Diagnostic sensors are demanded during plasma processes. Holograms
of plasma taken with laser light without a reference beam were used to
monitor behaviors of charged particles produced in nitrogen plasma as a
function of electrode temperature ranging between 50 and 300℃.
Holograms were characterized as a function of the pixel sum and grayscale
value. Pixel sum calculated in identified grayscale ranges strongly
correlated with ion density and emitted light intensity measured with a
langmuir probe and optical emission spectroscopy, respectively. The
performance was further evaluated with data acquired as a function of
N2 and NH3 flow rates and improved correlations
were observed in the new grayscale range. The confirmed correlations
indicate that a hologram is a viable means to diagnose behaviors of plasma
particles such as ions. Underlying principles are discussed in view of
particle and charge composing vacuum and light.
© 2016 Optical Society of Korea
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