a spectrometer

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A device for measuring the intensity of spectral lines at different wavelength positions with photodetectors such as photomultiplier tubes

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This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Spectrometer Spectrometer , widely known as Direct reading spectrometer 。 With photomultiplier tube, etc Photodetector A device for measuring the intensity of spectral lines at different wavelength positions. It is formed by an incident slit , a dispersion system, an imaging system and one or more Exit slit form. with Dispersive element Separate the electromagnetic radiation of the radiation source from the required wavelength or wavelength area, and wavelength Perform intensity measurement on (or scan a certain wave band). It is divided into monochromator and polychromator.

Chinese name: a spectrometer
Foreign name: Spectroscope
Alias: Spectrometer

Category: Scientific instruments
Field: Surveying and Mapping
Classification: Monochromator, etc

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brief introduction

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Spectroscope is used to decompose complex light into Spectral line Science of instrument , which is composed of prism or diffraction grating, and can measure the light reflected by the object surface with a spectrometer. The seven colored light in the sunlight is the part that can be separated by the naked eye (visible light), but if the sunlight is decomposed by the spectrometer and arranged according to the wavelength, the visible light only occupies a small range in the spectrum, and the rest are spectra that cannot be distinguished by the naked eye, such as infrared , microwave, ultraviolet X-ray wait. Through the capture of optical information by spectrometer, the development of photographic film, or the display and analysis of computerized automatic display numerical instrument, we can determine what elements are contained in the article. This technology is widely used in the detection of air pollution, water pollution, food hygiene, metal industry, etc.

take Polychromatic light An optical instrument that separates into spectra. There are many types of spectrometers, except in visible light In addition to the spectrometer used in the band Infrared spectrometer and Ultraviolet spectrometer 。 Press Dispersive element Can be divided into Prism spectrometer 、 Grating spectrometer and Interference spectrometer Etc. According to the detection method, there are direct eye observation Spectroscope , using Photosensitive film Recorded Spectrograph , and with photoelectricity or Thermoelectric element Spectral Spectrophotometer Etc. The monochromator outputs only through the slit Monochromatic line Spectrometer, often used with other Analysis instrument Used together.

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As shown in the Picture prism The basic structure of the chromatograph. Slit S and Prism Of section Vertical, placed on lens L's Square focal plane The photosensitive film is placed in the Image square focal plane Inside. Illuminate slit S with light source, S image Photosensitive film It becomes a spectral line because of the prismatic dispersion The spectral lines of different wavelengths are separated from each other incident light Spectrum of. Prism spectrograph Observable Spectral range Determined by prism, etc optical element Absorption of spectra. ordinary optical glass Only applicable to visible light band, with quartz Scalable to Ultraviolet region , on Infrared region General use sodium chloride 、 Potassium bromide And calcium fluoride. Universally used Reflective grating spectrometer Its spectral range depends on the design of grating fringes and can have a wide spectral range.

Characterization spectrometer Parameters of basic characteristics include spectral range Dispersion rate , bandwidth and Discriminative ability Etc. be based on Interference principle Designed spectrometer (e.g Fabry Perot interferometer 、 Fourier transformation Spectrometer) has high dispersion rate and resolution, and is often used for the analysis of spectral fine structure.

principle

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According to modern Spectral instrument The spectrometer can be divided into two categories: classic spectrometer and new spectrometer. Classical spectral instruments are based on the principle of spatial dispersion; The new spectral instrument is based on the modulation principle. Classical spectral instruments are all slit spectral instruments. Modulation spectrometer is non spatial light splitting, and it uses a circular hole to enter the light.

According to the light splitting principle of dispersion module, spectral instruments can be divided into prism spectrometer, diffraction grating spectrometer and interference spectrometer. optics Multichannel analyzer OMA (Optical Multi channel Analyzer) is a new type of light detector (CCD) and computer control Spectral analyzer It integrates the functions of information collection, processing and storage. Since OMA no longer uses photosensitive emulsion, it avoids and omits darkroom processing and a series of tedious processing and measurement work, which has fundamentally changed the traditional spectral technology, greatly improved the working conditions and improved the working efficiency; Using OMA to analyze spectrum, the measurement is accurate, fast, convenient, and has high sensitivity, fast response time, and high spectral resolution, measurement result It can be immediately read from the display screen or output by the printer or plotter. It has been widely used in almost all spectral measurement, analysis and research work, especially for the detection of weak signals and transient signals.

constitute

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A typical spectrometer is mainly composed of an optical platform and a detection system. It includes the following main parts:

1. Incident slit: the object point that forms the spectrometer imaging system under the irradiation of incident light.

2. Collimating element: make the light from the slit become parallel light. The collimating element can be an independent lens, a reflector, or a concave grating directly integrated on the dispersion element, such as the concave grating in the concave grating spectrometer.

3. Dispersion element: grating is usually used to disperse the optical signal into multiple beams according to the wavelength in space.

4. Focusing element: focus the dispersive light beam to form a series of images of incident slits on the focal plane, where each image point corresponds to a specific wavelength.

5. Detector array: placed on the focal plane, used to measure the light intensity of each wavelength image point. The detector array can be CCD array or other types Photodetector Array.

classification

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There are many kinds of spectrometers and classification methods. According to the principle of spectral decomposition adopted by spectrometers, they can be divided into two categories: classical spectrometers and new spectrometers. The classical spectrometer is an instrument based on the principle of spatial dispersion (light splitting); The new spectrometer is an instrument based on the modulation principle, so it is also called modulation spectrometer.^[1]

The classic spectrometer can be divided into prism spectrometer, diffraction grating spectrometer^[2] Interference spectrometer.

According to the spectrum range that the spectrometer can work normally, the spectrometer can be divided into:

classification

application

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Spectrometers are widely used in agriculture, astronomy, automobile, biology, chemistry, coating, colorimetry, environmental detection, film industry, food, printing, paper making, Raman spectroscopy, semiconductor industry, composition detection, color mixing and matching, biomedical applications, fluorescence measurement, gem composition detection, oxygen concentration sensor, vacuum chamber coating process monitoring Film thickness measurement, LED measurement, emission spectrum measurement, UV/visible absorption spectrum measurement, color measurement and other fields are widely used.^[3]

Transmission measurement

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The transmittance or its efficiency of the spectrometer can be measured with an auxiliary monochromator device. There is no difficulty in achieving these measurements in visible and near ultraviolet. The transmittance of the second monochromator is determined by measuring the luminous flux passing through the first monochromator, followed by the luminous flux passing through the two monochromators.

Absolute measurement requires knowing the absolute transmittance of the monochromator: for relative measurement, the transmittance can be measured in relative units at various wavelengths. These measurements of VUV have considerable experimental difficulties, so auxiliary monochromators are usually used. Measured separately at various incident angles diffraction The efficiency of the grating. The difficulties in calibration have been successfully avoided in many experimental steps.

The relationship between grating efficiency and wavelength, incident angle, coating thickness, coating material and other factors has been studied. All these measurements indicate that in many cases the energy loss is very significant, and the efficiency of the grating is less than 1%, and different parts of the grating may have significantly different efficiencies.

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