Kiel 2004 – wissenschaftliches Programm

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P: Plasmaphysik

P 3: Postersitzung: Niedertemperaturplasmen Plasmatechnologie I, Diagnostische Methoden I

P 3.4: Poster

Montag, 8. März 2004, 17:45–19:30, Foyer

Modulation techniques for the nested-cavity FIR laser interferometer — •Carsten Pargmann and Henning Soltwisch — Ruhr-Universität Bochum

The nested-cavity FIR laser interferometer consists of a FIR laser cavity (optically pumped in our setup) and an external mirror, reflecting the laser ouput power back into the FIR laser cavity. The power of the laser is monitored either by introducing a beamsplitter between laser cavity and external mirror or simply by placing the detector behind a hole of the external mirror. The detected intensity, plotted against the distance of the external mirror, shows very narrow peaks. The slope of a peak, the used wavelength and the detector determine the sensitivity of the interferometer. Modulation techniques can double the sensitivity by jumping between two points on either side of the peak. This has been done with a polyethylene chopper and with a silicon wafer irradiated by a diode laser. With a wavelength of 184.3 µm a line-integrated electron density change of 6×10¹⁰ cm⁻² can be detected.