chapter7- componentsof optical instruments（chapter 7 - componentsof optical instruments）.doc

Chapter 7- Components of Optical Instruments A: General Designs of Optical Instruments: Spectroscopic instruments that were developed for use in the visible region are optical instruments. Optical spectroscopic methods are based upon six phenomena namely, (1) absorption, (2) fluorescence, (3) phosphorescence, (4) scattering (5) emission, and (6) chemiluminescene. Although the instruments for measuring each differ somewhat in configuration, most of their basic components are remarkably similar. Typical spectroscopic instruments contain five components: (1) a stable source of radiant energy, (2) a transparent container for holding the sample, (3) a device that isolates a restricted region of the spectrum for measurement, (4) a radiation detector that converts radiant energy into a signal detector, (5) a signal processor and readout. Power Source: spectrochemical encoding system Sample: must be in form suitable for analysis, may involve a separation or speciation Sample cell: cuvette for UV-VIS, flame for atomic spectroscopy Wavelength Disperser: an information sorting system, spreads light out spatially according to its wavelength Photodetector: radiation transducer changing optical info into electrical info Readout: digital (ADC), meter, strip chart recorder Absorption- In atoms, electron transitions of outer-shell electrons correspond to the absorption or emission of electromagnetic radiation that is in the ultraviolet and visible regions. Because vibrational and rotational energy levels are not possible in atoms, the absorption and emission of radiation that occurs in molecules when an electron travels between the numerous vibrational and rotational energy states of one electron level are not possible. Only a single transition between each set of electron levels is possible. As a consequence, the bands of emitted or absorbed radiation are narrow in atoms. In flames, absorptive bandwidths of atoms typically vary from about 0.001 to 0.01nm. The narro