Terahertz sources

Keywords terahertz imaging subwavelength imaging millimeter-wave radar atmospheric effects terahertz sources terahertz detectors. 

INDIUM NITRIDE A NEW MATERIAL FOR HIGH EFFICIENCY, COMPACT, 1550nm LASER-BASED TERAHERTZ SOURCES IN CHEMICAL AND BIOLOGICAL DETECTION... 

Terahertz Sources and Systems, ed. by R. E. Miles, P. Harrison, D. Lippens, NATO Science Series (Dordrecht, Kluwer, 2001). 

Terahertz, or far infrared spectroscopy, covers the frequency range from 0.1 to lOTHz (300 to 3cm ) where torsional modes and lattice vibrations of molecules are detected. It is increasing in use in many application areas, including analysis of crystalline materials. Several dedicated conunercial instruments are available which use pulsed terahertz radiation which results in better signal to noise than those using blackbody sources for radiation (and associated with the terminology far infrared spectroscopy). Work using extended optics of FTIR instrumentation as weU as continuous-wave source THz has also been recently reported. ... 

Brighter, tunable ultrafast light sources would benefit many of the areas discussed in the report, particularly infrared-terahertz (between visible light and radio waves) vibrational and dynamical imaging, near-field scanning optical microscopy (NSOM), and X-ray imaging. 

At present, free-electron lasers are excellent light sources for basic studies on imaging in the terahertz range. The further development of this technique as a... 

While heterodyne detection is typically the most sensitive, it is problematic to extend its use to FPA systems. Each detector element in the FPA requires LO power, on the order of 1 mW for Schottky diode-based mixers. For large FPAs operating in the millimeter-wave or terahertz bands, this level of power is currently impractical. Various components including LNAs and mixers are available as MMICs at up to about 140 GHz and may eventually extend to 220 GHz or possibly higher [49], Schottky diode-based mixers are available at frequencies extending well into the terahertz range, to 2.5 THz and possibly higher, and can be used wherever a suitable LO source can be obtained [53],... 

Terahertz radiation lies between the microwave and the infrared regions of the electromagnetic spectrum. Terahertz typically ranges from 0.1 x 1012 to 10 x 1012Hz. One THz is equivalent to 300 microns in wavelength, 1 ps in time, 4.1 meV, and 47.6 K. THz radiation bridges the gap between photonic and electronic devices and offers a large expanse of unused, unexplored bandwidth. Historically, the lack of sources and detectors, as well as the perceived lack of need, had contributed to the dearth of activity in THz. For example, the first commercially available THz spectrometer did not arrive until 2000. 

Terahertz imaging approaches have typically used either short-pulsed laser or continuous wave (CW) THz generation and detection. The short-pulsed method usually involves the generation and detection of sub-picosecond THz pulses using either photoconductive antenna structures or optical rectification in a non-linear crystal. Pulsed sources seem to be more favorable (in particular for close proximity applications) because they can be used for acquiring depth information. Spectral information is retrieved by a Fourier transform of the time-domain data to the frequency domain. 

Figure 4.18. Cross-section schematic of an advanced transistor design. Features illustrated are (a) raised source and drain contacts, (b) an SOI substrate that prevents off-state leakage from source to drain, and (c) a high-K dielectric gate insulator. These three components employed in tandem are the basis of a faster generation of transistors referred to as terahertz transistors. ]...

To overcome the dominating terahertz absorption of water, we employ intense radiation sources (up to 10 kW) and sensitive detectors ( pW/Hz ) to precisely measure the extinctions of both protein solutions and their associated buffer blanks. The terahertz absorption measurements are dominated by water absorption. We then carefully assess the amount of bound water in the protein s hydration shell, allowing us to obtain an accurate estimation of the dominating solvent background and extract the molar extinction of the solvated protein " (Figure 1). 

A reflective circular polarizer is used to construct the terahertz circular dichroism spectrometer (Error Reference source not found.). The... 

Figure 3 Terahertz imaging of tablet coadng thickness. These 3D images Ulustrate ttie variabUity in coating thickness around a film-coated tablet and show how flie coating was thinner on the upper and lower axial surfaces than on the radial surface of the tablet The original illustration was color coded to highlight the variations in eveimess of coating, and some of these can also be seen in tins grayscale interpretation. The scales in the x, y, and z directions are in millimeter. Source From Ref. 55.

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