A gas refractive index measurement device based on quasi-holographic fringes

Abstract

The present application discloses a gas refractive index measuring device based on quasi-holographic fringes, which relates to the field of optical measurement. The device comprises: a light source module for emitting a light source; an optical path module, arranged on the outgoing light path of the light source module, for uniformly processing the light source to obtain parallel light; a quasi-holographic fringe module, arranged on the outgoing light path of the optical path module, for scattering or modulating the parallel light to obtain quasi-holographic fringes; an air cavity, arranged on the outgoing light path of the quasi-holographic fringe module, for placing a gas to be measured; an optical processing module, for optically processing the quasi-holographic fringes after passing through the gas to be measured; and a calculation module, arranged on the outgoing light path of the optical processing module, for calculating the refractive index of the quasi-holographic fringes after the optical processing to obtain the refractive index of the gas to be measured. The present application can improve the globality of the measurement area, improve the anti-disturbance capability of the gas refractive index measurement, improve the measurement accuracy, and reduce the equipment cost.

Description

Technical Field

[0001] The present application relates to the field of optical measurement, and in particular to a gas refractive index measurement device based on holographic-like fringes. Background Art

[0002] Dynamic gas refractive index monitoring technology demonstrates significant potential in numerous fields, including combustion process analysis, environmental quality monitoring, and industrial production control. For example, it plays a key role in detecting hazardous gas concentrations and optimizing combustion efficiency. However, in some cases, gas refractive index monitoring methods struggle to simultaneously meet both real-time and global requirements for complex application scenarios.

[0003] Specifically, there are the following limitations: (1) Gas refractive index measurement is mostly based on in-situ single-point fiber optic sensors. Although this type of sensor has the advantages of small size, strong anti-interference ability, and suitability for dynamic detection, it is difficult to achieve comprehensive perception and measurement of the refractive index of a large-scale gas field; (2) To overcome the limitations of single-point detection, existing solutions mostly use complex laser interferometers or thermal imagers and other equipment. These methods have shortcomings in spatial distribution, response speed, and interference light source separation, and the equipment cost is high, which limits their practical application in complex dynamic environments; (3) Holographic and quasi-holographic technologies achieve high-resolution, full-light field information acquisition by capturing light field information. Its interference fringes contain rich optical information and can simultaneously record the phase / wavefront and amplitude information of the target object. However, traditional holographic methods have the following problems: the fringes are highly correlated with the wavelength of the measurement light, making it difficult to apply to the measurement of macroscopic and large-scale targets; they rely on complex optical path systems and require beam splitters, reference optical paths, and high-stability environments, resulting in high costs, complex operations, and difficulty in achieving real-time measurement, making them difficult to adapt to complex and changing application environments. Summary of the Invention

[0004] The purpose of this application is to provide a gas refractive index measurement device based on holographic-like fringes, which can improve the globality and measurement accuracy of the measurement area, improve the anti-disturbance ability of the gas refractive index measurement, and reduce the equipment cost.

[0005] To achieve the above objectives, this application provides the following solutions.

[0006] The present application provides a gas refractive index measuring device based on quasi-holographic fringes, comprising: a light source module for emitting a light source; an optical path module, arranged on the outgoing light path of the light source module, for uniformly processing the light source to obtain parallel light; the optical path module is arranged in a Kohler illumination manner; a quasi-holographic fringe module, arranged on the outgoing light path of the optical path module, for scattering or modulating the parallel light to obtain quasi-holographic fringes; the quasi-holographic fringes are periodic fringes; the periodic fringes have a certain shape; an air cavity, arranged on the outgoing light path of the quasi-holographic fringe module, for placing a gas to be measured; an optical processing module, for optically processing the quasi-holographic fringes after passing through the gas to be measured; and a calculation module, arranged on the outgoing light path of the optical processing module, for calculating the refractive index of the quasi-holographic fringes after the optical processing to obtain the refractive index of the gas to be measured.

[0007] Optionally, the light source module is a monochromatic light source emitter or a laser.

[0008] Optionally, when the light source module is a monochromatic light source emitter, the optical path module includes: a first lens, arranged on the output light path of the light source module, for parallel processing of the light source; and a collimator, arranged on the transmission light path of the first lens, for expanding the size of the light after parallel processing to obtain parallel light.

[0009] Optionally, when the light source module is a monochromatic light source emitter, the optical path module is a condenser.

[0010] Optionally, when the light source module is a laser, the optical path module includes: a beam expander, which is arranged on the outgoing light path of the light source module and is used to expand the light beam size of the light source to obtain parallel light.

[0011] Optionally, the holographic fringe module is a grid.

[0012] Optionally, the quasi-holographic fringe module is frosted glass.

[0013] Optionally, the optical processing module includes: a conjugate mirror group, arranged on the output light path of the air cavity, for performing a beam reduction process on the holographic-like fringes after passing through the gas to be measured; the conjugate mirror group includes: a second lens, arranged on the output light path of the air cavity, for performing a beam reduction process on the fringes after passing through the gas to be measured; a third lens, arranged on the transmission light path of the second lens, for performing a divergent process on the concentrated fringes; and a filter group, arranged on the output light path of the conjugate mirror group, for performing a light filtering process on the holographic-like fringes after the beam reduction process.

[0014] Optionally, the optical processing module includes: a filter group, arranged on the output light path of the air cavity, for filtering the stripes after passing through the gas to be measured; a fourth lens, arranged on the output light path of the filter group, for focusing the filtered stripes.

[0015] Optionally, the calculation module includes: a high-speed imaging chip, arranged on the output light path of the optical processing module, for collecting the holographic-like fringes after optical processing; a computer, connected to the high-speed imaging chip, for calculating the refractive index of the holographic-like fringes after optical processing to obtain the refractive index of the gas to be measured.

[0016] According to the specific embodiments provided in this application, this application has the following technical effects.

[0017] 1. Compared with the in-situ single-point fiber optic sensor, this application can directly measure the gas refractive index of the gas to be measured in the entire surface of the entire air cavity. During the gas refractive index calculation process, the refractive index of the gas to be measured is finally calculated by the calculation module, which improves the globality of the measurement area.

[0018] 2. Compared with the holographic measurement method that relies on the interference method of reference light and object light, the present application only needs to use a light source module to emit a light source, and then transmit it through the air cavity through the optical path module and the quasi-holographic fringe module to generate quasi-holographic fringes. The optical path structure is simple, which improves the anti-disturbance ability of the gas refractive index measurement. At the same time, since holographic measurement generates holographic fringes by the interference of reference light and object light, and optical elements need to be separately set to ensure the anti-interference of the interference between reference light and object light, the present application does not need to set multiple optical elements to generate quasi-holographic fringes with strong anti-interference. Therefore, the optical elements for generating quasi-holographic fringes in the present application are reduced by 80% compared with the optical elements for generating holographic fringes, thereby reducing the equipment cost.

[0019] 3. This application uses optical processing to collect all the holographic-like fringes that pass through the gas to be measured. At the same time, the optical processing can filter out the stray light in the holographic-like fringes of the gas to be measured, making the data of the holographic-like fringes for calculating the refractive index more accurate, thereby improving the measurement accuracy of the gas refractive index. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0021] Figure 1A schematic structural diagram of a gas refractive index measurement device based on holographic-like fringes provided in one embodiment of the present application.

[0022] Figure 2 A schematic structural diagram of a second gas refractive index measurement device based on quasi-holographic fringes provided in an embodiment of the present application.

[0023] Figure 3 A schematic structural diagram of a third gas refractive index measurement device based on quasi-holographic fringes provided in an embodiment of the present application.

[0024] Figure 4 A schematic structural diagram of a fourth gas refractive index measurement device based on quasi-holographic fringes provided in an embodiment of the present application.

[0025] Figure numerals: monochromatic light source emitter-1; first lens-2; beam expander-3; grid-4; air cavity-5; second lens-6; third lens-7; filter imaging module-8; laser-9; frosted glass-10; filter group-11; fourth lens-12; high-speed imaging chip-13; condenser-14. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0027] The principle of the gas refractive index measurement device described in this application is that when light passes through a gas, the change in refractive index causes an optical path difference, which in turn causes fringes to shift or deform. By measuring the change in optical path difference caused by the gas being measured, the refractive index of the gas can be inferred. Since changes in the temperature, concentration, and pressure of the gas being measured all cause changes in the gas's refractive index, inferring changes in the gas's refractive index can provide a basis for inferring changes in the gas's temperature, concentration, and pressure.

[0028] This application innovatively proposes a quasi-holographic fringe technique that generates holographic fringes using a monochromatic light source (or laser) combined with a grid or frosted glass. This technique leverages the phase modulation of the fringe patterns by variations in the gas refractive index, combined with an image analysis algorithm to directly invert the refractive index. Compared to traditional holographic techniques, this technique offers a simpler optical path and greater resistance to interference, significantly improving measurement efficiency.

[0029] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0030] In an exemplary embodiment, a gas refractive index measurement device based on quasi-holographic fringes is provided. The device includes a light source module, an optical path module, a quasi-holographic fringes module, an air cavity 5, an optical processing module, and a calculation module. Each module is described in detail below.

[0031] (1) Light source module.

[0032] The light source module is used to emit light. Figure 1 As shown, the light source module is a monochromatic light source emitter 1. A typical 635nm monochromatic light source emitter 1 (such as an LED) is selected. The monochromatic light source is not limited to 635nm, and the corresponding detection window can be selected according to the actual use environment.

[0033] In the second embodiment, as Figure 2 As shown, the light source module is a laser 9. The laser 9 uses a typical wavelength =635nm He-Ne laser with an output power of 5mW.

[0034] (2) Optical path module.

[0035] The optical path module is arranged on the outgoing light path of the light source module and is used to uniformly process the light source to obtain parallel light; the optical path module is arranged using the Kohler illumination method.

[0036] When the light source module is a monochromatic light source emitter 1, as Figure 1 and Figure 3 As shown, the optical path module includes: a first lens 2, which is arranged on the outgoing light path of the light source module and is used to parallelize the light source; a beam expander 3, which is arranged on the transmitted light path of the first lens 2 and is used to expand the size of the parallelized light to obtain parallel light.

[0037] Specifically, Köhler illumination is used to uniformly illuminate the system, and beam expansion is used to amplify the light beam, ensuring uniform illumination of the gas under test. The light beam passes through a fixed-magnification beam expander 3, transforming it into parallel light and illuminating the grid 4. The first lens 2 is optimized for illumination uniformity during the experiment, with a focal length of 20-100mm being the preferred focal length, fine-tuned based on the experimental lighting conditions. A fixed-magnification beam expander 3 is used to expand the light beam into parallel light.

[0038] When the light source module is a monochromatic light source emitter 1, as Figure 4 As shown, the optical path module can also be a condenser 14, which improves the collection and uniformity of light, increases lighting efficiency, ensures uniform lighting, eliminates the influence of the light source structure on imaging, and enhances the stability of the system.

[0039] In the second embodiment, when the light source module is a laser 9, such as Figure 2As shown, the optical path module includes a beam expander 3, which is arranged on the outgoing optical path of the light source module and is used to expand the light beam size of the light source to obtain parallel light. The beam expander 3 expands the laser beam to a parallel light of 20mm.

[0040] (3) Quasi-holographic stripe module.

[0041] The quasi-holographic fringe module is placed on the outgoing light path of the optical module and is used to scatter or modulate parallel light to produce quasi-holographic fringes. Quasi-holographic fringes are periodic fringes with specific shapes, such as alternating light and dark stripes, triangular stripes, heart-shaped stripes, and circular stripes.

[0042] like Figure 1-Figure 4 As shown, the quasi-holographic stripe module can be a grid 4 or frosted glass 10 .

[0043] When the quasi-holographic stripe module is a grid 4, parallel light passing through the grid 4 of equal width can form uniform light and dark stripes, i.e., quasi-holographic stripes. The grid 4 can reduce the loss of light due to scattering, improve the utilization rate of light, and achieve the penetrability of the quasi-holographic stripes to stronger gases or dust. At the same time, the parallel light should be kept perpendicular to the grid 4 as much as possible, so as to ensure that the stripe spacing and the periodicity of the grid 4 itself are the same. Assuming that the period of the grid 4 is , the incident angle is , the fringe period after transmission is , from a geometric point of view, the projection of the incident light on the surface of the grid 4 will become longer, resulting in a change in the stripe spacing p, satisfying the following relationship.

[0044] .

[0045] This means that when light is incident vertically, the period of the stripes and the grid 4 are basically the same. If you want to artificially control the stripe spacing, you can adjust the incident angle appropriately. .

[0046] Specifically, when using a monochromatic light source emitter 1 as the light source, grid 4 will select a width of five laser wavelengths to form a quasi-holographic fringe pattern, ensuring primary zero-order transmission to prevent diffraction. The quasi-holographic fringe pattern generated by grid 4 has enhanced gas or dust penetration. The light then passes through the gas under test, carrying information about refractive index changes. The gas under test should be kept as close to grid 4 as possible to ensure that the quasi-holographic fringe information is clearly projected onto the high-speed imaging chip 13.

[0047] When the quasi-holographic fringe module is frosted glass 10, parallel light hits the frosted glass 10 with light and dark stripes, and forms light and dark stripes after scattering, i.e., quasi-holographic stripes, which reduces 80% of optical components compared to the holographic light path.

[0048] (4) Air cavity 5.

[0049] Air cavity 5 is positioned in the outgoing optical path of the quasi-holographic fringe module and is used to hold the gas to be measured. Cavity 5 is constructed of transparent quartz. When the quasi-holographic fringe module is a grid 4, cavity 5 is 10 cm long; when the quasi-holographic fringe module is frosted glass 10, cavity 5 is 4 cm long. Valve ports are located at both ends of cavity 5. Once the quasi-holographic fringe passes through the gas to be measured, it becomes a quasi-holographic fringe that can represent changes in refractive index.

[0050] When the quasi-holographic stripe module is a grid 4, the air cavity 5 is pressurized by an air pump or injected with gases of different concentrations, and after stabilization, the stripes at different pressure values ​​are continuously photographed using a high-speed imaging chip 13. When the quasi-holographic stripes pass through the gas to be measured, the refractive index of the gas to be measured is changes, and the length of the gas cavity and the period of the grid 4 It will have a certain impact on the change of fringes. If we assume that the incident angle with grille 4 cycles The relationship is as follows.

[0051] .

[0052] in, Indicates the thickness of the gas to be measured through which light passes.

[0053] .

[0054] in, Indicates the displacement of the center of the quasi-holographic fringe on the imaging surface. This means that after using the grid 4, the displacement of the quasi-holographic fringe is proportional to the period of the grid 4. and refractive index The change is proportional to the grid. In specific operations, the grid 4 period can be selected according to the accuracy of the camera. , so as to avoid the inability to detect fringe changes, ensure that zero-order transmission is dominant to prevent the influence of diffraction.

[0055] When the quasi-holographic stripe module is frosted glass 10, the air cavity 5 is also pressurized by an air pump or injected with gases of different concentrations. After stabilization, the high-speed imaging chip 13 is used to continuously capture stripes at different pressure values. When parallel light passes through the gas to be measured, the refractive index of the gas changes, and the following formula is obtained according to Snell's law.

[0056] .

[0057] in, is the angle of incidence of light in standard air, is the propagation angle of the quasi-holographic fringe in the gas to be measured. , the following formula can be simplified.

[0058] .

[0059] Because the refraction of light in the gas causes the entire beam to shift in angle, the fringes projected onto the imaging surface will also shift. The amount of this shift can be derived from geometric relationships.

[0060] .

[0061] in, Indicates the displacement of the center of the holographic fringe on the imaging surface. represents the thickness of the holographic fringe passing through the gas to be measured. Substituting this into the previous refraction relationship yields the following formula.

[0062] .

[0063] Since the light beam hits the frosted glass 10 with stripes, it is diffuse transmission, which will affect the angular distribution of light. Therefore, the angular deviation caused by the frosted glass 10 also needs to be considered. , assuming that the period of the surface structure of the frosted glass 10 is , then the scattering angle It can be approximated by the following formula.

[0064] .

[0065] Therefore, it is necessary to ensure that the surface period on the frosted glass 10 Much larger than the wavelength of light, in order to ensure that the angle deviation of the stripes caused by the scattering of the frosted glass is Small enough to ensure clear fringes without affecting the measurement.

[0066] (5) Optical processing module.

[0067] The optical processing module is used to perform optical processing on the holographic fringes after passing through the gas to be measured; the optical processing includes beam reduction processing and filtering processing, or filtering processing and focusing processing.

[0068] Furthermore, when the quasi-holographic stripe module is a grid 4, as Figure 1 As shown, the optical processing module includes: a conjugate mirror group and a filter group 11.

[0069] The conjugate mirror group is set on the outgoing light path of the air cavity 5, and is used to perform beam reduction processing on the holographic fringes after passing through the gas to be measured. Figure 1As shown, the conjugate lens group includes a second lens 6 and a third lens 7. The second lens 6 is arranged on the outgoing light path of the air cavity 5 and is used to focus the fringes after passing through the gas to be measured; the third lens 7 is arranged on the transmission light path of the second lens 6 and is used to diverge the focused fringes.

[0070] The filter group 11 is arranged on the outgoing light path of the conjugate mirror group, and is used to filter the holographic-like fringes after the beam is reduced.

[0071] Specifically, the conjugate lens group (composed of the second lens 6 and the third lens 7) processes the quasi-holographic fringes and also plays a role in beam reduction, which can reduce the width of the fringes to 4 times the width of the imaging unit, ensuring that the high-speed imaging chip 13 can capture the quasi-holographic fringes after optical processing. Figure 1 As shown, the second lens 6 and the third lens 7 form a conjugate optical path and constitute a 4f optical system ( Figure 1 middle and ), its function is to ensure that the stripe information is not distorted and to improve the utilization rate of light. Among them, the second lens 6 transmits the image to the frequency domain, and then the third lens 7 reconstructs the stripes, reducing the influence of environmental noise, and at the same time plays the role of beam reduction, so that the light can hit the high-speed imaging chip 13. The filter group 11 is a dual-band filter group, which includes a narrow-band pass filter and a short-wave pass filter, thereby filtering out stray light. The narrow-band pass filter selects the laser wavelength used as the central wavelength, and the bandwidth can be selected as ±5nm or ±10nm, so that the holographic stripes after beam reduction can be transmitted to the greatest extent, while shielding most of the ambient light interference; the short-wave pass filter shields infrared thermal radiation (IR) above 700nm, because in actual use, the environment where the gas to be measured is located may have the problem of infrared thermal radiation due to temperature changes.

[0072] When the quasi-holographic fringe module is frosted glass 10, as shown in FIG. Figure 2-Figure 4 As shown, the optical processing module includes a filter group 11 and a fourth lens 12 .

[0073] The filter group 11 is arranged on the outgoing light path of the air cavity 5, and is used to filter the fringes after passing through the gas to be measured; the fourth lens 12 is arranged on the outgoing light path of the filter group 11, and is used to focus the filtered fringes.

[0074] (6) Computation module.

[0075] The calculation module is arranged on the outgoing light path of the optical processing module and is used to calculate the refractive index of the quasi-holographic fringes after optical processing to obtain the refractive index of the gas to be measured.

[0076] like Figure 1-Figure 4As shown, the computing module includes: a high-speed imaging chip 13 and a computer (not shown in the figure).

[0077] The high-speed imaging chip 13 is arranged on the outgoing light path of the optical processing module and is used to collect the holographic-like fringes after optical processing.

[0078] The computer is connected to the high-speed imaging chip 13 and is used to calculate the refractive index of the holographic fringes after optical processing to obtain the refractive index of the gas to be measured. The filter group 11 and the high-speed imaging chip 13 together constitute Figure 1 The filtering imaging module 8 in.

[0079] Specifically, the high-speed imaging chip 13 is a charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS). A computer performs phase and refractive index calculations on the collected holographic fringes. Combining the angular spectrum method with the fast Fourier transform (FFT), the spatial interference fringes are converted to the frequency domain. Spectral filtering is then used to extract phase information. A single two-dimensional Fourier transform (FFT) is required on a single interferogram to separate the zero-order image, twin image, and true phase. The angular spectrum method decomposes the wavefield into plane waves with different propagation directions for diffraction calculations. Compared to the traditional Fresnel-Kirchhoff integral method, the angular spectrum method uses fast Fourier transforms (FFTs) to process fringe images, improving computational efficiency by approximately 30% and meeting high-precision requirements.

[0080] Specifically, the phase of the holographic fringes after optical processing is solved and the refractive index is inverted. Each image is subjected to a two-dimensional Fourier transform and combined with the angular spectrum method, the phase information is extracted by spectrum filtering. Phase of the moment The phase change is then calculated , is the initial phase. The phase distribution is calculated according to the following formula.

[0081] .

[0082] in, is the refractive index of the gas to be measured, is the wavelength, is the optical path, is the standard refractive index of air, The mean and standard deviation of the gas refractive index are obtained after spatial averaging.

[0083] The beneficial effects of the gas refractive index measurement device based on holographic-like fringes proposed in this application are mainly reflected in the following contents.

[0084] In response to the problems of poor anti-disturbance, insufficient globality and high equipment cost faced by gas refractive index detection in complex environments, a gas refractive index measurement device based on holographic stripes is proposed. Compared with traditional digital holographic systems, the device of the present application abandons the reference light interference structure and directly uses the light beam passing through the grid to form stripes. After passing through the gas to be measured, the refractive index changes of the gas to be measured due to factors such as pressure or gas concentration are converted into resolvable stripe changes. Finally, a conjugate optical path is constructed to improve the utilization rate of light, and at the same time, it plays a beam shrinking role, reducing the stripe width to 4 times the width of the imaging unit to ensure that the imaging system can capture the stripes. Finally, the stripe image is captured and the phase information is extracted by superimposing a filter group on a high-speed imaging chip, thereby realizing the measurement of the gas refractive index. The device has stronger anti-disturbance, lower system cost and better adaptability, significantly improving the anti-interference ability of gas refractive index detection and greatly reducing the actual application cost. It has a wider applicability in various application scenarios.

[0085] In addition, the main advantages of this application include the following aspects.

[0086] (1) Good globality. Traditional in-situ measurements usually rely on local detection, making it difficult to obtain large-scale changes in the gas refractive index. This application uses global analysis of holographic fringes. In principle, it can directly measure the gas refractive index of the gas to be measured within the entire surface of the entire air cavity. Therefore, it has better globality than in-situ sensors and can comprehensively measure the refractive index changes in the entire measurement area.

[0087] (2) Strong anti-disturbance capability. Traditional holographic measurement relies on the interference of reference light and object light, requiring two beams of light to interfere and diffract, and has high requirements for optical path stability. It also requires more components, and the fringes are highly correlated with the wavelength of the measurement light, making it difficult to measure macroscopic large-scale targets. It is also easily affected by vibration, air disturbances, etc. This application adopts a quasi-holographic stripe structure, which does not require reference light interference. A frosted glass (or grid) with stripes is set in front of the gas to be measured. The laser is scattered (or penetrated) to form stripes that can represent the change in refractive index, which reduces 80% of optical components compared to the holographic optical path. In order to improve the utilization of light, Kohler illumination is considered, which can also reduce diffraction stripes. The dual-band filter set consists of two layers: a narrow-bandpass filter and a short-wave filter. The narrow-bandpass filter uses the laser wavelength as the center wavelength, and the bandwidth can be selected as ±5nm or ±10nm. This allows the laser to pass through to the greatest extent while shielding most ambient light interference. The short-wave filter shields infrared thermal radiation (IR) above 700nm. In actual use, the environment where the gas to be measured is located may have infrared thermal radiation due to temperature changes. The combined transmittance of the dual-band filter set is greater than 85%, and the background light suppression ratio is 10 4 : 1. Therefore, it is insensitive to small disturbances in the external environment, which improves the stability of the measurement.

[0088] (3) High measurement accuracy. This application uses a dual-band filter set and a high-speed imaging chip to eliminate interference caused by the gas to be measured and the experimental environment, is sensitive to changes in the refractive index of the gas to be measured, and improves measurement accuracy. It also uses the angular spectrum method combined with Fourier transform and phase analysis methods to perform high-precision calculations of fringe offsets. At the same time, the optical path design also uses a conjugate mirror set to reduce the beam, reduce fringe distortion, improve fringe contrast, and enhance measurement accuracy. The gas refractive index can then be accurately obtained, and it is expected to further deduce characteristics such as the pressure / temperature or gas concentration of the gas to be measured.

[0089] (4) Low equipment cost. Traditional holographic systems require high-precision optical platforms and high-precision optical equipment. However, the present invention not only has a simple optical path structure but also requires only conventional optical elements such as a monochromatic light source, lenses, frosted glass, or a grid. The use of a 4f optical system makes fringe imaging more stable and the device structure more concise, greatly reducing the cost of practical application. The application environment is not limited to laboratories, but also applies to more complex and diverse environments.

[0090] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0091] This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above examples is only intended to help understand the method and core concept of this application. At the same time, for those skilled in the art, based on the concept of this application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A gas refractive index measuring device based on quasi-holographic fringes, characterized in that: The gas refractive index measuring device based on quasi-holographic fringes comprises: A light source module, used for emitting light; An optical path module is provided on the outgoing optical path of the light source module and is used to uniformly process the light source to obtain parallel light; the optical path module is arranged in a Kohler illumination manner; A quasi-holographic fringe module is provided on the outgoing light path of the optical path module and is used to scatter or modulate the parallel light to obtain quasi-holographic fringes; the quasi-holographic fringes are periodic fringes; the periodic fringes have a certain shape; the periodic fringes include: light and dark stripes, triangular stripes, heart-shaped stripes, or circular stripes; An air cavity, provided on the outgoing light path of the quasi-holographic fringe module, for accommodating the gas to be measured; An optical processing module, used for optically processing the holographic fringes after passing through the gas to be measured; a calculation module, arranged on the outgoing light path of the optical processing module, for calculating the refractive index of the holographic-like fringes after optical processing to obtain the refractive index of the gas to be measured; The optical processing module includes: A conjugate lens group is arranged on the outgoing light path of the air cavity and is used to perform a beam reduction process on the holographic-like fringes after passing through the gas to be measured. The conjugate lens group includes: a second lens, arranged on the outgoing light path of the air cavity and is used to perform a focusing process on the fringes after passing through the gas to be measured; and a third lens, arranged on the transmitted light path of the second lens and is used to perform a diverging process on the focused fringes. A filter set is arranged on the outgoing light path of the conjugate mirror set and is used for filtering the holographic fringes after the beam reduction; The optical processing module includes: A filter set is arranged on the outgoing light path of the air cavity and is used to filter the fringes after passing through the gas to be measured; The fourth lens is arranged on the outgoing light path of the filter group and is used for focusing the filtered fringes.

2. The gas refractive index measuring device based on quasi-holographic fringes according to claim 1, characterized in that: The light source module is a monochromatic light source emitter or a laser.

3. The gas refractive index measuring device based on quasi-holographic fringes according to claim 2, characterized in that: When the light source module is a monochromatic light source emitter, the optical path module includes: A first lens is provided on the outgoing light path of the light source module and is used for parallel processing of the light source; The beam expander is arranged on the transmission light path of the first lens and is used to expand the size of the parallel processed light to obtain parallel light.

4. The gas refractive index measuring device based on quasi-holographic fringes according to claim 2, characterized in that: When the light source module is a monochromatic light source emitter, the optical path module is a condenser.

5. The gas refractive index measuring device based on quasi-holographic fringes according to claim 2, characterized in that: When the light source module is a laser, the optical path module includes: The beam expander is arranged on the outgoing light path of the light source module and is used to expand the light beam size of the light source to obtain parallel light.

6. The gas refractive index measuring device based on quasi-holographic fringes according to claim 3, characterized in that: The quasi-holographic stripe module is a grid.

7. The gas refractive index measuring device based on quasi-holographic fringes according to claim 4 or 5, characterized in that: The quasi-holographic fringe module is frosted glass.

8. The gas refractive index measuring device based on quasi-holographic fringes according to claim 1, characterized in that: The calculation module includes: A high-speed imaging chip is provided on the outgoing light path of the optical processing module and is used to collect the holographic fringes after optical processing; The computer is connected to the high-speed imaging chip and is used to calculate the refractive index of the holographic-like fringes after optical processing to obtain the refractive index of the gas to be measured.

Images