Detector, linear pyroelectric

In IR array detectors using pyroelectric materials such as TOS mooocrystal or PbTiO ceramics, the detecting plate must be cut into the array of detector elements in order to reduce the cross-talk of response between adjacent elements, which is caused mainly by high thermal diffusion in the plate. On the other hand, since thin films of pyroelect polymers have low thermal diffusion, linear array detectors [23-25] using polymer film with an array of separated electrodes can have small cross-talk between adjacent elements without cutting the film. 

Sources and detectors Specific discussions of sources and detectors have been covered elsewhere in this article. The issues here are more service and performance related. Most sources have a finite lifetime, and are service replaceable items. They also generate heat, which must be successfully dissipated to prevent localized heating problems. Detectors are of similar concern. For most applications, where the interferometer is operated at low speeds, without any undesirable vibrational/mechanical problems, the traditional lithium tantalate or DTGS detectors are used. These pyroelectric devices operate nominally at room temperature and do not require supplemental cooling to function, and are linear over three or four decades. 

An example of quasi CW THz detection [86] uses a THz wave parametric oscillator (TPO) consisting of a Q-switched Nd YAG laser and parametric oscillator [87,88], In this technique, MgO LiNb3 is employed as a non-linear material to generate CW THz. Silicon prisms couple the THz radiation from the non-linear crystal where it is detected using a pyroelectric detector. THz images are collected at discrete THz frequencies and then spectroscopically analyzed using a component spatial pattern analysis method to determine sample composition. 

The ease of forming the smectic mesophase by this class of side-group type liquid crystalline polymers has rendered a great possibility in synthesizing polymeric chiral smectic materials useful in non-linear optics, transducers, pyroelectric detectors and display devices (Chapter 6). The first polymer forming a chiral smectic-C phase was synthesized by Shibaev et al. (1984). It has a polymethacrylate main chain, a long polymethylene spacer, and a mesogenic unit attached at the end with a chiral moiety (polymer (3.60)). Since then, a lot of polymers with chiral mesophases have been synthesized and studied (Le Barny and Dubois, 1989). 

A commercial chirped pulse amplification (CPA) Ti sapphire laser system (Spectra Physics, Spitfire), providing linearly polarized pulses with pulse duration of 120 fs and at a wavelength of = 800 nm, was used for irradiation. The laser pulse energy was measured by means of a pyroelectric detector (Ophir, PE-9). In the fs-irradiation set-up, the sample was placed at 36° of the normal incidence in the focal plane of a 15 cm lens resulting in an elliptical laser spot on the surface. The samples were irradiated at two laser fluences (2.6 and 5.6 J/cm ) with different number of pulses (1-50 pulses)... 

The standard detector in routine FT-IR instruments is the pyroelectric DTGS (deut-erated triglycine sulfate) detector, whose response in the MIR range is wavelength independent. The detector operates at ambient temperature and shows good linearity across the whole transmittance scale. The DTGS detector responds to signal frequencies of up to several thousand Hz, hence the time needed to scan one spectrum at a resolution of 4 cm is of the order of 1 s. 

E Bunnuel. D. Esieve, J. Fane. V. V. Pham, ai>d J. J. Stmniooc, Performance of a pyroelectric PVDF detector extensian to a linear array as a image detector, Proc. SPIE 702 35 (1966). 

If the interferometer mirror speed is such that the optical velocity is 0.316 cm s (HeNe laser frequency of 5 kHz), 4000-cm radiation is modulated at 1.25 kHz (see Eq. 2.11). Thus, the response time of a detector for FT-IR spectrometry must be less than 1 ms. Although several cryogenically cooled detectors have response times this low, the only mid-infrared detectors that have an appropriate combination of high speed, reasonably good sensitivity, low cost, good linearity, and operation at or near room temperature are the pyroelectric bolometers. 

For a FT-IR spectrometer to achieve perfect photometric accuracy, the response of the detector and its associated amplifiers and electronic filters must be independent of the photon flux on the detector. This condition is usually fulfilled with pyroelectric detectors but is particularly difficult to achieve in the mid-infrared with photo-conductive MCT detectors. The photometric response of MCT detectors is usually linear at very low signal levels but may be easily forced into nonlinear behavior by... 

The requirement for the uniform linear motion of the movable mirror in the continuous-scan type is imposed mainly by the frequency-response characteristics of the detector for the main interferometer. The response of the detectors to the beams (indicated by (g) and in Figure 5.4) of the laser interferometer is usually rapid, so that effects arising from the instability of the motion of the movable mirror which changes the modulated frequency can be disregarded. In contrast, the response characteristic of thermal detectors such as a pyroelectric detector commonly used for detecting the infrared beam from the main interferometer is not as rapid as that of the laser-interferometer detectors. As a result, any... 

Ferroelectric combs, if realizable in device form, may have valuable applications Le Barny and Dubois discuss their potential in the areas of display devices, transducers, pyroelectric detectors and non-linear optical devices (see below). 

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