High Resolution Terahertz Spectroscopy with Quantum Cascade Lasers
- PDF / 1,332,751 Bytes
- 17 Pages / 439.37 x 666.142 pts Page_size
- 27 Downloads / 266 Views
High Resolution Terahertz Spectroscopy with Quantum Cascade Lasers H.-W. Hübers & R. Eichholz & S. G. Pavlov & H. Richter
Received: 21 December 2012 / Accepted: 7 March 2013 / Published online: 4 April 2013 # Springer Science+Business Media New York 2013
Abstract High resolution terahertz (THz) spectroscopy is a powerful analytical tool for laboratory purposes as well as for remote sensing in astronomy, planetary research, and Earth observation. THz quantum cascade lasers (QCLs) are promising sources for implementation into THz spectrometers, in particular at frequencies above 3 THz, which is the least explored portion of the THz region. One application of QCLs in THz spectroscopy is in absorption spectrometers, where they can replace less powerful and somewhat cumbersome sources based on frequency mixing with gas lasers. Another one is using a QCL as local oscillator in a heterodyne spectrometer for remote sensing. This article will review the stateof-the art in high resolution THz spectroscopy with QCLs. Keywords Terahertz . Far-infrared . Quantum cascade laser . Spectroscopy . High resolution
1 Introduction Spectroscopy with high spectral resolution (i.e. 1/Δ1>106) at frequencies in the terahertz (THz) portion of the electromagnetic spectrum is a powerful analytical tool for investigations of the structure and energy levels of molecules and atoms. Besides information on the species itself, important information on Doppler and pressure broadening can be obtained from THz spectra, provided the spectral resolution is large enough that the measured line profile is not significantly affected by the instrumental resolution. These data are a prerequisite for the interpretation of spectra obtained from astronomical sources or planetary atmospheres including the Earth [1]. H.-W. Hübers (*) : R. Eichholz : S. G. Pavlov : H. Richter German Aerospace Center (DLR), Institute of Planetary Research, Rutherfordstr. 2, 12489 Berlin, Germany e-mail: [email protected] H.-W. Hübers Institut für Optik und Atomare Physik, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany
326
J Infrared Milli Terahz Waves (2013) 34:325–341
At terahertz (THz) frequencies two techniques are established for high resolution spectroscopy [2]. One technique is absorption spectroscopy where the emission of a coherent THz source with narrow linewidth is frequency-scanned across the molecular absorption and the transmission is detected as a function of frequency. This technique is hampered by the lack of widely and precisely tunable, narrow-band and powerful THz sources. In the lower part of the THz region these sources are backward wave oscillators or sources based on microwave oscillators in combination with some sort of multiplier [3]. With these sources absorption spectroscopy up to almost 3 THz is possible. Above approximately 3 THz such sources do not exist. Several alternative and somewhat cumbersome technologies providing tunable THz radiation for spectroscopy have been demonstrated. One approach is combining
Data Loading...
