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

Abstract

The present invention provides a system and method for simultaneously measuring the thermal expansion coefficient and temperature-dependent refractive index of an object. The system comprises a laser light source system, a Michelson-Fizeau interferometer system, a temperature control system, and a data acquisition system connected by an optical path. The laser light source system includes a laser and a beam expander or collimator. The Michelson-Fizeau interferometer system includes a 45° semi-transparent mirror, a reflector, and an object to be measured. The temperature control system includes a heat preservation device, a heating device, and a quartz material, with the object to be measured placed in the heat preservation device. The temperature control system, the 45° semi-transparent mirror, and the data acquisition system form a vertical optical path, while the laser light source system, the 45° semi-transparent mirror, and the reflector form a horizontal optical path. By combining the principles of Michelson and Fizeau interferometry, the present invention utilizes the reflector and the sample's two surfaces to simultaneously measure the changes in axial length and refractive index during the same heating process, thereby simultaneously measuring the thermal expansion coefficient and temperature-dependent refractive index of a material.

Description

Technical Field

[0001] The present invention relates to the technical field of material thermal deformation measurement, and in particular to a system and method for simultaneously measuring the thermal expansion coefficient and temperature refractive index coefficient of an object. Background Art

[0002] When a temperature field is applied to a translucent material, the spacing between the material's normally ordered molecules changes with temperature, manifesting macroscopically as a change in length or volume. The linear expansion coefficient, defined as the ratio of the change in length or volume of a material under varying temperature gradients to its length or volume at the original temperature, is a fundamental material characteristic.

[0003] Thermal deformation manifests itself in two ways at the microscopic level. First, the applied temperature field causes changes in the molecular structure of the transparent material itself. Second, thermal stress is generated by external constraints and the mutual constraints between internal components, which prevent the material from fully expanding and contracting. Both of these factors can alter certain optical properties of the material, with the refractive index being one of the most important optical parameters.

[0004] The linear expansion coefficient of optical lens materials is roughly on the order of 10 -7 -10 -5 Within this range, the thermal expansion of optical materials is very small. General length measurement tools cannot complete accurate measurements due to their low precision, and cannot simultaneously measure the changes in thermal expansion coefficient and temperature refractive index when transparent objects are heated.

[0005] An experimental device for measuring the thermal expansion coefficient and refractive index temperature coefficient of glass in the prior art is shown in FIG. Figure 1 As shown, the sample and optical path design diagram are as follows Figure 2 The sample used in this experiment is made of homogeneous isotropic glass, such as Figure 2 As shown in the left figure. In the figure, A is a glass cylinder with a portion cut off, and the upper and lower surfaces are basically parallel; B and B' are two circular glass plates with portions cut off, and the upper and lower surfaces of each glass plate are not parallel. The three glass plates A, B, and B' are glued together. The refractive index of the glue is the same as that of the glass, and the thickness can be ignored. The laser is directed at the sample from above, as shown in the figure below. Figure 2 As shown in the middle right picture.

[0006] When laser light reflects from the double-layer surface of the sample, three reflected light spots are visible on the screen, with interference fringes in the center. This is caused by the interference of two beams of light reflected from the lower surface of the upper thin glass plate and the upper surface of the lower thin glass plate. The optical path difference between these two beams is 2L. If the sample is heated, assuming the sample temperature increases by ΔL = Lβ·ΔT (β is the thermal expansion coefficient of the glass), the interference fringes will be observed to shift by m1 stripes.

[0007] When the laser is reflected from a single layer of the sample, only one light spot with interference fringes is visible on the screen. This is formed by the interference of the light reflected from the upper and lower surfaces of the glass cylinder. The optical path difference between these two beams is 2nL. Assume that the interference fringes shift by m2 during heating. Then:

[0008]

[0009]

[0010] Given L and n, as long as the relationship between the interference fringe movement numbers m1 and m2 and the temperature T is measured respectively, and the graphs m1-T and m2-T are plotted, the thermal expansion coefficient β and the refractive index temperature coefficient γ can be calculated respectively.

[0011] During the experiment, first carefully slide the sample into the sample cavity in the middle of the large aluminum block and insert the temperature sensor at the same time. Then, place the large aluminum block on top of the electric furnace and place them on the lifting platform. Place the laser, lifting platform, etc. on the optical stand. Turn on the laser power supply and adjust the position of the laser and sample so that when the laser is reflected from the sample, three reflected light spots can be seen on the screen, and one in the middle has interference fringes. Turn on the electric furnace and heat the sample to a certain temperature. Turn off the electric furnace and measure the relationship between the number of interference fringes m1 and the temperature T during the natural cooling process of the sample. After measuring the data, rotate the sample to the other side. A light spot with interference fringes can be seen on the screen. Heat the sample in the same way. During the cooling process of the sample, measure the relationship between the number of interference fringes m2 and the temperature T.

[0012] The disadvantages of the above-mentioned prior art method for measuring the thermal expansion coefficient and the temperature coefficient of refractive index of glass are: it is not possible to simultaneously measure the thermal expansion coefficient and the temperature coefficient of refractive index during the same temperature change process, and it is not possible to fully explore the change mechanism of the two; it only considers the state where the equal-thickness interference pattern is stripes, but does not consider the state where the equal-inclination interference pattern is circular spots. Summary of the Invention

[0013] The present invention provides a system and method for simultaneously measuring the thermal expansion coefficient and the temperature refractive index coefficient of an object, so as to achieve the simultaneous measurement of the thermal expansion coefficient and the temperature refractive index coefficient of an object during the same temperature change process.

[0014] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions.

[0015] According to one aspect of the present invention, there is provided a system for simultaneously measuring the thermal expansion coefficient and the temperature refractive index coefficient of an object, comprising: a laser light source system, a Michelson-Fizeau interferometer system, a temperature control system, and a data acquisition system connected by an optical path;

[0016] The laser light source system includes a laser, a beam expander or a collimator, the Michelson-Fizeau interferometer system includes a 45° semi-transparent and semi-reflective mirror, a reflector, and an object to be measured; the temperature control system includes a heat preservation device, a heating device, and a quartz material, the quartz material serving as an experimental reference surface, the heat preservation device and the heating device are connected, the object to be measured 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° semi-transparent and semi-reflective mirror;

[0017] The temperature control system, the 45° semi-transparent and semi-reflective mirror and the data acquisition system constitute an optical path in the vertical direction, and the laser, the beam expander or collimator, the 45° semi-transparent and semi-reflective mirror and the reflector constitute an optical path in the horizontal direction.

[0018] Preferably, the laser light emitted by the laser is collimated and hits the center of the reserved position of the 45° half-reflecting mirror by adjusting the position of the laser, the beam expander or the collimator, and the horizontal incident light beam and the reflected light beam of the 45° half-reflecting mirror are overlapped by adjusting the mirror angle of the 45° half-reflecting mirror;

[0019] The distance from the reflector to the 45° half-reflector is not equal to the distance from the 45° half-reflector to the reference surface of the quartz material.

[0020] Preferably, the laser emitted by the laser is divided into two beams after passing through a beam expander or a collimator and a 45° semi-transparent and semi-reflective mirror. One beam of light passes through a reflector and a 45° semi-transparent and semi-reflective mirror and finally reaches an observation screen; the other beam of light is reflected by the 45° semi-transparent and semi-reflective mirror to the upper and lower surfaces of the object to be measured, and is divided into two beams of light. The two beams of light then pass through the 45° semi-transparent and semi-reflective mirror and reach the observation screen.

[0021] The light beam reflected by the reflector, the light beam reflected by the upper surface of the object to be measured, and the light beam reflected by the lower surface of the object to be measured interfere with each other on the observation screen, generating circular light spots or stripes on the observation screen.

[0022] Preferably, when the laser system is a laser and a beam expander, the light source formed is a point light source, and when the reflector and the sample surface are completely perpendicular, it is equal-inclination interference, and the interference light is displayed on the observation screen as circular equal-inclination interference fringes; when the laser system is a laser and a collimator, the light source formed is a parallel light source, and when the reflector and the sample surface are not perpendicular, it is equal-thickness interference, and the interference light is displayed on the observation screen as straight stripes symmetrical with the equal-thickness intersection line as the center.

[0023] Preferably, when a circular ring light spot is generated, the translation and refractive index change of the light beam reflected from the upper surface of the object to be measured are calculated by the throughput number of the circular ring light spot; the direction of change of the upper surface angle of the light beam reflected from the upper surface of the object to be measured is calculated by the movement direction of the center of the circular ring light spot; the magnitude of the change of the upper surface angle of the light beam reflected from the upper surface of the object to be measured is obtained according to the calibration data by the movement distance of the center of the circular ring light spot; and the change of the translation and refractive index of the light beam reflected from the upper surface of the object to be measured at different positions can be known by the change of the shape of the circular ring of the circular ring light spot.

[0024] When fringes are generated, the change in the fringes' order is calculated through the fringes' translation, and the upper surface translation and refractive index change are calculated. The change in the slope of the fringes indicates a change in the angle of the light beam reflected from the upper surface of the object to be measured. The change in the density of the fringes is used to calculate the magnitude of the upper surface angle change of the light beam reflected from the upper surface of the object to be measured. The change in the fringes at different positions of the fringes is used to calculate the magnitude of the upper surface angle change, upper surface translation, and refractive index change of the object to be measured.

[0025] Preferably, for anisotropic objects, the laser system uses a laser and a collimator, and uses straight stripes symmetrically centered around equal-thickness intersection lines to observe the thermal expansion coefficient and temperature refractive index coefficient in different directions;

[0026] For isotropic objects, the laser system uses a laser and a beam expander to observe its thermal expansion coefficient and temperature refractive index coefficient using circular equal-inclination interference fringes.

[0027] Preferably, the heat preservation device is cylindrical and is placed on the quartz gasket. The surface of the heat preservation device is perforated, and the aperture is close to the size of the light spot.

[0028] The heating device includes a heating plate, a temperature controller and a temperature probe. The heating plate is attached to a cylindrical stainless steel product and clamped in the cylindrical shell. The heating plate is connected to the temperature controller via an electric wire for heating. The temperature of the heating plate is adjusted by the temperature controller. The temperature probe penetrates into the interior of the cylindrical shell through a small hole at the top and transmits temperature data back to the temperature controller.

[0029] According to another aspect of the present invention, a method for simultaneously measuring the thermal expansion coefficient and the temperature refractive index coefficient of an object is provided, characterized in that it is applicable to the system according to any one of claims 1 to 7, and the method comprises:

[0030] Step (1), installing the system on an optical platform, fixing the laser on the optical platform, turning on the laser power supply, and adjusting the pitch angle of the laser so that the laser emitted by the laser is parallel to the optical platform;

[0031] Step (2): Install a reflector in the optical path, adjust the reflector so that the incident light beam and the reflected light beam coincide, then block the horizontal reflector, install a 45° semi-transparent and semi-reflective mirror and adjust its mirror angle so that the horizontal incident light beam and the reflected light beam of the 45° semi-transparent and semi-reflective mirror can coincide, install a beam expander or collimator, adjust the height and direction of the beam expander or collimator, adjust the laser to a horizontal state, and on the optical platform, adjust the distance between the beam expander or collimator and the laser, adjust the light spot to a set size range, and then fix the beam expander;

[0032] Step (3), placing the object to be tested on a quartz gasket, which is then placed in a heat preservation device, wherein the heating plate is embedded in the heat preservation device and connected to a heating box via a circuit;

[0033] Step (4), building a data acquisition system;

[0034] Step (5), observing the interference pattern, fine-tuning the laser so that the laser emitted by the laser is parallel to the horizontal plane and hits the center of the reserved position of the 45° semi-transparent and semi-reflective mirror, and adjusting the mirror angles of the 45° semi-transparent and semi-reflective mirror and the reflector so that the horizontal incident light beam and the reflected light beam of the 45° semi-transparent and semi-reflective mirror and the reflector can coincide; or fine-tuning the object to be measured and the reflector until the interference pattern is clear and the distance from the reflector to the 45° semi-transparent and semi-reflective mirror is not equal to the distance from the 45° semi-transparent and semi-reflective mirror to the reference plane of the quartz material;

[0035] Step (6), turning on the heating device, controlling the sample temperature according to the set temperature curve, and recording the stripe state during this process;

[0036] Step (7), obtaining the circular spot throughput number or fringe movement number k1′-k1 formed by the interference between the upper surface of the object to be measured and the reflector, and the circular spot throughput number or fringe movement number k2′-k2 formed by the interference between the lower surface of the object to be measured and the reflector;

[0037] The axial elongation of the object to be measured is obtained according to the circular spot throughput number or the fringe movement number k1′-k1, and the thermal expansion coefficient of the object to be measured is further calculated; the refractive index change Δn of the object to be measured is obtained according to the circular spot throughput number or the fringe movement number k2′-k2, and the temperature refractive index coefficient of the object to be measured is further calculated.

[0038] Preferably, the step of obtaining the axial extension of the object to be measured based on the circular spot throughput number or the fringe movement number, and then calculating the thermal expansion coefficient of the object to be measured, includes:

[0039] Substituting k1′-k1 into formula (7) we can obtain the axial extension l2′-l2 of the object to be measured:

[0040] 2n0(l2′-l2)=(k1′-k1)λ (7)

[0041] n0 is the refractive index of air, λ is the wavelength of the laser emitted by the laser;

[0042] Substitute k3′-k3 obtained from the blank experiment into formula (7) to obtain l4′

[0043] Calculate the axial extension of the object to be measured dl = l2′-l2-l4′.

[0044] According to the temperature values recorded during the measurement process, the thermal expansion coefficient α of the object to be measured is calculated using formula (3):

[0045]

[0046] l represents the initial length of the solid material, and t represents the temperature.

[0047] Preferably, the step of obtaining the refractive index change Δn of the object to be measured based on the circular spot throughput number or the fringe movement number k2′-k2, and then calculating the temperature refractive index coefficient of the object to be measured, includes:

[0048] Substitute k2′-k2 into formula (12) to obtain the refractive index change Δn of the object to be measured

[0049] 2n0(l2′-l2)+2n(l3′-l3)+2Δnl3′+2n(l4-l4′)-2Δnl4′=(k2′-k2) (12)

[0050] According to the temperature value recorded during the measurement process and the refractive index change Δn of the object to be measured, the temperature refractive index coefficient of the object to be measured is obtained using formula (4):

[0051]

[0052] Where n represents the refractive index of the solid material and t represents the temperature;

[0053] In addition, the device can also measure the temperature refractive index coefficient of the object by separately measuring the change in the interference order between the light beam reflected by the reflector and the light reflected by the upper surface of the object to be measured.

[0054] Preferably, the data acquisition system consists of frosted glass and a camera or CCD. When using the combination of frosted glass and a camera, the interference pattern is reflected on the frosted glass through a reflector and recorded by the camera; when using CCD, the interference pattern is converted into a digital signal by the CCD and displayed on a computer for screen recording.

[0055] Preferably, the step 7 specifically includes:

[0056] The first step is to use opencv to cut and process the video frames to obtain each frame image;

[0057] The second step is to perform denoising on the frame image;

[0058] The third step is to perform a binarization operation on the denoised image;

[0059] The fourth step is to identify whether the image after the binarization operation is a circular spot or a stripe and count them;

[0060] If the object to be identified is a circular spot, after obtaining the coordinates of the center of the interference spot, take the average pixel value of the eight points around the center as the vertical coordinate, plot its change curve with the frame number, and calculate the number of peaks of the curve to obtain the circular spot throughput;

[0061] If the object to be identified is a stripe, the deepsort tracking algorithm is used to track the position of a stripe, count the change in the stripe, calculate the number of stripes it passes through, and use a computer to fit the curve of the change in the number of stripes versus the number of video frames. The number of peaks at which the curve exceeds the threshold set by the experiment is the stripe throughput;

[0062] Thus, the circular spot throughput number or fringe movement number k1′-k1 formed by the interference between the upper surface of the object to be measured and the reflector, and the circular spot throughput number or fringe movement number k2′-k2 formed by the interference between the lower surface of the object to be measured and the reflector are obtained.

[0063] It can be seen from the technical solution provided by the above-mentioned embodiments of the present invention that the embodiment of the present invention combines the principles and designs of Michelson and Fizeau interference, and can simultaneously measure the changes in axial length and refractive index during the same heating process, while improving the sensitivity of the device, and has the advantages of convenient measurement and high precision.

[0064] Additional aspects and advantages of the present invention will be set forth in part in the following description, will become apparent from the following description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0066] Figure 1 A diagram of an experimental device for measuring the thermal expansion coefficient and refractive index temperature coefficient of glass in the prior art;

[0067] Figure 2 A sample and optical path design diagram for a method for measuring the thermal expansion coefficient and temperature coefficient of refractive index of glass in the prior art;

[0068] Figure 3 An experimental optical path diagram of a device for simultaneously measuring the thermal expansion coefficient and temperature refractive index coefficient of a transparent object provided by an embodiment of the present invention;

[0069] Figure 4 A three-dimensional diagram of the use status of each device in the experimental optical path of a device for simultaneously measuring the thermal expansion coefficient and temperature refractive index coefficient of a transparent object provided by an embodiment of the present invention;

[0070] Figure 5 A schematic diagram of a portion of the optical path of a system for simultaneously measuring the thermal expansion coefficient and temperature refractive index coefficient of an object provided by an embodiment of the present invention;

[0071] Figure 6 A processing flow chart of a computer image processing algorithm provided by an embodiment of the present invention;

[0072] Figure 7 A schematic diagram of the change of a central circular spot provided by an embodiment of the present invention.

[0073] In the figure, 1-laser; 2-beam expander or collimator; 3-object to be measured; 4-quartz gasket; 5-45° semi-transparent and semi-reflective mirror; 6-observation screen; 7-heating device; 8-heating device; 9-reflecting mirror. DETAILED DESCRIPTION

[0074] The embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and are not to be construed as limiting the present invention.

[0075] It will be understood by those skilled in the art that, unless expressly stated otherwise, the singular forms "a", "an", "said" and "the" used herein may also include the plural forms. It should be further understood that the term "comprising" used in the description of the present invention refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. It should be understood that when we refer to an element as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or there may be intermediate elements. In addition, "connected" or "coupled" as used herein may include wireless connections or couplings. The term "and / or" used herein includes any unit and all combinations of one or more associated listed items.

[0076] 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 those skilled in the art in the art to which the present invention pertains. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and, unless defined as such herein, will not be interpreted in an idealized or overly formal sense.

[0077] To facilitate understanding of the embodiments of the present invention, several specific embodiments will be further explained below with reference to the accompanying drawings, and each embodiment does not constitute a limitation on the embodiments of the present invention.

[0078] Example 1:

[0079] The principle of thermal deformation includes: as the temperature of a translucent material changes (increases or decreases), the arrangement of its internal molecules will change, which manifests itself macroscopically as slight changes in length in all directions (expansion or contraction). When the temperature of a solid material rises, its structural volume will increase. Microscopically, solid molecules are usually tightly arranged. As the temperature rises, the molecules begin to vibrate at a faster rate and push each other. This process increases the distance between adjacent atoms, causing the solid to expand, thereby increasing the volume of the solid structure. The change in the axial length of a solid is a linear function of temperature. The ratio of the increase in length per unit temperature change to the original length is called the linear expansion coefficient, and the calculation formula is as follows:

[0080]

[0081] Where l is the initial length of the solid material, t is the temperature, and α is the linear expansion coefficient to be measured.

[0082] At the same time, the change in the molecular structure caused by the temperature increase also causes the refractive index of the material to change. The refractive index of the material will be affected by two factors with opposite effects: on the one hand, as the temperature rises, the glass expands due to heat, causing the density to decrease and the refractive index to decrease; on the other hand, as the temperature rises, the cations will react with O 2- The effect of the electron vibration decreases, the polarization rate increases, and the refractive index increases. The eigenfrequency of the electron vibration decreases with increasing temperature, causing the ultraviolet absorption limit caused by the overlap of the eigenfrequency to move toward the long-wave direction, and the refractive index increases. The refractive index of the material is related to temperature. When the temperature changes by 1°C without causing stress, the change in refractive index is called the temperature refractive index coefficient of the refractive index. The calculation formula is:

[0083]

[0084] Here, n represents the refractive index of the solid material, and t represents the temperature.

[0085] The present invention explores the thermal effect mechanism by measuring the linear expansion coefficient and the temperature refractive index coefficient, so as to be applied in administration, precision instrument correction and other aspects.

[0086] The principle behind Michelson and Fizeau interferometry in measuring the refractive index of a transmissive material is that two coherent beams of light with the same frequency, identical vibration direction, and constant phase difference will mutually reinforce or weaken each other at their intersection, a phenomenon known as optical interference. The relationship between the changes in the interference pattern, the optical path difference, and the wavelength allows for the derivation of minute length changes (on the order of the wavelength of the light wave) and minute angle changes.

[0087] When the laser system consists of a laser and a beam expander, the light source is a point source. When the reflector and the sample surface are completely perpendicular, this is called equal-inclination interference. The interference light can be detected on the screen as circular equal-inclination interference fringes. When the laser system consists of a laser and a collimator, the light source is a parallel source. When the reflector and the sample surface are not perpendicular, this is called equal-thickness interference. This produces straight fringes symmetrically centered around the equal-thickness intersection line. For different samples, the optimal interference method can be selected.

[0088] Compared to circular rings, straight fringes are more capable of displaying the amount of translation and refractive index change, as well as the direction and magnitude of angular change, at each point on the surface of the object being measured. However, they are more difficult to measure. In summary, for anisotropic objects, the thermal expansion coefficient and refractive index vary in different directions, making it suitable to use straight fringes symmetrically centered around equal-thickness intersection lines to observe the thermal expansion coefficient and temperature-dependent refractive index in different directions. For isotropic objects, the thermal expansion coefficient and refractive index are the same in different directions, making it suitable to use circular, equal-inclination interference fringes to observe their thermal expansion coefficient and temperature-dependent refractive index.

[0089] Table 2 Comparison of interference rings and fringes

[0090]

[0091] The above Table 2 is explained as follows:

[0092] When a circular light spot is generated, the translation and refractive index change of the light beam reflected from the upper surface of the object to be measured are calculated through the throughput number of the circular light spot; the direction of change of the upper surface angle of the light beam reflected from the upper surface of the object to be measured is calculated through the movement direction of the center of the circular light spot; the magnitude of the upper surface angle change of the light beam reflected from the upper surface of the object to be measured is obtained based on the calibration data through the movement distance of the center of the circular light spot; and the change in the shape of the circular ring of the circular light spot can be used to know the changes in the translation and refractive index of the light beam reflected from the object to be measured at different positions.

[0093] When fringes are generated, the change in the fringes' order is calculated through the fringes' translation, and the upper surface translation and refractive index change are calculated. The change in the slope of the fringes indicates a change in the angle of the light beam reflected from the upper surface of the object to be measured. The change in the density of the fringes is used to calculate the magnitude of the upper surface angle change of the light beam reflected from the upper surface of the object to be measured. The change in the fringes at different positions of the fringes is used to calculate the magnitude of the upper surface angle change, upper surface translation, and refractive index change of the object to be measured.

[0094] The experimental optical path diagram of a device for simultaneously measuring the thermal expansion coefficient and temperature refractive index coefficient of an object provided by an embodiment of the present invention is as follows: Figure 3 As shown in the figure, the three-dimensional usage status diagram of each device in the experimental optical path is as follows Figure 4 As shown, the above-mentioned device includes a laser light source system, a Michelson-Fizeau interferometer system, a temperature control system and a data acquisition system connected through an optical path.

[0095] The laser light source system includes a laser, a beam expander, or a collimator. The Michelson-Fizeau interferometer system includes a 45° semi-transparent, semi-reflective mirror, two optical plane reflectors, and an object to be measured. The temperature control system includes a heat preservation device, a heating device, and a quartz material. The quartz material serves as the experimental reference surface and also as thermal insulation. The heat preservation device and the heating device are connected, and the object to be measured is placed in the heat preservation device, which is mounted on a quartz gasket. The data acquisition system is placed above the 45° semi-transparent, semi-reflective mirror. The data acquisition system includes frosted glass, a camera, and a processor; alternatively, it includes a charge-coupled device (CCD) camera and a processor.

[0096] The temperature control system, the 45° semi-transparent and semi-reflective mirror and the data acquisition system constitute an optical path in the vertical direction, and the laser, the beam expander or collimator, the 45° semi-transparent and semi-reflective mirror and the reflector constitute an optical path in the horizontal direction.

[0097] The above device can be used for experiments to simultaneously measure the thermal expansion coefficient and temperature refractive index coefficient of an object. Figure 3 and Figure 4 The optical path diagram of the embodiment of the present invention provides a method for simultaneously measuring the thermal expansion coefficient and the temperature refractive index coefficient of a transparent object. The processing flow includes the following processing steps:

[0098] Step (1) Install the system on the optical platform. First, install the laser and fix it on the optical platform. Turn on the laser power supply and adjust the laser's pitch angle so that its output light is parallel to the optical platform.

[0099] Step (2): Install a reflector in the optical path and adjust the horizontal reflector so that the horizontal incident beam and the reflected beam coincide. That is, the laser light returns to its original path through the reflector. Then block the horizontal reflector, install a 45° semi-transparent and semi-reflective mirror, and adjust its mirror angle so that the 45° semi-horizontal incident beam and the reflected beam can coincide. Install a beam expander, adjust its height and direction, and adjust the laser to a horizontal state. On the optical platform, adjust the distance between the beam expander and the laser, adjust the light spot to the set size range, and then fix the beam expander.

[0100] Step (3): placing the object to be measured on the quartz gasket, which is then enclosed in a heat preservation device, wherein the heating plate is embedded in the heat preservation device and connected to a heating box via a circuit, wherein the heating box is independent of the optical path.

[0101] Step (4): construct a data acquisition system including a camera, install an observation screen, and position the camera so that it can clearly capture the image on the observation screen.

[0102] Step (5): Check the interference pattern on the observation screen. To make the image clearer, you can fine-tune the laser so that the laser it emits is parallel to the horizontal plane and hits the center of the reserved position of the 45° semi-transparent and semi-reflective mirror. By adjusting the mirror angles of the 45° semi-transparent and semi-reflective mirror and the reflector, the horizontal incident light beam and the reflected light beam of the 45° semi-transparent and semi-reflective mirror and the reflector can coincide. Or you can fine-tune the object to be measured, the reflector, etc. until the interference pattern shape is clear and meets the requirements. It is worth noting that the distance from the reflector to the 45° semi-transparent and semi-reflective mirror should not be equal to the distance from the 45° semi-transparent and semi-reflective mirror to the quartz material reference plane.

[0103] Step (6): Turn on the heating device and the camera, and heat the temperature in the heat preservation device to the set temperature and then keep it warm. After the temperature of the heat preservation device stabilizes, the camera will obtain the image of the interference pattern throughput change displayed on the observation screen in the form of video.

[0104] Step (7), data processing. As an emerging precision measurement technology, image measurement technology has many advantages, such as high resolution, high speed, large dynamic range, rich information, and automation. It has been gradually and widely used in various industrial measurements. The experiment of the present invention combines the high precision of the Michelson interferometer with the above advantages of image measurement technology to achieve non-contact, high-precision, large-scale, and highly automated real-time measurement of refractive index.

[0105] The video data is opened on a computer and transcoded into an image. The image is subjected to noise reduction and binarization. If it is a circular spot, the center of the circular interference and the minimum circle radius in the current frame are found. The circular spot throughput is determined based on the number of peaks and troughs generated in the radius variation image. If it is a stripe, the position change of the stripe is captured. This method can obtain the circular spot throughput (fringe movement number) k1′-k1 formed by the interference between the upper surface of the object to be measured and the reflector, and the circular spot throughput (fringe movement number) k2′-k2 formed by the interference between the lower surface of the object to be measured and the reflector.

[0106] By changing the light source to collimated light and ensuring that other devices remain unchanged, repeating steps (2) to (7), the thermal expansion coefficient and temperature refractive index coefficient of the object can be measured simultaneously by changing the equal thickness interference order.

[0107] In practical applications, a data acquisition system consisting of frosted glass and a camera can be built to reflect the interference pattern on the frosted glass through a mirror and record it with a camera.

[0108] The observation screen in the data acquisition system can also be set to CCD, and the interference pattern can be converted into a digital signal by CCD and displayed on the computer, so that the interference image can be clearly presented on the computer screen.

[0109] By repeating steps (1) to (7) while ensuring that other devices remain unchanged, the thermal expansion coefficient and temperature refractive index coefficient of the object can still be measured simultaneously.

[0110] Calculate the thermal expansion coefficient and temperature refractive index of a single material using the above steps. Measure the sample multiple times and calculate the average value to reduce errors. This method can also be used to calculate the thermal expansion coefficient and temperature refractive index of multiple materials.

[0111] In practical applications, the light source can be changed to collimated light, and steps (2) to (7) can be repeated while ensuring that other devices remain unchanged. The thermal expansion coefficient and temperature refractive index coefficient of the object can be measured simultaneously by changing the equal thickness interference order.

[0112] During the experiment, we found that the interference ring had fluctuations and continuous swallowing and spitting, which made manual observation extremely difficult. In addition, the entire experiment lasted for a long time, resulting in lengthy manual readings. Therefore, computer image processing technology was used to achieve the purpose of quickly and conveniently observing the ring's swallowing and fringe movement.

[0113] The processing flow of a computer image processing algorithm provided by an embodiment of the present invention is as follows: Figure 6 As shown, the following processing steps are included:

[0114] Step S1: Use OpenCV to perform video frame cutting and processing. It is important to ensure that the captured equi-inclined fringes are centered and evenly exposed, otherwise it will be difficult to perform subsequent image processing and counting.

[0115] Step S2: De-noise the image to facilitate the identification of image features. In this experiment, a motion filter is used to enhance high-frequency information such as edges and contours of the image, while retaining low-frequency information of the image content, thereby improving the clarity of the boundary stripes.

[0116] Step S3: Binarization is performed. Since the brightness of the experimental interference image fluctuates significantly during the recording process, it is difficult to define the shape fitting standard without binarization. Therefore, binarization is extremely necessary. This experiment uses an adaptive threshold algorithm to binarize the image, converting it into an image with only two grayscales, 0 and 255, to eliminate the interference background image other than the interference image.

[0117] Step S4: Identify whether the image obtained above is a circular spot or a stripe and count them.

[0118] If the identified object is a circular spot, after obtaining the coordinates of the center of the interference spot, take the average pixel value of the eight points around the center as the vertical coordinate, plot its change curve with the frame number, and calculate the number of peaks in the curve to obtain the circular spot throughput.

[0119] The final information read can be used to obtain the spot throughput number based on the following criteria:

[0120] 1. If the fitted curve has smooth peaks and valleys and no sudden, drastic changes, the object being identified has not changed and is the same level of central circular spot, so there is no spot throughput.

[0121] 2. If the fitted curve shows a transient increase or decrease (ignoring bad values), it indicates that the recognition object has changed, with spots being swallowed or ejected. If there is a sudden drop, it means the radius of the recognition object has suddenly decreased, indicating the appearance of a new central spot inside, thus indicating ejection; Figure 7 A schematic diagram of the change of the central circular spot provided by an embodiment of the present invention. When a sudden increase occurs, it means that the radius of the identified object suddenly increases, indicating that the inner central circular spot disappears, and the original outer circular spot becomes a new central circular spot, which is spitting.

[0122] If the object to be identified is a stripe, a deepsort tracking algorithm is used to track the position of a particular stripe, counting the change in the stripe and calculating the number of stripes it passes through. A computer is used to fit a curve showing the change in the number of stripes as a function of the number of video frames. The number of peaks at which the curve exceeds a threshold set by the experiment is the stripe throughput.

[0123] Thus, the circular spot throughput number (fringe movement number) k1′-k1 formed by the interference between the upper surface of the object to be measured and the reflector and the circular spot throughput number (fringe movement number) k2′-k2 formed by the interference between the lower surface of the object to be measured and the reflector can be obtained.

[0124] A partial optical path diagram of a system for simultaneously measuring the thermal expansion coefficient and temperature refractive index coefficient of an object provided by an embodiment of the present invention is shown in FIG. Figure 5 As shown in the figure. The laser light emitted by the laser passes through the beam expander to form a light spot, which facilitates the formation of an interference image that is easier to observe. The laser light is then split into two beams by a 45° semi-transparent and semi-reflective mirror. One beam travels along the horizontal optical path through the reflector and semi-reflective mirror to finally reach the observation screen; the other beam travels along the vertical optical path through the lower surface of the 45° semi-transparent and semi-reflective mirror and propagates downward. It is reflected by the upper and lower surfaces of the object to be measured and split into two beams. The two reflected beams then pass through the 45° semi-transparent and semi-reflective mirrors to reach the observation screen.

[0125] The three beams of light, namely the light beam reflected by the reflector, the light beam reflected by the upper surface of the object to be measured, and the light beam reflected by the lower surface of the object to be measured, interfere with each other on the observation screen, producing circular light spots and stripes on the observation screen. Through actual experiments, it was found that the interference light intensity generated by the light beams reflected by the upper and lower surfaces and the surface of the object to be measured was the smallest, the light beam reflected by the reflector and the light beam reflected by the lower surface of the object to be measured was the second largest, and the light beam reflected by the reflector and the light beam reflected by the upper surface of the object to be measured was the strongest. Among them, by simultaneously measuring the change in the interference order generated by the light beams reflected by the upper and lower surfaces of the object, and the change in the interference order between the light beam reflected by the reflector and the light beam reflected by the lower surface of the object to be measured, the thermal expansion coefficient and the temperature refractive index coefficient of the object can be obtained simultaneously. In addition, by simultaneously measuring the change in the interference order 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 change in the interference order between the light beam reflected by the reflector and the light beam reflected by the lower surface of the object to be measured, the thermal expansion coefficient and the temperature refractive index coefficient of the object can also be obtained simultaneously.

[0126] When the laser system consists of a laser and a beam expander, the light source is a point source. When the reflector and the sample surface are completely perpendicular, this is called equal-inclination interference. The interference light can be detected on the screen as circular equal-inclination interference fringes. When the laser system consists of a laser and a collimator, the light source is a parallel source. When the reflector and the sample surface are not perpendicular, this is called equal-thickness interference. This produces straight fringes symmetrically centered around the equal-thickness intersection line. For different samples, the optimal interference method can be selected.

[0127] Compared to circular rings, straight fringes are more capable of displaying the amount of translation and refractive index change, as well as the direction and magnitude of angular change, at each point on the surface of the object being measured. However, they are more difficult to measure. In summary, for anisotropic objects, the thermal expansion coefficient and refractive index vary in different directions, making it suitable to use straight fringes symmetrically centered around equal-thickness intersection lines to observe the thermal expansion coefficient and temperature-dependent refractive index in different directions. For isotropic objects, the thermal expansion coefficient and refractive index are the same in different directions, making it suitable to use circular, equal-inclination interference fringes to observe their thermal expansion coefficient and temperature-dependent refractive index.

[0128] Table 2 Comparison of interference rings and fringes

[0129]

[0130] The upper surface of the quartz gasket at room temperature is used as the reference plane, which does not change with temperature changes and is fixed. Figure 3 Where l1 is the distance from the semi-transparent mirror to the reflector, l2 is the distance from the semi-transparent mirror to the upper surface of the object to be measured, and l3 is the distance from the upper surface of the object to be measured to the reference plane. Considering that the quartz gasket will also have a smaller deformation when heated, l4 is defined as the distance from the lower surface of the object to be measured to the reference plane, which is 0 at room temperature.

[0131] The interference between the light beam reflected by the reflector and the light beam reflected by the upper surface of the object to be measured is:

[0132] 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:

[0133]

[0134] Among them, n0 is the refractive index of air, λ is the wavelength of the laser emitted by the laser, and k1 is the fringe order.

[0135] In the formula, l and k both change with temperature, so we have:

[0136]

[0137] Wherein, l2′ is the distance from the heated half-transparent half-reflective mirror to the upper surface of the object to be measured, and k1′ is the fringe order after heating.

[0138] Subtracting (6) from (5) yields:

[0139] 2n0(l2′-l2)=(k1′-k1)λ (7)

[0140] Here, l2′-l2 can be calculated by the throughput number of circular spots or the number of stripe movements k′-k.

[0141] Interference caused by the light beam reflected by the reflector and the light beam reflected by the lower surface of the object to be measured:

[0142] First, the expansion of the quartz gasket under the object to be measured due to heat is temporarily not considered, that is, it is assumed that the lower surface of the object to be measured is fixed.

[0143] 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:

[0144] δ=2n0l2+2nl3-2n0l1=k2λ (8)

[0145] Among them, n0 is the refractive index of air, n is the refractive index of the sample being measured, and λ is the wavelength of the laser emitted by the laser.

[0146] In the formula, l2, n, l3, and k all change with temperature, so we have:

[0147] δ′=2n0l2′+2n′l3′-2n0l1=k2′λ (9)

[0148] Wherein, l2′ is the distance from the half-transparent mirror to the upper surface of the object to be measured after heating, l3′ is the distance from the upper surface of the object to be measured to the reference plane after heating, and k2′ is the fringe order after heating.

[0149] Subtracting (9) from (8) yields:

[0150] 2n0(l2′-l2)+2n′l3′-2nl3=(k2′-k2)λ (10)

[0151] Let n′=n+Δn, we can get:

[0152] 2n0(l2′-l2)+2n(l a ′-l3)+2Δnl3′=(k2′-k2)λ (11)

[0153] It is easy to see that l2 + l3 is a constant, always equal to the distance from the semi-transparent and semi-reflective mirror to the reference surface, so l2′ - l2 = -(l3′ - l3). From Equation (5), we know that l2′ - l2. At the same time, l3 is also easy to find, being the thickness corresponding to the initial temperature. Therefore, we only need to obtain the throughput k2′ - k2 through image processing to calculate the refractive index change Δn of the object to be measured.

[0154] Error correction for quartz spacers: A quartz disc is placed beneath the object being measured. The linear expansion coefficient of quartz is one to two orders of magnitude smaller than that of the object being measured, so its effect on the experiment is small but not negligible. This is equivalent to considering the distance l4 between the quartz spacer (equivalent to the lower surface of the object being measured) and the reference plane, assuming the imaginary reference plane remains unchanged. At room temperature, l4 is zero. As the temperature rises, the value of l4 may no longer be zero.

[0155] The principle of correction is similar to the principle of interference between the reflector and the light beam reflected from the upper surface. Here is a corrected formula based on formula (5):

[0156] 2n0(l2′-l2)+2n(l3′-l3)+2Δnl3′+2n(l4-l4′)-2Δnl4′=(k2′-k2)λ (12)

[0157] Among them, l4-l4′ and l4′ (l4 is initially 0) can both be calculated from a blank experiment, and n represents the refractive index of the sample being tested.

[0158] In summary, we only need to obtain the spot throughput numbers (fringe movement numbers) k1′-k1, k2′-k2, and k3′-k3 in the blank experiment to calculate the value of Δn within a certain temperature range, and then calculate the thermal expansion coefficient and temperature refractive index coefficient of the object to be measured.

[0159] Principle of the inclination angle of the surface of the object to be measured: If it is a circular spot interference pattern, the movement of the center of the light spot represents a small inclination angle on the surface of the object to be measured. Through calibration, the relationship between the size of the inclination angle and the direction of movement of the center of the circular spot in the two-dimensional plane can be obtained. Use a screw micrometer to calibrate the angle. First, place the screw micrometer horizontally, place the object to be measured on the micrometer plane, and rotate it in the same direction (clockwise or counterclockwise) to raise the table. At this time, the distance the center of the circle in the observation screen moves can be observed as Δx, and the difference in vertical height changes before and after is recorded as Δh. The distance from the fulcrum of the angle change of the screw micrometer to the lifting point is recorded as L s , from this calculation, the angle change can be obtained, which is recorded as Δθ.

[0160] If it is a fringe interference pattern, the change in the slope of the fringe represents a small inclination angle on the surface of the object to be measured. Through calibration, the size of the inclination angle and its relationship with the slope change can be obtained. Use a screw micrometer to calibrate the angle. First, place the screw micrometer horizontally, place the object to be measured on the micrometer plane, and rotate it in the same direction (clockwise or counterclockwise) to raise the table. At this time, you can observe that the slope of the fringe on the observation screen changes as Δα. Record the difference in vertical height changes before and after as Δh. Record the distance from the fulcrum of the angle change of the screw micrometer to the lifting point as L. s , from this calculation, the angle change can be obtained, which is recorded as Δθ.

[0161] To eliminate the effects of thermal expansion and other factors on the quartz gasket, a blank experiment is performed first. The experimental setup and steps remain unchanged, with only the object to be tested removed. The principle of the blank experiment is similar to the interference between a reflector and a light beam reflected from an upper surface. The formula is given directly here:

[0162] 2n0(l4′-l4)=(k3′-k3)λ (13)

[0163] Based on this, we can get l4′-l4 as a known quantity in formula (9).

[0164] To enhance systemicity, ease of operation, and aesthetics, the aforementioned device was integrated into a system constructed from acrylic panels and secured to an optical platform using an optical base. The integrated device only required adjusting the laser and beam expander to collimate the light and center it on the semi-transparent, semi-reflective mirror. The heating system and camera were then activated to perform experimental measurements. The following describes the connections and structural features of the various components within the device:

[0165] Step (1) Place the object to be measured on the quartz gasket of the heating device, turn on the power of the He-Ne laser, adjust the laser pitch angle, adjust the laser to a horizontal state, and align the light beam with the center position of the 45° semi-transparent and semi-reflective mirror.

[0166] Step (2) fine-tune the object to be measured, the 45° semi-transparent and semi-reflective mirror, and the reflector so that the interference pattern has a good shape and is easy to observe.

[0167] Step (3) turns on the heating device and the camera, and heats the temperature in the heat preservation device to the set temperature and then keeps it warm. After the temperature of the heat preservation device stabilizes, the camera will obtain the image of the interference pattern throughput change displayed on the observation screen in the form of video recording.

[0168] Step (4) opens the video data on a computer, uses image processing related codes to transcode the video data into an image at a speed of 60 frames per second, performs noise reduction and binarization on the image, and processes each frame of the image to obtain the circular spot throughput number (fringe throughput number) k1′-k1 formed by the interference between the upper surface of the object to be measured and the reflector, and the circular spot throughput number (fringe throughput number) k2′-k2 formed by the interference between the lower surface and the reflector.

[0169] In step (5), substituting k1′-k1 into formula (7) yields the axial extension l2′-l2 of the object under test. Then, using the blank experiment to determine l4′ (substituting k3′-k3 obtained in the blank experiment into formula (7) yields l4′), calculate l2′-l2-l4′. The thermal expansion coefficient of the object under test can be obtained using formula (3). Substituting k2′-k2 into formula (12) yields the refractive index change Δn of the object under test, which can then be obtained by substituting this into formula (4) to yield the temperature refractive index coefficient of the object under test.

[0170] Step (6) Replace different samples and repeat steps (3)-(6) to obtain multiple sets of data.

[0171] The embodiment of the present invention has low requirements on the sample shape; a relatively flat surface is sufficient and no adhesion is required. Furthermore, the thermal expansion coefficient and temperature refractive index coefficient are calculated using the interference spot throughput (or fringe movement number), which is easier to computerize than fringe analysis.

[0172] In summary, the present invention combines Michelson and Fizeau interferometry techniques, utilizing both the reflector and the sample's two surfaces to simultaneously measure changes in axial length and refractive index during the same heating process. This allows for simultaneous measurement of both the thermal expansion coefficient and the temperature-dependent refractive index of a material, thereby exploring thermal deformation mechanisms and providing applications in criminal investigation and precision instrument calibration. Compared to other techniques, which often require more complex operations and equipment, this technique can more easily and simultaneously measure changes in both the thermal expansion coefficient and the temperature-dependent refractive index of a transparent object when heated.

[0173] To ensure the accuracy of the measurement, the present invention abandons the temperature increase measurement technology used in traditional devices and adopts the temperature reduction process to collect data, thus avoiding the influence of air disturbance on the accuracy of the experiment to a great extent.

[0174] This application uses Motion filter and adaptive threshold algorithm to binarize and enhance image information.

[0175] Those skilled in the art will appreciate that the accompanying drawings are merely schematic diagrams of an embodiment, and the modules or processes in the accompanying drawings are not necessarily required to implement the present invention.

[0176] From the above description of the embodiments, it can be seen that those skilled in the art can clearly understand that the present invention can be implemented by means of software plus the necessary general-purpose hardware platform. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a storage medium such as ROM / RAM, a magnetic disk, or an optical disk, and includes a number of instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in various embodiments of the present invention or certain parts of the embodiments.

[0177] Each embodiment in this specification is described in a progressive manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments. In particular, for the device or system embodiments, since they are basically similar to the method embodiments, the description is relatively simple. For the relevant parts, refer to the partial description of the method embodiments. The device and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the scheme of this embodiment. A person of ordinary skill in the art can understand and implement it without making any creative efforts.

[0178] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A system for simultaneously measuring the thermal expansion coefficient and temperature refractive index coefficient of an object, characterized in that: include: Laser light source system, Michelson-Fizeau interferometer system, temperature control system and data acquisition system connected by optical path; The laser light source system includes a laser, a beam expander or a collimator, the Michelson-Fizeau interferometer system includes a 45° semi-transparent and semi-reflective mirror, a reflector, and an object to be measured; the temperature control system includes a heat preservation device, a heating device, and a quartz material, the quartz material serving as an experimental reference surface, the heat preservation device and the heating device are connected, the object to be measured 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° semi-transparent and semi-reflective mirror; The temperature control system, the 45° semi-transparent and semi-reflective mirror and the data acquisition system constitute an optical path in the vertical direction, and the laser, the beam expander or collimator, the 45° semi-transparent and semi-reflective mirror and the reflector constitute an optical path in the horizontal direction; By adjusting the position of the laser, beam expander or collimator, the laser light emitted by the laser is collimated and hits the center of the reserved position of the 45° half-transparent reflector. By adjusting the mirror angle of the 45° half-transparent reflector, the horizontal incident beam and the reflected beam of the 45° half-transparent reflector can coincide. The distance from the reflector to the 45° half-transparent reflector is not equal to the distance from the 45° half-transparent reflector to the reference surface of the quartz material; The laser emitted by the laser is divided into two beams after passing through a beam expander or collimator and a 45° semi-transparent and semi-reflective mirror. One beam of light passes through a reflector and a 45° semi-transparent and semi-reflective mirror and finally reaches the observation screen; the other beam of light is reflected by a 45° semi-transparent and semi-reflective mirror to the upper and lower surfaces of the object to be measured, and is divided into two beams of light. These two beams of light then pass through a 45° semi-transparent and semi-reflective mirror and reach the observation screen. The light beam reflected by the reflector, the light beam reflected by the upper surface of the object to be measured, and the light beam reflected by the lower surface of the object to be measured, these three beams of light interfere with each other on the observation screen, and produce circular light spots or stripes on the observation screen; When the laser system consists of a laser and a beam expander, the light source formed is a point light source, and when the reflector and the sample surface are completely perpendicular, it is equal-inclination interference, and the interference light appears as circular equal-inclination interference fringes on the observation screen; when the laser system consists of a laser and a collimator, the light source formed is a parallel light source, and when the reflector and the sample surface are not perpendicular, it is equal-thickness interference, and the interference light appears as straight fringes symmetrical with the equal-thickness intersection line as the center on the observation screen; When a circular light spot is generated, the translation and refractive index change of the light beam reflected from the upper surface of the object to be measured are calculated by the throughput of the circular spot. The direction of the change in the upper surface angle of the light beam reflected from the upper surface of the object to be measured is calculated by the movement direction of the center of the circular spot. The change in the upper surface angle of the light beam reflected from the upper surface of the object to be measured is obtained based on the calibration data by the movement distance of the center of the circular spot. The change in the shape of the circular spot ring can be used to determine the changes in the translation and refractive index of the light beam reflected from the object to be measured at different positions. When fringes are generated, the change in the fringes' order is calculated by the fringes' translation, and the upper surface translation and refractive index change are calculated. The change in the slope of the fringes indicates a change in the angle of the light beam reflected from the upper surface of the object to be measured. The change in the density of the fringes is used to calculate the magnitude of the upper surface angle change of the light beam reflected from the upper surface of the object to be measured. The change in the fringes at different positions on the fringes is used to calculate the magnitude of the upper surface angle change, upper surface translation, and refractive index change of the object to be measured. The heat preservation device is cylindrical and is placed on the quartz gasket. The surface of the heat preservation device is perforated, and the aperture is close to the size of the light spot. The heating device includes a heating plate, a temperature controller and a temperature probe. The heating plate is attached to a cylindrical stainless steel product and clamped in the cylindrical shell. The heating plate is connected to the temperature controller via an electric wire for heating. The temperature of the heating plate is adjusted by the temperature controller. The temperature probe penetrates into the interior of the cylindrical shell through a small hole at the top and transmits temperature data back to the temperature controller.

2. The system according to claim 1, wherein: For anisotropic objects, the laser system uses a laser and a collimator, and uses straight stripes symmetrically centered around equal-thickness intersection lines to observe the thermal expansion coefficient and temperature refractive index coefficient in different directions. For isotropic objects, the laser system uses a laser and a beam expander to observe its thermal expansion coefficient and temperature refractive index coefficient using circular equal-inclination interference fringes.

3. A method for simultaneously measuring the thermal expansion coefficient and temperature refractive index coefficient of an object, characterized in that: Applicable to the system according to any one of claims 1 to 2, the method comprising: Step (1), installing the system on an optical platform, fixing the laser on the optical platform, turning on the laser power supply, and adjusting the pitch angle of the laser so that the laser emitted by the laser is parallel to the optical platform; Step (2): Install a reflector in the optical path, adjust the reflector so that the incident light beam and the reflected light beam coincide, then block the horizontal reflector, install a 45° semi-transparent and semi-reflective mirror and adjust its mirror angle so that the horizontal incident light beam and the reflected light beam of the 45° semi-transparent and semi-reflective mirror can coincide, install a beam expander or collimator, adjust the height and direction of the beam expander or collimator, adjust the laser to a horizontal state, and on the optical platform, adjust the distance between the beam expander or collimator and the laser, adjust the light spot to a set size range, and then fix the beam expander; Step (3), placing the object to be tested on a quartz gasket, which is then placed in a heat preservation device, wherein the heating plate is embedded in the heat preservation device and connected to a heating box via a circuit; Step (4), building a data acquisition system; Step (5), observing the interference pattern, fine-tuning the laser so that the laser emitted by the laser is parallel to the horizontal plane and hits the center of the reserved position of the 45° semi-transparent and semi-reflective mirror, and adjusting the mirror angles of the 45° semi-transparent and semi-reflective mirror and the reflector so that the horizontal incident light beam and the reflected light beam of the 45° semi-transparent and semi-reflective mirror and the reflector can coincide; or fine-tuning the object to be measured and the reflector until the interference pattern is clear and the distance from the reflector to the 45° semi-transparent and semi-reflective mirror is not equal to the distance from the 45° semi-transparent and semi-reflective mirror to the reference plane of the quartz material; Step (6), turning on the heating device, controlling the sample temperature according to the set temperature curve, and recording the stripe state during this process; Step (7), obtaining the circular spot throughput number or fringe movement number k1′-k1 formed by the interference between the upper surface of the object to be measured and the reflector, and the circular spot throughput number or fringe movement number k2′-k2 formed by the interference between the lower surface of the object to be measured and the reflector; The axial elongation of the object to be measured is obtained according to the circular spot throughput number or the fringe movement number k1′-k1, and the thermal expansion coefficient of the object to be measured is further calculated; the refractive index change Δn of the object to be measured is obtained according to the circular spot throughput number or the fringe movement number k2′-k2, and the temperature refractive index coefficient of the object to be measured is further calculated.

4. The method according to claim 3, characterized in that The axial elongation of the object to be measured is obtained according to the circular spot throughput number or the fringe movement number k1′-k1, and then the thermal expansion coefficient of the object to be measured is calculated. include: Substituting k1′-k1 into formula (7) we can obtain the axial extension l2′-l2 of the object to be measured: 2n0(l2′-l2)=(k1′-k1)λ (7) n0 is the refractive index of air, λ is the wavelength of the laser emitted by the laser; Substitute k3′-k3 obtained from the blank experiment into formula (7) to obtain l4′; Calculate the axial extension of the object to be measured dl = l2′-l2-l4′; According to the temperature values recorded during the measurement process, the thermal expansion coefficient α of the object to be measured is calculated using formula (3): l represents the initial length of the solid material, and t represents the temperature.

5. The method according to claim 3, characterized in that: The refractive index change Δn of the object to be measured is obtained according to the circular spot throughput number or the fringe movement number k2′-k2, and then the temperature refractive index coefficient of the object to be measured is calculated. include: Substitute k2′-k2 into formula (12) to obtain the refractive index change Δn of the object to be measured 2n0(l2′—l2)+2n(l3′—l3)+2△nl3′+2n(l4-l4′)-2△nl4′=(k2′-k2)λ (12) According to the temperature value recorded during the measurement process and the refractive index change Δn of the object to be measured, the temperature refractive index coefficient of the object to be measured is obtained using formula (4): Where 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 change in the interference order between the light beam reflected by the reflector and the light reflected by the upper surface of the object to be measured.

6. The method according to claim 3, characterized in that: The data acquisition system consists of frosted glass and a camera or CCD. When the frosted glass and camera are used, the interference pattern is reflected on the frosted glass through a reflector and recorded by the camera; when the CCD is used, the interference pattern is converted into a digital signal by the CCD and displayed on the computer for screen recording.

7. The method according to claim 3, characterized in that The step (7) specifically includes: The first step is to use opencv to cut and process the video frames to obtain each frame image; The second step is to perform denoising on the frame image; The third step is to perform a binarization operation on the denoised image; The fourth step is to identify whether the image after the binarization operation is a circular spot or a stripe and count them; If the object to be identified is a circular spot, after obtaining the coordinates of the center of the interference spot, take the average pixel value of the eight points around the center as the vertical coordinate, plot its change curve with the frame number, and calculate the number of peaks of the curve to obtain the circular spot throughput; If the object to be identified is a stripe, the deepsort tracking algorithm is used to track the position of a stripe, count the change in the stripe, calculate the number of stripes it passes through, and use a computer to fit the curve of the change in the number of stripes versus the number of video frames. The number of peaks at which the curve exceeds the threshold set by the experiment is the stripe throughput; Thus, the circular spot throughput number or fringe movement number k1′-k1 formed by the interference between the upper surface of the object to be measured and the reflector, and the circular spot throughput number or fringe movement number k2′-k2 formed by the interference between the lower surface of the object to be measured and the reflector are obtained.

Images