Abstract
Diode lasers have been used for ion temperature measurements in ArII plasmas by finding new laser-induced fluorescence (LIF) schemes suited to the present range of available wavelengths. The new LIF schemes require excitation at 664, 669, and 689 nm, all near industry-standard wavelengths. Conventional LIF measurements performed by dye lasers in ArII use 611.66 nm in vacuum, shorter than any commercially available red diode laser line, and depend on the population of the 3d′ 2G9/2 metastable state. The metastable state density of the conventional LIF scheme was found to be larger than the populations of the other metastable states by an order of magnitude or less. A master oscillator power amplifier diode laser was used both in a Littman–Metcalf cavity and as an optical amplifier for a low power diode laser which was in a Littman–Metcalf cavity. Both systems provided intensity of up to 500 mW, continuously tunable over 10 nm centered at 666 nm, and were used to obtain high resolution ion velocity distribution functions.
Highlights
Diode laser technology has advanced to the point of being useful for basic plasma dynamics research in noble gas discharge plasmas
While quantum physics issues have been the primary reason for those studies, they have shown the usefulness of diode lasers for measuring the sort of physical quantities relevant to plasma dynamics, such as number density of a given atom or molecule, and its velocity space distribution functions, as shown by Uzelac[5] in an Ar discharge
Suitable LIF schemes found in noble gas discharges have been exploited for plasma dynamics measurements for over a decade.[8]
Summary
Diode laser technology has advanced to the point of being useful for basic plasma dynamics research in noble gas discharge plasmas. The point of this work is to compare the usefulness of the diode laser with that of the dye laser for making LIF measurements of ivdfs in argon plasma discharges. Even one must be sure that lasing modes can be tuned across the spectral line of choice and that mode hops do not prohibit the diode laser from reaching the target wavelength This problem can be eliminated by placing the diode laser, if one or more facets have been AR coated, in a simple external optical cavity.[2,13,14] The minimum power requirements, typically on the order of tens of mW, can be met by use of tapered optical amplifiers.[15] One still needs to find a useful line, and the target wavelength depends upon the choice of working gas. Since the new tool is simpler to use, we hope that a wider number of researchers will be attracted to its use
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