Self-focusing spinning terahertz emitter and preparation method thereof

Abstract

The invention discloses an achromatic self-focusing spinning terahertz emitter and a preparation method, and particularly relates to the field of spinning terahertz emitting equipment, and the achromatic self-focusing spinning terahertz emitter comprises a glass substrate, a spinning terahertz thin film and a magnet pair, wherein the spin terahertz film is formed by alternately arranging a ferromagnetic material and two heavy metal non-magnetic materials with the same spin Hall angle and opposite directions on the ferromagnetic material. According to the achromatic self-focusing spin terahertz emitter, the spin terahertz Fresnel zone plate is constructed by specially arranging two heavy metal non-magnetic materials with the spin Hall angles equal in size and opposite in direction, so that generated spin terahertz waves of more than two frequency bands are converged to the same point, the terahertz generation efficiency is high, and the terahertz wave generation efficiency is high. And meanwhile, the integration level of the spinning terahertz emitter is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of spin terahertz emission equipment, and more specifically, to a self-focusing spin terahertz emitter. Background Art

[0002] The terahertz frequency band is located between infrared and microwave (frequency 0.1 ~ 10THz), which is the transition frequency band between macro electronics and micro optoelectronics. It has many advantages such as broadband, low energy, high transparency, and uniqueness. It has great scientific value and broad application prospects in the fields of non-destructive testing, satellite communications, medical diagnosis, satellite communications, etc. Spin terahertz sources have the advantages of low cost and high efficiency due to their unique terahertz generation mechanism, and are an important development direction of terahertz technology in the future.

[0003] Since existing terahertz devices include a series of components such as terahertz sources and terahertz collimating lenses to generate, collimate and focus terahertz waves, the system has low integration and large size. Fresnel zone plates can collimate or focus light waves, and have the characteristics of small size, thin thickness and simple manufacturing process. However, the existing terahertz Fresnel zone plates can only collimate and focus the generated terahertz, and have not realized the integration of terahertz sources and Fresnel zone plates. At the same time, only half of the area of ​​the Fresnel zone plate can transmit and collimate terahertz waves, and the efficiency is low. In addition, the spin terahertz transmitter integrated with the Fresnel zone plate can only work in a specific frequency band, and its dispersion phenomenon is serious, which limits its application. In order to solve the above problems, a dispersion-free self-focusing spin terahertz transmitter is proposed. Summary of the invention

[0004] In order to overcome the above defects of the prior art, the present invention provides an achromatic self-focusing spin terahertz emitter to solve the problems raised in the above background technology.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solution: a de-dispersive self-focusing spin terahertz emitter, comprising a glass substrate, a spin terahertz film, and a magnet pair, wherein the spin terahertz film is composed of a ferromagnetic material and a heavy metal non-magnetic material, and a heavy metal non-magnetic material, wherein the ferromagnetic material is arranged on the front side of the glass substrate, and the heavy metal non-magnetic material and the heavy metal non-magnetic material are arranged on the ferromagnetic material, and the magnet pair is fixed on both sides of the substrate, and the magnetic poles of the two opposite sides are opposite.

[0006] Furthermore, the spin Hall angles of the two heavy metal non-magnetic materials are equal in magnitude and opposite in direction.

[0007] Furthermore, the magnet pair is fixed on two sides of the substrate, and the magnetic poles of the two opposite sides are opposite. The heavy metal non-magnetic material (103) and the heavy metal non-magnetic material (104) are arranged alternately in a fan-shaped ring shape, and are divided into 2m fan-shaped areas (m=1, 2, 3...), and the center angle of the circle is 180° / m, where m is the terahertz waves of m frequency bands to be focused on the same point according to the design requirements. For example, if the terahertz waves of the three frequency bands of 0.5THz, 1THz, and 1.5THz need to be focused on the same point, then m is 3. The radius of the nth ring of each fan-shaped area is Where d is the working focal length of the achromatic self-focusing spin terahertz emitter, λ is the central wavelength of the spin terahertz to be focused in the sector, which satisfies λ=c / f, where c is the speed of light and f is the corresponding terahertz frequency.

[0008] Furthermore, the structures of the two opposite sectors are completely the same.

[0009] A dispersive self-focusing spin terahertz transmitter is used for generating, focusing and collimating spin terahertz waves, as well as for dispersiveness, so that the generated spin terahertz waves of two or more frequency bands converge to the same point.

[0010] The following steps are involved:

[0011] S1: The ferromagnetic layer material of the spin terahertz film is prepared on the front side of the glass substrate by magnetron sputtering method;

[0012] S2: Using photolithography, mask and other technologies, prepare a non-magnetic layer of a spin terahertz film arranged in a sector-shaped alternating ring on the ferromagnetic layer material of the spin terahertz film, wherein the spin Hall angles of adjacent non-magnetic layer materials are opposite, and it is divided into 2m sector areas (m = 1, 2, 3 ...), and its central angle is 180° / m, wherein m is the terahertz waves of m frequency bands to be focused on the same point according to the design requirements, for example, if the terahertz waves of three frequency bands of 0.5THz, 1THz and 1.5THz need to be focused on the same point, then m is 3;

[0013] S3: The ferromagnetic layer of the spin terahertz film is magnetized by a magnet, and based on the inverse Hall effect between the magnetic layer and the non-magnetic layer, when the femtosecond laser is irradiated on the spin terahertz film, an ultrafast charge flow is generated at the interface between the magnetic layer and the non-magnetic layer of the spin terahertz film, and the directions of the adjacent fan-shaped ring-shaped ultrafast charge flows are opposite, thereby generating terahertz radiation with a phase difference of 180° and a polarization direction perpendicular to the magnetic field direction.

[0014] In a further solution, by controlling the radius of the heavy metal non-magnetic material of each sector-shaped ring structure and making the structures of the two opposite sector-shaped areas completely identical, the interference constructive of the terahertz wave in a specific band is achieved, thereby improving the efficiency of terahertz wave generation. Therefore, the radius of the nth ring of the sector-shaped area in the present invention is Where d is the focal length of the spin terahertz emitter, λ is the central wavelength of the spin terahertz focused in the fan-shaped area, which satisfies λ=c / f, where c is the speed of light and f is the frequency of the corresponding terahertz.

[0015] Compared with the prior art, the technical effects and advantages of the present invention are as follows:

[0016] The present invention constructs an achromatic spin terahertz Fresnel zone plate by preparing two heavy metal non-magnetic materials with equal and opposite spin Hall angles in a special arrangement on a ferromagnetic material, so that the spin terahertz waves of more than two frequency bands generated converge to the same point, the terahertz generation efficiency is high, and the integration of the spin terahertz transmitter is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0018] Figure 2 The light field distribution of terahertz waves with frequencies of f=0.5THz, f=1THz, and f=1.5THz is generated for the spin terahertz emitter. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0020] As attached Figure 1 In the embodiment, a de-dispersive self-focusing spin terahertz emitter includes a glass substrate 101, a spin terahertz film, and a magnet pair 105, wherein the spin terahertz film is composed of a ferromagnetic material 102 and heavy metal non-magnetic materials 103 and 104, the ferromagnetic material 102 is arranged on the front side of the glass substrate 101, the heavy metal non-magnetic material 103 and the heavy metal non-magnetic material 104 are arranged on the ferromagnetic material 102, and the magnet pair 105 is fixed on both sides of the substrate 101, and the magnetic poles of the two opposite sides are opposite.

[0021] As a preferred technical solution of the present invention, the ferromagnetic material 102 is cobalt iron boron, and the heavy metal non-magnetic materials 103 and 104 are platinum and tungsten respectively, and the thickness of the three is the same, preferably 2 nm.

[0022] As a preferred technical solution of the present invention, as shown in the attached Figure 1 As shown, the magnet pair 105 has opposite magnetic poles on two opposite sides, which can generate an in-plane magnetic field parallel to the glass substrate 101 to facilitate magnetization of the ferromagnetic material 102 .

[0023] An achromatic self-focusing spin terahertz transmitter in the embodiment is used for generating, collimating, and focusing spin terahertz waves and focusing terahertz waves in three frequency bands of 0.5THz, 1THz, and 1.5THz at a focal length of 3cm, comprising the following steps:

[0024] S1: The ferromagnetic layer material of the spin terahertz film is prepared on the front side of the glass substrate by magnetron sputtering method;

[0025] S2: Using photolithography, mask and other technologies, a non-magnetic layer of a spin terahertz film with alternating fan-shaped rings is prepared on the ferromagnetic layer material of the spin terahertz film, wherein the spin Hall angles of adjacent non-magnetic layer materials are opposite, and the non-magnetic layer is divided into 6 fan-shaped areas, and the central angle of the circle is 60°;

[0026] S3: Use a magnet to magnetize the ferromagnetic layer of the spin terahertz film, and based on the inverse Hall effect between the magnetic layer and the non-magnetic layer, when the femtosecond laser is irradiated on the spin terahertz film, an ultrafast charge flow is generated at the interface between the magnetic layer and the non-magnetic layer of the spin terahertz film, and the directions of the adjacent fan-shaped ring-shaped ultrafast charge flows are opposite, thereby generating terahertz radiation with a phase difference of 180° and a polarization direction perpendicular to the magnetic field direction;

[0027] In a further solution, by controlling the radius of the heavy metal non-magnetic material of each sector-shaped ring structure and making the structures of the two opposite sector-shaped areas completely identical, the interference constructive of the terahertz wave in a specific band is achieved, thereby improving the efficiency of terahertz wave generation. Therefore, the radius of the nth ring of the sector-shaped area in the present invention is Where d is the focal length of the spin terahertz emitter, λ is the central wavelength of the spin terahertz focused in the fan-shaped area, which satisfies λ=c / f, where c is the speed of light and f is the frequency of the corresponding terahertz.

[0028] In one embodiment, a femtosecond laser pumps the spin terahertz emitter with a self-focusing function from the back of the glass substrate 101. If the terahertz waves of three frequency bands of 0.5THz, 1THz, and 1.5THz are selected to focus on a focal length of d=3cm, then m is 3, and the entire emitter is divided into three regions (region I, region II, and region III), wherein region I focuses the terahertz wave of f=0.5THz on d=3cm, region II focuses the terahertz wave of f=1THz on d=3cm, and region III focuses the terahertz wave of f=1.5THz on d=3cm. The radii of the first eight rings of the three regions are shown in the following table:

[0029] um r1 r2 r3 r4 r5 r6 r7 r8 Ⅰ 4251.8 6027.8 7400.8 8566.7 9601.3 10543 11416 12233 Ⅱ 3002.7 4251.8 5213.8 6027.8 6747.6 7400.8 8003.6 8566.7 Ⅲ 2450.7 3468.7 4251.8 4913.6 5498.1 6027.8 6516.2 6971.8

[0030] Attached Figure 2The three regions of the achromatic self-focusing spin terahertz emitter generate terahertz wave distributions of 0.5THz, 1THz, and 1.5THz respectively. It can be seen that the terahertz waves in this frequency band are focused, and the focal length is 3cm.

[0031] Among them, the common magnetron sputtering method is: for example, filling a proper amount of argon gas in a high vacuum, applying a DC voltage of several hundred kilovolts between the cathode (columnar target or planar target) and the anode (coating chamber wall), generating a magnetron type abnormal glow discharge in the coating chamber, and ionizing the argon gas. The argon ions are accelerated by the cathode and bombard the cathode target surface, sputtering the surface atoms of the target materials such as cobalt iron boron, platinum and tungsten and depositing them on the substrate surface to form cobalt iron boron, platinum and tungsten thin films.

[0032] In summary, the embodiment of the present invention prepares and arranges two heavy metal non-magnetic materials with equal and opposite spin Hall angles on a ferromagnetic material to construct an achromatic spin terahertz Fresnel zone plate, so that the spin terahertz waves of more than two frequency bands are generated and converge at the same point, the terahertz generation efficiency is high, and the integration of the spin terahertz transmitter is improved.

[0033] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0034] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A dispersive self-focusing spin terahertz transmitter, used for generating, focusing and collimating spin terahertz waves, and dispersing, so that the generated spin terahertz waves of two or more frequency bands converge to the same point, comprising a glass substrate (101), a spin terahertz film, and a magnet pair (105), characterized in that: The spin terahertz film is composed of a ferromagnetic material (102) and a heavy metal non-magnetic material (103) and a heavy metal non-magnetic material (104), wherein the ferromagnetic material (102) is arranged on the front side of a glass substrate (101), and the heavy metal non-magnetic material (103) and the heavy metal non-magnetic material (104) are arranged on the ferromagnetic material (102); The magnet pair (105) is fixed on two sides of the substrate (101), and the magnetic poles of the two opposite sides are opposite.

2. The achromatic self-focusing spin terahertz emitter according to claim 1, characterized in that: The spin Hall angles of the heavy metal non-magnetic material (103) and the heavy metal non-magnetic material (104) are equal in magnitude and opposite in direction.

3. The achromatic self-focusing spin terahertz emitter according to claim 2, characterized in that: The heavy metal non-magnetic material (103) and the heavy metal non-magnetic material (104) are arranged alternately in a fan-shaped ring shape, and are divided into 2m fan-shaped areas, m=1, 2, 3..., and the center angle is 180° / m, wherein m is the terahertz waves of m frequency bands to be focused on the same point according to design requirements, and the radius of the nth ring of each fan-shaped area is Where d is the working focal length of the achromatic self-focusing spin terahertz emitter, λ is the central wavelength of the spin terahertz to be focused in the sector, which satisfies λ=c / f, where c is the speed of light and f is the corresponding terahertz frequency.

4. The achromatic self-focusing spin terahertz emitter according to claim 3, characterized in that: The structures of the two opposite sectors are exactly the same.

5. The achromatic self-focusing spin terahertz emitter according to claim 1, characterized in that: The ferromagnetic material (102) is cobalt iron boron, the heavy metal non-magnetic material (103) is platinum, and the heavy metal non-magnetic material (104) is tungsten, and the three have the same thickness.

6. A method for preparing a dispersive self-focusing spin terahertz emitter, characterized in that: The following steps are included: S1: The ferromagnetic layer material of the spin terahertz film is prepared on the front side of the glass substrate by magnetron sputtering method; S2: Using photolithography and mask technology, a non-magnetic layer of a spin terahertz film with alternating fan-shaped rings is prepared on the ferromagnetic layer material of the spin terahertz film, wherein the spin Hall angles of adjacent non-magnetic layer materials are opposite, and it is divided into 2m fan-shaped areas, m = 1, 2, 3..., and its central angle is 180° / m, wherein m is the terahertz waves of m frequency bands to be focused on the same point according to the design requirements; S3: The ferromagnetic layer of the spin terahertz film is magnetized by a magnet, and based on the inverse Hall effect between the magnetic layer and the non-magnetic layer, when the femtosecond laser is irradiated on the spin terahertz film, an ultrafast charge flow is generated at the interface between the magnetic layer and the non-magnetic layer of the spin terahertz film, and the directions of the adjacent fan-shaped ring-shaped ultrafast charge flows are opposite, thereby generating terahertz radiation with a phase difference of 180° and a polarization direction perpendicular to the magnetic field direction.

7. The method for preparing a dispersive self-focusing spin terahertz emitter according to claim 5, characterized in that: The following steps are included: By controlling the radius of the heavy metal non-magnetic material of each sector-shaped ring structure and making the structures of the two opposite sector-shaped areas exactly the same, the interference constructive phase of the terahertz wave in the specified band is achieved, thereby improving the generation efficiency of the terahertz wave; The radius of the nth ring in the sector area is Where d is the focal length of the spin terahertz emitter, λ is the central wavelength of the spin terahertz focused in the fan-shaped area, which satisfies λ=c / f, where c is the speed of light and f is the frequency of the corresponding terahertz.

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