Dual-wavelength achromatic focusing spin terahertz wave emitter and preparation method thereof

Abstract

The invention provides a dual-wavelength achromatic focusing spin terahertz wave emitter and a preparation method thereof. The dual-wavelength achromatic focusing spin terahertz wave emitter comprises a glass substrate, a spin terahertz film, a first super-structure lens integrated at the front end of the spin terahertz film, and a second super-structure lens and a one-dimensional photonic crystal which are sequentially integrated at the rear end of the spin terahertz film, silicon dioxide insertion layers are arranged between the spin terahertz thin film and the first super-structure lens and between the spin terahertz thin film and the second super-structure lens; the one-dimensional photonic crystal is prepared at the front end of the glass substrate. Based on the characteristics of forward radiation and backward radiation of a spin terahertz emitter, a first super-structure lens is integrated on the front side of a spin terahertz film, a second super-structure lens and a one-dimensional photonic crystal structure are integrated on the rear side of the spin terahertz film, and the wavefronts of terahertz waves of two wavebands which are radiated front and back are regulated and controlled respectively, so that the terahertz waves are converged to the same point; and an achromatic function is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of spin terahertz emission equipment, and in particular to a dual-wavelength achromatic focusing spin terahertz wave emitter and a preparation method thereof. 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 integration is low and the volume is large. Meta-lenses have the advantages of small size, convenience and flexibility, and easy integration with other devices. However, existing meta-lenses can only collimate and focus the generated terahertz waves, and they have dispersion, which limits their application. Summary of the invention

[0004] The object of the present invention is to provide a dual-wavelength achromatic focused spin terahertz wave transmitter to solve the above-mentioned deficiencies of the prior art.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A dual-wavelength achromatic focusing spin terahertz wave transmitter comprises a glass substrate and a spin terahertz film, and also comprises a first meta-lens integrated at the front end of the spin terahertz film, and a second meta-lens and a one-dimensional photonic crystal sequentially integrated at the rear end of the spin terahertz film; a silicon dioxide insertion layer is arranged between the spin terahertz film and the first meta-lens and the second meta-lens; the one-dimensional photonic crystal is prepared at the front end of the glass substrate, and uses silicon dioxide and poly-4-methyl-1-pentene (TPX) alternately stacked in sequence as primitives; the first meta-lens and the second meta-lens both use a plurality of silicon cylinders with the same axial length but different radii as primitives, and one axial end of each silicon cylinder conflicts with the silicon dioxide insertion layer.

[0007] Furthermore, the spin terahertz film is composed of ferromagnetic material and heavy metal non-magnetic material.

[0008] Furthermore, the thickness of the silicon dioxide insertion layer is 20-25 um.

[0009] Furthermore, the number of primitives of the one-dimensional photonic crystal is 10-25.

[0010] A method for preparing a dual-wavelength achromatic focused spin terahertz wave emitter, used for preparing the dual-wavelength achromatic focused spin terahertz wave emitter, the preparation method comprising the following steps:

[0011] S1. Calculating thickness parameters of silicon dioxide and poly-4-methyl-1-pentene (TPX), and phase parameters of the first meta-lens and the second meta-lens based on the two wavelengths of the terahertz wave to be generated;

[0012] S2, preparing a one-dimensional photonic crystal consisting of silicon dioxide and 4-methyl-1-pentene (TPX) alternately stacked in sequence on a glass substrate by a chemical vapor deposition method according to thickness parameters;

[0013] S3, preparing a silicon dioxide insertion layer on a silicon substrate by a chemical vapor deposition method;

[0014] S4, preparing a spin terahertz film composed of cobalt iron boron and platinum or tungsten on a silicon dioxide insertion layer by a magnetron sputtering method;

[0015] S5, preparing a silicon dioxide insertion layer again on the spin terahertz film by a chemical vapor deposition method;

[0016] S6, preparing a first meta-lens and a second meta-lens consisting of a plurality of silicon cylinders on a silicon substrate by photolithography or mask technology according to the phase parameters;

[0017] S7. From left to right, in the order of glass substrate, one-dimensional photonic crystal, second meta-lens, any silicon dioxide insertion layer, spin terahertz film, another silicon dioxide insertion layer, and first meta-lens, the devices are combined to obtain a dual-wavelength achromatic focusing spin terahertz wave emitter.

[0018] Furthermore, the thickness of the silicon dioxide and poly (4-methyl-1-pentene) (TPX) are calculated by the following formulas (1) and (2), respectively:

[0019] d1=λ1 / 4n1(1);

[0020] d2=λ1 / 4n2(2);

[0021] In formulas (1) and (2), d1 represents the thickness of silicon dioxide; d2 represents the thickness of poly (4-methyl-1-pentene) (TPX); λ1 represents the wavelength of any terahertz wave to be generated; n1 represents the refractive index of silicon dioxide at a wavelength of λ1; n1 represents the refractive index of poly (4-methyl-1-pentene) (TPX) at a wavelength of λ1.

[0022] Furthermore, the phases of the first metalens and the second metalens are calculated by the following formulas (3) and (4), respectively:

[0023]

[0024] In formulas (3) and (4): represents the phase of the first meta-lens; represents the phase of the second meta-lens; λ1 represents the wavelength of any terahertz wave to be generated; λ2 represents the wavelength of another terahertz wave to be generated; r represents the polar coordinate position of each silicon cylindrical unit; f represents the focal length of the dual-wavelength achromatic focusing spin terahertz wave emitter.

[0025] It can be seen from the above technical solutions that the present invention has the following technical advantages compared with the prior art:

[0026] (1) Based on the characteristics of forward radiation and backward radiation of the spin terahertz emitter, the present invention integrates a first meta-lens on the front side of the spin terahertz film to focus the terahertz wave of the first frequency band generated by the spin terahertz emitter, and integrates a second meta-lens and a one-dimensional photonic crystal structure on the back side to regulate and reflect the wavefront of the terahertz wave of another frequency band generated by the spin terahertz emitter for backward radiation, so that the terahertz waves of the two bands converge to the same point, thereby realizing the de-dispersion function.

[0027] (2) The present invention integrates a one-dimensional photonic crystal and a double-layer meta-lens by alternately stacking silicon dioxide and TPX, which has both good femtosecond laser transmission function and high terahertz emission function, and can more efficiently generate achromatic focused terahertz waves. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the overall structure of the dual-wavelength achromatic focusing spin terahertz wave transmitter of the present invention;

[0029] Figure 2 is the transmission and reflection spectrum of the one-dimensional photonic crystal;

[0030] Figure 3 is the terahertz energy distribution diagram;

[0031] In the figure: 1. Glass substrate; 2. Spin terahertz film; 3. First meta-lens; 4. Second meta-lens; 5. One-dimensional photonic crystal; 6. Silicon dioxide insertion layer. DETAILED DESCRIPTION

[0032] A preferred embodiment of the present invention is described in detail below with reference to the accompanying drawings.

[0033] like Figure 1The dual-wavelength achromatic focusing spin terahertz wave emitter shown comprises a glass substrate 1 and a spin terahertz film 2, and also comprises a first meta-lens 3 integrated at the front end of the spin terahertz film 2 and a second meta-lens 4 and a one-dimensional photonic crystal 5 sequentially integrated at the rear end of the spin terahertz film 2; a silicon dioxide insertion layer 6 is arranged between the spin terahertz film 2 and the first meta-lens 4 and the second meta-lens 5; the one-dimensional photonic crystal 5 is prepared at the front end of the glass substrate 1, and uses silicon dioxide and poly-4-methyl-1-pentene (TPX) alternately stacked in sequence as primitives; the first meta-lens 4 and the second meta-lens 5 both use a plurality of silicon cylinders with the same axial length but different radii as primitives, and one axial end of each silicon cylinder is in conflict with the silicon dioxide insertion layer 6.

[0034] The spin terahertz film 2 described in this preferred embodiment is composed of ferromagnetic material and heavy metal non-magnetic material. In specific use, the ferromagnetic material is cobalt iron boron, and the heavy metal non-magnetic material is platinum or tungsten. The three have the same thickness, preferably 2nm; specifically, the combination of ferromagnetic material and heavy metal non-magnetic material efficiently generates terahertz waves based on spin-orbit interaction (such as inverse spin Hall effect), and optimizes interface coupling through the silicon dioxide insertion layer, thereby improving energy transmission efficiency.

[0035] The number of the primitives of the one-dimensional photonic crystal 5 is 10-25; the thickness of the silicon dioxide insertion layer 6 described in this preferred embodiment is 20-25 um.

[0036] A method for preparing a dual-wavelength achromatic focused spin terahertz wave emitter, used for preparing the dual-wavelength achromatic focused spin terahertz wave emitter, the preparation method comprising the following steps:

[0037] S1. Calculate the thickness parameters of silicon dioxide and poly-4-methyl-1-pentene (TPX), and the phase parameters of the first meta-lens and the second meta-lens based on the two wavelengths of the terahertz wave to be generated.

[0038] In a specific operation, the thickness of the silicon dioxide and poly (4-methyl-1-pentene) (TPX) are calculated by the following formulas (1) and (2), respectively:

[0039] d1=λ1 / 4n1(1);

[0040] d2=λ1 / 4n2(2);

[0041] In formulas (1) and (2), d1 represents the thickness of silicon dioxide; d2 represents the thickness of poly (4-methyl-1-pentene) (TPX); λ1 represents the wavelength of any terahertz wave to be generated; n1 represents the refractive index of silicon dioxide at a wavelength of λ1; n1 represents the refractive index of poly (4-methyl-1-pentene) (TPX) at a wavelength of λ1.

[0042] Specifically, the formulas (1) and (2) accurately design the thickness of silicon dioxide and poly (4-methyl-1-pentene) (TPX) according to the quarter-wavelength principle, and combine 10-25 periodic primitives to form an effective band gap structure to achieve the regulation of a specific wavelength, namely λ1.

[0043] Furthermore, the phases of the first metalens and the second metalens are calculated by the following formulas (3) and (4), respectively:

[0044]

[0045] In formulas (3) and (4): represents the phase of the first meta-lens; represents the phase of the second meta-lens; λ1 represents the wavelength of any terahertz wave to be generated; λ2 represents the wavelength of another terahertz wave to be generated; r represents the polar coordinate position of each silicon cylindrical unit; f represents the focal length of the dual-wavelength achromatic focusing spin terahertz wave emitter.

[0046] Specifically, the two metalenses are designed with phase distributions for wavelengths λ1 and λ2 respectively. Through the dispersion compensation algorithm, the two wavelengths are focused at the same focal length. The phase distribution is jointly optimized through the collaborative design of the double-layer metalens to achieve a dual-wavelength confocal effect.

[0047] S2. A one-dimensional photonic crystal consisting of silicon dioxide and 4-methyl-1-pentene (TPX) alternately stacked in sequence is prepared on a glass substrate by a chemical vapor deposition method according to thickness parameters.

[0048] S3. Prepare a silicon dioxide insertion layer on a silicon substrate by chemical vapor deposition.

[0049] S4. Prepare a spin terahertz film composed of cobalt iron boron and platinum or tungsten on a silicon dioxide insertion layer by a magnetron sputtering method.

[0050] S5. A silicon dioxide insertion layer is again prepared on the spin terahertz film by a chemical vapor deposition method.

[0051] S6. Prepare a first meta-lens and a second meta-lens consisting of a plurality of silicon cylinders on a silicon substrate by photolithography or mask technology according to phase parameters.

[0052] S7. From left to right, in the order of glass substrate, one-dimensional photonic crystal, second meta-lens, any silicon dioxide insertion layer, spin terahertz film, another silicon dioxide insertion layer, and first meta-lens, the devices are combined to obtain a dual-wavelength achromatic focusing spin terahertz wave emitter.

[0053] For example, the preferred embodiment generates focused terahertz waves of two frequency bands, 0.85 THz and 1 THz, and the focal points of both are 3.5 mm. According to the frequency bands, the wavelength λ1 is 300 um and the wavelength λ2 is 352.94 um. The focal length f of the dual-wavelength achromatic focused spin terahertz wave emitter to be prepared is 3.5 mm. It is calculated that the refractive indices of silicon dioxide and 4-methyl-1-pentene are 1.9 and 1.46, respectively, and their thicknesses are 46.44 um and 60.435 um, respectively.

[0054] Furthermore, a silicon cylinder with an axial length of 150um and a radius range of 15-45um is used as the primitive element of the first metalens and the second metalens, and the distance between adjacent silicon cylinder primitive elements is 100um, the number of primitive elements of the one-dimensional photonic crystal is 20, and the thickness of the silicon dioxide insertion layer is 25um. According to the above preparation method, a dual-wavelength achromatic focused spin terahertz wave emitter is prepared to generate focused terahertz waves in two frequency bands of 0.85THz and 1THz.

[0055] Specifically, the specific working process of the dual-wavelength achromatic focused spin terahertz wave emitter prepared in this way is as follows: the ferromagnetic layer of the spin terahertz film is magnetized under the action of an external magnetic field, and the femtosecond laser pumps the dual-wavelength achromatic focused spin terahertz wave emitter from the back of the glass substrate. When the femtosecond laser irradiates the spin terahertz film, due to the inverse Hall effect between the magnetic layer and the non-magnetic layer, an ultrafast charge flow is generated at the interface between the magnetic layer and the non-magnetic layer of the spin terahertz film, and ultra-wide terahertz waves radiating forward and backward are generated respectively. The terahertz wave of the 1THz band radiated forward is focused at 3.5mm by the first meta-lens, and the terahertz waves of other frequency bands are focused at other positions respectively. The backward 0.85THz terahertz wave is reflected by the second meta-lens, the one-dimensional photonic crystal, and then the second meta-lens. Finally, it is regulated by the first meta-lens and finally focused at 3.5mm through three phase adjustments, thus achieving the 1THz and 0.85THz terahertz waves focusing at the same point. Since the spin terahertz film is very thin, its transmission of the 0.85THz terahertz wave can be ignored.

[0056] like Figure 2As shown in FIG. 1 , they are the transmission and reflection spectra of the one-dimensional photonic crystal, with a central frequency band of 0.85 THz. The terahertz transmittance and terahertz phase shift of the two meta-lenses silicon cylindrical units are related to their radius. The operating frequency bands of the two meta-lenses are 1 THz and 0.85 THz, and their phases satisfy formulas (4) and (5).

[0057] Figure 3 The dual-wavelength achromatic focusing spin terahertz wave generator focuses the terahertz waves of the two frequency bands of 1THz and 0.85THz to f=3.5cm, where (a) and (c) are the terahertz energy distribution diagrams along the xz plane, and (b) and (d) are the terahertz energy distribution diagrams along the xy plane.

[0058] The above-described embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A dual-wavelength achromatic focused spin terahertz wave emitter, comprising a glass substrate and a spin terahertz film, characterized in that: It also includes a first meta-lens integrated at the front end of the spin terahertz film, and a second meta-lens and a one-dimensional photonic crystal integrated in sequence at the rear end of the spin terahertz film; A silicon dioxide insertion layer is provided between the spin terahertz film and the first meta-lens and the second meta-lens; The one-dimensional photonic crystal is prepared at the front end of a glass substrate, using silicon dioxide and poly-4-methyl-1-pentene (TPX) stacked alternately in sequence as a primitive; The first meta-lens and the second meta-lens both use a plurality of silicon cylinders with the same axial length but different radii as primitives, and one axial end of each silicon cylinder is in conflict with the silicon dioxide insertion layer.

2. A dual-wavelength achromatic focused spin terahertz wave transmitter according to claim 1, characterized in that: The spin terahertz film is composed of ferromagnetic material and heavy metal non-magnetic material.

3. The dual-wavelength achromatic focused spin terahertz wave transmitter according to claim 1, characterized in that: The thickness of the silicon dioxide insertion layer is 20-25 um.

4. The dual-wavelength achromatic focused spin terahertz wave transmitter according to claim 1, characterized in that: The number of primitives of the one-dimensional photonic crystal is 10-25.

5. A method for preparing a dual-wavelength achromatic focused spin terahertz wave emitter, used for preparing the dual-wavelength achromatic focused spin terahertz wave emitter according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: S1. Calculating thickness parameters of silicon dioxide and poly-4-methyl-1-pentene (TPX), and phase parameters of the first meta-lens and the second meta-lens based on the two wavelengths of the terahertz wave to be generated; S2, preparing a one-dimensional photonic crystal consisting of silicon dioxide and 4-methyl-1-pentene (TPX) alternately stacked in sequence on a glass substrate by a chemical vapor deposition method according to thickness parameters; S3, preparing a silicon dioxide insertion layer on a silicon substrate by a chemical vapor deposition method; S4, preparing a spin terahertz film composed of cobalt iron boron and platinum or tungsten on a silicon dioxide insertion layer by a magnetron sputtering method; S5, preparing a silicon dioxide insertion layer again on the spin terahertz film by a chemical vapor deposition method; S6, preparing a first meta-lens and a second meta-lens consisting of a plurality of silicon cylinders on a silicon substrate by photolithography or mask technology according to the phase parameters; S7. From left to right, in the order of glass substrate, one-dimensional photonic crystal, second meta-lens, any silicon dioxide insertion layer, spin terahertz film, another silicon dioxide insertion layer, and first meta-lens, the devices are combined to obtain a dual-wavelength achromatic focusing spin terahertz wave emitter.

6. The method for preparing a dual-wavelength achromatic focused spin terahertz wave transmitter according to claim 5, characterized in that: The thickness of the silicon dioxide and poly (4-methyl-1-pentene) (TPX) are calculated by the following formulas (1) and (2), respectively: d1=λ1 / 4n1(1); d2=λ1 / 4n2(2); In formulas (1) and (2), d1 represents the thickness of silicon dioxide; d2 represents the thickness of poly (4-methyl-1-pentene) (TPX); λ1 represents the wavelength of any terahertz wave to be generated; n1 represents the refractive index of silicon dioxide at a wavelength of λ1; n1 represents the refractive index of poly (4-methyl-1-pentene) (TPX) at a wavelength of λ1.

7. According to the method for preparing a dual-wavelength achromatic focused spin terahertz wave transmitter according to claim 5, the phases of the first meta-lens and the second meta-lens are calculated by the following formulas (3) and (4), respectively: In formulas (3) and (4): represents the phase of the first meta-lens; represents the phase of the second meta-lens; λ1 represents the wavelength of any terahertz wave to be generated; λ2 represents the wavelength of another terahertz wave to be generated; r represents the polar coordinate position of each silicon cylindrical unit; f represents the focal length of the dual-wavelength achromatic focusing spin terahertz wave emitter.

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