Terahertz absorption spectroscopy

Terahertz absorption spectroscopy directly probes such collective vibrational modes, and provides valuable experimental data to test the validity of these theoretical calculations. Previously we have reported the first measurements of the terahertz... 

By direct absorption measurements, we have directly probed the low frequency collective motions of proteins in water by terahertz absorption spectroscopy. We have isolated, for the first time, the 0.075 - 3.72 THz absorption of bovine semm albumin " and hen egg white lysozyme in water, and made direct comparison with existing... 

J. Xu, K. W. Plaxco and S. J. Allen, Probing the Collective Vibrational Dynamics of a Protein in Liquid Water by Terahertz Absorption Spectroscopy. Protein Sci., 15(5), 1175-1181 (2006). 

Kim, S.J., Born, B., Havenith, M., and Gmebele, M. (2008) Real-time detection of protein-water dynamics upon protein folding by terahertz absorption spectroscopy. Angew. Chem. Int. Ed.,... 

Transient terahertz spectroscopy Time-resolved terahertz (THz) spectroscopy (TRTS) has been used to measure the transient photoconductivity of injected electrons in dye-sensitised titanium oxide with subpicosecond time resolution (Beard et al, 2002 Turner et al, 2002). Terahertz probes cover the far-infrared (10-600 cm or 0.3-20 THz) region of the spectrum and measure frequency-dependent photoconductivity. The sample is excited by an ultrafast optical pulse to initiate electron injection and subsequently probed with a THz pulse. In many THz detection schemes, the time-dependent electric field 6 f) of the THz probe pulse is measured by free-space electro-optic sampling (Beard et al, 2002). Both the amplitude and the phase of the electric field can be determined, from which the complex conductivity of the injected electrons can be obtained. Fitting the complex conductivity allows the determination of carrier concentration and mobility. The time evolution of these quantities can be determined by varying the delay time between the optical pump and THz probe pulses. The advantage of this technique is that it provides detailed information on the dynamics of the injected electrons in the semiconductor and complements the time-resolved fluorescence and transient absorption techniques, which often focus on the dynamics of the adsorbates. A similar technique, time-resolved microwave conductivity, has been used to study injection kinetics in dye-sensitised nanocrystalline thin films (Fessenden and Kamat, 1995). However, its time resolution is limited to longer than 1 ns. 

Flame Photometry and Gas Chromatography (CyTerra) -Aerodynamic Particle Size and Shape Analysis (BIRAL) -Flow Cytometry (Luminex, LLNL) -Semiconductor-Based Ultraviolet Light (DARPA) -Polymer Fluorochrome (Echo Technology) -Laser-Induced Breakdown Spectroscopy -Raman Scattering -Infrared Absorption -Terahertz Spectroscopy -UV LIDAR... 

Additional experiments observing MEG have been reported for CdSe (Schaller et al., 2005b), PbTe (Murphy et al., 2006) and InAs (Pijpers et al, 2007). In addition to transient absorption studies, these optical experiments use time-resolved photoluminescence, terahertz spectroscopy, and quasi-CW spectroscopy. 

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