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The principle of the spectrometer

The principle of the spectrometer
Update Time:2018-03-24
[My EcoNetwork] Introduction to the Spectrometer

Spectroscope is a scientific instrument that decomposes complex light into spectral lines. It consists of a prism or a diffraction grating. The spectrometer can measure the light reflected from the surface of the object. The seven-color light in the sunlight is part of the visible light (visible light), but if the sunlight is decomposed by a spectrometer, the visible light only occupies a very small range in the spectrum, and the others are invisible to the naked eye, such as infrared and microwave. UV, X-ray, etc. The optical information is captured by a spectrometer, developed by photographic negatives, or displayed and analyzed by a computerized automatic display numerical instrument to determine what elements are contained in the article. This technology is widely used in the detection of air pollution, water pollution, food hygiene, and metal industries.
An optical instrument that separates polychromatic light into a spectrum. Spectrometers come in a variety of types. In addition to spectrometers used in the visible light range, there are infrared spectrometers and ultraviolet spectrometers. According to different dispersive elements can be divided into prism spectrometer, grating spectrometer and interference spectrometer. According to the detection method, there are spectrophotometers that directly observe with the eye, spectrographs that record with a photosensitive sheet, and spectrophotometers that detect spectra with photoelectric or thermoelectric elements. A monochromator is a spectrometer that outputs only a single chromatogram through a slit and is often used with other analytical instruments.
The figure shows the basic structure of a tri-prism chromatograph. The slit S is perpendicular to the main section of the prism, is placed in the object-side focal plane of the lens L, and the photosensitive sheet is placed in the image-side focal plane of the lens L. Illuminating the slits S and S with the light source becomes a spectral line on the photosensitive sheet. Due to the dispersion effect of the prisms, spectral lines of different wavelengths are separated from each other to obtain a spectrum of the incident light. The spectral range that the prism spectrograph can observe is determined by the absorption of the spectrum by optical elements such as prisms. Ordinary optical glass is only suitable for the visible light band, and can be extended to the ultraviolet region with quartz. Crystals such as sodium chloride, potassium bromide, and calcium fluoride are generally used in the infrared region. The spectral range of commonly used reflective grating spectrometers depends on the grating stripe design and can have a wide spectral range.
The parameters that characterize the basic characteristics of the spectrometer include spectral range, dispersion rate, bandwidth, and resolution. Spectrometers designed based on the principle of interference (such as Fabry-Perot interferometers and Fourier transform spectrometers) have high dispersion rates and resolution capabilities and are often used for the analysis of spectral fine structures.

The principle of the spectrometer

According to the working principle of modern spectroscopic instruments, spectrometers can be divided into two categories: classic spectrometers and new spectrometers. Classical spectroscopic instruments are instruments based on the principle of spatial dispersion; new spectroscopic instruments are instruments based on modulation principles. Classical spectroscopic instruments All are slit spectroscopy instruments. Modulated spectrometers are non-spatially spectroscopic and use circular apertures to enter the light.
According to the principle of dispersion of dispersive components, spectroscopic instruments can be divided into: prism spectrometers, diffraction grating spectrometers and interference spectrometers. Optical multi-channel analyzers (OMAs) have emerged in recent decades as photodetectors (CCDs). And a new type of computer-controlled spectroscopic analysis instrument, which integrates information acquisition, processing, and storage of various functions. Since OMA no longer uses photosensitive emulsions, it avoids and eliminates the need for dark room processing and subsequent cumbersome processing, measurement, and tradition. Spectral technology has undergone a fundamental change, greatly improving the working conditions and improving work efficiency. Using OMA analysis of the spectrum, the measurement is accurate, rapid, convenient, and has high sensitivity, fast response time, high spectral resolution, and the measurement results can be immediately displayed. Read out on the screen or output by a printer or plotter. It has been widely used in almost all spectral measurement, analysis and research work, and is especially suitable for the detection of weak signals and transient signals.