Method for observing lightning spectrum

Abstract

The embodiment of the invention provides a method for observing a lightning spectrum, and relates to the field of lightning observation equipment. The method comprises the following steps of: plating a thin film of which the thickness is changed according to a certain geometric shape rule on a lens of the high-speed camera; by utilizing the thin film, transmission light of light waves passing through the thin film and transmission light reflected by the upper and lower surfaces of the thin film can form an anti-reflection effect due to interference; light waves emitted by thunder and lightning are polychromatic light, light with different wavelengths needs to respectively correspond to different coating thicknesses to achieve the anti-reflection effect, and thunder and lightning spectrums which are distributed according to a certain rule and arranged according to different wavelengths can be obtained by coating a thin film with the thickness changing according to a certain rule on a lens of a high-speed camera or a camera. The frame speed of the applied high-speed camera can reach hundreds of thousands to millions of frames per second, and compared with other spectrograph equipment, the time resolution is higher.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of lightning monitoring equipment, and in particular to a method for observing a lightning spectrum. Background Art

[0002] Lightning is a long-distance instantaneous discharge phenomenon that occurs in thunderstorms. The physical effects such as high temperature, light radiation, electromagnetic radiation, and shock waves generated during the discharge process can cause great harm to ground buildings, aviation and aerospace, and people's production and life. Lightning spectrum research is the basis for in-depth understanding of the discharge process of lightning channels and the mechanism of lightning disasters. Therefore, it is particularly important to further study lightning by observing the spectrum of lightning.

[0003] Spectral observation can record the emission spectrum of the lightning channel. By studying the optical image information of lightning, the speed of lightning development, duration, channel morphology and structure, brightness change and other characteristics can be measured. Based on spectral data, physical information inside the channel can be obtained, which is an effective method to study the physical characteristics inside the lightning discharge channel. In addition, with the deepening of research, the study of lightning discharge process has become more and more refined, which requires the use of observation equipment and instruments with high time resolution.

[0004] At present, the spectrum of lightning is usually obtained by splitting light using optical devices such as prisms and gratings. However, the prism has different refractive indices for light of different wavelengths, which will cause chromatic aberration. In some cases, it will also produce astigmatism. The light is reflected on the surface of the prism, and a certain proportion of the light energy is reflected back each time it is reflected. It cannot pass through the prism, and the reflection loss is relatively large. Similar to the prism, the grating surface will also have reflection losses. The center position of the spectrum of obliquely incident light will shift after passing through the grating. The frame rates of existing grating spectrographs and industrial application spectrographs are also relatively low, usually at several hundred frames per second, and the best ones are only thousands of frames per second. Therefore, it is very necessary to design a method that can observe lightning spectra with finer time resolution, simpler, and more effective. Summary of the invention

[0005] To this end, an embodiment of the present invention provides a method for observing lightning spectra, which uses a high-speed camera to obtain lightning optical images with high time resolution, so as to solve the problems of insufficient time resolution, easy deviation and large reflection loss in existing instruments and technologies.

[0006] In order to achieve the above purpose, the embodiment of the present invention provides the following technical solutions:

[0007] According to the first aspect of the embodiments of the present invention, a method for observing lightning spectrum is provided, comprising: coating a thin film of a specific thickness that changes according to a certain geometric shape law on a high-speed camera lens, utilizing thin film interference, the light directly transmitted by the light wave and the transmitted light after being reflected once by the upper and lower interfaces of the thin film, the two beams of light will achieve an anti-reflection effect due to mutual interference enhancement; the complex light emitted by lightning has various wavelengths of light, and different wavelengths of light need to correspond to different thicknesses of anti-reflection films to achieve an anti-reflection effect. When the complex light passes through a dielectric thin film whose thickness changes according to a certain geometric shape law, the light of different wavelengths will undergo an anti-reflection phenomenon due to the different thicknesses of the thin film, and a continuous colored light band arranged according to a certain law will be projected.

[0008] A high-speed camera is used to quickly capture the spectrum of transmitted light generated after lightning passes through the film and camera lens.

[0009] Furthermore, the film is an anti-reflection film, which can reduce or eliminate reflected light from the optical surface, thereby increasing the transmittance of light of a specific wavelength and reducing or eliminating stray light in the system.

[0010] Furthermore, the antireflection film material may be MgF 2 、SiO 2 、Al 2 O 3 , SiO and other materials, whose refractive index is smaller than that of the camera lens.

[0011] Furthermore, the antireflection film can be a circular film that is thin in the middle and thick at the periphery (or thick in the middle and thin at the periphery), the center of the circular film coincides with the center of the circular lens, the radius of the film is equal to the radius of the lens, and the thickness of the film increases or decreases uniformly along the radius of the circular film, that is, the thickness of the film increases or decreases uniformly along the radial direction. When complex light is incident on a film of different thicknesses, and the optical path difference is only related to the film thickness, light with a wavelength that is the same, close, or multiple of the optical path difference will be enhanced, and light of other wavelengths will be weakened.

[0012] Further, the center thickness and edge thickness of the anti-reflection film correspond to the minimum anti-reflection film thickness for red light or purple light, respectively.

[0013] Furthermore, the frame rate of the high-speed camera can reach hundreds of thousands to millions of frames per second.

[0014] The embodiments of the present invention have the following advantages:

[0015] In the embodiment of the present invention, a thin film that is thin in the middle and thick at the periphery (or thick in the middle and thin at the periphery) or a film whose thickness varies according to other rules is plated on the lens surface of a high-speed camera. When lightning light passes through films of different thicknesses, light with a wavelength that is the same as, similar to, or a multiple of the optical path difference will be enhanced, while light of other wavelengths will become weak. The light is then quickly photographed by a high-speed camera, thereby enabling a spectral image of lightning with high time resolution to be obtained simply and quickly. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0017] The structures, proportions, sizes, etc. illustrated in this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with the technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantial technical significance. Any structural modification, change in proportion or adjustment of size shall still fall within the scope of the technical contents disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0018] Figure 1 A schematic diagram of an antireflection film in which the thickness of the film changes according to a certain rule provided by an embodiment of the present invention;

[0019] Figure 2 A diagram of a coating method for observing lightning spectrum when the thickness of a thin film varies according to a radial rule provided by an embodiment of the present invention;

[0020] Figure 3 A distribution diagram of different wavelength regions of visible light in the lens field of view when the thickness of a film provided by an embodiment of the present invention changes according to a radial rule;

[0021] Figure 4 A spectrum distribution diagram of a lightning channel in a lens field of view when the film thickness varies according to a radial rule provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The following is a description of the implementation of the present invention by specific embodiments. People familiar with the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] The technical solution disclosed in the present invention is to coat a thin film whose thickness changes according to a certain rule on the lens of a high-speed camera, and utilize the thin film interference principle to enhance the mutual interference of the light transmitted through the thin film and the transmitted light reflected once by the upper interface and the lower interface of the thin film to achieve the anti-reflection effect; and utilize a high-speed camera to quickly shoot, so as to obtain the spectrum of the transmitted light generated after the lightning light passes through the thin film and the lens.

[0024] It should be noted that the principle of anti-reflection film is as follows Figure 1 As shown in the figure, when light is emitted from air (optically sparse medium) to film (optically dense medium), part of it will be directly transmitted to the lens of the camera lens, which is recorded as beam 1; another part of the light will be reflected on the lower surface of the lens and the film, and then reach the upper surface of the film and pass through the film after reflection, and reach the lens of the camera lens, which is recorded as beam 2. When beam 2 is reflected on the lower surface of the film, half-wave loss will be generated because the refractive index of the lens is greater than the refractive index of the film. Then the above beams 1 and 2 will interfere with each other, and the interference enhancement formula is expressed as:

[0025]

[0026] Where λ is the wavelength, n 1 is the refractive index of the coated film, e is the film thickness, and k is an integer corresponding to different orders.

[0027] For vertical incidence, it can be seen from the above formula that when the thickness of the film coated on the lens surface is constant, that is, the minimum thickness of the film is:

[0028]

[0029] At this time, the interference of transmitted light is enhanced, and the light with the same, similar or multiple wavelength as the optical path difference will be enhanced, while the light of other wavelengths will become weaker. In addition, when the interference of transmitted light is enhanced, the interference of reflected light will cancel each other out, thereby reducing the intensity of reflected light, increasing the proportion of transmitted light, and improving the light transmittance of optical instruments.

[0030] When light waves are incident at an angle, the optical path will change. 1 Correct the thickness. Generally, the effective optical thickness d is used. eff , effective optical thickness d eff Equivalent thickness to normal incidence min The relationship is roughly:

[0031] d eff =e min cosθ 2

[0032] where θ 2is the refraction angle of light after entering the anti-reflection film, which can be calculated by Snell's law. Snell's law is:

[0033] n 1 sinθ 1 =n 2 sinθ 2

[0034] Example

[0035] The embodiment of the present invention provides a method for observing lightning spectrum, referring to Figure 2 The device comprises a plated film 1, a high-speed camera lens 2, and a lightning light 3. The film 1 is plated on the lens 2 of the high-speed camera.

[0036] Specifically, when lightning light is incident on the surface of a thin film that is thin in the middle and thick around the edges (or thick in the middle and thin around the edges) at a certain angle, the optical path difference is only related to the thickness of the film. Light with a wavelength that is the same, similar, or a multiple of the optical path difference will be enhanced, and light of other wavelengths will become weaker. The enhanced light can be quickly photographed by a high-speed camera, thereby obtaining a lightning spectrum with high time resolution.

[0037] If the thickness of the center and edge of the plated circular film is set to correspond to the wavelength of red and violet light of visible light, the distribution of the area where light of different wavelengths appears in the field of view is as follows: Figure 3 As shown in the figure, the superposition of the lightning channel and these areas is the distribution of the spectrum of the lightning channel. Figure 4 shown.

[0038] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A method for observing lightning spectrum, characterized in that: include: A thin film with thickness varying according to a certain geometric shape is coated on the lens of a high-speed camera; Using the thin film interference principle, when the thickness of the film is a certain value, the transmitted light of the light wave and the light reflected and transmitted by the upper and lower interfaces of the film will form an anti-reflection effect due to mutual interference; In the complex light waves emitted by lightning, different wavelengths of light need to have different corresponding coating thicknesses to achieve the effect of enhancing transmittance. By coating a thin film whose thickness varies according to a certain pattern on the lens of a high-speed camera or camera, a lightning spectrum with wavelengths distributed according to a certain pattern can be obtained. A high-speed camera is used to quickly capture the spectrum of transmitted light generated after lightning waves pass through the film and lens.

2. A method for observing lightning spectrum according to claim 1, characterized in that: The film is an anti-reflection film, which can reduce or eliminate the reflected light on the optical surface, thereby increasing the light transmittance and reducing or eliminating the stray light of the system.

3. A method for observing lightning spectrum according to claim 1, characterized in that: The anti-reflection film is a circular film that is thick in the middle and thin at the edges (or thin in the middle and thick at the edges) or whose thickness varies according to other rules. When parallel light is incident on the film whose thickness varies according to a certain rule, the optical path difference is only related to the thickness of the film. Light with a wavelength that is the same as, close to, or in a multiple relationship with the optical path difference will be enhanced, and light of other wavelengths will be weakened.

4. A method for observing lightning spectrum according to claim 1, characterized in that: The anti-reflection film material can be a material having a refractive index smaller than that of the camera lens, such as MgF2, SiO2, Al2O3, SiO, etc.

5. A method for observing lightning spectrum according to claim 1, characterized in that: The frame rate of the high-speed camera is as high as hundreds of thousands of frames per second.

6. A method for observing lightning spectrum according to claim 1, characterized in that: The center thickness and edge thickness of the antireflection film correspond to the minimum antireflection film thickness for red light and violet light (or violet light and red light), respectively, and the thickness increases (or decreases) linearly from the center to the edge in a radial direction.

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