Continuous spectrum refers tolight（radiation）strengthalong withfrequencyContinuously distributedspectrum。according toQuantum Theory，atom、moleculeCan be in a series of discrete states.InterstatetransitionproduceSpectral line。Each spectral line system tends to a short wave limit,wavelengthShorter than this limit, a continuous region of the spectrum appears (seeAtomic spectrum）。This limit is called linear limit.From the limit position of the line system, the intensity of the continuous region decreases rapidly. This continuous region is a continuous spectrum.[1]
Chinese name
Continuous spectrum
Foreign name
continuous spectrum
Features
The light intensity is continuously distributed with the change of frequency
As shown in the figure Continuous SpectrumAtomic hydrogen spectroscopyBalmer systemThe continuous spectral region from HsevenThe seventh line of the Balmer system（n=7) Start, H∞Indicates the theoretical position of the line system limit.[1]
By incandescentsolid、liquidOr high pressure gaslightCan form continuous spectrum.
Liquid or solid substances at high temperatureinspireThe continuous spectrum will be generated by the light of various wavelengths emitted by the.
stayvisible lightThe area is red, orange, yellow, green, green, blue and purplespectrumIt is also a continuous spectrum.
Detection application
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In recent years, the application of continuous spectrum analysis technology in the scientific and technological field of water quality monitoring instruments has been increasingly developed. Based on the principle of continuous spectrum analysis, it can not only detect multiple water quality parameters (i.e. the measured substance in the water sample), but also carry important information about the measured substance, and can carry out signal processing in a wide spectral range,In order to effectively eliminate the error of the detection instrument system, reduce the background spectral interference (such as turbidity) and noise interference, so as to greatly improve the accuracy of online water quality detection[3]。
Classic explanation
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The continuous spectrum produced by hot solid and liquid as well as high temperature and high pressure gas cannot be simply understood by the Bohr atomic energy level transition theory.Different from the ionization of thin gases, the distribution of electrons outside the nucleus of hot solids and liquids and high-temperature and high-pressure gases is more complex, and the atomic distribution is more dense. Due to the interaction between atoms, the atomic orbital energy will change slightly, and the Bohr theory is no longer applicable.It can be explained from the classical theory that the electrons around the atom are ionized, and when the high-speed electrons collide with the ions, they will produce a large negative acceleration, which will produce a rapidly changing electromagnetic field around them, that is, electromagnetic radiation.Because the collision process and conditions as well as the energy change of each collision are random, the electromagnetic radiation with different wavelengths and continuous spectrum is generated[4]。
Quantum interpretation
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The generation of continuous spectrum can also be explained from the quantum theory, which believes that the electrons outside the nucleus move on the atomic orbit and are at different discrete energy levels.When N atoms are close to each other, due to the interaction between atoms, the atomic orbital energy will change slightly, resulting in the overlap of atomic orbits and energy level splitting.The original energy levels of N atoms with the same energy will be split into N energy levels with slightly different energy levels.Due to the large number of atoms (N=10nineteen～ 10twenty-one/mmthree）Therefore, the difference between the N split energy levels is so small that it can be regarded as a continuous distribution, that is, an energy band with a certain width is formed.
With any two energy bands EmAnd En(Em> En）And its energy band width is Δ Em= Emt- Emb(t represents the top of the energy band; b represents the bottom of the energy band.The same below);ΔEn= Ent- Enb, and the spectral selection law is satisfied between the two energy bands, then when a radiative transition occurs between the two energy bands, the radiation spectral lines will be widened into spectral bands, and the partial overlap of adjacent spectral bands will form a continuous spectrum.Due to the strong attraction of the inner orbital electrons of the atomic nucleus and the shielding effect of the outer orbital electrons, the inner electrons almost do not participate in the transition of the outer electrons. Therefore, this phenomenon of broadening the corresponding spectral lines due to the energy band structure mainly corresponds to the transition of the outer orbital electrons of the atom, so its spectrum is mainly distributed in the infrared, visible and ultraviolet regions,Its short wave part overlaps with soft X-ray.
Supercontinuum laser
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Supercontinuum spectrum laser can be described by "incandescent lamp spectral width, laser brightness".The discovery of supercontinuum spectrum laser was discovered in an accidental experiment. The initial purpose of laser irradiation of crystals such as calcite was to determine the lifetime of phonons in crystals, but the generation of white laser was observed.The input green laser pulse interacts with the medium in some way, resulting in a sharp broadening of the frequency range of the laser.Later, liquid medium and gas medium were also used in supercontinuum laser technology, which extended the spectrum of supercontinuum laser to the infrared band.
There are two main views on the causes of supercontinuum laser in fiber, one is thatSelf phase modulationThe effect is the main reason for the generation of supercontinuum laser, and the other is that the supercontinuum laser is self phase modulation, four wave mixing andCross phase modulationHowever, there is no systematic theoretical research report on these two statements.
Supercontinuum laser generated in fiber has been widely used.Among them, the most important and mature ones are ultra precision frequency measurement and precision clock.
Atomic energy level
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There is indeed a discontinuous distribution of steady state energy levels in the atom, and the energy level spacing decreases with the increase of the quantum number n. The transition of electrons between the energy levels produces a linear spectrum.n=
The line system limit corresponds to a line system, and within the system limit is the quantized energy level corresponding to the linear spectrum;n》 1, the linear spectrum gradually transits to the continuous spectrum;If the linear limit is exceeded, the non quantized positive energy range corresponds to the continuous spectrum[5]。
