Introduction to spectroscopy

Spectroscopy is an important interdisciplinary subject, which mainly involves physics and chemistry. The interaction between electromagnetic waves and substances is studied through spectroscopy. Light is a kind of electromagnetic radiation composed of electromagnetic waves with various wavelengths (or frequencies). Spectrum is a graph that analyzes a certain property of a beam of electromagnetic radiation into the contribution of each component wavelength of radiation to this property by means of grating, prism and Fourier transform. For example, the absorption spectrum can list the absorption degree of a substance at a certain wavelength in order from low to high wavelength. With the development of science and technology, the electromagnetic wave band involved in spectroscopy is getting wider and wider, from gamma rays with picometer wavelength to X rays, ultraviolet rays, visible light regions, infrared rays, microwaves and radio waves with several kilometers wavelength, all of which have their characteristic forms of interaction with matter. According to the form of interaction between light and matter, spectra can generally be divided into absorption spectra, emission spectra, scattering spectra and so on. Through spectral research, people can analyze the microscopic and macroscopic properties of atoms and molecules, the reaction rate of specific chemical processes, the concentration distribution of a substance in a specific region in space and so on. People can also use the specific composition structure of substances to generate spectra with special optical properties, such as lasers with specific frequencies. Spectroscopy is not only a basic science, but also an important qualitative and quantitative measurement method in daily application, such as analyzing the content of various substances in water, preventing and monitoring diseases by analyzing the content of protein in blood, and using the best wave band for optical fiber communication. Since the discovery of laser in the middle of last century, the control of light has reached a new stage, which can produce electromagnetic radiation with unprecedented brightness, frequency distribution and time resolution, opening the door to nonlinear optics and nonlinear spectroscopy, and making spectroscopy in a brand-new period of rapid development.