Chapter 7 - Chapter 7 Components of Optical Instruments...

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Chapter 7 Components of Optical Instruments Optical spectroscopic methods are based upon six phenomena: 1. Absorption 2. Fluorescence 3. Phosphorescence 4. Scattering 5. Emission 6. Chemiluminescence
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Components of typical spectroscopic instruments: 1. A stable source of radiant energy (sources of radiation). 2. A transparent container for holding the sample (sample cell). 3. A device that isolates a restricted region of the spectrum for measurement (wavelength selector, monochromator or grating). 4. A radiation detector, which converts radiant energy to a usable electrical signal. 5. A signal processor and readout, which displays the transduced signal.
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Sources of Radiation In order to be suitable for spectroscopic studies, a source must generate a beam of radiation with sufficient power for easy detection and measurement and its output power should be stable for reasonable periods. Sources are of two types. 1. Continuum sources 2. Line Sources
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Continuum Sources: Continuum sources emit radiation that changes in intensity only slowly as a function of wavelength. It is widely used in absorption and fluorescence spectroscopy. For the ultraviolet region, the most common source is the deuterium lamp. High pressure gas filled arc lamps that contain argon, xenon, or mercury serve when a particular intense source is required. For the visible region of the spectrum, the tungsten filament lamp is used universally. The common infrared sources are inert solids heated to 1500 to 2000 K.
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Line Sources: Sources that emit a few discrete lines find wide use in atomic absorption spectroscopy, atomic and molecular fluorescence spectroscopy, and Raman spectroscopy. Mercury and sodium vapor lamps provide a relatively few sharp lines in the ultraviolet and visible regions and are used in several spectroscopic instruments. Hollow cathode lamps and electrodeless discharge lamps are the most important line sources for atomic absorption and fluorescence methods.
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Laser Sources The term ‘LASER’ is an acronym for L ight A mplification by S timulated E mission of R adiation. Laser are highly useful because of their very high intensities, narrow bandwidths, single wavelength, and coherent radiation. Laser are widely used in high-resolution spectroscopy .
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Component of Lasers: The important components of laser source are lasing medium, pumping source, and mirrors. The heart of the device is the lasing medium. It may be a solid crystal such as ruby, a semiconductor such as gallium arsenide, a solution of an organic dye or a gas such as argon or krypton.
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Four processes in Lasing Mechanism: 1. Pumping 2. Spontaneous emission (fluorescence) 3. Stimulated emission 4. Absorption
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This note was uploaded on 05/06/2010 for the course CHEM 4414 at Arkansas Tech.

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Chapter 7 - Chapter 7 Components of Optical Instruments...

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