Overview of the development of the hottest near in

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Overview of the development of near-infrared spectrometer

in the past 50 years, the near-infrared spectrometer has experienced the following development stages:

the spectroscopic system of the first near-infrared spectrometer (in the late 1950s) is the filter spectroscopic system. The measuring samples must be pre dried to make their moisture content less than 15%, and then the samples are ground to make their particle size less than 1 mm, and loaded into the sample pool. This kind of instrument can only be measured at a single or a few wavelengths (discontinuous wavelengths), which has poor flexibility, wavelength stability and reproducibility. If the matrix of the sample changes, it will often cause large measurement errors! "Filter" is called the first generation of spectroscopic technology

from the mid-1970s to 1980s, the grating scanning spectroscopic system began to be applied, but there are the following shortcomings: slow scanning speed, poor wavelength reproducibility, and many internal moving parts. The biggest weakness of this kind of instrument is that the mechanical shaft of grating or reflector is easy to wear after long-term continuous use, which affects the accuracy and reproducibility of wavelength, and is not suitable for use as a process analysis instrument. "Grating" is called the second generation spectroscopic technology

from the late 1980s to the early 1990s, the "Fourier transform" spectroscopic system was applied, but due to the existence of moving mirror in the interferometer, the reliability of the instrument was limited, especially the strict requirements for the use and placement environment of the instrument, such as room temperature, humidity, stray light, vibration, etc. "Fourier transform" Uranus (a pseudonym), the head of transportation and marketing of a large coal enterprise in Shanxi, has a sad face and is known as the third generation spectroscopic technology

in the mid-1990s, there began to be a near-infrared spectrometer using diode array technology. This near-infrared spectrometer adopts a fixed grating scanning mode. The wavelength range and resolution of the instrument are limited, and the wavelength usually does not exceed 1750nm. Because this band mainly detects the third and fourth order frequency doubling of the sample, the molar absorption coefficient of the sample is low and easy to handle, so the optical path is often long. "Diode array" is called the fourth generation spectroscopic technology

at the end of the 1990s, the advent of "acoustooptic tunable filter" (abbreviated as AOTF) technology from aerospace technology is considered to be "the most prominent development of near-infrared spectroscopy in the 1990s". AOTF is an optoelectronic device that uses ultrasound to interact with specific crystals to produce light splitting. Compared with the usual monochromator that also makes the sample slip in the experimental process, AOTF adopts acoustooptic modulation, that is, to realize spectral scanning through the change of ultrasonic RF, The optical system has no mobile parts, fast wavelength switching and good reproducibility. The programmed wavelength control makes the application of this instrument more flexible, especially the external dust prevention and the built-in temperature and humidity integrated control device, which greatly improves the environmental adaptability of the instrument. In addition, the all solid-state integrated design produces excellent shock absorption performance, which makes it more and more widely used in industry and field (outdoor) analysis in recent years. (end)

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