CN114739954A

CN114739954A - System and method for simultaneously measuring thermal expansion coefficient and temperature refractive index coefficient of object

Info

Publication number: CN114739954A
Application number: CN202210321842.1A
Authority: CN
Inventors: 赵宇琼; 常迈; 邹婕; 许柏恺; 王智; 王亚平
Original assignee: Beijing Jiaotong University
Current assignee: Beijing Jiaotong University
Priority date: 2022-03-30
Filing date: 2022-03-30
Publication date: 2022-07-12

Abstract

The invention provides a system and a method for simultaneously measuring the thermal expansion coefficient and the temperature refractive index coefficient of an object. The system comprises a laser light source system, a Michelson Fizeau interference system, a temperature control system and a data acquisition system which are connected through a light path; the laser light source system comprises a laser, a beam expander or a collimator, and the Michelson Fizeau interference system comprises a 45-degree semi-transparent and semi-reflective mirror, a reflector and an object to be detected; the temperature control system comprises a heat preservation device, a heating device and a quartz material, and the object to be measured is placed in the heat preservation device. The temperature control system, the 45-degree semi-transparent and semi-reflective mirror and the data acquisition system form a light path in the vertical direction, and the laser light source system, the 45-degree semi-transparent and semi-reflective mirror and the reflector form a light path in the horizontal direction. The invention combines the Michelson and Fizeau interference principles, and utilizes two surfaces of the reflector and the sample to simultaneously measure the change quantity of the axial length and the refractive index in the same temperature rise process, thereby simultaneously measuring the thermal expansion coefficient and the temperature refractive index coefficient of the material.

Description

System and method for simultaneously measuring thermal expansion coefficient and temperature refractive index coefficient of object

Technical Field

The invention relates to the technical field of material thermal deformation measurement, in particular to a system and a method for simultaneously measuring a thermal expansion coefficient and a temperature refractive index coefficient of an object.

Background

After a temperature field is applied to the light-transmitting material, the molecules arranged in order according to the principle in the material change the distance along with the temperature, and the change of the length or the volume is represented in a macroscopic manner. The linear expansion coefficient is defined as the ratio of the relative change of length or volume of the material under the action of temperature fields with different gradients to the length or volume of the material at the original temperature, and is one of the basic characteristic parameters of the material.

The thermal deformation is microscopically manifested in two ways. On one hand, the applied temperature field causes the arrangement structure of the molecules in the light-transmitting material to change; on the other hand, thermal stresses are generated due to the fact that the external constraint and the mutual constraint between the internal parts cannot be completely freely expanded and contracted. Both of which result in a change in certain optical properties of the material, with refractive index being one of the most important optical parameters.

The linear expansion coefficient of the optical lens material is approximately in the order of 10^-7-10^-5In the range, the thermal expansion of the optical material is very small, and the common tool for measuring the length cannot accurately measure due to low precision, and cannot simultaneously measure the change of the thermal expansion coefficient and the temperature refractive index of the transparent object when the transparent object is heated.

An experimental apparatus for measuring the thermal expansion coefficient and the temperature coefficient of refractive index of glass in the prior art is shown in fig. 1, and a sample and light path design diagram is shown in fig. 2. The samples used in this experiment were made of homogeneous isotropic glass as shown in the left panel of fig. 2. In the figure, A is a glass cylinder with a part cut away, and the upper and lower surfaces are basically parallel; b and B' are 2 circular glass plates also partially cut out, the upper and lower surfaces of each glass plate being non-parallel. 3 pieces of glass A, B, B' are glued together. The refractive index of the glue is the same as that of glass, and the thickness of the glue can be ignored. The laser was directed to the sample from above as shown in the right hand figure of fig. 2.

When the laser light is reflected from both sides of the sample, 3 reflected spots are visible on the screen, and the intermediate spots have interference fringes. It is formed by the interference of the lower surface of the upper thin glass plate and the upper surface 2 beams of reflected light of the lower thin glass plate. The optical path difference of these 2 beams is 2L. When the sample is heated, if the sample temperature is increased by Δ L ═ L β · Δ T (β is the coefficient of thermal expansion of glass), it can be observed that the interference fringe has moved by m₁And (3) strips.

When the laser light is reflected from a single surface of the sample, only 1 spot with interference fringes, formed by the interference of the reflected light from the upper and lower surfaces of the glass cylinder, is visible on the screen. The optical path difference of these 2 beams is 2 nL. Assuming that the interference fringe upon heating has moved by m₂And (3) strips. Then there are:

knowing L and n, provided that the number of fringe shifts m is measured separately₁、m₂In relation to the temperature T, from m₁－T，m₂And (4) plotting T, so as to obtain the thermal expansion coefficient beta and the refractive index temperature coefficient gamma respectively.

During the experiment, the sample is firstly carefully slid into the sample cavity in the middle of the large aluminum block, the temperature sensor is inserted, then the large aluminum block is placed on the electric furnace, and the large aluminum block and the electric furnace are placed on the lifting platform. A laser, a lift table, etc. are placed on the optical bench. And (3) turning on a laser power supply, and adjusting the positions of the laser and the sample to ensure that 3 reflection light spots can be seen on the screen when the laser is reflected from the sample, wherein 1 interference fringe is arranged in the middle. Starting the electric furnace to heat the sample to a certain temperature, closing the electric furnace, and measuring the number m of interference fringes in the process of naturally cooling the sample₁And the temperature T. After the data is measured, the sample is rotated to the other side, 1 light spot with interference fringes can be seen on the screen, and the sample is heated in the same wayDuring the cooling of the sample, the number of interference fringes m is measured₂And temperature T.

The technical scheme for measuring the thermal expansion coefficient and the refractive index temperature coefficient of the glass in the prior art has the following defects: the thermal expansion coefficient and the refractive index temperature coefficient can not be measured simultaneously in the same temperature change process, and the change mechanisms of the thermal expansion coefficient and the refractive index temperature coefficient can not be well researched; only the state that the uniform thickness interference pattern is a fringe is considered, and the state that the uniform inclination interference pattern is a circular spot is not considered.

Disclosure of Invention

The invention provides a system and a method for simultaneously measuring the thermal expansion coefficient and the temperature refractive index coefficient of an object, which can simultaneously measure the thermal expansion coefficient and the temperature refractive index coefficient of the object in the same temperature change process.

In order to achieve the purpose, the invention adopts the following technical scheme.

According to one aspect of the present invention, there is provided a system for simultaneously measuring the coefficient of thermal expansion and the temperature index of refraction of an object, comprising: the system comprises a laser light source system, a Michelson Fizeau interference system, a temperature control system and a data acquisition system which are connected through an optical path;

the laser light source system comprises a laser, a beam expander or a collimator, and the Michelson Fizeau interference system comprises a 45-degree semi-transparent and semi-reflective mirror, a reflector and an object to be detected; the temperature control system comprises a heat preservation device, a heating device and a quartz material, the quartz material is used as an experiment reference surface, the heat preservation device is connected with the heating device, the object to be tested is placed in the heat preservation device, the heat preservation device is arranged on a quartz gasket, and the data acquisition system is placed above the 45-degree semi-transparent semi-reflective mirror;

the temperature control system, 45 degrees semi-transparent semi-reflecting mirror and the data acquisition system constitute the light path of vertical direction, the laser instrument, beam expanding mirror or collimater, 45 degrees semi-transparent semi-reflecting mirror with the speculum constitutes the light path of horizontal direction.

Preferably, the position of the laser, the beam expander or the collimator is adjusted to enable laser emitted by the laser to be collimated and hit the center of the reserved position of the 45-degree half mirror, and the angle of the surface of the 45-degree half mirror is adjusted to enable the horizontal incident beam and the reflected beam of the 45-degree half mirror to coincide;

the distance from the mirror to the 45 ° half mirror is not equal to the distance from the 45 ° half mirror to the reference plane of quartz material.

Preferably, laser emitted by the laser penetrates through the beam expander or the collimator and the 45-degree semi-transparent and semi-reflective mirror and then is divided into two beams of light, and one beam of light finally reaches the observation screen through the reflector and the 45-degree semi-transparent and semi-reflective mirror; the other beam of light is reflected by the 45-degree semi-transparent semi-reflecting mirror to the upper surface and the lower surface of the object to be measured respectively and divided into two beams of light, and the two beams of light reach the observation screen through the 45-degree semi-transparent semi-reflecting mirror;

the three beams of light generate interference in pairs on the observation screen to generate circular light spots or stripes on the observation screen.

Preferably, when the laser system is a laser and a beam expander, the formed light source is a point light source, and when the reflector is completely vertical to the surface of the sample, the light is isocline interference, and the interference light is displayed as annular isocline interference fringes on the observation screen; when the laser system is a laser and a collimator, the formed light source is a parallel light source, and when the reflector and the surface of the sample are not vertical, the light source is equal-thickness interference, and interference light is displayed on an observation screen as straight stripes which are symmetrical by taking an equal-thickness intersection line as a center.

Preferably, when the circular light spot is generated, the translation and the refractive index variation of the light beam reflected by the upper surface of the object to be detected are calculated through the throughput of the circular light spot; calculating the angle change direction of the upper surface of the light beam reflected by the upper surface of the object to be measured according to the moving direction of the circle center of the circular light spot; obtaining the angle change of the upper surface of the light beam reflected by the upper surface of the object to be measured according to the calibration data through the circle center moving distance of the circular light spot; the translation and the refractive index change of different positions of the light beam reflected by the object to be detected can be known through the change of the shape of the circular ring light spot;

when the stripe is generated, calculating the change of the stripe level through the translation of the stripe, and calculating to obtain the translation of the upper surface and the refractive index variation; the angle of the light beam reflected by the upper surface of the object to be detected can be known to change through the slope change of the stripes; calculating the size of the angle change of the upper surface of the light beam reflected by the upper surface of the object to be measured through the density change of the stripes; and calculating the angle change size of the upper surface of the object to be measured, the translation of the upper surface and the refractive index change quantity through the change of the stripes at different positions of the stripes.

Preferably, for an object with anisotropy, a laser system adopts a laser and a collimator, and the thermal expansion coefficients and the temperature refractive index coefficients in different directions of the object are observed by using straight stripes with equal-thickness intersecting lines as centrosymmetry;

for an object with isotropy, a laser system adopts a laser and a beam expander, and the thermal expansion coefficient and the temperature refractive index coefficient of the object are observed by using annular equal-inclination interference fringes.

Preferably, the heat preservation device is cylindrical and is buckled on a quartz gasket, the surface of the heat preservation device is perforated, and the aperture is close to the size of the light spot;

heating device includes heating plate, thermostat and temperature probe, the heating plate pastes on cylindrical stainless steel goods, and the card is put in the cylinder shell, the heating plate heats through the connection of electric lines thermostat, adjusts the heating plate temperature by the temperature controller, inside the temperature probe gos deep into the cylinder shell by the upper portion aperture, passes the temperature data back the thermostat.

According to another aspect of the present invention, there is provided a method for simultaneously measuring the thermal expansion coefficient and the temperature refractive index coefficient of an object, which is adapted to the system of any one of claims 1 to 7, the method comprising:

the method comprises the following steps that (1) the system is installed on an optical platform, a laser is fixed on the optical platform, a power supply of the laser is turned on, and the pitch angle of the laser is adjusted to enable laser emitted by the laser to be parallel to the optical platform;

step (2), installing a reflector in a light path, adjusting the reflector to enable an incident beam to coincide with a reflected beam, blocking a horizontal reflector, installing a 45-degree semi-transparent semi-reflective mirror and adjusting the angle of the mirror surface of the 45-degree semi-transparent semi-reflective mirror to enable the horizontal incident beam and the reflected beam to coincide, installing a beam expander or a collimator, adjusting the height and the direction of the beam expander or the collimator to adjust the laser to be in a horizontal state, adjusting the distance between the beam expander or the collimator and a laser on an optical platform, adjusting a light spot to be within a set size range, and then fixing the beam expander;

placing the object to be detected on a quartz gasket, sleeving the quartz gasket in a heat preservation device, and embedding a heating sheet in the heat preservation device to be connected with a heating box through a circuit;

step (4), building a data acquisition system;

observing an interference pattern, finely adjusting the laser to enable the laser emitted by the laser to be parallel to a horizontal plane and to hit the center of the reserved position of the 45-degree semi-transparent and semi-reflective mirror, and enabling horizontal incident beams and reflected beams of the 45-degree semi-transparent and semi-reflective mirror and the 45-degree reflective mirror to coincide by adjusting the mirror surface angles of the 45-degree semi-transparent and semi-reflective mirror and the 45-degree reflective mirror; or finely adjusting the object to be measured and the reflector until the shape of the interference pattern is clear, wherein the distance from the reflector to the 45-degree semi-transparent and semi-reflective mirror is not equal to the distance from the 45-degree semi-transparent and semi-reflective mirror to the reference surface of the quartz material;

step (6), turning on a heating device, controlling the temperature of the sample according to a set temperature curve, and recording the stripe state in the process;

step (7), obtaining the round spot throughput number or fringe movement number k formed by the interference of the upper surface of the object to be measured and the reflecting mirror₁′-k₁Round spot throughput number or fringe movement number k formed by interference of lower surface of object to be measured and reflecting mirror₂′-k₂；

According to the round spot throughput number or the stripe moving number k₁′-k₁Obtaining the axial elongation of the object to be measured, and further calculating the thermal expansion coefficient of the object to be measured; according to the round spot throughput number or the stripe moving number k₂′-k₂And obtaining the refractive index change quantity delta n of the object to be measured, and further calculating the temperature refractive index coefficient of the object to be measured.

Preferably, the obtaining the axial elongation of the object to be measured according to the round spot throughput or the fringe movement number, and further calculating the thermal expansion coefficient of the object to be measured includes:

will k₁′-k₁Substituting the axial elongation l of the object to be measured into a formula (7)₂′-l₂：

2n₀(l₂′-l₂)＝(k₁′-k₁)λ (7)

n₀Is the refractive index of air, and λ is the wavelength of the laser light emitted by the laser;

k obtained by blank experiment₃′-k₃Substituting into equation (7) to obtain l₄′

Calculating the axial elongation dl ═ l of the object to be measured₂′-l₂-l₄′。

According to the temperature value recorded in the measuring process, the thermal expansion coefficient alpha of the object to be measured is obtained by using the formula (3):

l represents the initial length of the solid material and t represents the temperature.

Preferably, the number k of the round spot throughputs or the stripe movements is used₂′-k₂Obtaining the refractive index change quantity delta n of the object to be measured, and further calculating the temperature refractive index coefficient of the object to be measured, wherein the method comprises the following steps:

will k₂′-k₂Substituting the formula (12) to obtain the refractive index change quantity delta n of the object to be measured

2n₀(l₂′-l₂)+2n(l₃′-l₃)+2Δnl₃′+2n(l₄-l₄′)-2Δnl₄′＝(k₂′-k₂) (12)

According to the temperature value recorded in the measuring process and the refractive index change quantity delta n of the object to be measured, the temperature refractive index coefficient of the object to be measured is obtained by using a formula (4):

wherein n represents the refractive index of the solid material and t represents the temperature;

in addition, the device can also measure the temperature refractive index coefficient of the object by separately measuring the light beam reflected by the reflecting mirror and the interference level change reflected by the upper surface of the object to be measured.

Preferably, the data acquisition system consists of ground glass and a camera or a CCD, and when the ground glass and the camera are combined, the interference pattern is reflected on the ground glass through a reflector, and the camera is used for recording; when the CCD is used, the interference pattern is converted into a digital signal through the CCD and displayed on a computer for screen recording.

Preferably, the step 7 specifically includes:

firstly, performing video frame cutting and processing by using opencv to obtain each frame image;

secondly, denoising the frame image;

thirdly, performing binarization operation processing on the denoised image;

fourthly, identifying whether the image processed by the binarization operation is a circular spot or a stripe and counting;

if the identification object is a circular spot, after the circle center coordinate of the interference circular spot is obtained, the average value of 8 point pixel values around the circle center is taken as a vertical coordinate, a curve of the change along with the frame number is drawn, and the number of wave crests of the curve is calculated to obtain the round spot throughput;

if the identification object is a stripe, tracking the position of a certain stripe by adopting a depsort tracking algorithm, counting the variation of the stripe, calculating the number of the passing stripes, fitting a variation curve of the number of the stripes along with the number of video frames by using a computer, and calculating the number of wave peaks of the curve exceeding a threshold set by an experiment, namely the stripe throughput;

thereby obtaining the round spot throughput number or fringe movement number k formed by the interference of the upper surface of the object to be measured and the reflecting mirror₁′-k₁Round spot throughput number or fringe movement number k formed by interference of lower surface of object to be measured and reflecting mirror₂′-k₂。

According to the technical scheme provided by the embodiment of the invention, the principle and design of Michelson and Fizeau interference are combined, the axial length and the refractive index change can be measured simultaneously in the same temperature rise process, the sensitivity of the device is improved, and the device has the advantages of convenience in measurement and high precision.

Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the description below are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a diagram of an experimental setup for measuring the temperature coefficient of thermal expansion and refractive index of glass according to the prior art;

FIG. 2 is a sample and optical path layout of a prior art solution for measuring the temperature coefficient of thermal expansion and refractive index of glass;

FIG. 3 is an experimental optical path diagram of an apparatus for simultaneously measuring a thermal expansion coefficient and a temperature refractive index coefficient of a transparent object according to an embodiment of the present invention;

FIG. 4 is a three-dimensional using state diagram of each device in the experimental optical path of the device for simultaneously measuring the thermal expansion coefficient and the temperature refractive index coefficient of the transparent object according to the embodiment of the present invention;

FIG. 5 is a schematic diagram of a partial optical path of a system for simultaneously measuring the thermal expansion coefficient and the temperature refractive index coefficient of an object according to an embodiment of the present invention;

FIG. 6 is a flowchart illustrating a computer image processing algorithm according to an embodiment of the present invention;

fig. 7 is a schematic diagram of a central circular spot variation according to an embodiment of the present invention.

In the figure, 1-laser; 2-a beam expander or collimator; 3-an object to be measured; 4-quartz spacers; 5-45 degrees of semi-transparent and semi-reflective mirror; 6-a viewing screen; 7-a heat preservation device; 8-a heating device; 9-mirror.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.

As used herein, the singular forms "a", "an", "the" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may also be present. Further, "connected" or "coupled" as used herein may include wirelessly connected or coupled. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

For the convenience of understanding the embodiments of the present invention, the following description will be further explained by taking several specific embodiments as examples in conjunction with the drawings, and the embodiments are not to be construed as limiting the embodiments of the present invention.

The first embodiment is as follows:

the principle of thermal deformation includes: the light-transmitting material changes its internal molecular arrangement with a change in temperature (rise or fall), which macroscopically shows a slight change in length (expansion or contraction) in various directions. When the temperature of the solid material rises, the structural volume thereof increases accordingly. On a microscopic level, the solid molecules are usually tightly packed and as the temperature rises, the molecules begin to vibrate at a faster rate and push against each other. This process increases the distance between adjacent atoms, causing the solid to expand, which in turn increases the volume of the solid structure. The change of the axial length of the solid is a linear function of the temperature, the ratio of the length increment to the original length under the change of unit temperature is called as a linear expansion coefficient, and the calculation formula is as follows:

where l represents the initial length of the solid material and t represents the temperature. α is a solid linear expansion coefficient as a linear expansion coefficient to be measured.

Meanwhile, the refractive index of the material is changed due to the change of the intermolecular structure caused by the increase of the temperature. The refractive index of a material will be affected by two factors that act in opposition: on one hand, due to temperature rise, the density of the glass is reduced by thermal expansion, and the refractive index is reduced; on the other hand, the temperature is increased, resulting in cation pair O^2-The effect of (2) is reduced, the polarizability is increased, and the refractive index is made larger. And the eigenfrequency of the electronic vibration is reduced along with the temperature rise, so that the ultraviolet absorption limit caused by the superposition of the eigenfrequency is moved to the long wave direction, and the refractive index is raised. The refractive index of the material is related to temperature, and under the condition of not causing stress, the temperature changes by 1 ℃ every time, the change quantity of the refractive index is called the temperature refractive index coefficient of the refractive index, and the calculation formula is as follows:

where n represents the refractive index of the solid material and t represents the temperature.

The invention explores the thermal effect mechanism by measuring the linear expansion coefficient and the temperature refractive index coefficient, thereby being applied to the aspects of administration, precision instrument correction and the like.

The principle of measuring the refractive index of the light-transmitting material by Michelson and Fizeau interference comprises the following steps: two rows of coherent light beams with the same frequency, the same vibration direction and constant phase difference have mutual strengthening or weakening phenomena in a space intersection region, namely, the interference phenomenon of the light beams. The micro length change (light wave wavelength order) and the micro angle change can be deduced according to the relation between the change of the light interference pattern and the optical path difference and wavelength.

When the laser system is a laser and a beam expander, the formed light source is a point light source, and when the reflector is completely vertical to the surface of the sample, the light source is equal-inclination interference, and the interference light can be received as annular equal-inclination interference fringes on a screen; when the laser system is a laser and a collimator, the formed light source is a parallel light source, and when the reflector and the surface of the sample are not vertical, the light source is equal-thickness interference, so that straight stripes which are symmetrical by taking an equal-thickness intersection line as a center can be obtained. The mode for optimizing the interference effect can be selected for different samples.

The straight stripe can show translation and refractive index variation, angle change direction and size of each point of the object upper surface that awaits measuring more in the ring than comparing, but the measurement degree of difficulty is bigger than the ring. In summary, the anisotropic object has different thermal expansion coefficients and refractive indexes in different directions, and is suitable for observing the thermal expansion coefficients and the temperature refractive index coefficients in different directions by using straight stripes with equal-thickness intersecting lines as centrosymmetry; an isotropic object has the same thermal expansion coefficient, refractive index, and the like in different directions, and the thermal expansion coefficient and the temperature refractive index coefficient are preferably observed using circular equi-tilt interference fringes.

TABLE 2 comparison of interference circles and fringes

Table 2 above illustrates the following:

when the circular light spots are generated, calculating the translation and refractive index variation of the light beams reflected by the upper surface of the object to be measured through the throughput of the circular light spots; calculating the angle change direction of the upper surface of the light beam reflected by the upper surface of the object to be measured according to the moving direction of the circle center of the circular light spot; obtaining the angle change of the upper surface of the light beam reflected by the upper surface of the object to be measured according to the calibration data through the circle center moving distance of the circular light spot; the translation and the refractive index change of different positions of the light beam reflected by the object to be measured can be known through the change of the shape of the circular ring light spot.

When the stripe is generated, calculating the change of the stripe level through the translation of the stripe, and calculating to obtain the translation of the upper surface and the refractive index variation; the angle of the light beam reflected by the upper surface of the object to be detected can be known to change through the slope change of the stripes; calculating the size of the angle change of the upper surface of the light beam reflected by the upper surface of the object to be measured through the density change of the stripes; and calculating to obtain the angle change size of the upper surface of the object to be measured, the translation of the upper surface and the refractive index change quantity through the change of the stripes at different positions of the stripes.

An experimental light path diagram of the device for simultaneously measuring the thermal expansion coefficient and the temperature refractive index coefficient of an object provided by the embodiment of the invention is shown in fig. 3, a three-dimensional use state diagram of each device in the experimental light path is shown in fig. 4, and the device comprises a laser light source system, a michelson fizeau interference system, a temperature control system and a data acquisition system which are connected through a light path.

The laser light source system comprises a laser, a beam expander or a collimator, and the Michelson Fizeau interference system comprises 1 45-degree semi-transparent and semi-reflective mirror, 2 optical plane reflectors and an object to be measured; the temperature control system comprises a heat preservation device, a heating device and a quartz material, wherein the quartz material is used as an experiment reference surface and is used for heat insulation. The heat preservation device is connected with the heating device, the object to be measured is placed in the heat preservation device, the heat preservation device is arranged on the quartz gasket, and the data acquisition system is placed above the 45-degree semi-transparent semi-reflecting mirror. The data acquisition system comprises ground glass, a camera and a processor; or a charge coupled device CCD camera and processor.

The above-mentioned apparatus can be used for the experiment of measuring the thermal expansion coefficient and the temperature refractive index coefficient of the object at the same time, based on the optical path diagrams of fig. 3 and fig. 4, the processing flow of the method for measuring the thermal expansion coefficient and the temperature refractive index coefficient of the transparent object at the same time provided by the embodiment of the invention includes the following processing steps:

and (1) installing the system on an optical platform. The laser is first mounted and fixed to the optical platform. And opening a power supply of the laser, and adjusting the pitch angle of the laser to enable emergent light of the laser to be parallel to the optical platform.

And (2) installing a reflector in the light path, and adjusting the reflector in the horizontal direction to enable the horizontal incident beam and the reflected beam to be superposed, namely, the light emitted by the laser returns through the original path of the reflector. And then blocking the horizontal reflecting mirror, installing a 45-degree semi-transparent semi-reflecting mirror and adjusting the mirror surface angle of the semi-transparent semi-reflecting mirror to enable the 45-degree semi-horizontal incident light beam and the reflected light beam to coincide. And installing a beam expander, adjusting the height and direction of the beam expander, and adjusting the laser to be in a horizontal state. And on the optical platform, adjusting the distance between the beam expander and the laser, and fixing the beam expander after adjusting the light spot to a set size range.

And (3) placing the object to be detected on a quartz gasket, sleeving the quartz gasket in the heat preservation device, embedding the heating sheet in the heat preservation device, connecting the heating box through a circuit, and enabling the heating box to be independent of the optical path.

And (4) building a data acquisition system comprising a camera, installing an observation screen, and erecting the camera so that the camera can clearly shoot images on the observation screen.

Step (5), viewing interference patterns on the observation screen, finely adjusting the laser to enable the laser to be parallel to a horizontal plane and to hit the center of the reserved position of the 45-degree semi-transparent and semi-reflective mirror, and enabling horizontal incident beams and reflected beams of the 45-degree semi-transparent and semi-reflective mirror and the reflecting mirror to coincide by adjusting the mirror surface angles of the 45-degree semi-transparent and semi-reflective mirror and the reflecting mirror; or finely adjusting the object to be measured, the reflector and the like until the shape of the interference pattern is clear and meets the requirement, and it is noted that the distance from the reflector to the 45-degree half-transmitting mirror is not equal to the distance from the 45-degree half-transmitting mirror to the reference surface of the quartz material.

And (6) opening the heating device and the camera, raising the temperature in the heat preservation device to a set temperature, preserving the heat, and after the temperature of the heat preservation device is stable, obtaining the image of the throughput change of the interference pattern displayed on the observation screen by the camera in a video recording mode.

And (7) processing data. As a new precise measurement technology, the image measurement technology has many advantages such as high resolution, high speed, large dynamic range, rich information content and automation, and is now widely used in various industrial measurements. The experiment of the invention combines the high precision of the Michelson interferometer and the advantages of the image measuring technology, and aims to realize the non-contact, high-precision, large-range and high-automation real-time measurement of the refractive index.

Opening the video data on a computer, transcoding the video data into an image, performing noise reduction and binarization processing on the image, if the image is a circular spot, finding a circular interference center position and a minimum circle radius under a current frame, and determining the circular spot throughput according to the number of wave crests and wave troughs generated on the radius change image; if the position of the stripe is a stripe, the position variation of the stripe is captured. Thereby obtaining the throughput (fringe movement number) k of the round spot formed by the interference between the upper surface of the object to be measured and the reflecting mirror₁′-k₁Round spot throughput (fringe movement number) k formed by interference of lower surface of object to be measured and reflecting mirror₂′-k₂。

And (3) changing the light source into collimated light, repeating the steps (2) to (7) under the condition of ensuring that other devices are not changed, and simultaneously measuring the thermal expansion coefficient and the temperature refractive index coefficient of the object through the change of the equal-thickness interference series.

In practical application, a data acquisition system consisting of ground glass and a camera can be built, the interference pattern is reflected on the ground glass through a reflector, and the camera is used for recording.

The observation screen in the data acquisition system can be set as a CCD, and the interference pattern is converted into a digital signal through the CCD to be displayed on a computer, so that the interference pattern can be clearly displayed in a computer picture.

And (3) repeating the steps (1) to (7) under the condition that other devices are not changed, and simultaneously measuring the thermal expansion coefficient and the temperature refractive index coefficient of the object.

And respectively calculating the thermal expansion coefficient and the temperature refractive index coefficient of the object made of a single material according to the steps, measuring the sample for multiple times, and solving the average value to reduce the error when solving the result. The thermal expansion coefficients and temperature refractive index coefficients of the various materials were determined in the manner described above.

In practical application, the light source can be changed into collimated light, the steps (2) to (7) are repeated under the condition that other devices are not changed, and the thermal expansion coefficient and the temperature refractive index coefficient of the object can be measured simultaneously through the change of the equal-thickness interference series;

in the experimental process, the situations of fluctuation, continuous swallowing and continuous spitting and the like of the interference circular ring are found, and manual observation is very difficult; in addition, the whole experiment has long duration, so that the manual reading time is long, and the purpose of rapidly and conveniently observing the circular ring throughput and the stripe movement is achieved by adopting a computer image processing technology.

The processing flow of the computer image processing algorithm provided by the embodiment of the invention is shown in fig. 6, and comprises the following processing steps:

step S1: and (5) performing video frame cutting and processing by using opencv. It is noted that the captured isocline fringes must be centered and uniformly exposed, otherwise it is not conducive to subsequent image processing and counting.

Step S2: the picture is mainly denoised so as to identify the image characteristics. In the experiment, the Motion filter is adopted to enhance high-frequency information such as edges, outlines and the like of the images, and retain low-frequency information of image content, so that the definition of boundary stripes is improved.

Step S3: since the brightness of the experimental interference image fluctuates significantly during the imaging process, it is difficult to specify the standard of shape fitting without performing the binarization process, and thus the binarization process is very necessary. In the experiment, the image is subjected to binarization processing by adopting an adaptive threshold algorithm, so that the image becomes an interference background image except for an interference image, wherein the interference image is only an image with 0 gray level and an image with 255 gray levels.

Step S4: and identifying whether the obtained image is a circular spot or a stripe and counting.

If the identification object is the circular spot, after the center coordinates of the interference circular spot are obtained, the average value of 8 point pixel values around the center is taken as the vertical coordinate, the change curve of the change curve along with the frame number is drawn, and the number of wave crests of the curve is calculated to obtain the throughput number of the circular spot.

The final read information yields the round spot throughput by the following criteria:

1. if the fitted curve has smooth peaks and valleys and does not have instantaneous great change, the identified object is not changed and is the central circular spot of the same level, so that the handling of the circular spots is not caused;

2. if the curve after the fitting process has a tendency of instantaneous increase or decrease (ignoring bad values), it indicates that the recognition target is changed and that there is a swallow or a spit of a round spot. When the sudden drop occurs, the radius of the identified object is suddenly reduced, and a new central circular spot appears in the identified object, so that the identified object is spit; fig. 7 is a schematic diagram of a change of a central circular spot according to an embodiment of the present invention, where a sudden increase indicates that a radius of an identification object suddenly increases, which indicates that an inner central circular spot disappears, and an original outer circular spot is changed into a new central circular spot, and thus the identification object is spitted.

If the identification object is a stripe, tracking the position of a certain stripe by adopting a depersort tracking algorithm, counting the variation of the stripe, and calculating the number of the stripes passing through the variation. Fitting a curve of the number of the stripes along with the change of the number of the video frames by using a computer, and calculating the number of wave crests of which the curve exceeds a threshold set by an experiment, namely the stripe throughput.

Thereby obtaining the throughput (fringe movement number) k of the round spot formed by the interference between the upper surface of the object to be measured and the reflecting mirror₁′-k₁Round spot throughput (fringe movement number) k formed by interference of lower surface of object to be measured and reflecting mirror₂′-k₂。

Fig. 5 is a schematic diagram of a partial optical path of a system for simultaneously measuring a thermal expansion coefficient and a temperature refractive index of an object according to an embodiment of the present invention. Laser emitted by the laser penetrates through the beam expander to form light spots, so that an interference image is formed and is easier to observe. Then the laser is divided into two beams of light by a 45-degree semi-transparent semi-reflecting mirror, and one beam of light finally reaches the observation screen through a reflecting mirror and the semi-reflecting mirror through a horizontal light path; the other beam of light which passes through the vertical direction is transmitted downwards through the lower surface of the 45-degree semi-transparent semi-reflecting mirror and is respectively reflected by the upper surface and the lower surface of the object to be detected to be divided into two beams of light, and the two beams of reflected light respectively reach the observation screen through the 45-degree semi-transparent semi-reflecting mirror.

The three beams of light generate interference in pairs on the observation screen, and annular light spots and stripes are generated on the observation screen. Practical experiments show that the interference light intensity generated by the light beams reflected by the upper surface, the lower surface and the surface of the object to be measured is the smallest, the light intensity reflected by the reflector is the second of the light intensity reflected by the lower surface of the object to be measured, and the light intensity reflected by the reflector is the strongest with the light intensity reflected by the upper surface of the object to be measured. The method comprises the following steps of measuring the interference level change generated by light beams reflected by the upper surface and the lower surface of an object, the light beams reflected by a reflector and the interference level change reflected by the lower surface of the object to be measured simultaneously, and obtaining the thermal expansion coefficient and the temperature refractive index coefficient of the object simultaneously; in addition, the thermal expansion coefficient and the temperature refractive index coefficient of the object can be obtained by simultaneously measuring the changes of the interference levels of the light beam reflected by the reflector and the light beam reflected by the upper surface of the object to be measured and the changes of the interference levels of the light beam reflected by the reflector and the light beam reflected by the lower surface of the object to be measured.

TABLE 2 comparison of interference circles and fringes

The upper surface of the quartz gasket at room temperature is taken as a reference surface, and the reference surface is fixed and does not change along with the change of temperature. L in FIG. 3₁Is the distance from the half mirror to the mirror, l₂Is the distance from the semi-transparent semi-reflective mirror to the upper surface of the object to be measured, l₃Defining l for the distance from the upper surface of the object to be measured to the reference surface and considering that the quartz gasket has more micro deformation when being heated₄The distance between the lower surface of the object to be measured and the reference surface is 0 at room temperature.

The interference generated by the light beam reflected by the reflector and the light beam reflected by the upper surface of the object to be measured is as follows:

the optical path difference between the light beam reflected by the reflector and the light beam reflected by the upper surface of the object to be measured and the interference fringe k have the following relationship:

wherein n is₀Is the refractive index of air, λ is the wavelength of the laser light emitted by the laser, k₁In the order of stripes.

In the formula, l and k both vary with temperature, so that:

wherein l₂' is the distance, k, from the heated half-mirror to the upper surface of the object to be measured₁' is the striation order after heating.

(5) Subtracting (6) from formula:

2n₀(l₂′-l₂)＝(k₁′-k₁)λ (7)

here, l can be calculated from the number of round spots or the number of fringe shifts k' -k₂′-l₂。

Interference generated by the light beam reflected by the reflector and the light beam reflected by the lower surface of the object to be measured:

firstly, the expansion caused by the heating of the quartz pad under the object to be measured is temporarily not considered, i.e. the lower surface of the object to be measured is considered to be fixed.

The optical path difference between the light beam reflected by the reflector and the light beam reflected by the lower surface of the object to be measured and the interference fringe k have the following relationship:

δ＝2n₀l₂+2nl₃-2n₀l₁＝k₂λ (8)

wherein n is₀Is the refractive index of air, n is the refractive index of the sample to be measured, and lambda is the wavelength of the laser light emitted by the laser.

In the formula I₂、n、l₃And k vary with temperature, so there are:

δ′＝2n₀l₂′+2n′l₃′-2n₀l₁＝k₂′λ (9)

wherein l₂' is the distance from the heated semi-transparent semi-reflecting mirror to the upper surface of the object to be measured, /)₃' is the distance, k, from the upper surface of the object to be measured to the reference surface after heating₂' is the striation order after heating.

(8) Subtracting (9) from formula:

2n₀(l₂′-l₂)+2n′l₃′-2nl₃＝(k₂′-k₂)λ (10)

by making n' ═ n + Δ n, we can obtain:

2n₀(l₂′-l₂)+2n(l_a′-l₃)+2Δnl₃′＝(k₂′-k₂)λ (11)

is easy to know₂+l₃Is constant and equal to the distance between the half mirror and the reference plane, so that₂′-l₂＝-(l₃′-l₃). According to the formula (5) < CHEM >₂′-l₂While l₃Is also easy to obtain and is the thickness corresponding to the initial temperature, so that the throughput k can be obtained only by image processing₂′-k₂The refractive index change Δ n of the object to be measured can be obtained.

Error correction of the quartz shim: the quartz wafer is padded under the object to be detected. The linear expansion coefficient of quartz is one to two orders of magnitude smaller than that of the object to be measured, so the influence on the experiment is small but not negligible. This corresponds to considering the distance l of the quartz pad (corresponding to the lower surface of the object to be measured) from the reference plane under the condition that the virtual reference plane is not changed₄0 at room temperature, with increasing temperature, l₄May no longer be 0.

The principle of the correction is similar to the principle of the interference produced by the mirror and the beam reflected by the upper surface, where the formula of the correction based on formula (5) is given directly:

2n₀(l₂′-l₂)+2n(l₃′-l₃)+2Δnl₃′+2n(l₄-l₄′)-2Δnl₄′＝(k₂′-k₂)λ (12)

wherein l₄-l₄′、l₄′(l₄Initial 0) can be obtained by blank experiment, and n represents the refractive index of the tested sample.

In summary, it is only necessary to obtain the circular spot throughput (fringe movement number) k₁′-k₁、k₂′-k₂And k in blank experiment₃′-k₃The value of delta n in a certain temperature range can be calculated, and the thermal expansion coefficient and the temperature refractive index coefficient of the object to be measured can be further calculated.

Principle of surface inclination angle of object to be measured: if the interference pattern is a circular spot interference pattern, the movement of the circle center of the light spot represents that the surface of the object to be detected generates a tiny inclination angle, and the relationship between the size of the inclination angle and the movement direction of the circle center of the circular spot on the two-dimensional plane can be obtained through calibration. The angle was calibrated using a micrometer screw. Firstly, horizontally placing the spiral micrometer, placing an object to be measured on the plane of the micrometer, rotating in the same direction (clockwise or anticlockwise) to lift the table top, observing the distance of circle center movement in the observation screen and recording the distance as delta x, recording the difference between two times of vertical height changes before and after as delta h, and recording the distance from the angle change fulcrum of the spiral side micrometer to a lifting point as L_sFrom this, the angle change is calculated, denoted as Δ θ.

If the interference pattern is a fringe interference pattern, the change of the slope of the fringe represents that the surface of the object to be detected generates a tiny inclination angle, and the relation between the size of the inclination angle and the change of the slope can be obtained through calibration. The angle was calibrated using a micrometer screw. Firstly, horizontally placing a spiral micrometer, placing an object to be measured on a micrometer plane, rotating in the same direction (clockwise or anticlockwise) to lift a table top, observing that the slope of stripes in an observation screen is changed into delta alpha, recording the difference between two vertical height changes before and after being changed into delta h, and recording the distance from an angle change fulcrum of the spiral side micrometer to a lifting point as L_sFrom this, the angle change is calculated, denoted as Δ θ.

In order to eliminate the influence of thermal expansion and other factors of the quartz gasket, a blank experiment is firstly carried out, the experimental device is unchanged, the experimental steps are unchanged, and only the object to be tested is taken away. The principle of the blank experiment is similar to that of the interference generated by the mirror and the beam reflected by the upper surface, where the formula is given directly:

2n₀(l₄′-l₄)＝(k₃′-k₃)λ (13)

from this, it can be obtained₄′-l₄As a known quantity of equation (9).

In order to increase systematicness, easy operation and aesthetic property, the device is integrated in a system made of acrylic plates, and an optical base is fixed on an optical platform. The integrated device can realize experimental measurement only by adjusting the positions of the laser and the beam expander to collimate the light, irradiating the light at the center of the semi-transparent semi-reflective mirror and turning on the heating device and the camera. The connection and structural features between the various components of the device are now described as follows:

putting an object to be detected on a quartz gasket of a heating device, turning on a helium-neon laser power supply, adjusting a laser pitch angle, adjusting the laser to be in a horizontal state, and aligning a light beam to the center position of a 45-degree half-transmitting mirror.

And (2) finely adjusting the object to be measured, the 45-degree semi-transparent and semi-reflective mirror and the reflector to ensure that the interference pattern has a good shape and is easy to observe.

And (3) opening the heating device and the camera, raising the temperature in the heat preservation device to a set temperature, preserving the heat, and after the temperature of the heat preservation device is stable, obtaining the throughput change image of the interference pattern displayed on the observation screen by the camera in a video recording mode.

Opening video data on a computer, transcoding the video data into an image at a speed of 60 frames per second by using related codes of image processing, performing noise reduction and binarization processing on the image, and processing each frame of image to obtain the round spot throughput (fringe throughput) k formed by the interference of the upper surface of the object to be measured and the reflector₁′-k₁And the throughput of circular spots (fringe throughput) k formed by the interference of the lower surface and the reflecting mirror₂′-k₂。

Step (5) k₁′-k₁By substituting into equation (7)Axial elongation l of the object to be measured₂′-l₂And then l is obtained by blank experiment₄' (blank experiment obtained k)₃′-k₃Substituting into equation (7) to obtain l₄') calculate l₂′-l₂-l₄' the thermal expansion coefficient of the object to be measured can be obtained according to the formula (3). Will k₂′-k₂The refractive index change quantity delta n of the object to be measured can be obtained by substituting the formula (12), and the temperature refractive index coefficient of the object to be measured can be obtained by substituting the formula (4).

And (6) replacing different samples, and repeating the steps (3) to (6) to obtain multiple groups of data.

The embodiment of the invention has low requirements on the shape of the sample, and only needs to be smooth without adhesion. And interference circle spot throughput (or fringe movement) is used to calculate the thermal expansion coefficient and temperature index of refraction coefficient, relative to the fringes, which is easily computerised.

In summary, the embodiment of the invention combines michelson and fexol interference, and the two surfaces of the reflector and the sample can simultaneously measure the change amount of the axial length and the refractive index in the same temperature rise process, and can simultaneously measure the thermal expansion coefficient and the temperature refractive index coefficient of the material, thereby exploring the thermal deformation mechanism and being applied to the aspects of criminal investigation, precision instrument correction and the like. Compared with other technologies, the technology has the advantages that the operation and the device are complex, and the change of the thermal expansion coefficient and the temperature refractive index coefficient when the transparent object is heated can be simply and simultaneously measured.

In order to ensure the precision of measurement, the invention abandons the temperature rise measurement technology adopted in the traditional device, adopts the temperature reduction process to collect data, and avoids the influence of air disturbance on the experimental accuracy to a great extent.

The Motion filter and the adaptive threshold algorithm are adopted to binarize and enhance the image information.

Those of ordinary skill in the art will understand that: the figures are merely schematic representations of one embodiment, and the blocks or flow diagrams in the figures are not necessarily required to practice the present invention.

From the above description of the embodiments, it is clear to those skilled in the art that the present invention can be implemented by software plus necessary general hardware platform. Based on such understanding, the technical solutions of the present invention may be embodied in the form of a software product, which may be stored in a storage medium, such as ROM/RAM, magnetic disk, optical disk, etc., and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute the method according to the embodiments or some parts of the embodiments.

The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, for apparatus or system embodiments, since they are substantially similar to method embodiments, they are described in relative terms, as long as they are described in partial descriptions of method embodiments. The above-described embodiments of the apparatus and system are merely illustrative, and the units described as separate parts may or may not be physically separate, and the parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A system for simultaneously measuring the coefficient of thermal expansion and the temperature index of refraction of an object, comprising: the system comprises a laser light source system, a Michelson Fizeau interference system, a temperature control system and a data acquisition system which are connected through an optical path;

the temperature control system 45 semi-transparent semi-reflecting mirror with the data acquisition system constitutes the light path of vertical direction, the laser instrument, beam expanding lens or collimater 45 semi-transparent semi-reflecting mirror with the speculum constitutes the light path of horizontal direction.

2. The system as claimed in claim 1, wherein the laser emitted by the laser is collimated to hit the center of the reserved position of the 45 ° semi-reflecting mirror by adjusting the position of the laser, the beam expander or the collimator, and the horizontal incident beam and the reflected beam of the 45 ° semi-reflecting mirror can be coincided by adjusting the angle of the 45 ° semi-reflecting mirror;

the distance from the mirror to the 45 ° half mirror is not equal to the distance from the 45 ° half mirror to the reference plane of the quartz material.

3. The system of claim 1, wherein laser emitted by the laser is divided into two beams of light after passing through the beam expander or the collimator and the 45 ° half mirror, and one beam of light finally reaches the observation screen through the reflector and the 45 ° half mirror; the other beam of light is reflected by the 45-degree semi-transparent semi-reflecting mirror to the upper surface and the lower surface of the object to be measured respectively and divided into two beams of light, and the two beams of light reach the observation screen through the 45-degree semi-transparent semi-reflecting mirror;

4. The system of claim 1, wherein when the laser system is a laser and a beam expander, the light source is a point light source, and when the reflector is completely vertical to the surface of the sample, the light source is isocline interference, and the interference light is displayed as annular isocline interference fringes on the observation screen; when the laser system is a laser and a collimator, the formed light source is a parallel light source, and when the reflector and the surface of the sample are not vertical, the light source is equal-thickness interference, and interference light is displayed on an observation screen as straight stripes which are symmetrical by taking an equal-thickness intersection line as a center.

5. The system of claim 4, wherein:

when the circular light spot is generated, calculating the translation and refractive index variation of the light beam reflected by the upper surface of the object to be measured according to the throughput of the circular light spot; calculating the angle change direction of the upper surface of the light beam reflected by the upper surface of the object to be measured according to the moving direction of the circle center of the circular light spot; obtaining the angle change of the upper surface of the light beam reflected by the upper surface of the object to be measured according to the calibration data through the circle center moving distance of the circular light spot; the translation and the refractive index change of different positions of the light beam reflected by the object to be detected can be known through the change of the shape of the circular ring light spot;

6. The system of claim 5, wherein for the object with anisotropy, the laser system adopts a laser and a collimator, and the thermal expansion coefficient and the temperature refractive index coefficient in different directions are observed by using a straight stripe which is symmetrical by taking an isopachous intersection line as a center;

7. The system of claim 1, wherein the thermal insulation device is cylindrical and is buckled on a quartz gasket, and the surface of the thermal insulation device is perforated, and the aperture is close to the size of the light spot;

heating device includes heating plate, thermostat and temperature probe, the heating plate pastes on cylindrical stainless steel goods, and the card is put in the cylinder shell, the heating plate heats through the connection of electric lines thermostat, adjusts the heating plate temperature by the temperature controller, inside the temperature probe goes deep into the cylinder shell by the upper portion aperture, passes the temperature data back the thermostat.

8. A method for simultaneously measuring the coefficient of thermal expansion and the temperature index of refraction of an object, adapted for use with the system of any of claims 1-7, the method comprising:

step (4), building a data acquisition system;

step (6), turning on a heating device, controlling the temperature of the sample according to the set temperature curve, and recording the stripe state in the process;

According to the round spot throughput number or the stripe moving number k₁′-k₁Obtaining the axial elongation of the object to be measured, and further calculating the thermal expansion coefficient of the object to be measured; according to the round spot throughput number or the stripe moving number k₂′-k₂And obtaining the refractive index change quantity delta n of the object to be detected, and further calculating the temperature refractive index coefficient of the object to be detected.

9. The method of claim 8, wherein the calculating the axial elongation of the object to be measured according to the round spot throughput or the fringe movement number and further calculating the thermal expansion coefficient of the object to be measured comprises:

2n₀(l₂′-l₂)＝(k₁′-k₁)λ (7)

k obtained by blank experiment₃′-k₃Substituting into equation (7) to obtain l₄′；

Calculating the axial elongation dl ═ l of the object to be measured₂′-l₂-l₄′；

10. The method of claim 8, wherein the round spot throughput or fringe movement k is based on the round spot throughput or fringe movement₂′-k₂Obtaining the refractive index change quantity delta n of the object to be measured, and further calculating the temperature refractive index coefficient of the object to be measured, wherein the method comprises the following steps:

2n₀(l₂′-l₂)+2n(l₃′-l₃)+2Δnl₃′+2n(l₄-l₄′)-2Δnl₄′＝(k₂′-k₂)) (12)

11. The method of claim 8, wherein the data acquisition system is composed of ground glass and a camera or CCD, and when the combination of ground glass and camera is used, the interference pattern is reflected on the ground glass through a reflector and is recorded by the camera; when the CCD is used, the interference pattern is converted into a digital signal through the CCD and displayed on a computer for screen recording.

12. The method according to claim 8, wherein the step 7 specifically comprises:

secondly, denoising the frame image;

thirdly, performing binarization operation processing on the denoised image;