Electromagnetic radiation detectors for

Photographic emulsions and photoelectric detection devices can be used as detectors for electromagnetic radiation between 150 and 800 nm. Among the photoelectric devices, photomultipliers are the most important but new solid state devices have become a useful alternative. 

Photomultiplier tube A sensitive detector of electromagnetic radiation amplification is accomplished by a series of dynodes that produce a cascade of electrons for each photon received by the tube. 

Surface atoms can be transferred into an excited state. Different types of surface excitations (vibrational or electronic) result in features within different spectral ranges (infrared and visible or around it, respectively) and they require different light sources and detectors for their investigation. It is reasonable, therefore, to classify the corresponding spectroscopic techniques as infrared and optical, where the term "optical" is used for electromagnetic radiation in and aroimd the visible region of the spectrum. 

The first detector for optical spectroscopy was the human eye, which, of course, is limited both by its accuracy and its limited sensitivity to electromagnetic radiation. Modern detectors use a sensitive transducer to convert a signal consisting of photons into an easily measured electrical signal. Ideally the detector s signal, S, should be a linear function of the electromagnetic radiation s power, P,... 

Spectrometers are designed to measure the absorption of electromagnetic radiation by a sample. Basically, a spectrometer consists of a source of radiation, a compartment containing the sfflnple through which the radiation passes, and a detector. The frequency of radiation is continuously varied, and its intensity at the detector is compar ed with that at the source. When the frequency is reached at which the sample absorbs radiation, the detector senses a decrease in intensity. The relation between frequency and absorption is plotted as a spectrum, which consists of a series of peaks at characteristic frequencies. Its interpretation can furnish structural information. Each type of spectroscopy developed independently of the others, and so the data format is different for each one. An NMR spectrum looks different from an IR spectrum, and both look different from a UV-VIS spectrum. 

The single most useful and versatile physicochemical detectors in drug residue analysis are probably those based on ultraviolet-visible (UV-Vis) spectrophotometry. These detectors allow a wide selection of detection wavelengths, thus offering high sensitivity for analytes that exhibit absorbance in either the ultraviolet or the visible region of the electromagnetic radiation. 

There are two categories of remote sensing, active and passive. Passive techniques utilise electromagnetic radiation emitted from or transmitted through the atmosphere, the radiation source being for example the black body emission from the earth s surface or solar and stellar irradiances. The most critical part of a passive remote sensing instrument is its detector. In contrast, active remote sensing systems have their own radiation source and a detector, for example, radar and lidar techniques. 

There exists a need for high-power pulsed CW radiation sources to enable fast switching times and high repetition rates for electromagnetic resonance experiments. In addition, commercial development of THz sources is needed so that this technology can be made more widely available to the research community. Furthermore, current detectors for THz spectroscopy have high cooling requirements to minimize noise in spectral data further developments are needed to provide inexpensive and user-friendly detector options. 

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