Any complex vibration can be decomposed into the sum of many simple harmonic vibrations with different amplitudes and frequencies. In order to analyze the nature of actual vibration, the image in which the amplitude of vibration is arranged according to its frequency is called the frequency spectrum of this complex vibration. In the vibration spectrum, the abscissa represents the circumferential frequency of local vibration, and the ordinate represents the amplitude of local vibration.
For aperiodic vibration (such as damping vibration or short shock), it can be decomposed into the sum of infinite simple harmonic vibration with continuous frequency distribution according to Fourier integral.
Because the spectral lines become infinite, the vibration spectrum is no longer a discrete linear spectrum, and the dense spectral lines make the top of it form a continuous curve, the so-called continuous spectrum, which is the envelope of various spectral lines; It can also be decomposed into many simple harmonic vibrations with incommensurable frequencies, forming a discrete frequency spectrum.
Extended data
The emission spectrum can be divided into three different categories: linear spectrum, band spectrum and continuous spectrum.
Linear spectrum is mainly produced by atoms and consists of some discontinuous bright lines; Band spectrum is mainly composed of molecules composed of some dense light in a certain wavelength range; Continuous spectrum is mainly produced by electromagnetic radiation excited by hot solid, liquid or high-pressure gas, and consists of light with all wavelengths continuously distributed.
Sunlight spectrum is a typical absorption spectrum. Because the strong light from the sun passes through the lower temperature solar atmosphere, various atoms in the solar atmosphere will absorb some wavelengths of light, resulting in dark lines in the generated spectrum.
When white light passes through a gas, the gas will absorb the light with the same wavelength as its characteristic spectral line from the white light passing through it, so that dark lines appear in the continuous spectrum formed by white light. At this time, the spectrum produced by the absorption of certain wavelengths of light by substances in the continuous spectrum is called absorption spectrum. Usually, there are fewer characteristic lines in absorption spectrum than in linear spectrum.
When light strikes a substance, inelastic scattering occurs. In the scattered light, there are elastic components (Rayleigh scattering) with the same wavelength as the excitation light, and components longer and shorter than the excitation light wave. The latter phenomenon is collectively called Raman effect.
This phenomenon was discovered by Indian scientist Raman in 1928, so the scattering of light with new wavelength is called Raman scattering, and the generated spectrum is called Raman spectrum or Raman scattering spectrum.