Ii slits slits are constructed by machining a sharp

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ii) Slits Slits are constructed by machining a sharp edge onto two metal pieces. These lie in a plane and the spacing between them, the slit width, can be adjusted. The smaller the slit width, the better the spectral resolution. III) Filters: Filters are used to pass on only desired wavelengths of light. A filter could be colored glass. Most likely they are also based on constructive or destructive interference of light waves. IV) Interferometers - alternative wavelength selection process allows all wavelengths to simultaneously reach the detector Radiation from source reaches beam splitter, where half of the radiation hits the moving mirror and half hits the fixed mirror. The beams reflect and re-combine, the emerging radiation for a wavelength exhibits constructive or destructive interference. With constant mirror velocity, the wavelength modulates in a regular sinusoidal manner. Both the sampling rate of radiation reaching the detector and the mirror velocity is modulated by a helium-neon laser. The resulting detector signal typically is stored as a time domain spectrum (interferogram).
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Converted to a spectrum in the frequency domain using the mathematical process of Fourier Transform. Fourier transform: 1) allows for signal averaging 2) allows all wavelengths to be monitored simultaneously 3) mathematical process that converts data obtained in the time domain to be converted into the frequency domain. FT is used quite extensively in IR (infrared), mass spectroscopy and in NMR (nuclear magnetic resonance) applications. In addition to IR spectroscopy, the use of Fourier transform has become quite common in certain spectroscopic methods due to the a ff ordability of PCs. Types of Detectors A detector produces an electric signal when struck by photons. Phototube detector The phototube is used frequently as a detector in UV-Vis spectrometers. The cathode consists of a photo-emissive surface. Electrons are ejected from the cathode proportional to the radiant power (photons) striking its surface. The emitted electrons are attracted to the anode.
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The accompanying voltage is fed to an amplifier and converted to a signal. Photomultiplier tubes The Photo Multiplier Tube (PMT) is similar to the photo tube, but is a vast improvement. In addition to the cathode and anode, the PMT has dynodes, which produce a cascade e ff ect on the electron emission production. Each photon causes a ~ 10 7 additional electrons to be produced. The PMT possesses high sensitivity, good S/N ratio, and excellent dynamic range. PMTs are highly sensitive to visible and UV excitations at extremely low power conditions, (very low concentrations of analyte). Intense light sources (such as daylight or stray light) can destroy and damage PMTs. PHOTO DIODE ARRAY: silicon diode
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Silicon diode detectors, such as those used in a photo diode arrays (PDA), are composed of reverse-biased p-n junctions formed on a silicon chip.
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