A dual-wavelength achromatic focused spin terahertz wave emitter and its preparation method

Abstract

The present invention provides a dual-wavelength achromatic focusing spin terahertz wave emitter and its preparation method, comprising a glass substrate, a spin terahertz film, 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 sequentially at the rear end of the spin terahertz film; a silicon dioxide insertion layer is provided between the spin terahertz film and both the first and second meta-lenses; and the one-dimensional photonic crystal is prepared at the front end of the glass substrate. Based on the forward and backward radiation characteristics of spin terahertz emitters, the present invention integrates the first meta-lens at the front end of the spin terahertz film and the second meta-lens and a one-dimensional photonic crystal structure at the rear end. These structures respectively regulate the wavefronts of the two terahertz waves radiating forward and backward, converging them to the same point, thus achieving achromatic ...

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-focused spin terahertz wave emitter and a preparation method thereof. Background Art

[0002] The terahertz (THz) frequency band, located between infrared and microwaves (frequencies of 0.1 to 10 THz), represents a transitional frequency range 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, including a terahertz source and a terahertz collimating lens, to generate, collimate, and focus terahertz waves, they lack system integration and are bulky. Metalenses offer advantages such as small size, flexibility, and ease of integration with other devices. However, existing metalenses can only collimate and focus generated terahertz waves and suffer from dispersion, limiting their applications. Summary of the Invention

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

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

[0006] A dual-wavelength achromatic focused spin terahertz wave emitter comprises a glass substrate and a spin terahertz film, 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 both the first and second meta-lenses. The one-dimensional photonic crystal is fabricated at the front end of the glass substrate and uses silicon dioxide and poly-4-methyl-1-pentene (TPX) alternately stacked in sequence as its basic elements. The first and second meta-lenses each use a plurality of silicon cylinders with the same axial length but different radii as their basic elements, with one axial end of each silicon cylinder abutting against 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 μm.

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

[0010] A method for preparing a dual-wavelength achromatic focused spin terahertz wave emitter is provided, and the method comprises the following steps:

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

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

[0013] S3, preparing a silicon dioxide insertion layer on the 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-on terahertz film by a chemical vapor deposition method;

[0016] S6. Fabricating 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, combine the devices to obtain a dual-wavelength achromatic focusing spin terahertz wave emitter.

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

[0019] (1);

[0020] (2);

[0021] In formulas (1) and (2): Indicates the thickness of silicon dioxide; Indicates the thickness of poly-4-methyl-1-pentene (TPX); represents the wavelength of any terahertz wave to be generated; Indicates that the wavelength is The refractive index of silicon dioxide when Indicates that the wavelength is The refractive index of poly (4-methyl-1-pentene) (TPX) at .

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

[0023] (3);

[0024] (4);

[0025] In formulas (3) and (4): represents the phase of the first meta-lens; represents the phase of the second meta-lens; represents the wavelength of any terahertz wave to be generated; represents the wavelength of another terahertz wave to be generated; Indicates the polar coordinate position of each silicon cylindrical unit; Represents the focal length of the dual-wavelength achromatic focusing spin terahertz wave emitter.

[0026] It can be seen from the above technical solutions that the present invention has the following technical advantages compared with the prior art:

[0027] (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 waves 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 waves of the other frequency band generated by the spin terahertz emitter in the backward direction, so that the terahertz waves of the two bands converge to the same point, thereby realizing the dispersion elimination function.

[0028] (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

[0029] Figure 1 Schematic diagram of the overall structure of the dual-wavelength achromatic-focused spin terahertz wave emitter of the present invention;

[0030] Figure 2 is the transmission and reflection spectrum of the one-dimensional photonic crystal;

[0031] Figure 3 is the terahertz energy distribution diagram;

[0032] 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

[0033] A preferred embodiment of the present invention is described in detail below with reference to the accompanying drawings.

[0034] like Figure 1 The dual-wavelength achromatic focused spin terahertz wave emitter shown includes a glass substrate 1 and a spin terahertz film 2, as well as 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 integrated in sequence at the rear end of the spin terahertz film 2; a silicon dioxide insertion layer 6 is provided 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 the basic unit; 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 the basic unit, and one axial end of each silicon cylinder is in conflict with the silicon dioxide insertion layer 6.

[0035] 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 2 nm; specifically, the combination of ferromagnetic material and heavy metal non-magnetic material efficiently generates terahertz waves based on spin-orbit interaction (such as the inverse spin Hall effect), and the interface coupling is optimized through the silicon dioxide insertion layer, thereby improving the energy transmission efficiency.

[0036] The number of primitives in the one-dimensional photonic crystal 5 is 10-25; the thickness of the silicon dioxide insertion layer 6 in this preferred embodiment is 20-25 μm.

[0037] A method for preparing a dual-wavelength achromatic focused spin terahertz wave emitter is provided, and the method comprises the following steps:

[0038] S1. Calculate the thickness parameters of silicon dioxide and poly (4-methyl-1-pentene) (TPX), and the phase parameters of the first metalens and the second metalens based on the two wavelengths of the terahertz wave to be generated.

[0039] 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:

[0040] (1);

[0041] (2);

[0042] In formulas (1) and (2): Indicates the thickness of silicon dioxide; Indicates the thickness of poly-4-methyl-1-pentene (TPX); represents the wavelength of any terahertz wave to be generated; Indicates that the wavelength is The refractive index of silicon dioxide when Indicates that the wavelength is The refractive index of poly (4-methyl-1-pentene) (TPX) at .

[0043] Specifically, the formulas (1) and (2) are based on the quarter-wavelength principle, accurately designing the thickness of silicon dioxide and poly (4-methyl-1-pentene) (TPX), and combining 10-25 periodic primitives to form an effective band gap structure, achieving the specific wavelength, i.e. regulation.

[0044] Furthermore, the phases of the first metalens and the second metalens are calculated by the following formulas (3) and (4), respectively:

[0045] (3);

[0046] (4);

[0047] In formulas (3) and (4): represents the phase of the first meta-lens; represents the phase of the second meta-lens; represents the wavelength of any terahertz wave to be generated; represents the wavelength of another terahertz wave to be generated; Indicates the polar coordinate position of each silicon cylindrical unit; Represents the focal length of the dual-wavelength achromatic focusing spin terahertz wave emitter.

[0048] Specifically, the two meta-lenses are respectively targeted at wavelengths and The phase distribution is designed, and the dispersion compensation algorithm is used to focus the two wavelengths at the same focal length. The phase distribution is jointly optimized through the collaborative design of the double-layer meta-lens to achieve a dual-wavelength confocal effect.

[0049] S2. Prepare a one-dimensional photonic crystal consisting of silicon dioxide and 4-methyl-1-pentene (TPX) alternately stacked on a glass substrate by chemical vapor deposition according to thickness parameters.

[0050] S3. Prepare a silicon dioxide insertion layer on the silicon substrate by chemical vapor deposition method.

[0051] S4. Prepare a spin terahertz film composed of cobalt iron boron and platinum or tungsten on a silicon dioxide insertion layer by magnetron sputtering.

[0052] S5. A silicon dioxide insertion layer is again prepared on the spin terahertz film by a chemical vapor deposition method.

[0053] 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 the phase parameters.

[0054] 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, combine the devices to obtain a dual-wavelength achromatic focusing spin terahertz wave emitter.

[0055] For example, the preferred embodiment generates focused terahertz waves of 0.85THz and 1THz, and the focal points of both are 3.5mm. According to the frequency bands, the wavelength 300um, wavelength The focal length of the dual-wavelength achromatic focused spin terahertz wave emitter to be prepared is 352.94 μm. is 3.5mm; from this, 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 46.44um and 60.435um respectively.

[0056] Furthermore, silicon cylinders with an axial length of 150 μm and a radius range of 15-45 μm are used as the primitives of the first meta-lens and the second meta-lens, and the distance between adjacent silicon cylinder primitives is 100 μm. The number of primitives of the one-dimensional photonic crystal is 20, and the thickness of the silicon dioxide insertion layer is 25 μm. According to the above preparation method, a dual-wavelength achromatic focused spin terahertz wave emitter is prepared to generate focused terahertz waves in the two frequency bands of 0.85 THz and 1 THz.

[0057] Specifically, the fabricated dual-wavelength achromatic-focused spin terahertz wave emitter operates as follows: Under the action of an external magnetic field, the ferromagnetic layer of the spin terahertz film is magnetized. A femtosecond laser pumps the dual-wavelength achromatic-focused spin terahertz wave emitter from the back of a glass substrate. When the femtosecond laser irradiates the spin terahertz film, an inverse Hall effect between the magnetic and non-magnetic layers generates ultrafast charge flows at the interface, generating ultra-broadband terahertz waves radiating forward and backward. The forward-radiating 1THz band terahertz wave is focused at 3.5mm by the first meta-lens, while terahertz waves in other frequency bands are focused at other locations. The backward-radiated 0.85THz terahertz wave passes through the second meta-lens, is reflected by the one-dimensional photonic crystal, passes through the third meta-lens again, and finally is controlled by the first meta-lens. Through three-stage phase control, it is finally focused at a distance of 3.5mm, thus achieving the same focus for both the 1THz and 0.85THz terahertz waves. Due to the thinness of the spin terahertz film, its transmission of the 0.85THz terahertz wave is negligible.

[0058] like Figure 2 As shown in Figure 2, 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 elements 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).

[0059] Figure 3 The dual-wavelength achromatic focused spin terahertz wave generator focuses the terahertz waves of 1THz and 0.85THz into =3.5cm, where (a) and (c) are along The terahertz energy distribution diagram of the plane, (b) and (d) are along Planar terahertz energy distribution diagram.

[0060] 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 fall within the scope of protection 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: The device 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 sequentially integrated 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) alternately stacked in sequence as the basic unit; The first metalens and the second metalens 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. The dual-wavelength achromatic focused spin terahertz wave emitter 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 emitter according to claim 1, characterized in that: The thickness of the silicon dioxide insertion layer is 20-25 μm.

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

5. A method for preparing a dual-wavelength achromatic focused spin terahertz wave emitter, 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 metalens and the second metalens based on the two wavelengths of the terahertz wave to be generated; S2. Prepare a one-dimensional photonic crystal consisting of silicon dioxide and 4-methyl-1-pentene (TPX) alternately stacked on a glass substrate by chemical vapor deposition according to thickness parameters; S3, preparing a silicon dioxide insertion layer on the 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-on terahertz film by a chemical vapor deposition method; S6. Fabricating 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, combine the devices to obtain a dual-wavelength achromatic focusing spin terahertz wave emitter.

6. The method for preparing a dual-wavelength achromatic focused spin terahertz wave emitter 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: （1）； （2）； In formulas (1) and (2): Indicates the thickness of silicon dioxide; Indicates the thickness of poly-4-methyl-1-pentene (TPX); represents the wavelength of any terahertz wave to be generated; Indicates that the wavelength is The refractive index of silicon dioxide when Indicates that the wavelength is The refractive index of poly (4-methyl-1-pentene) (TPX) at .

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

Images