JP2000074954A - Superconductive current detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make detectable in a noncontact free space the two-dimensional current density image of a superconductive current by applying a light pulse to a superconductor to be detected and detecting electromagnetic waves being emitted from its light application region. SOLUTION: The superconductive current detection device 20 is provided with a light pulse light source 1 that is a laser or the like and an electromagnetic wave detection device 8 that is a bolometer or a semiconductor light switch or the like with an antenna structure. The semiconductor light switch with an antenna structure can detect radiation electromagnetic waves corresponding to the direction of a superconductive current. And, when a light pulse is applied to a superconductor 6 with a pulse width of approximately 10 pico seconds, a superconductive current at the application region is partially and momentarily decreases and a light application region excites and emits electromagnetic waves with time change of current modulation. By performing scanning with light pulses two-dimensionally and detecting the intensity and direction of radiation electromagnetic waves by the electromagnetic wave detection device 8 and converting them to a current density corresponding to each region, the two-dimensional current density image of the superconductor 6 can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the detection of superconducting current, and more particularly to a superconducting current detection for detecting a two-dimensional current density image of a superconducting current in a non-contact space by using both photoexcitation and radiation electromagnetic wave detection. Related to the device.

[0002]

2. Description of the Related Art Conventionally, as a two-dimensional superconducting current detecting device, there are a laser heating type detecting device, a magneto-optical effect application detecting device, a superconducting quantum flux interferometer scanning type detecting device, and the like.

Further, A.I. J. Kent et al.
percond. Sci. Technol. (Vo
l. 4, pp. 602 to 605, issued in 1991), a normal conductor transition is induced by irradiating a superconductor in a superconducting state with a laser, and a generated voltage is detected to generate a superconducting current. It reports that two-dimensional detection is possible. T. H. Johansen et al. Disclose the paper "Physical Review B" (Vol. 5).
4, No22, pp. 16264-16269, published in 1996), a magneto-optical material is placed just above a superconductor, and the magnetic field generated by the flowing current is observed by the Faraday effect of light, so that the superconducting current is reduced. It reports that two-dimensional detection is possible.

[0004]

However, A.I.
J. In the proposal of Kent et al., The superconducting state is destroyed by laser heating, and the distribution of current flowing due to the change in the state changes, so that it is impossible to detect the superconducting current in the superconducting state. There are problems to be solved, such as the necessity of wiring and non-contact detection. T. H. In the proposal of Johansen et al., It is necessary to dispose a magneto-optical material near a superconductor in order to detect a superconducting current, and it is impossible to detect a non-contact space from the outside. There are problems to be solved, such as significantly worsening than the diameter.

As described above, in the conventional two-dimensional superconducting current detecting device, the installation of electrodes, the installation of a magneto-optical material, the installation of a superconducting quantum flux interferometer, and the like are performed directly on the superconductor to detect the superconducting current. Alternatively, it is necessary to perform the measurement in a very close vicinity, and it has been difficult to improve the method to detect a superconducting current in a non-contact free space.

[0006] In view of the above problems, the present invention provides a superconducting current detecting device capable of detecting a two-dimensional current density image of a superconducting current in a non-contact free space by photoexcitation and detection of radiated electromagnetic waves. The purpose is to:

[0007]

According to a first aspect of the present invention, there is provided a superconducting current detecting device for irradiating a light pulse to a superconductor of an object to be detected.
An electromagnetic wave detection device that detects radiated electromagnetic waves is provided, and the electromagnetic wave detection device detects the electromagnetic waves excited and emitted from the light irradiation region based on modulating the superconducting current of the superconductor by irradiating light pulses, In this configuration, the direction of the superconducting current flowing in the superconductor and the two-dimensional distribution of the superconducting current density are detected without contact with the superconductor. According to a second aspect of the present invention, in addition to the above configuration, the width of the light pulse is 10 picoseconds or less.

Further, the invention according to claim 3 is configured so that the electromagnetic wave detecting device detects the direction of the current flowing through the semiconductor optical switch having the antenna structure. Claim 4
The described invention, when detecting the superconducting current of the superconductor,
The superconductor, which is the object to be detected, moves two-dimensionally while irradiating the light pulse, or the light pulse is two-dimensionally scanned with respect to the superconductor, which is the object to be detected, to radiate the superconductor. An electromagnetic wave is detected.

In the superconducting current detecting device according to the first aspect of the present invention, a part of the superconducting current is modulated by irradiating the superconductor with an optical pulse from the outside, and the modulation is performed with the modulation. The generated electromagnetic wave is detected using an external electromagnetic wave detection device. Therefore, the superconducting current can be detected in the two-dimensional non-contact free space of the superconducting current with the minimum spatial resolution being the wavelength of light. According to the second aspect of the present invention, since the light pulse having a maximum pulse width of about 10 picoseconds or less that does not have a thermal effect is applied, when the electromagnetic wave is excited due to the modulation of the superconducting current, the superconductivity is reduced. Electromagnetic waves corresponding to the increase and decrease of the superconducting current can be excited without significant influence. Therefore, the superconducting current can be detected while maintaining the superconductivity.

Further, according to the third aspect of the present invention, since the semiconductor optical switch having the antenna structure is used as the electromagnetic wave detecting device, the radiated electromagnetic wave corresponding to the direction in which the superconducting current flows can be detected. Therefore, the current density and the direction of the superconducting current can be detected.
According to the fourth aspect of the invention, when detecting a radiated electromagnetic wave, the superconductor which is the object to be detected moves two-dimensionally, or two-dimensionally scans a light pulse for exciting the electromagnetic wave. Therefore, a current image flowing in the superconductor can be detected two-dimensionally.

As described above, by configuring the superconducting current detecting device using both the light pulse and the electromagnetic wave detection, a two-dimensional superconducting current detecting device which has never existed before can be realized.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a superconducting current detecting device according to the present invention will be described in detail based on an embodiment shown in the drawings.
FIG. 1 is a schematic diagram of a superconducting current detecting device according to an embodiment of the present invention. Referring to FIG. 1, a superconducting current detecting device 20 of the present embodiment irradiates a superconductor 6 in which a superconducting current flows placed in a cooling device 4 with an optical pulse 2 through an optical window 5 of the cooling device. And a light condensing lens 3 for condensing the light pulse 2 on a superconductor 6 which is an object to be detected.
An electromagnetic wave detecting device 8 for detecting a radiated electromagnetic wave 7 generated in a superconductor region irradiated with the light pulse 2, and a superconducting device for producing a two-dimensional current density image based on the generated region and intensity of the radiated electromagnetic wave 7 A current mapping control device 13;
The superconducting current mapping control device 13 converts the intensity of the generated radiated electromagnetic wave into a current, and displays or displays a two-dimensional current density image on the display 14 or a printer (not shown) from the area of the object to be detected and the sectional area. Output.

As the light pulse light source 1 for induction, a laser beam having a pulse width of about 50 femtoseconds generated by a mode-locked titanium sapphire laser excited by an argon ion laser can be used. It is preferable that the light pulse can excite the electromagnetic wave without affecting the superconductivity of the superconductor, and the maximum light pulse width not affecting the thermal effect is about 10 picoseconds. Further, it is preferable that the light pulse scans the superconductor of the object to be detected two-dimensionally. Instead of scanning the light pulse two-dimensionally, the light pulse may be irradiated by moving the detection target itself two-dimensionally.

As the electromagnetic wave detecting device 8, a hot electron bolometer made of indium antimony or a semiconductor optical switch having an antenna structure, for example, an optical switch made of low-temperature grown gallium arsenide can be used. A bolometer can measure the intensity of a radiated terahertz (THz) electromagnetic wave with high sensitivity, and a semiconductor optical switch having an antenna structure, for example, LT-GaAs, has a limited detectable polarization direction of the electromagnetic wave. The direction of the superconducting current corresponding to the radiated electromagnetic wave can be detected.

Next, the correspondence between the detected radiated electromagnetic wave and the detected superconducting current will be described. In the superconducting current detection device 20 of the present invention, the detection signal intensity greatly differs depending on the detection conditions such as the distance between the superconductor 6 as the object to be detected and the electromagnetic wave detection device 8 and the intensity of the irradiation light pulse 2. The current density is calculated by applying a known current to a standard sample whose shape is clear and comparing it with a detection result corresponding to the current to obtain a conversion coefficient. For example, a known current is applied to the standard sample in the x direction, and a conversion coefficient is calculated such that the integral of the signal intensity in the y direction corresponding to this current and the integral of the signal intensity in the y direction of the actual detection object match. , Divided by the known width in the y direction and the thickness of the superconducting material is defined as the current density. That is, the actual current density is calculated by comparing the standard sample with the standard sample. Therefore, after obtaining the conversion coefficient, there is no need to compare with the standard sample even if the sample of the object to be detected is different as long as detection is performed under the same conditions.

Next, the operation of the present embodiment will be described. When a light pulse is applied to the superconductor of the object where the superconducting current flows, a part of the superconducting current in the irradiated area is instantaneously reduced. The region excites and emits electromagnetic waves. The radiated electromagnetic wave is detected by an electromagnetic wave detecting device to detect the intensity and direction of the electromagnetic wave, and is converted into a current density corresponding to the area of the object to be detected to output a two-dimensional current density image. Therefore, in this embodiment, the superconducting current can be detected in a non-contact manner.

[0017]

Next, an embodiment in which the superconducting current of the superconductor is detected as a two-dimensional current density image using the superconducting current detecting device of the present invention will be described. FIG. 2 shows an example of the structure of a superconducting stripline used as an object to be detected. Referring to FIG. 2, in the superconducting current detecting device of the present invention, for example, YBa ₂ Cu ₃ O _7-x (hereinafter, referred to as a superconducting material)
Abbreviated as "YBCO". ) Is used to form a superconducting strip line 10 and two-dimensionally scan an object passing a current from the electrode J1 to the electrode J2 with a light pulse focused to a beam diameter of 30 μm. Is generated, and this radiated electromagnetic wave is two-dimensionally detected using a bolometer, and a superconducting current is detected.

FIG. 3 shows a two-dimensional image of the superconducting current flowing in the superconducting strip line detected by the present superconducting current detecting device. As shown in FIG. 3, the superconducting current flowing in the superconducting stripline formed on the substrate is large at the end of the stripline and small at the center. In this embodiment, the superconducting current of the superconducting strip line formed on the substrate surface is detected. However, even in a sandwich structure in which the superconductor is sandwiched between the substrates, if the superconducting layer is sandwiched between light transmitting substrates, Conduction current can be detected.

FIG. 4 is a diagram showing the current density in the cross section taken along the line AA ′ in FIG. 2, and the solid line indicates that the light pulse beam diameter is 5 μm.
m and the dotted line show the current density when the light pulse beam diameter is 30 μm. As shown in FIG. 4, the light pulse beam diameter was 5 μm.
When the beam diameter is 5 μm, the distribution of the current flowing through the cross section at m and 30 μm is sharper, and the resolution is improved by reducing the beam diameter. Therefore, in the superconducting current detecting device of the present invention, the superconducting current flowing in the superconducting strip line can be detected in a non-contact manner, and the smaller the beam diameter, the higher the resolution.

Next, an example in which the direction and the current density of the superconducting current flowing in the superconducting loop trapped by the magnetic flux are detected using the superconducting current detecting device of the present invention will be described. FIG. 5 shows an example of the structure of a superconducting loop used as a detection object. Using YBCO as a superconducting material, a magnetic flux 12 of about 100 gauss is trapped in a central hole, and a superconducting permanent current along a superconducting loop 11 is circulated. A light pulse focused at a beam diameter of 30 μm was scanned on the superconducting loop 11 of the object to be detected, and a radiated electromagnetic wave was detected by a semiconductor optical switch.

FIG. 6 shows the current x detected in the superconducting loop.
3 shows a two-dimensional image of a directional component. FIG. 7 is a diagram showing a current distribution in a cross section taken along line BB ′ of FIG. In FIG. 6, the arrow represents the x-direction component of the superconducting current flowing when the magnetic flux is captured at the center of the superconducting loop. The black portion represents a positive current, and the white portion represents a negative current. I have. As shown in FIG. 6, the x component exists above and below the superconducting loop, and does not exist on the left and right. Also, as shown in FIG. 7, the current flows in the x direction above the superconducting loop,
The current flows in the −x direction on the lower side, and the superconducting current detecting device of the present invention can detect not only the superconducting current density but also the direction in which the current flows.

[0022]

As described above, in the superconducting current detecting device according to the present invention, the superconducting body of the object through which the superconducting current flows is irradiated with the light pulse, and a part of the superconducting current in the irradiated area is irradiated. Is instantaneously reduced, the light irradiation area of the superconductor emits electromagnetic waves with the time change of the current modulation, and the intensity and direction of the electromagnetic waves can be detected by using the emitted electromagnetic waves with an electromagnetic wave detection device. Therefore, there is an effect that a two-dimensional current density image of the superconducting current can be detected in a non-contact free space. Further, the superconducting current detecting device of the present invention has an effect that the superconducting current can be detected without significantly affecting the superconductivity.

[Brief description of figures]

FIG. 1 is a schematic diagram of a superconducting current detection device showing an embodiment of the present invention.

FIG. 2 shows a structural example of a superconducting stripline used as a detection target.

FIG. 3 shows a two-dimensional image of a superconducting current flowing in a superconducting stripline detected by the present superconducting current detecting device.

4 is a diagram showing a current density at a position AA ′ in FIG. 2, wherein a solid line shows a current density when the light pulse beam diameter is 5 μm, and a dotted line shows a current density when the light pulse beam diameter is 30 μm.

FIG. 5 is a structural example of a superconducting loop used as an object to be detected.

FIG. 6 shows a two-dimensional image of an x-direction component of a current detected in a superconducting loop.

FIG. 7 is a diagram showing a current distribution on a section BB ′ in FIG. 5;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light pulse light source 2 light pulse 3 light focusing lens 4 cooling device 5 optical window 6 unmeasured superconductor 7 radiated electromagnetic wave 8 electromagnetic wave detection device 9 substrate 10 superconducting stripline 11 superconducting loop 12 magnetic flux 13 superconducting current mapping control Device 14 Display

Continued on the front page F term (reference) 2G017 AA02 AA03 AA06 AA07 AA08 AA15 AB07 AD11 BA15 BA16 BA18 2G035 AB01 AB04 AC12 AC25 AD35 AD66 2G036 AA16 BB22 CA08

Claims (4)

[Claims] 1. An optical pulse light source for irradiating a superconductor of a detection target with a light pulse, and an electromagnetic wave detection device for detecting a radiated electromagnetic wave, wherein the superconducting current of the superconductor is irradiated by the light pulse. The electromagnetic wave excited and emitted from the light irradiation area based on the modulation is detected by the electromagnetic wave detection device, and the direction of the superconducting current flowing in the superconductor and the two-dimensional distribution of the superconducting current density are determined by the superconductivity. A superconducting current detection device that detects without contact with a conductor. 2. The superconducting current detecting device according to claim 1, wherein the width of the light pulse is 10 picoseconds or less. 3. The superconducting current detecting device according to claim 1, wherein said electromagnetic wave detecting device detects a direction of a current flowing through a semiconductor optical switch having an antenna structure. 4. A superconductor which is an object to be detected moves two-dimensionally while irradiating the light pulse when detecting a superconducting current of the superconductor, or a superconductor which is an object to be detected. 2. The superconducting current detecting device according to claim 1, wherein the light pulse is two-dimensionally scanned to detect a radiation electromagnetic wave of the superconductor.