser. The two ICCD cameras with the two bandpass filters simultaneously captured the plasma to measure emission intensities at two wavelengths. The two-line ratio method using N II lines was applied in each pixel to examine the two-dimensional temperature distribution. Two laser energies and focal lengths were utilized to ensure spatially and temporally consistent temperature results considering the characteristics of the plasma temperature at the experiment conditions. The signal-to-noise ratio increased with increasing the incident energy and decreasing the focal length. The highest temperature was observed at the high incident energy and the short focal length. The location in the plasma with the maximum temperature varied over time. The temperature significantly reduced with time at the long focal length and low incident energy. The plasma temperature was measured using the two-line ratio method with a spectrometer. Average emission intensity images at the two wavelengths were used to examine the plasma temperature. The results of the three temperature measurement methods were compared to evaluate the accuracy of the methods. Generally, in the three methods, the temperature changes were similar along the x-axis of the plasma. The temperature difference between the two-filtered imaging method and the spectrometer was between 1 and 7%. The temperature difference between the average image method and the spectrometer was between 1 and 10%. The two-filtered imaging method simultaneously captures spectral emissions at two wavelengths and hence effectively shows a two-dimensional temperature distribution.