[Zurück]

J. Hayden, F. Fuchs, S. Hugger, B. Lendl:
"A QCL-based Mach-Zehnder interferometer for chemical sensing";
Vortrag: FLAIR 2016, Aix-les-Bains; 12.09.2016 - 16.09.2016.

We present a novel type of spectrometer for the simultaneous measurement of absorption - and refractive index spectra of liquid samples in the mid infrared (MIR) spectral regime. The setup is based on a Mach-Zehnder interferometer (MZI) and an external cavity quantum cascade laser (EC-QCL) as a widely tuneable source of high spectral brightness. Due to the interferometric principle of measurement absorption spectra are recorded with much lower levels of false intensity compared to common types of transmission spectroscopy, or even background free. The simultaneous recording of refractive index spectra with accuracies down to ~ 5*10-6 is accomplished by measurement of the relative phase of the two arms of the MZI.
Due to the interferometric nature of measurement the recorded signals strongly deviate from those of common transmission spectroscopy. The unique features and signal characteristics as deduced from basic theory of interferometry will be briefly outlined. Experimental results will be presented that prove theoretical predictions and demonstrate the capability of the setup for simultaneous differential measurement of the complex refractive index over a broad spectral range. A comparison with state of the art transmission spectroscopy will be provided.