A self-focusing spin terahertz emitter and its preparation method

Abstract

The present invention discloses a dispersive self-focusing spin terahertz emitter and a preparation method, specifically relating to the field of spin terahertz emission equipment. The emitter comprises a glass substrate, a spin terahertz film, and a magnet pair. The spin terahertz film is composed of a ferromagnetic material and two heavy metal non-magnetic materials with equal and opposite spin Hall angles, alternately arranged on the ferromagnetic material. The dispersive self-focusing spin terahertz emitter of the present invention constructs a spin terahertz Fresnel zone plate by specially arranging the two heavy metal non-magnetic materials with equal and opposite spin Hall angles. This allows the generated spin terahertz waves of two or more frequency bands to converge at the same point, thereby improving the terahertz generation efficiency and enhancing the integration of the spin terahertz emitter.

Description

Technical Field

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

[0002] The terahertz (THz) frequency band, located between infrared and microwaves (frequencies of 0.1 to 10 THz), represents a transitional frequency band between macroscopic electronics and microscopic photonics. It possesses numerous advantages, including broadband, low energy, high transparency, and uniqueness. It holds significant scientific value and broad application prospects in fields such as nondestructive testing, satellite communications, medical diagnostics, and satellite communications. Spin THz sources, due to their unique THz generation mechanism, offer advantages such as low cost and high efficiency, making them a key development direction for future THz technology.

[0003] Because existing terahertz devices require a series of components, such as a terahertz source and a terahertz collimating lens, to generate, collimate, and focus terahertz waves, the systems have low system integration and are relatively large. Fresnel zone plates can collimate or focus light waves and are characterized by their small size, thinness, and simple manufacturing process. However, existing terahertz Fresnel zone plates can only collimate and focus generated terahertz waves and do not integrate the terahertz source and Fresnel zone plate. Furthermore, only half of the Fresnel zone plate's area can transmit and collimate terahertz waves, resulting in low efficiency. Furthermore, spin terahertz emitters with integrated Fresnel zone plates can only operate within a specific frequency band and suffer from severe dispersion, which limits their application. To address these issues, a dispersion-free, self-focusing spin terahertz emitter is proposed. Summary of the Invention

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

[0005] To achieve the above-mentioned objectives, 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 top of the ferromagnetic material, and the magnet pair is fixed on both sides of the substrate, and the magnetic poles of the magnets on the two opposite sides are opposite.

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

[0007] Furthermore, the magnet pair is fixed on both 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 sector-shaped ring shape, and are divided into 2m sector-shaped areas (m=1, 2, 3...), and the center angle of the circle is 180° / m, where m is the terahertz wave 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 are required to be focused on the same point, then m is 3. The radius of the nth ring of each sector 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 identical.

[0009] A dispersive self-focusing spin terahertz emitter 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;

[0012] S2: Using photolithography, mask and other technologies, a non-magnetic layer of the 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. The film is divided into 2m fan-shaped areas (m = 1, 2, 3...), and the central angle of the circle is 180° / m, where m is the terahertz wave of m frequency bands to be focused on the same point according to the design requirements. For example, if the terahertz waves of 0.5THz, 1THz and 1.5THz frequency bands need to be focused on the same point, then m is 3;

[0013] 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.

[0014] A further solution is to control the radius of the heavy metal non-magnetic material of each sector-shaped ring structure and make the structures of the two opposite sector-shaped areas exactly the same, so as to achieve constructive interference of terahertz waves in a specific band, 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 sector, and it 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:

[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. This allows the generated spin terahertz waves of two or more frequency bands to converge at the same point, resulting in high terahertz generation efficiency and improved integration of the spin terahertz emitter. 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 optical 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 solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to 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 an 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, 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 both sides of the substrate 101, and its magnetic poles on 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. 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] In one embodiment, a dispersive self-focusing spin terahertz emitter is used for generating, collimating, and focusing spin terahertz waves, and focusing terahertz waves in three frequency bands of 0.5 THz, 1 THz, and 1.5 THz at a focal length of 3 cm, 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;

[0025] S2: Using photolithography, mask and other technologies, a non-magnetic layer of the spin terahertz film is prepared on the ferromagnetic layer material of the spin terahertz film. The non-magnetic layer has a sector-shaped alternating ring arrangement, where the spin Hall angles of adjacent non-magnetic layers are opposite. The film is divided into 6 sectors with a central angle of 60°.

[0026] S3: Using 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 a 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 ultrafast charge flows in adjacent fan-shaped rings are opposite, thereby generating terahertz radiation with a phase difference of 180° and a polarization direction perpendicular to the magnetic field direction;

[0027] A further solution is to control the radius of the heavy metal non-magnetic material of each sector-shaped ring structure and make the structures of the two opposite sector-shaped areas exactly the same, so as to achieve constructive interference of terahertz waves in a specific band, 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 sector, and it 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 self-focusing spin terahertz emitter from the back of the glass substrate 101. If terahertz waves of three frequency bands, 0.5THz, 1THz, and 1.5THz, are selected and focused at 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). Region I focuses the terahertz wave of f = 0.5THz at d = 3cm, region II focuses the terahertz wave of f = 1THz at d = 3cm, and region III focuses the terahertz wave of f = 1.5THz at 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] Attachment 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 their focal length is 3cm.

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

[0032] In summary, the embodiments of the present invention construct a dispersion-free 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. This allows the generated spin terahertz waves of two or more frequency bands to converge at the same point, resulting in high terahertz generation efficiency and improved integration of the spin terahertz emitter.

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

[0034] While 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 these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A dispersive self-focusing spin terahertz emitter 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, 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), 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 surface of the 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; 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; The heavy metal non-magnetic material (103) and the heavy metal non-magnetic material (104) are alternately arranged 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, where m is the terahertz wave of m frequency bands to be focused on the same point according to design requirements, and each fan-shaped area is divided into 2m fan-shaped areas. n The ring radius is ,in d is the working focal length of the adispersive self-focusing spin terahertz emitter, λ is the central wavelength of the spin terahertz that the sector region is to focus on, which satisfies λ = c / f ,in c is the speed of light, f is the frequency corresponding to terahertz.

2. The achromatic self-focusing spin terahertz emitter according to claim 1, characterized in that: The structures of the two opposite sectors are exactly the same.

3. 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.

4. A method for preparing an achromatic self-focusing spin terahertz emitter, for preparing an achromatic self-focusing spin terahertz emitter according to any one of claims 1 to 3, 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; S2: Using photolithography and mask technology, a non-magnetic layer of the spin terahertz film is prepared on the ferromagnetic layer material of the spin terahertz film. The non-magnetic layer materials of adjacent layers have opposite spin Hall angles. The film is divided into 2m sectors, m = 1, 2, 3..., and the central angle is 180° / m, where m is the terahertz wave of m frequency bands to be focused on the same point according to the design requirements. 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.

5. The method for preparing a dispersive self-focusing spin terahertz emitter according to claim 4, 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 sectors identical, constructive interference of terahertz waves in a specified band is achieved, thereby improving the efficiency of terahertz wave generation; 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 sector, which satisfies λ=c / f, where c is the speed of light and f is the frequency of the corresponding terahertz.

Images