A device for measuring the spatial distribution of gas refractive index

Abstract

The present invention discloses a gas refractive index spatial distribution measuring device, comprising a light source, a first beam splitter, a first spherical reflector, a plurality of spherical dichroic mirrors, a second spherical reflector, a collimating lens, a detector, and a data processing module. The light source comprises more than one frequency, and the light emitted by the light source is divided into two beams by the first beam splitter, one beam is incident on the first spherical reflector and then returns to the first beam splitter as a reference beam, and the other beam is incident on a test area containing a gas to be measured and then returns to the first beam splitter as a measurement beam, and the reference beam and the measurement beam interfere with each other on the first beam splitter, and a plurality of spherical dichroic mirrors are arranged in the test area to divide the test area into a plurality of sub-areas in space; the data processing module obtains the spatial distribution of the gas refractive index in the test area according to the radius of the plurality of spherical dichroic mirrors and the second spherical reflector and the scanning angle of the galvanometer. The present invention can measure the spatial dynamic distribution of the gas refractive index in real time.

Description

Technical Field

[0001] The invention belongs to the technical field of gas refractive index measurement, and in particular relates to a gas refractive index spatial distribution measurement device. Background Art

[0002] The gas refractive index is one of the important physical quantities in optical measurement. It is also the basis for measuring other physical quantities related to the refractive index, such as air pressure measurement, and is of great significance in precision measurement.

[0003] At present, the measurement results of devices that measure the refractive index of gas based on the optical interference phenomenon are often the average of the integrated refractive index of gas in the measured area, which means that the gas in the measured area is assumed to be uniform. When the optical refractive index of the internal medium in the measured area has a gradient distribution due to dynamic gas pressure, such instruments often have difficulty measuring the spatial distribution (field) of the refractive index. Summary of the invention

[0004] The purpose of the present invention is to provide a gas refractive index spatial distribution measuring device capable of measuring the gas refractive index spatial dynamic distribution in real time.

[0005] In order to achieve the above-mentioned object, one aspect of the present invention provides a gas refractive index spatial distribution measurement device, comprising a light source, a first beam splitter, a first spherical reflector, a plurality of spherical dichroic mirrors, a second spherical reflector, a collimating lens, a detector, and a data processing module.

[0006] The light source includes more than one frequency. The light emitted by the light source is divided into two beams by the first beam splitter. One beam is incident on the first spherical reflector and then returns to the first beam splitter along the original path as a reference beam. The other beam is incident on the test area containing the gas to be tested and then returns to the first beam splitter along the original path as a measurement beam. The reference beam and the measurement beam interfere with each other on the first beam splitter. The detector receives the interference signal and generates interference data and then sends it to the data processing module.

[0007] The multiple spherical dichroic mirrors are arranged in the area to be measured, and are used to spatially divide the area to be measured into multiple sub-areas corresponding to the frequency of the light source. The measurement light beams of multiple frequencies are respectively incident on the multiple sub-areas, and are respectively reflected by the multiple spherical dichroic mirrors and the second spherical reflector and then return to the first beam splitter. The collimating lens is arranged between the first beam splitter and the detector, and is used to collimate the measurement light beam returned to the first beam splitter. The focal points of the multiple spherical dichroic mirrors, the second spherical reflector and the collimating lens are all located at the position on the first beam splitter where the reference light beam and the measurement light beam interfere with each other;

[0008] The first beam splitter can be used as a galvanometer to scan in three-dimensional space, and the data processing module obtains the spatial distribution of the gas refractive index in the area to be measured according to the radius of the multiple spherical dichroic mirrors and the second spherical reflector and the scanning angle of the galvanometer.

[0009] Preferably, the light source comprises three frequency-stabilized lasers with different frequencies and a plane dichroic mirror for integrating laser light paths of different frequency-stabilized lasers into the same path.

[0010] Preferably, the number of the plurality of spherical dichroic mirrors is two, the area to be measured is divided into first to third sub-areas, and the data processing module obtains the refractive index in each sub-area through the following equation group:

[0011]

[0012] Among them, n0l0 is the optical path of the reference light path that the reference beam passes through, λ1~λ3 represent the wavelengths of the three frequency-stabilized lasers respectively, They respectively represent the difference between the number of interference fringes measured in the 1st to 3rd sub-regions and the number of initial interference fringes in a vacuum environment, n1 to n3 respectively represent the refractive index of the 1st to 3rd sub-regions, and l1 to l3 respectively represent the propagation distance of light in the 1st to 3rd sub-regions.

[0013] Preferably, the device also includes a polarizer, a λ / 2 wave plate, and two λ / 4 wave plates. The polarizer is arranged between the first beam splitter and the collimating lens, the λ / 2 wave plate is arranged between the plane dichroic mirror and the first beam splitter, and the two λ / 4 wave plates are respectively arranged between the first beam splitter and the first spherical reflector and between the first beam splitter and the spherical dichroic mirror.

[0014] Preferably, the device further comprises a second beam splitter and a color image sensor, and the reference beam and the measuring beam are split into two beams after interference on the first beam splitter, one beam is received by the detector, and the other beam is received by the color image sensor for analyzing the interference pattern.

[0015] According to the gas refractive index spatial distribution measurement device of the above aspect of the present invention, by dividing the measurement area in three-dimensional space and measuring the refractive index of each sub-area in real time, the spatial dynamic distribution of the gas refractive index in the measurement area can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings used in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work:

[0017] Figure 1 It is a schematic diagram of the structure of a gas refractive index spatial distribution measurement device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only 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.

[0019] One embodiment of the present invention provides a device for measuring the spatial distribution of gas refractive index. Figure 1 FIG. 1 is a schematic diagram of the structure of a gas refractive index spatial distribution measurement device according to an embodiment of the present invention. Figure 1 As shown, the gas refractive index spatial distribution measuring device of an embodiment of the present invention includes a light source, a first beam splitter 2, a first spherical reflector 3, a plurality of spherical dichroic mirrors 4, a second spherical reflector 5, a collimating lens 6, a detector 7, and a data processing module (not shown).

[0020] The light source includes more than one frequency. The light source can be a laser light source composed of multiple frequency-stabilized lasers with different frequencies and a dichroic mirror, or a frequency-sweeping light source, or a light source array with different frequencies in each row, column or sub-light source, and its wavelength range covers ultraviolet, visible and infrared bands.

[0021] The light emitted by the light source is divided into two beams by the first beam splitter 2. One beam is incident on the first spherical reflector 3 and then returns to the first beam splitter 2 as a reference beam. The other beam is incident on the test area containing the gas to be tested and then returns to the first beam splitter 2 as a measurement beam. The reference beam and the measurement beam interfere with each other on the first beam splitter 2. The detector 7 receives the interference signal and generates interference data and then sends it to the data processing module.

[0022] exist Figure 1 In the embodiment shown, the light source includes three different frequencies, using three frequency-stabilized lasers 11 with different frequencies and two plane dichroic mirrors 12 for integrating laser light paths of different wavelengths into the same path. The three frequency-stabilized lasers with output light wavelengths (λ) of 633 nm, 532 nm and 473 nm are transmitted and reflected by two long-pass dichroic mirrors to the same position on the reflection surface of the first beam splitter. Figure 1For the convenience of description, the three optical paths are separated. In fact, the lasers of three frequencies are on the same optical path, which will not be described in detail later. It should be noted that in actual measurement, the target cannot be a point, so the measurement result of the refractive index should be the result of the joint action of the medium in a space with a certain size, that is, the output result is an equivalent value of the refractive index.

[0023] A plurality of spherical dichroic mirrors 4 are arranged in the area to be measured, and are used to spatially divide the area to be measured into a plurality of sub-areas corresponding to the frequency of the light source. The measurement beams of the plurality of frequencies are respectively incident on the plurality of sub-areas, and are respectively reflected by the plurality of spherical dichroic mirrors 4 and the second spherical reflector 5 and then return to the first beam splitter 2. The collimating lens 6 is arranged between the first beam splitter 2 and the detector 7, and is used to collimate the measurement beam returned to the first beam splitter 2. The focal points of the plurality of spherical dichroic mirrors 4, the second spherical reflector 5 and the collimating lens 6 are all located at the position on the first beam splitter 2 where the reference beam and the measurement beam interfere with each other.

[0024] exist Figure 1 In the embodiment shown, the area to be measured within the dotted box is divided into three parts by two spherical dichroic mirrors (numbered by numbers in the boxes in the figure, namely the first sub-area, the second sub-area and the third sub-area), and the results of three refractive index measurements using three frequencies are the refractive index of the gas in the first area, the equivalent refractive index of the gas in the first sub-area and the second sub-area, and the equivalent refractive index of all the gas in the first sub-area, the second sub-area and the third sub-area. After the measurement light beams of the three frequencies enter the area to be measured, they are reflected by the short-pass dichroic mirrors and propagate different distances. Figure 1 Taking the first sub-region as an example, according to the principle of optical interference, the relationship between the measured optical refractive index and the propagation distance of light is as follows:

[0025]

[0026] Among them, n0l0 is the optical path of the reference optical path, and n1l1 is the optical path of the measuring optical path when measuring area 1. By performing a measurement in a vacuum environment, the initial number of interference fringes can be obtained and the calibration is completed. is the difference between the number of interference fringes measured and the number of initial fringes, n represents the refractive index, l represents the propagation distance of light, and specifically, λ1~λ3 represent the wavelengths of the three frequency-stabilized lasers, They respectively represent the difference between the number of interference fringes measured in the 1st to 3rd sub-regions and the number of initial interference fringes in a vacuum environment, n1 to n3 respectively represent the refractive index of the 1st to 3rd sub-regions, and l1 to l3 respectively represent the propagation distance of light in the 1st to 3rd sub-regions.

[0027] The following set of equations can be listed for the measurement optical path of each frequency, and the refractive index in each sub-region can be calculated separately after calculation:

[0028]

[0029] Since the refractive index measurement results are detected at different wavelengths, in order to unify them to the same wavelength for characterization, the following conversion is required:

[0030] Since the frequency of light remains unchanged in the medium, the relationship between its wavelength λ, speed v, and frequency f is:

[0031] λ=v / f(4)The relationship between the speed of light v and the refractive index n is:

[0032] v=c / n(5)

[0033] Among them, c is the speed of light in vacuum, which is a constant. Therefore, the refractive index (n1, n2) of light of different wavelengths (λ1, λ2) in the same medium has the following relationship:

[0034]

[0035] or:

[0036]

[0037] According to equation (6) or (7), all refractive index measurement results can be uniformly converted to the same wavelength λ1 or λ2.

[0038] exist Figure 1 In the embodiment, the frequency of the light source is 3 and the number of the spherical dichroic mirrors is 2, but not limited thereto. The frequency of the light source, the type (such as long pass or short pass), quantity and position of the dichroic mirrors in the measured area can be determined according to measurement requirements.

[0039] The first beam splitter 2 can be used as a galvanometer to perform three-dimensional space scanning. The first beam splitter 2 can be driven by a motor to control the propagation direction of the light beam in space, that is, to perform scanning as a galvanometer.

[0040] The above illustrates how to divide the area to be measured in two-dimensional space (using the two-dimensional coordinate system xoy to establish the paper surface) before the galvanometer starts scanning, so as to achieve preliminary refractive index gradient measurement. The following will illustrate how to expand the area division to three-dimensional space (i.e. the galvanometer starts scanning) to achieve three-dimensional spatial distribution measurement of the medium refractive index.

[0041] Figure 1The positions of all spherical mirrors (spherical dichroic mirrors and spherical reflectors) in the galvanometer satisfy that their focal points coincide with the light beam exit points on the galvanometer reflective surface. In this way, when the galvanometer scans to any angle in three-dimensional space, it is incident on the first spherical mirror in the reference light path and returns along the original path. In addition, a collimating lens is placed on the other side of the galvanometer, and its focal position coincides with the focal point of the spherical mirror. Then the light beam returned by the spherical mirror passes through the focal point of the collimating lens and is collimated by the collimating lens and output to the detector. The scanning angle of the galvanometer and the spatial position of the spherical dichroic mirror determine the sub-area division of the area to be measured (i.e., spatial resolution). The measurement results are jointly expressed by spatial coordinates and refractive index: (x, y, z, n), where x, y, z represent the spatial coordinates of the measurement target position (which can be calculated based on the galvanometer angle and the position of the spherical dichroic mirror), n is the corresponding refractive index, and the origin of the coordinate system is at the laser exit point on the galvanometer reflective surface.

[0042] The data processing module obtains the spatial distribution of the gas refractive index in the measured area according to the radius of the multiple spherical dichroic mirrors 4 and the second spherical reflector 5 and the scanning angle of the galvanometer. The data processing module can calculate the spatial coordinates (x, y, z) as follows:

[0043] As mentioned above, all wavelengths of light are emitted from the same point on the first beam splitter 2, which is the origin of the spatial coordinate (0, 0, 0), and a right-handed coordinate system is established with the propagation direction of light (from left to right on the paper) as the positive direction of the x-axis and the reverse direction of the light source emission direction (from bottom to top on the paper). Assume Figure 1 The radii of the three spherical mirrors are r1, r2, and r3. When the galvanometer scans to the angle (ρ, u, v), the refractive index measurement results (x, y, z, n) in the first to third regions can be expressed as: (r1cosρ, r1cosu, r1cos v, n1), (r2cosρ, r2cos u, r2cosv, n2) and (r3cosρ, r3cosu, r3cosv, n3). The coordinate system can also be established in different ways, as long as the measurement of the spatial distribution of the refractive index can be achieved.

[0044] exist Figure 1 In the illustrated embodiment, the device of the present invention further includes a second beam splitter 8 and a color image sensor 9. The reference beam and the measuring beam are separated into two beams after interference on the first beam splitter 2. One beam is received by the detector 7, and after generating interference data, it is sent to the data processing module to obtain the spatial distribution of the refractive index of the gas in the measured area. The other beam is received by the color image sensor 9 for analyzing the interference pattern.

[0045] exist Figure 1In the illustrated embodiment, the device of the present invention further includes a polarizer 10, a λ / 2 wave plate 13, and two λ / 4 wave plates 14. The polarizer 10 is arranged between the first beam splitter 2 and the collimating lens 6, the λ / 2 wave plate 13 is arranged between the plane dichroic mirror 12 and the first beam splitter 2, and the two λ / 4 wave plates 14 are respectively arranged between the first beam splitter 2 and the first spherical reflector 3 and between the first beam splitter 2 and the spherical dichroic mirror 4.

[0046] According to the measuring device of the above embodiment of the present invention, a spherical dichroic mirror is introduced into the measuring optical path, so that the area to be measured can be divided in space, and the refractive index of each sub-area can be measured in real time, so that the spatial dynamic distribution of the refractive index of the gas in the measuring area can be obtained, and the size and orientation of the measuring area can be divided as needed. The spatial distribution of the air pressure can be further calculated based on prior knowledge such as the gas state equation, the Lorentz-Lorenz equation, the Edlen equation, and the Virial expansion, so as to be suitable for the scene of dynamic pressure measurement. The measuring device of the embodiment of the present invention can be designed as a common optical path with some existing Michelson interferometers and laser Doppler vibrometers, and a beam analysis channel can be reserved at the end of the optical path, so that the instrument can be multifunctional without sacrificing the volume of the instrument.

[0047] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A gas refractive index spatial distribution measurement device, characterized in that: The invention comprises a light source, a first beam splitter, a first spherical reflector, a plurality of spherical dichroic mirrors, a second spherical reflector, a collimating lens, a detector, and a data processing module. The light source includes more than one frequency. The light emitted by the light source is divided into two beams by the first beam splitter. One beam is incident on the first spherical reflector and then returns to the first beam splitter along the original path as a reference beam. The other beam is incident on the test area containing the gas to be tested and then returns to the first beam splitter along the original path as a measurement beam. The reference beam and the measurement beam interfere with each other on the first beam splitter. The detector receives the interference signal and generates interference data and then sends it to the data processing module. The multiple spherical dichroic mirrors are arranged in the area to be measured, and are used to spatially divide the area to be measured into multiple sub-areas corresponding to the frequency of the light source. The measurement light beams of multiple frequencies are respectively incident on the multiple sub-areas, and are respectively reflected by the multiple spherical dichroic mirrors and the second spherical reflector and then return to the first beam splitter. The collimating lens is arranged between the first beam splitter and the detector, and is used to collimate the measurement light beam returned to the first beam splitter. The focal points of the multiple spherical dichroic mirrors, the second spherical reflector and the collimating lens are all located at the position on the first beam splitter where the reference light beam and the measurement light beam interfere with each other; The first beam splitter can be used as a galvanometer to scan in three-dimensional space, and the data processing module obtains the spatial distribution of the gas refractive index in the area to be measured according to the radii of the multiple spherical dichroic mirrors and the second spherical reflector and the scanning angle of the galvanometer; The light source includes three frequency-stabilized lasers with different frequencies and a plane dichroic mirror for integrating the laser light paths of the different frequency-stabilized lasers into the same path; The number of the plurality of spherical dichroic mirrors is 2, the area to be measured is divided into first to third sub-areas, and the data processing module obtains the refractive index in each sub-area through the following equation group: Among them, n0l0 is the optical path of the reference light path that the reference beam passes through, λ1~λ3 represent the wavelengths of the three frequency-stabilized lasers respectively, They respectively represent the difference between the number of interference fringes measured in the 1st to 3rd sub-regions and the number of initial interference fringes in a vacuum environment, n1 to n3 respectively represent the refractive index of the 1st to 3rd sub-regions, and l1 to l3 respectively represent the propagation distance of light in the 1st to 3rd sub-regions.

2. The gas refractive index spatial distribution measuring device according to claim 1, characterized in that: It also includes a polarizer, a λ / 2 wave plate, and two λ / 4 wave plates. The polarizer is arranged between the first beam splitter and the collimating lens, the λ / 2 wave plate is arranged between the plane dichroic mirror and the first beam splitter, and the two λ / 4 wave plates are respectively arranged between the first beam splitter and the first spherical reflector and between the first beam splitter and the spherical dichroic mirror.

3. The gas refractive index spatial distribution measuring device according to claim 1, characterized in that: It also includes a second beam splitter and a color image sensor. The reference beam and the measuring beam are split into two beams after interference on the first beam splitter, one beam is received by the detector, and the other beam is received by the color image sensor for analyzing the interference pattern.

Images