Terahertz detectors

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

Keywords Terahertz Detector Resonant Photoeonduetion Double Quantum Well. 

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. 

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 high mobility two-dimensional electron system exhibits large changes in the resistance, and zero-resistance states, under microwave and Terahertz excitation. We describe associated experimental results and the possibility of using this system as a radiation detector. 

Fig. 5) This figure shows a sketch of the investigated detector concept. An irradiated high mobility two-dimensional electron gas device is subjected to a constant magnetic field Bo, where Bo is chosen to correspond to a fixed point (marked as a dot on the top inset) of the resistance oscillations for incident radiation at a frequency f. The detector device function is realized by superimposing on the static magnetic field, a small time varying component, which has been shown here in blue. Then, a high harmonic, tuned band Terahertz sensor is realized by detecting the device resistance at a odd-harmonic multiple of the field modulation frequency, as the detector is illuminated by Terahertz radiation.

Numerical simulations of this model were carried out to test expectations. The results are shown in Figs. 8 and 9. The figure 8 shows the amplitude of the detected signal at the third harmonic of the modulation frequency when the operating point corresponds to the second node, i.e., n = 2, and the Bo is selected for the detection of radiation in the vicinity of 400 GHz, which lies near the lower edge of the Terahertz band, where the device sensitivity to such radiation has been confirmed by our experiments, see Fig. 3, for example. As confirmed by the simulations, the 3 harmonic sensing concept yields indeed a narrow band detector, with sensitivity between roughly 200 and 800 GHz, as... 

TERAHERTZ-BASED DETECTORS USING COLD-ATOM OPTICS... 

As we explore the interaction of cold-atom systems with microwave and terahertz radiation, we find that they have some unique properties as detectors. A comparison with superconductor-based detectors such as SQUlDs is instractive. Because of the third law of thermodynamics, i.e., a system in a single quantum state has zero entropy, the response of a SQUID is almost free of thermal noise. But an additional properly of SQUIDs is that they exhibit the phenomenon of coherence, i.e., wave interference, which leads to entirely new effects, e.g. the AC and DC Josephson effects. Cold atom clouds share this behavior, as we will discuss below. 

Terahertz-Based Detectors Using Cold-Atom Optics 163... 

In an applied perspective, the interest in the spectroscopy of shallow impurities in semiconductors has been linked for a long time with the production of detectors for the medium and far infrared, but the possibility to produce terahertz lasers based on the transitions between discrete shallow levels has aroused a renewed interest in this spectroscopy in silicon. Another new potential field of application is the domain of quantum computing. A large part of the results presented in this book concerns silicon and this reflects the relative volume of investigations devoted to this material. 

It has been proposed that nanotube-based transistors can operate at frequencies in the terahertz region as generators, frequency multipliers and detectors [84] though carbon nanotube transistors are good candidates for RF and opto electronics [85], fabrication of nanotube arrays with controllable chirality and diameters is stiU a challenge for large scale fabrication of the devices. 

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