Using Laser Induced Fluorescence to Measure Temperature in the Caltech Water-Ice Dusty Plasma*

A Laser Induced Fluorescence (LIF) diagnostic has been built to measure temperatures and flows in the Caltech Water-Ice Dusty Plasma Experiment. This diagnostic uses a tunable, ultra-narrow-band diode laser, a photomultiplier, a mechanical chopper, and a lock-in amplifier. Two separate laser heads operate one at a time to perform LIF on either neutral or singly ionized argon. Neutral argon LIF measurements yield signal-to-noise ratios greater than 100. Remarkably, the LIF signal can be clearly seen without the use of signal averaging. As a consequence, substitution of the photomultiplier, mechanical chopper, and lock-in amplifier by a fast CMOS camera still reliably detects LIF emission. Lamb Dip has been observed using the photomultiplier which allows for absolute calibration of the laser wavelength and a way to measure flows [1]. Work is underway to program a motorized 5-axis stage to allow for automated temperature measurement as a function of position. Work is also underway to focus light from the plasma through lenses onto the camera chip to create images of the plasma using the LIF photons. To date, argon ion LIF has been unsuccessful and further investigation will begin shortly.

[1] Kohei Ogiwara et al 2011 Jpn. J. Appl. Phys. 50 036101