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Topic: THz

	NIST: CW THz Spectroscopy of Biomolecules
		THz vibrational features, therefore, provide a sensitive probe of the force constants influencing the collective nuclear motions that extend over a large portion of the framework and may be used to validate and improve current force field and biomolecular dynamics models.
		The THz absorption spectra of the hydrated and dehydrated forms of AV and its retro-analog, VA, are shown in Fig.
		THz spectra of AV and its retro-analog, VA. The two spectra in each panel were obtained for dehydrated samples (blue) and for samples where water is present in the hydrophobic core region (red).
	physics.nist.gov /Divisions/Div844/facilities/thz/cwthz.html (1920 words)

	Fraunhofer IPM THz-Spectroscopy
		THz radiation can, for instance, be generated with the help of pulsed femtosecond lasers (fs) combined with photoconductive antennae, semiconductor surfaces or optical rectification in non-linear media.
		The THz pulses are generated by means of an IR ultrashort pulsed laser with a puls duration of less than 100 fs at a center wavelength of 800 nm and a repetition rate of 80 MHz.
		Having passed the sample the transmitted THz radiation is focused on a EO detector crystal (EOC) and overlaid with a linearly polarized IR probe beam.
	www.ipm.fhg.de /fhg/ipm_en/technologies/terahertz/THzSpectroscopy.jsp (532 words)

	Lehigh researchers hone radiation source for THz devices
		Ding hopes to develop a compact THz radiation source with wide tunability in the wavelength range of 30 to 3,000 microns (a micron is equal one one-millionth of a meter).
		THz devices are also promising for homeland security tasks such as detecting the presence of toxic and semitoxic gases, says Ding.
		To miniaturize his THz device, Ding is using nanostructure quantum dots and including photonic bandgap crystals that act as a special waveguide by tightly focusing the THz beam on a particular detector.
	www.eurekalert.org /pub_releases/2004-02/lu-lrh022004.php (731 words)

	Z
		The THz wave microscope is a new vehicle for exciting research projects for terahertz imaging, biomolecular spectroscopy, and the diagnostics of diseases such as skin and breast cancer.
		To overcome this limit, one solution is to use near-field THz imaging technology by focusing the optical beams into an electro-optic crystal to generate (by optical rectification) and detect (by the electro-optic effect) the THz wave with sub-micron resolution.
		THz wave microscopic imaging promises to open new opportunities in functional imaging, such as the detection of changes at the molecular level in biological cells.
	www.rpi.edu /~zhangxc/thzimagingintro_act.htm (488 words)

	New Scientific Possibilities with High Power THz Sources ::29-30th June 2006:: index
		One of the most unique aspects of THz spectroscopy is that the pulses are of sub-picosecond duration, and it is possible to carry out time-dependent measurements in the FIR on a ultrafast timescales.
		THz spectra are shown to be sensitive to tube diameter and to various trapped solvents in the tubes.
		A THz near-field imaging technique which benefits from the broadband and highly brilliant coherent synchrotron radiation from an electron storage ring is established at BESSY utilizing a detection method based on locking on to the intrinsic time structure of the synchrotron radiation.
	www.srs.ac.uk /meetings/THz_sources_workshop (2900 words)

	Erik Bründermann, THz time domain spectroscopy, T-ray
		Single pulses of terahertz (THz) light lasting only picoseconds (ps) or femtoseconds (fs) can be generated by using a fs laser exciting a semiconductor or a non-linear optical crystal of ZnTe.
		The pump pulse generates a single THz pulse in the LTG GaAs semiconductor if a voltage of up to 20 V is applied.
		If the THz pulse reaches the antenna of the detector it induces an electric field varying in time, accelerating the carriers, leading to a measurable current which is positive or negative depending on the impinging electric field.
	homepage.ruhr-uni-bochum.de /Erik.Bruendermann/THz-TDS.html (411 words)

	THz Generation and Detection in ZnTe (Site not responding. Last check: 2007-10-21)
		The THz pulse induces a birefringence in ZnTe crystal which is read out by a linearly polarized visible pulse.
		When both the visible pulse and the THz pulse are in the crystal at the same time, the visible polarization will be rotated by the THz pulse.
		Note, the visible and THz pulses are collinearly propagated through the ZnTe crystal even though in the figure they appear to be propagate at an angle.
	www.chem.yale.edu /~cas/ZnTe.html (321 words)

	Basic THz Spectroscopy
		The generated THz radiation is collimated by a silicon lens and an off-axis paraboloidal mirror.
		The THz receiver consists of a paraboloidal mirror which focuses the beam onto a silicon lens, which in turn focuses it onto the THz receiver chip having the antenna geometry shown in the figure below.
		The electric field of the focused incoming THz radiation induces a transient bias voltage across the 5 μm gap between the two arms of this receiving antenna, which are directly connected to a low-noise current amplifier.
	utol.ecen.ceat.okstate.edu /thz-tds.html (857 words)

	JHU - Center for Materials Sensing Detection
		Terahertz (THz) radiation, electromagnetic radiation in a frequency interval from 0.1 THz to 10 THz, occupies the portion of the electromagnetic spectrum between the infrared and microwave bands.
		During the past decade, THz waves have been used to characterize the electronic, vibrational and compositional properties of solid, liquid and gas phase materials.
		One of the attractive features of THz time-domain spectroscopy is that it has the capability of high-resolution imaging of dielectric features as well as remote spectroscopy of dielectric materials.
	www.wse.jhu.edu /~cmsd/Thz (447 words)

	THz Spectroscopy
		THz time domain spectroscopy has recently emerged as an extremely useful and powerful probe of charge transport in materials, owing to the fact that it provides a probe of the complex conductivity over a wide frequency range, with sub-picosecond time resolution.
		The time domain spectrum of the THz pulse, E(t), is measured by scanning the delay of the 800nm detection pulse, allowing the short 800nm pulse to overlap in time with different parts of the longer THz pulse.
		The pump-induced change in the THz response decays bi-exponentially: the largest part of the amplitude decays with a ~1 ps time constant, and a smaller part decays over longer timescales (~200 ps).
	www.amolf.nl /research/biosurface_spectroscopy/web_AMOLF_THz_rev.html (1282 words)

	EKSPLA > Products > THz Spectroscopy Kit (Site not responding. Last check: 2007-10-21)
		The terahertz (THz) and sub-THz frequency region (100 GHz — 10 THz) of electromagnetic spectrum bridges the gap between microwaves and infrared.
		The “THz gap” is very attractive because of many possible applications in spectroscopy and imaging of biological objects, and in novel communication systems as well.
		THz lenses of various radiuses can be made from various materials such as teflon and silicon.
	www.ekspla.com /en/main/products/84?PID=525 (495 words)

	K.L.Vodopyanov
		Terahertz waves, which have a wavelength between those of microwaves and infrared (1 THz corresponds to the wavelength of 300 mm), can permeate a wide range of materials including paper, fabrics, plastics, wood and human tissue, and are very suitable for imaging and spectroscopy applications.
		THz wave generation in quasi-phase-matched (QPM) crystals via the process of optical rectification is illustrated in the time-domain animation of Fig.
		Each inverted domain of a nonlinear crystal contributes a half-cycle of the THz pulse [2,3] and thus the THz wave packet (provided that THz-wave attenuation is low) has as many oscillation cycles as the number of quasi-phase-matched periods over the length of the crystal.
	www.stanford.edu /~vodopyan/thz_generation.htm (428 words)

	Kawase Initiative Research Unit
		After more than a dozen years of basic research into the submillimeter and far infrared range, THz wave research has finally come into its own, and is recognized by the world scientific community as a new frontier.
		THz imaging, on the other hand, is safe, and its application in food inspection and other uses should not meet with objections from customers.
		The spatial distribution and the composition of the targets are obtained from THz multispectral transillumination images, using absorption spectra measured with a tunable THz wave source.
	www.riken.go.jp /lab-www/THz (536 words)

	Semiconductor Physics Group; Generation, detection and application of THz radiation (Site not responding. Last check: 2007-10-21)
		Although THz frequencies are potentially very interesting, it took the development of a new technique to generate them to push them into the limelight.
		The THz signal shown in figure 4 has some interesting features, not the least of which is that the signal appears to be a half-cycle pulse.
		The electric field of the THz pulse modifies the refractive index of the detector crystal which induces a rotation of the polarization of the synchronized laser pulse.
	www.tn.tudelft.nl /ti/group/thzgen.html (1456 words)

	What is terahertz? - a definition from Whatis.com - see also: THz
		An EM wave having a frequency of 1 THz has a wavelength of 0.3 millimeters (mm), or 300 micrometers (?).
		An EM wave of 540 THz is in the middle of the visible-light spectrum.
		THz, and the gigahertz (GHz), equal to 10
	searchnetworking.techtarget.com /sDefinition/0,,sid7_gci752929,00.html (239 words)

	THZ-Technologies (Site not responding. Last check: 2007-10-21)
		Terahertz radiation (frequency range 0,1 to 10 THz) can transmit a lot of materials which are not transparent in the visible spectral range.
		THz radiation has a low energy and is thus non-ionizing.
		Goal of this group is the development of THz components and systems for industrial applications, especially imaging and tomography in material and quality control, but also for security techniques/homeland security.
	www.iof.fhg.de /departments/optical-systems/thz-technology/content_e.html (247 words)

	Continuous Wave THz Spectroscopy of Biomolecules
		For the pulsed THz system, a Nd -pumped, mode-locked, Ti :Sapphire high-repetition-rate femtosecond laser is used to illuminate the photomixer to produce broad-band THz radiation, which is detected with a similarly designed optically gated antenna structure.
		One high resolution CW THz system combines two near infrared laser beams, one from a fixed-frequency 855 nm CW diode laser and the other from a tunable CW Ti :Sapphire laser in a photomixer antenna to produce THz radiation at the difference frequency of the two pump beams.
		Torsional modes are responsible for the conformation flexibility of biomolecules and have fundamental frequencies in the THz spectral region.
	physics.nist.gov /Divisions/Div844/facilities/thz/combthz.html (993 words)

	Terahertz Imaging
		Terahertz (THz) light is special since many materials like plastics and ceramics are transparent whereas many biomolecules have distinct spectral signatures or fingerprints.
		THz imaging is considered as a new tool in security screening at airports since clothing, plastic bags are transparent while drugs and metal objects are detectable.
		THz scan of a bank note hologram at 2.4 THz and a razor blade behind paper.
	www.ruhr-uni-bochum.de /pc2/thz_imaging_en.html (299 words)

	BCP/ultrafast: THz FAQs (Site not responding. Last check: 2007-10-21)
		THz pulses have a duration of a few hundred femtoseconds and a wavelength of about a few hundred micrometers.
		THz pulses are generated when one induces a picosecond current or polarisation surge in an "antenna." The antenna can be a DC-biased semiconductor wafer or a nonlinear crystal or some other sample.
		In the conduction band, the carriers (essentially electrons, holes are too heavy to move) are accelerated by the DC field resulting in the emission of an electromagnetic pulse (that is, a THz pulse).
	bcp.phys.strath.ac.uk /ultrafast/thzFAQs.php (1586 words)

	Laser Focus World - Poled lithium niobate crystals enable multicycle THz pulse generation (Site not responding. Last check: 2007-10-21)
		One approach to THz generation is via nonlinear optics with ultrafast lasers: because the low-THz frequency range corresponds to the inverse of femtosecond pulse duration, femtosecond lasers have been widely used to generate ultra-broadband, single-cycle THz waves.
		Tuning of the THz frequency is accomplished simply by scanning the sample laterally to the beam propagation direction, and the THz wave from the shorter domains is generated with higher frequency as expected.
		Similarly, chirped THz pulses are applicable to adiabatic transfer between excitonic wave packets in semiconductor nanostructures or between rotational and vibrational modes of molecules.
	lfw.pennnet.com /Articles/Article_Display.cfm?Section=ARTCL&ARTICLE_ID=226759&VERSION_NUM=3&p=12 (1868 words)

	Session IC15 - THz-Spectroscopy and Ultra Fast Optics.
		The THz pump-beam is transmitted through the sample and time-resolved by mixing it with half-cycle THz probe-pulses and detecting the superposition /2/.
		The THz pulses are generated from the dynamic screening of the built-in surface field by photoexcited carriers generated by ultra fast NIR pulses.
		We have built a compact interferometer in which the autocorrelation of the THz pulses is detected as a function of the delay between pairs of NIR pulses.
	flux.aps.org /meetings/YR99/CENT99/abs/S3190.html (1518 words)

	THz code for simple THz propagation (Site not responding. Last check: 2007-10-21)
		The article for which this code was written, "Simple Method for Calculating the Propagation of THz Radiation In Experimental Geometries" (D. Côté, J.E. Sipe, H.M. van Driel), has been published in JOSA B and is available in preprint form below.
		The purpose of the formalism is to allow calculations of the THz radiation arising from any current (think photoconductive antennas) or polarization source (think rectification and other nonlinear mixing).
		It considers near and far fields, dispersion, reflections from interfaces as well as the important case where a THz beam is collimated, then refocused with two identical mirrors (i.e.
	www.novajo.ca /thzcode.html (428 words)

	The Keith Nelson Group - THz Spectroscopy
		These phonon-polaritons contain spectral components in air from 100 GHz to 5 THz (3000 mm to 60 mm, 3 cm-1 to 167 cm-1) and we refer to this as the “THz region.” Many of the projects in the Nelson lab, FDTD simulations, 2D pulse shaping, and
		The THz portion of the spectrum is relatively unstudied and offers the possibility of new insights into important phenomena.
		Dielectric spectroscopy in the THz region and acoustic spectroscopy in the GHz regime (~1-500GHz) will provide important information on the relaxation dynamics of glass forming liquids in a region that has not been experimentally well characterized.
	web.mit.edu /nelsongroup/research/thz_spectroscopy.shtml (457 words)

	CIRCE: Filling the THz Gap (Site not responding. Last check: 2007-10-21)
		The terahertz (THz) and sub-THz region of the electromagnetic spectrum lies between the infrared and the microwave.
		Only over the past decade has this THz region become scientifically available with broadband sources of moderate intensity being produced by ultra-fast laser pulses incident on biased semiconductors or non-linear crystals.
		With such a high-power THz source, new opportunities for scientific research and applications are enabled across a diverse array of disciplines from condensed matter physics, to medical, technological, manufacturing, space and defense industries.
	circe.lbl.gov /THzGap.html (223 words)

	National Synchrotron Light Source
		The first workshop on intense coherent THz pulses at Brookhaven National Laboratory (BNL) was held during the spring of 2005.
		He emphasized applications where the THz pulses serve as an excitation source rather than simply a probe of a material's response.
		It has been noted that the magnetic field portion of a THz wave could be sufficient to change the magnetization state of some magnetic alloys, a topic Dario Arena (NSLS) summarized in his talk.
	www.nsls.bnl.gov /newsroom/news/2005/05-THzWorkshop.htm (425 words)

	Markus Walther
		The THz pulse is focussed onto a similar detector chip, that measures the temporal shape of the electric field of the incident THz pulse.
		THz time-domain spectroscopy allows the direct determination of the characteristic mode structure of individual molecular systems.
		Due to the sensitivity to molecular structure and conformation, the measurement of the THz spectra allows an unambigous identification of different chemicals or a determination of the molecular configuration, as for example in the case of different isomers.
	dr-walther.com (985 words)

	Oxford Terahertz Photonics Group (Site not responding. Last check: 2007-10-21)
		The carrier dynamics of photoexcited electrons in the vicinity of the surface of (NH S-passivated GaAs were studied via terahertz (THz) emission spectroscopy and optical-pump THz-probe spectroscopy.
		Terahertz (THz) emission from arsenic-ion implanted GaAs surfaces is studied via experiment and a three-dimensional carrier dynamics simulation.
		We have just developed a new THz detector which recovers the full polarisation state of a THz pulse.
	www-thz.physics.ox.ac.uk /thzhome.html (396 words)

	THz Chip, Imager Research Presented at CLEO/QELS
		Using this method, they could distinguish powders of cocaine, which absorbs a maximum of radiation at 0.8 THz, and amphetamine (1.03 THz) from powders of potato starch, flour and lactose (0.53 THz) in only 2 to 5 seconds per scan.
		The drugs' distinctive THz signatures makes them possible to detect even if they are mixed with an additional ingredient, such as flour.
		The biochip could also identify specific molecules dissolved in water, which tends to absorb terahertz radiation strongly and obscure the signals from other molecules, for potential applications such as DNA identification in saliva and for molecular biology applications such as studying the folding patterns of proteins, which would be helpful for designing new drugs.
	www.photonics.com /content/tradeshows/2006/May/24/82812.aspx (1292 words)

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