(1) Institute of Spectrochemistry and Applied Spectroscopy (ISAS), Bunsen-Kirchhoff-Strasse 11, 44139 Dortmund, Germany;(2) Institute of Spectroscopy, Russian Academy of Sciences, 142190 Troitzk, Moscow reg., Russia
Abstract:
A simple and robust absorption technique is developed which combines cavity enhanced absorption spectroscopy and wavelength modulation spectroscopy and measures the integrated output of unlocked cavities. The detection power of the technique is affected by peculiarities of the laser injection into a cavity causing excess noise which exceeds the shot noise. The noise and ways for its reduction are discussed. The new method is demonstrated by absorption measurements of excited carbon atoms in a microwave induced plasma. Preliminary detection limits equivalent to optical depths below 10-6 were obtained. PACS 42.55.Px; 42.62.Fi; 42.60.Mi