A simple far-infrared laser interferometer for measuring electron densities in reactive low-temperature plasmas
- Institute for Experimental Physics, Ruhr University Bochum, 44780 Bochum (Germany)
A sensitive far-infrared (fir) interferometer for electron density measurements in reactive low-temperature plasmas is described. The instrument is based on an optically pumped fir laser (wavelength range 50-600 {mu}m depending on the working gas) and makes use of the nonlinear relation between output power and cavity loss. The fir beam, which leaves the resonator through a coupling hole in the end mirror, is reflected back into the cavity, such that the coupling hole behaves like a variable 'leak' with a loss rate depending on the phase of the reentering wave relative to the standing wave within the resonator. As a result of the feedback, the output intensity undergoes strong nonlinear variations if the optical distance of the external mirror is changed by small amounts, {delta}z. The power variation is monitored through a small opening in the external mirror. Test experiments using a wavelength of 432.6 {mu}m and a Schottky-diode detector have yielded a minimum detectable pathlength variation of {delta}z=0.4 {mu}m, corresponding to a change of the line-integrated electron density n{sub e}xL of about 5x10{sup 15} m{sup -2}. A first application to argon plasmas in inductively coupled rf discharges has been made, and the results have been compared to concomitant Langmuir probe measurements.
- OSTI ID:
- 20723248
- Journal Information:
- Review of Scientific Instruments, Vol. 76, Issue 11; Other Information: DOI: 10.1063/1.2134355; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0034-6748
- Country of Publication:
- United States
- Language:
- English
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