Near infrared detector

Many common infrared and near-infrared detectors are subject to phenomena that are mainly thermal in origin, and therefore the detector noise is independent of the signal level. 

Fourth, while fluorescence was not a problem in this system, some bioreactor components may be highly fluorescent. Until more experience is gained, this makes it difficult to make generalizations about the likelihood of success with new systems. Finally, water is a weak Raman scatterer and can be hard to track. While Ulber etal. considered the challenge in obtaining a spectrum of the aqueous cell culture broth to be a disadvantage, others consider it an advantage since these solutions overwhelm mid- or near-infrared detectors.33 34 36... 

Near infrared detectors These are usually photoconductive cells which detect infrared radiation in the range 0.8 3.0 p. The sensing element is a semiconductor (germanium, lead sulphide, or lead tellurlde). Upon illumination with radiation of appropriate wavelength, the electrons of the semiconductor are raised to conduction bands. Tills causes a drop in electrical resistance. Consequently, if a small voltage is applied, a large Increase in current can be noted. The resistance of the system is such that the current may be amplified and finally indicated on a meter is recorded. 

Figure 3 Specific detectivities and wavelength ranges for near-infrared detectors.

CMOS ROICs designed for infrared applications are dedicated to signal amplification and processing and not photon detection the detector is a separate component or array that is interconnected or hybridized to the ROIC. Since the detector and ROIC are separate elements, they can be separately optimized for their specific purpose. Silicon p-i-n stmctures, a special case of a visible/near-infrared detector, also have a detector array separate from the ROIC component. 

Large arrays of low noise near infrared detectors at the South Pole are opening up exciting new possibUities for astrophysics research. 

Abstract. The U.S. Air Force Phillips Laboratory will build the 3.63 m Advanced Electro Optical System (AEOS) telescope on Halealiala, Maui. The Listitute for Astronomy will participate in this project and will develop astronomical instruments optimized for nsing the AEOS telescope in survey projects. As part of this instrument development program 1024 X 1024 HgCdTe near-infrared detector arrays will be developed at the Rockwdl fritemational Science Center. 

For radiofrequency and microwave radiation there are detectors which can respond sufficiently quickly to the low frequencies (<100 GHz) involved and record the time domain specttum directly. For infrared, visible and ultraviolet radiation the frequencies involved are so high (>600 GHz) that this is no longer possible. Instead, an interferometer is used and the specttum is recorded in the length domain rather than the frequency domain. Because the technique has been used mostly in the far-, mid- and near-infrared regions of the spectmm the instmment used is usually called a Fourier transform infrared (FTIR) spectrometer although it can be modified to operate in the visible and ultraviolet regions. 

Detectors aie all intrinsic unless otherwise noted. See Fig. 1. Visible bandwidth near infrared = 0.700-1.00 fim. 

Information on ionization energies, solubiUties, diffusion coefficients, and soHd—Hquid distribution coefficients is available for many impurities from nearly all columns of the Periodic Table (86). Extrinsic Ge and Si have been used almost exclusively for infrared detector appHcations. Of the impurities,... 

Photometric Moisture Analysis TTis analyzer reqiiires a light source, a filter wheel rotated by a synchronous motor, a sample cell, a detector to measure the light transmitted, and associated electronics. Water has two absorption bands in the near infrared region at 1400 and 1900 nm. This analyzer can measure moisture in liquid or gaseous samples at levels from 5 ppm up to 100 percent, depending on other chemical species in the sample. Response time is less than 1 s, and samples can be run up to 300°C and 400 psig. 

An optical detector with appropriate electronics and readout. Photomultiplier tubes supply good sensitivity for wavelengths in the visible range, and Ge, Si, or other photodiodes can be used in the near infrared range. Multichannel detectors like CCD or photodiode arrays can reduce measurement times, and a streak camera or nonlinear optical techniques can be used to record ps or sub-ps transients. 

In many ways, today s optical and infrared detectors are nearly perfect, with high quantum efficiency, low readout noise, high dynamic range and large arrays of pixels. However, as good as the detectors are, there are limitations that must be understood and respected in order to produce the best astronomical instm-ments and thereby, the best science. 

Ideally, an observatory would install perfect detectors in the focal plane of its instruments. What makes a perfect detector The attributes of an ideal detector and the performance achieved by today s technology are given in Table 1. Optical and infrared detectors are nearly ideal in several ways ... 

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