A Terahertz VRT spectrometer employing quantum cascade lasers

Abstract

a b s t r a c tThe first application of a commercial Terahertz quantum cascade laser (QCL) system for high resolution spectroscopy of supersonic beams is presented. The QCLs exhibited continuous linear voltage tuning over a 2 GHz range about a center frequency of 3.762 THz with ∼1 ppm resolution. A sensitivity of ∼1 ppm fractional absorption was measured with a single pass optical system. Multipass operation at the quantum noise limit of the stressed photoconductor detector would produce a 100-fold improvement.

Far-infrared VRT spectroscopy of the water dimer: Characterization of the 20 μm out-of-plane librational vibration

“…46 The limited availability of suitable radiation sources in the terahertz region has traditionally been the limitation on VRT experiments with water clusters but emerging technologies may soon mitigate this problem. 53 In any case, the realization of a truly complete characterization of the water dimer is clearly near at hand.…”

THz QCLs for heterodyne receivers and wavelength modulation spectroscopy

“…The high power and continuous tunability of QCLs make them an attractive source for elucidating the intermolecular behavior of chemically relevant species such as water and water-hydrocarbon clusters through probing their energy level structures. To that end a new QCL based spectrometer for pulsed gas expansions of methanol has recently been reported [21]. In brief, a single QCL device's voltage is scanned across its entire operating range.…”

Gas-Phase Infrared Spectroscopy of Neutral Peptides: Insights from the Far-IR and THz Domain

“…100−102 Here, tunable THz light is generated either by using the sum and difference frequencies that are obtained by mixing the output of an IR gas laser with tunable frequency-modulated microwaves 103 or by using quantum cascade lasers. 104 The light is then directed into a multipass cell to coincide with a supersonic expansion containing the sample molecules. By detecting the emitted radiation, very high resolution spectra can be obtained, as was shown for water complexes 102,105 and the propane−water dimer.…”

“…Additionally, broad range FT-IR spectra of small biomolecules have been obtained for molecules such as N -methylformamide, glycine, alanine, and their dimers . Another technique, which is mainly advanced by the group of Saykally, is THz vibration–rotation-tunneling spectroscopy (THz-VRT spectroscopy). − Here, tunable THz light is generated either by using the sum and difference frequencies that are obtained by mixing the output of an IR gas laser with tunable frequency-modulated microwaves or by using quantum cascade lasers . The light is then directed into a multipass cell to coincide with a supersonic expansion containing the sample molecules.…”