InSb detector

Fig. 3. Schematic diagram of the Northwestern apparatus for IR laser kinetic measurements in the gas phase. D, and D2 are InSb detectors with D2 being a high speed photovoltaic detector. M = Mirror, I = iris, C = chopper, BS = beam splitter, P = photolysis cell. [Reproduced with permission from Ouderkirk et al. (75).]...

Thus, the region 2100-1830 cm 1 can be covered. This allows us to monitor CO(v,J) by resonance absorption and various M(CO)n [n = 3-6] as a result of near coincidences between the CO laser lines and the carbonyl stretching vibrations of these species. The temporal response of the detection system is ca. 100 ns and is limited by the risetime of the InSb detector. Detection limits are approximately 10 5 torr for CO and M(CO)n. The principal limitation of our instrumentation is associated with the use of a molecular, gas discharge laser as an infrared source. The CO laser is line tuneable laser lines have widths of ca. lO cm 1 and are spaced 3-4 cm 1 apart. Thus, spectra can only be recorded point-by-point, with an effective resolution of ca. 4 cm 1. As a result, band maxima (e.g. in the carbonyl stretching... 

A band was observed at 2260 cm- which did not shift as a function of potential, which we assign to v(CN) of solution phase CI CCN nea the electrode surface. We were unable to look for the 1615 cm band reported by Sexton et. al. (20), since this frequency lies beyond the lower energy limit of the InSb detector in our spectrometer, and in a spectral region where there is severe background absorbance by the H O solvent. 

The photomultipliers equipped in the Jasco J-500A and Jasco 500C are Hamatsu R-376 and R-316, respectively. The latter is of S-l type. An InSb photovoltaic cell (Judson) is used as a detector for the wavelength region from 1000 to 2400 nm 283). The InSb detector is cooled with liquid nitrogen. An extension of the CD measurements to 11 p can be conducted by using HgCdTe detectors cooled at liquid He temperature 287). 

The far-infrared emission of the idler frequency was also detected 81) with an InSb detector cooled with liquid He. The power of the pulses was estimated to be about 5 W. Their frequency was not directly measured but only inferred from energy conservation. Later measurements 83> gave a power from 0.25 W at 60 gm to 3 W at 200 jum and a linewidth of 0.1 to 0.5 cm"1 for the signal radiation. 

There are three classes of instruments for the measurement of VCD. The first is based on a dispersive grating monochromator as the source of wavelength discrimination. This was the first kind of VCD instrument to be built and this design was used in the discovery of VCD in 1974 [1]. The early versions of these instruments have been described in detail [3,4,44-47], The low-frequency limit was initially 1900 cm"l, the cut-off of the InSb detector. Using a PbSnTe detector the low-frequency limit was extended to 1550 cm l [46], and subsequently using HgCdTe detectors the limit was lowered to 1250 cm l[48] and then 900 cm l [49], and finally using a Si As detector it was lowered to 650 cm l [50]. 

The IR pulse is split into a weak probe beam, which passes down a computer-controlled variable delay line with up to 12 ns of delay and a strong pump beam. The pump and probe pulses are counterpropagating and focused into the center of the SCF cell. Typical spot sizes (1/e radius of E-field) were oj0 120 pm for the pump beam and oj0 60 pm for the probe beam. A few percent of the transmitted probe beam is split off and directed into an InSb detector. A reference beam is sent through a different portion of the sample. The reference beam is used to perform shot-to-shot normalization. The pump beam is chopped at half the laser repetition rate (900 Hz). The shot-to-shot normalized signal is measured with a lock-in amplifier and recorded by computer. 

IR spectra were taken at room temperature (300 K) and liquid-helium temperatures (5-15 K), using a Bomem DAS Fourier transform infrared (FTIR) spectrometer and an InSb detector. For the low-temperature measurements, a Janis continuous-flow liquid-helium cryostat with wedged, IR-transparent windows was utilized. Hall-effect measurements, in the Van der Pauw geometry, were performed at room temperature using a system from MMR Technologies. Wires were attached to the ZnO using silver paint, which provided adequate Ohmic contacts for the electron concentrations (10 cm ) in these samples. 

The most commonly used mid-infrared thermal detectors arc TGS (Iriglycinc sulphate) and DTGS (deuterated triglycinc sulphate). The variation in temperature on the surface of the detector causes the appearance of an electrical signal. The response is constant over the spectral domain. In the far-infrared, a bolometer (Si or InSb detector) with high detective capacity is preferred. 

Figure 3. Block diagram of the millimeter wave spectrometer used by the Ziurys group. The instrument uses a phase locked Gunn oscillator as a source of radiation and an InSb detector. [Reprinted with permission from ref. 37. Copyright 1994 American Institute of Physics.]...

This graph summarizes the wavelength response of some semiconductors used as detectors for infrared radiation. The quantity D (X) is the signal to noise ratio for an incident radiant power density of 1 W/cm and a bandwidth of 1 Hz (60° field of view). The Ge, InAs, and InSb detectors are photovoltaics, while the HgCdTe series are photoconductive devices. The cutoff wavelength of the latter can be varied by adjusting the relative amounts of Hg, Cd,... 

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