A liquid helium-free cryogenic magneto-optical imager and its working method

Abstract

This invention discloses a liquid helium-free cryogenic magneto-optical imager and its operating method, comprising a support column and an optical vibration damping platform; a cold head fixed to a stainless steel support column and connected to a compressor via a helium gas pipe; a vibration damping airbag connected below the cold head and fixed to the optical vibration damping platform; the vibration damping airbag connected to a sample chamber, which is connected to a molecular pump unit via a corrugated pipe; an observation window is provided above the sample chamber, which is fitted with a high-precision solenoid coil magnet; a high-resolution observation system is provided above the observation window, which includes an objective lens, an analyzer, a polarizer, and a light source, with the analyzer connected to a high-resolution CCD via an optical path; the cold head, high-precision magnet, and high-resolution CCD are respectively connected to a computer. This invention uses a liquid helium-free cooling system, avoiding the high cost of liquid helium, and uses a vibration damping airbag to effectively reduce the vibration of the cold head, enabling the observation of clear magneto-optical images and the observation of magneto-optical images of samples in the sample chamber under different temperature and magnetic field environments.

Description

Technical Field

[0001] This invention relates to a magneto-optical imager and its operating method, and more particularly to a liquid helium-free cryogenic magneto-optical imager and its operating method. Background Technology

[0002] Magneto-optical imagers utilize the Faraday magneto-optical effect to convert the magnetic flux density in a sample into an optical signal, providing direct observation capabilities. Magneto-optical imagers are characterized by not causing damage to the sample and visualizing the magnetic flux density signal.

[0003] Currently, common industrial magneto-optical imagers are typically used to detect damage to iron objects and can only perform detection at room temperature. Common laboratory magneto-optical imagers usually require liquid helium to maintain a cryogenic environment, have insufficient external magnetic field range, and some imagers cannot perform mapping image measurements. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a liquid helium-free cryogenic magneto-optical imager that operates at ultra-low temperatures and with a sufficiently large external magnetic field, enabling two-dimensional image observation.

[0005] The second objective of this invention is to provide a method for operating the above-mentioned liquid helium-free cryogenic magneto-optical imager.

[0006] Technical Solution: The liquid helium-free cryogenic magneto-optical imager of the present invention includes a support column and an optical vibration damping platform; a cold head is fixed on a stainless steel support column and connected to a compressor via a helium gas pipe; a vibration damping airbag is connected below the cold head and fixed on the optical vibration damping platform; the vibration damping airbag is connected to a sample chamber and connected to a molecular pump unit via a corrugated pipe; an observation window is provided above the sample chamber; a high-precision solenoid coil magnet is fitted onto the observation window; a high-resolution observation system is provided above the observation window, the high-resolution observation system including an objective lens located above the observation window, an analyzer located above the objective lens, a polarizer located on one side of the analyzer, and a light source located on one side of the polarizer; the analyzer is connected to a high-resolution CCD via an optical path; the cold head, the high-precision magnet, and the high-resolution CCD are respectively connected to a computer.

[0007] Furthermore, the shock-absorbing airbag is equipped with a heat-conducting copper pillar connected to the cold head, a helium airbag is located below the heat-conducting copper pillar, and a T-shaped heat-conducting copper pipe is connected below the helium airbag. The T-shaped heat-conducting copper pipe extends into the sample chamber and connects to the sample stage.

[0008] Furthermore, the cold head is connected to the shock-absorbing airbag, and the shock-absorbing airbag is connected to the optical shock-absorbing platform via vacuum chambers.

[0009] Furthermore, the vacuum cavity between the cold head and the shock-absorbing airbag is fixed to the support column by a crossbar.

[0010] The above-mentioned working method of the liquid helium-free cryogenic magneto-optical imager includes the following steps:

[0011] (a) Attach the sample to the substrate, lay a thin film on top of the sample to obtain a sample assembly, and place the sample assembly in the sample chamber;

[0012] (b) Evacuate the sample chamber and replenish helium into the shock-absorbing airbag until the air pressure inside the airbag is equal to atmospheric pressure.

[0013] (c) The computer controls the cold head to maintain the required temperature, and then changes the magnetic field of the high-precision solenoid coil magnet to generate a magneto-optical image;

[0014] (d) The computer receives a two-dimensional magneto-optical image acquired by the high-resolution observation system, wherein the light is emitted from an LED white light source, the white light is converted into pre-polarized light by a polarizer, then reflected by a thin film and passed through an analyzer, and finally received by a CCD.

[0015] (e) Optical signals obtained by software adapted in a computer.

[0016] Furthermore, in step (a), the sample is a superconducting material or a ferromagnetic material.

[0017] Furthermore, in step (a), the gap between the sample and the thin film is less than 10 micrometers. The thin film is a gallium-doped yttrium iron garnet thin film.

[0018] Furthermore, in step (c), for superconducting materials, the required temperature is below the superconducting critical temperature, and for ferromagnetic materials, it is the Curie temperature.

[0019] Furthermore, in step (c), the magnetic field strength is changed by controlling the magnitude of the current in the copper wire of the solenoid.

[0020] Furthermore, the temperature range that can be maintained in the sample chamber of the cryogenic thermostat of the present invention is 4.2K-305K. The high-resolution observation system can achieve a spatial resolution of 10 micrometers for sample observation and a magnetic induction intensity resolution of 1 Oe for sample observation. The high-precision solenoid coil magnet can maintain an applied magnetic field range of -1680 Oe to +1680 Oe, where the vertical direction from bottom to top is taken as +.

[0021] Furthermore, in step (e), based on the provided software and data processing program, the magneto-optical grayscale image of the two-dimensional mapping of the sample can be directly observed, the superconducting sample can be observed in a fully automatic manner, and the image can be processed to obtain the remanent magnetic induction intensity distribution image and the superconducting critical current distribution image of the superconducting sample, and the magnitude of the superconducting critical current can be estimated.

[0022] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects: (1) The magneto-optical instrument adopts a liquid helium-free cooling system, which avoids the high cost of liquid helium. The shock-absorbing airbag effectively reduces the vibration of the cold head, so that clear magneto-optical images can be observed. It can also observe magneto-optical images of samples in the sample chamber under different temperatures and magnetic fields. (2) The magneto-optical images obtained by the present invention are area scan mapping images, which are clearer and more systematic. (3) Clear magnetic induction intensity distribution map and critical current distribution map can be obtained by software processing. (4) The operation is simple, the cost is low, and the results are intuitive, making it suitable for units without a liquid helium recovery system. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure of the liquid helium-free cryogenic magneto-optical imager of the present invention;

[0024] Figure 2 This is a schematic diagram of the connection structure between the shock-absorbing airbag and the sample chamber of the present invention;

[0025] Figure 3 This is a schematic diagram of the sample chamber structure of the present invention;

[0026] Figure 4 This is a schematic diagram of the top structure of the sample stage of the present invention;

[0027] Figure 5 FeTe was captured by the high-resolution observation system in Embodiment 1 of the present invention. 0.8 Se 0.2 The magnetic induction intensity of a superconducting single crystal can be directly observed in grayscale.

[0028] Figure 6 FeTe was captured by the high-resolution observation system in Embodiment 2 of the present invention. 0.5 Se 0.5 Grayscale image of direct observation of magnetic induction intensity of superconducting tape;

[0029] Figure 7 The FeTe after software processing in Embodiment 3 of the present invention 0.5 Se 0.5 Magnetic induction intensity distribution of superconducting tape;

[0030] Figure 8 In Embodiment 3 of the present invention Figure 7 Magnetic induction intensity line scan distribution map at the red line;

[0031] Figure 9 FeTe in Embodiment 4 of the present invention 0.8 Se 0.2 Remanent magnetic flux density distribution of a superconducting single crystal at 4.2 K;

[0032] Figure 10 FeTe in Embodiment 4 of the present invention 0.8 Se 0.2 Critical current distribution of a superconducting single crystal at 4.2 K (including current direction) a;

[0033] Figure 11 FeTe in Embodiment 4 of the present invention 0.8 Se 0.2 Critical current distribution of a superconducting single crystal at 4.2K (including current direction) b;

[0034] Figure 12 FeTe in Embodiment 4 of the present invention 0.8 Se 0.2 The magnitude distribution of the critical current of a superconducting single crystal at 4.2K (excluding the current direction). Detailed Implementation

[0035] The present invention will now be described in further detail.

[0036] Example 1

[0037] like Figure 1-4 As shown, this invention provides a liquid helium-free cryogenic magneto-optical imager, which is supported by a stainless steel support column 13 and an optical vibration damping platform 8. A cold head 1 is fixed to the stainless steel support column 13 and connected to a compressor 9 via a helium gas pipe 10. A vibration damping airbag 2 is connected below the cold head 1 and fixed to the optical vibration damping platform 8. The vibration damping airbag is connected to the sample chamber 3, specifically via a stainless steel "T"-shaped pipe on the right side. The vibration damping airbag 2 is connected to a molecular pump unit 12 via a corrugated pipe 11. An observation window 6, specifically a cylindrical quartz observation window, is provided above the sample chamber 3. A high-precision solenoid coil magnet 4 is fitted onto the observation window 6. A high-resolution observation system 5 is provided above the window 6. The high-resolution observation system 5 includes an objective lens 506 located above the observation window 6, an analyzer 503 located above the objective lens 506, a polarizer 502 located to the right of the analyzer 503, and a light source 501 located to the right of the polarizer 502. The light source 501 is an LED white light source. The analyzer 503 is connected to a high-resolution CCD 504 via an optical path. The cold head 1, the high-precision magnet 4, and the high-resolution CCD 504 are respectively connected to the computer 7.

[0038] The cold head 1 and the shock-absorbing airbag 2 are connected through a first vacuum chamber 102; the first vacuum chamber 102 is fixed to the support column 13 by two crossbars 103 and 104. The shock-absorbing airbag 2 and the optical shock-absorbing platform 8 are connected through a second vacuum chamber 303; the cold head 1, the first vacuum chamber 102, the shock-absorbing airbag 2, and the second chamber 303 are interconnected; the shock-absorbing airbag 2 is connected to the molecular pump unit 12 through the second vacuum chamber 303 and the bellows 11.

[0039] The optical vibration damping platform 8 includes a support rod and a rigid platform located at the top of the support rod. The bottom surface of the support rod is provided with damping material, which can absorb most of the vibrations from the table legs. The damping material can be a damping material commonly used in the prior art.

[0040] like Figure 2 As shown, the shock-absorbing airbag 2 is equipped with a heat-conducting copper pillar 201 connected to the cold head. Below the heat-conducting copper pillar 201 is a helium airbag 202. Below the helium airbag 202 is a T-shaped heat-conducting copper pipe 302. The T-shaped heat-conducting copper pipe 302 extends into the sample chamber 3 and connects to the sample stage 301.

[0041] The above-mentioned working method of the liquid helium-free cryogenic magneto-optical imager includes the following steps:

[0042] (a) First, FeTe is attached to the substrate 601. 0.8 Se 0.2 A superconducting single crystal sample 602 is covered with a gallium-doped yttrium iron garnet thin film 603 to complete the sample assembly, as shown in the attached figure. Figure 3 , 4 As shown;

[0043] (b) Place the assembled sample components into sample chamber 3;

[0044] (c) Evacuate the sample chamber to a vacuum level of less than 10^-4 mbar, and add a small amount of helium to the shock-absorbing airbag 2 until the air pressure inside the airbag is equal to atmospheric pressure.

[0045] (d) The computer 7 controls the cold head 1 to decrease from room temperature to 4.2K and maintain it, and then changes the magnetic field of the magnet 4 to 1000 Oe and then reduces it to zero field;

[0046] (e) The computer 7 receives the two-dimensional mapping magneto-optical image acquired by the high-resolution observation system, wherein the light is emitted from the LED white light source 501, the white light is converted into pre-polarized light by the polarizer 502, then reflected by the yttrium iron garnet film and passed through the analyzer 503, and finally received by the CCD 504.

[0047] (f) Obtain the direct observation grayscale image of magnetic induction intensity by processing the software adapted in computer 7, such as Figure 5 As shown.

[0048] FeTe 0.8 Se 0.2 Image of the remanent magnetic flux density of a superconducting single crystal sample at 1000 Oe after zero-field cooling, as shown below. Figure 5 As shown, this demonstrates that the liquid helium-free cryogenic magneto-optical imager of the present invention can effectively observe superconducting single-crystal materials.

[0049] Example 2

[0050] A method for operating a liquid helium-free cryogenic magneto-optical imager includes the following steps:

[0051] (a) First, FeTe is attached to the substrate. 0.5 Se 0.5 Superconducting tape sample-1: A gallium-doped yttrium iron garnet film is tightly covered on the sample to complete the sample assembly;

[0052] (b) Place the assembled sample assembly into sample chamber 3, wherein the sample is located between the substrate and the gallium-doped yttrium iron garnet film shown in the figure;

[0053] (c) Evacuate the sample chamber to a vacuum level of less than 10^-4 mbar, and add a small amount of helium to the shock-absorbing airbag 2 until the air pressure inside the airbag is equal to atmospheric pressure.

[0054] (d) The computer 7 controls the cold head 1 to drop from room temperature to 8K and maintain it, and then changes the magnetic field of the magnet 4 to 1000 Oe and then drops it to zero field.

[0055] (e) The computer 7 receives the two-dimensional mapping magneto-optical image acquired by the high-resolution observation system, wherein the light is emitted from the LED white light source 501, the white light is converted into pre-polarized light by the polarizer 502, then reflected by the yttrium iron garnet film and passed through the analyzer 503, and finally received by the CCD 504.

[0056] (f) Obtain the direct observation grayscale image of magnetic induction intensity by processing the software adapted in computer 7, such as Figure 6 As shown.

[0057] FeTe 0.5 Se 0.5 Image of the remanent magnetic flux density of the superconducting tape sample at 1000 Oe after zero-field cooling is shown below. Figure 6 As shown, this demonstrates that the liquid helium-free cryogenic magneto-optical imager of the present invention can effectively observe superconducting tape materials.

[0058] Example 3

[0059] (a) First, FeTe is attached to the substrate. 0.5 Se 0.5 Superconducting tape sample-2: A gallium-doped yttrium iron garnet film is tightly covered on the sample to complete the sample assembly;

[0060] (b) Place the assembled sample assembly into sample chamber 3, wherein the sample is located between the substrate and the gallium-doped yttrium iron garnet film shown in the figure;

[0061] (c) Evacuate the sample chamber to a vacuum level of less than 10^-4 mbar, and add a small amount of helium to the shock-absorbing airbag 2 until the air pressure inside the airbag is equal to atmospheric pressure.

[0062] (d) The computer 7 controls the cold head 1 to drop from room temperature to 8K and maintain it, and then changes the magnetic field of the magnet 4 to 1000 Oe and then drops it to zero field.

[0063] (e) The computer 7 receives the two-dimensional mapping magneto-optical image acquired by the high-resolution observation system, wherein the light is emitted from the LED white light source 501, the white light is converted into pre-polarized light by the polarizer 502, then reflected by the yttrium iron garnet film and passed through the analyzer 503, and finally received by the CCD 504.

[0064] (f) The magnetic field strength distribution map is obtained by software processing adapted in computer 7, such as... Figure 7 As shown.

[0065] (g) Cut FeTe 0.5 Se 0.5 A line scan distribution of the magnetic flux density along a straight line in the magnetic flux density distribution map of superconducting tape sample-2 is shown below. Figure 8 As shown, the superconducting critical current density is estimated using the Bean model.

[0066]

[0067] Where ΔB is Figure 8 The peak value is given by , where 'a' is the sample width, '2d' is the sample thickness, and the rest are correlation constants. The FeTe values ​​estimated from this are... 0.5 Se 0.5 The superconducting critical current density of the superconducting tape is 1.1 × 10^6 A / cm. 2 Among them, from Figure 8 The optimal resolution for visible light (B) is ~1 Oe, and the spatial resolution is ~10 micrometers.

[0068] This demonstrates that the liquid helium-free cryogenic magneto-optical imager of the present invention can obtain linearly scanned magnetic induction intensity distribution images, with an optimal magnetic induction intensity resolution of up to 1 Oe and a spatial resolution of 10 micrometers.

[0069] Example 4

[0070] (a) First, FeTe is attached to the substrate. 0.8 Se 0.2 A superconducting single crystal sample is covered with a gallium-doped yttrium iron garnet film to complete the sample assembly.

[0071] (b) Place the assembled sample assembly into sample chamber 3, wherein the sample is located between the substrate and the gallium-doped yttrium iron garnet film shown in the figure;

[0072] (c) Evacuate the sample chamber to a vacuum level of less than 10^-4 mbar, and add a small amount of helium to the shock-absorbing airbag 2 until the air pressure inside the airbag is equal to atmospheric pressure.

[0073] (d) The computer 7 controls the cold head 1 to decrease from room temperature to 4.2K and maintain it, and then changes the magnetic field of the magnet 4 to 1000 Oe and then reduces it to zero field;

[0074] (e) The computer 7 receives the two-dimensional mapping magneto-optical image acquired by the high-resolution observation system, wherein the light is emitted from the LED white light source 501, the white light is converted into pre-polarized light by the polarizer 502, then reflected by the yttrium iron garnet film and passed through the analyzer 503, and finally received by the CCD 504.

[0075] (f) The magnetic field strength distribution map is obtained by software processing adapted in computer 7, such as... Figure 9 As shown, the critical current distribution image is obtained by calculating the gradients in the x and y directions from the magnetic induction intensity distribution map, as shown below. Figure 10 , 11 As shown in Figure 12.

[0076] like Figure 9 As shown, FeTe 0.8 Se 0.2 The superconducting single-crystal sample exhibits a bright "X"-shaped pattern in the remanent magnetic flux density plot at 4.2 K and 1000 Oe, a typical characteristic of superconducting materials. Current is defined as positive from top to bottom and right to left, and negative from the opposite direction. The magnetic flux density distribution gradient is calculated by the program, as shown below. Figure 10 As shown, one can observe a branch in the "X" shaped pattern from the lower left to the upper right; defining current as positive from bottom to top and from right to left as negative, then from... Figure 11 One branch from the top left to the bottom right in the "X" shaped pattern can be observed; when all current directions are defined as positive, the distribution diagram of the critical current magnitude can be obtained, such as... Figure 12 As shown, it can be observed that the sample has obvious brightness on all four sides and darkness inside, indicating that the critical current is the largest at the edge of the sample and the critical current is small inside, which is consistent with the characteristics of superconducting materials.

[0077] In summary, the liquid helium-free cryogenic magneto-optical imager of this invention can conveniently and simply obtain the spatial distribution image of the critical current of superconducting materials, and can also determine the homogeneity of the sample.

Claims

1. A liquid helium-free cryogenic magneto-optical imager, characterized in that, Includes a support column (13) and an optical damping platform (8); a cold head (1) is fixed on a stainless steel support column (13) and connected to a compressor (9) via a helium pipe (10); a damping airbag (2) is connected below the cold head (1) and is fixed on the optical damping platform (8); the damping airbag (2) is connected to the sample chamber (3) and is connected to the molecular pump unit (12) via a bellows pipe (11); an observation window (6) is provided above the sample chamber (3); a high-precision solenoid coil magnet (4) is fitted onto the observation window (6); the observation window ( 6) A high-resolution observation system (5) is provided above. The high-resolution observation system (5) includes an objective lens (506) located above the observation window (6), an analyzer (503) located above the objective lens (506), a polarizer (502) located on one side of the analyzer (503), and a light source (501) located on one side of the polarizer (502). The analyzer (503) is connected to a high-resolution CCD (504) via an optical path. The cold head (1), the high-precision magnet (4), and the high-resolution CCD (504) are respectively connected to a computer (7). The shock-absorbing airbag (2) is provided with a heat-conducting copper column (201) connected to the cold head (1). A helium airbag (202) is provided below the heat-conducting copper column (201). A T-shaped heat-conducting copper tube (302) is connected below the helium airbag (202). The T-shaped heat-conducting copper tube (302) extends into the sample chamber (3) and is connected to the sample stage (301). The cold head (1) and the shock-absorbing airbag (2) are connected through a first vacuum chamber (102). The shock-absorbing airbag (2) and the optical shock-absorbing platform (8) are connected through a second vacuum chamber (303). The cold head (1), the first vacuum chamber (102), the shock-absorbing airbag (2), and the second vacuum chamber (303) are interconnected.

2. The liquid helium-free cryogenic magneto-optical imager according to claim 1, characterized in that, The vacuum cavity between the cold head (1) and the shock-absorbing airbag (2) is fixed to the support column (13) by a crossbar.

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