A non-magnetic spin terahertz emission device, detection system and preparation method

Abstract

This invention relates to a non-magnetic spin terahertz emitting device, detection system, and fabrication method, belonging to the field of electromagnetic wave electronic equipment technology. It solves the problems of small size and low energy utilization of pump laser in existing spin terahertz emitters. The non-magnetic spin terahertz emitting device of this invention includes a laser amplifier, a beam splitter, a beam expander module, and a spin terahertz emitting module. The beam splitter is disposed at the output end of the laser amplifier to separate the pump light from the laser generated by the laser amplifier. The beam expander module includes a concave mirror and a convex mirror, with the concave lens disposed between the beam splitter and the convex lens. The spin terahertz emitting module is disposed on the light-emitting side of the convex mirror. The spin terahertz emitting module has multiple spin terahertz emitters arranged in parallel at a preset distance. The pump light generates a terahertz wave through the spin terahertz emitting module.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave electronic equipment technology, specifically relating to a non-magnetic spin terahertz transmitting device, detection system, and preparation method. Background Technology

[0002] Terahertz waves have applications in radar, remote sensing, security monitoring, high-speed data communication, atmospheric and environmental monitoring, and medical diagnostics. Therefore, the development of terahertz research is of great value.

[0003] Spin-generated terahertz radiation is a common method for generating terahertz waves. For example, Kampfrath et al. fabricated nanostructures of ferromagnetic and non-ferromagnetic metals, excited spin electrons in the heterostructure using laser pumping, and converted the spin current into a charge current using the inverse spin Hall effect through an external magnetic field, generating terahertz radiation. They later studied numerous materials and upgraded bilayer heterostructures to trilayers, using a W / CoFeB / Pt trilayer structure to significantly enhance terahertz radiation. However, current spin terahertz emitters require an external magnetic field, making it difficult to provide a uniform magnetic field at large sizes. Furthermore, the magnetic field strength decreases inversely with the distance between the positive and negative poles, limiting their size. Additionally, large-sized spin terahertz emitters are difficult to manufacture, and maintaining the flatness and precision of the substrate and coating is challenging. Moreover, after laser excitation of the spin terahertz emitter, half of the laser energy is still wasted. Summary of the Invention

[0004] In view of the above problems, the present invention provides a non-magnetic spin terahertz emission device, detection system and preparation method, which solves the problems of small size and low energy utilization of pump laser in the prior art.

[0005] On one hand, the present invention provides a non-magnetic spin terahertz emission device, including a laser amplifier, a beam splitter, a beam expander module and a spin terahertz emission module;

[0006] A beam splitter is placed at the output end of the laser amplifier to separate the pump light from the laser generated by the laser amplifier.

[0007] The beam expander module includes a concave mirror and a convex mirror, with the concave lens positioned between the beam splitter and the convex lens;

[0008] The spin terahertz emission module is located on the light-emitting side of the convex mirror; the spin terahertz emission module is equipped with multiple spin terahertz emitters, which are arranged in parallel at a preset distance; the pump light generates terahertz waves through the spin terahertz emission module.

[0009] Optionally, three spin terahertz transmitters are provided: a first spin terahertz transmitter, a second spin terahertz transmitter, and a third spin terahertz transmitter; the three spin terahertz transmitters are arranged in parallel at a preset distance.

[0010] Optionally, the expression for the preset distance is:

[0011] △d=(△t*c) / △n;

[0012] △n=n 环 -n THz ;

[0013] Where Δd is the distance between two adjacent spin terahertz emitters; Δt is the time difference between the terahertz wave generated by the spin terahertz emitter and the laser; Δn is the refractive index difference; c is the speed of light; n 环 n is the refractive index of the laser in the environment. THz The refractive index of terahertz light in the environment.

[0014] On the other hand, the present invention also provides a detection system for a non-magnetic spin terahertz emitting device, characterized in that it includes a spin terahertz emitting device, a delay unit, ITO glass, a parabolic mirror assembly, a detector crystal, and an electro-optic sampling detector; wherein the spin terahertz emitting device uses the aforementioned spin terahertz emitting device; wherein the spin terahertz emitting device uses the spin terahertz emitting device of any one of claims 1-3.

[0015] Thirdly, the present invention also provides a method for preparing a non-magnetic spin terahertz transmitter for a non-magnetic spin terahertz emission device, the specific steps of which are as follows:

[0016] The substrate is ultrasonically cleaned;

[0017] Dry the moisture on the substrate surface with nitrogen gas;

[0018] A non-magnetic spin terahertz emitter was obtained by sputtering a magnetron coating on a substrate: IrMn, CoFeB and W coatings were sputtered sequentially on the substrate to obtain a non-magnetic spin terahertz emitter, with the thickness ratio of IrMn, CoFeB and W being 0.5~1.5:0.5~1.5:0.5~1.5.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects:

[0020] (1) The transmitting device of the present invention can still generate terahertz radiation without the need for an external magnetic field, thereby making it possible to manufacture large-sized spin terahertz transmitters, such as 4-inch spin terahertz transmitters, which are 100 times larger in area, and thus the intensity of the generated terahertz radiation is also increased by 100 times, generating strong-field terahertz waves. The terahertz radiation generated by the spin terahertz transmitter is brought into the strong-field stage.

[0021] (2) The transmitting device of the present invention utilizes multiple large-size, magnetic field-free spin terahertz transmitters to achieve the reuse of pump femtosecond laser energy, thereby increasing the total energy of terahertz generation and realizing strong field terahertz output.

[0022] (3) The present invention adopts the cascade emission method to improve the laser energy utilization rate, and the terahertz output energy reaches the strong field range. The structure is simple and the operation is convenient. Attached Figure Description

[0023] The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of the invention.

[0024] Figure 1 This is a schematic diagram of the detection system of the non-magnetic spin terahertz emission device of the present invention.

[0025] Figure 2 This is a schematic diagram of the structure of the non-magnetic spin terahertz transmitting device of the present invention;

[0026] Figure label:

[0027] 1. Laser generated by laser amplifier; 2. Beam splitter; 3 and 4. First interval reflector; 5. First reflection module; 6. Second reflection module; 7. Delay unit; 8 and 9. Third interval reflector; 10. First interval reflector; 11. Concave mirror; 12. Convex mirror; 13. First spin terahertz emitter; 14. Second spin terahertz emitter; 15. Third spin terahertz emitter; 16. ITO glass; 17. First parabolic mirror; 18. Second parabolic mirror; 19. Terahertz wave; 20. Third parabolic mirror; 21. Detector crystal; 22. Optical sampling detector. Detailed Implementation

[0028] To better understand the above-described objectives, features, and advantages of the present invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other. Furthermore, the present invention can be implemented in other ways different from those described herein; therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0029] A specific embodiment of the present invention, such as Figure 1-2 A non-magnetic spin terahertz emission device is disclosed, including a laser amplifier, a beam splitter 2, a beam expander module, and a spin terahertz emission module.

[0030] Optionally, a beam splitter 2 is disposed at the output end of the laser amplifier to split the laser 1 generated by the laser amplifier into pump light and probe light; preferably, the beam splitting ratio of the pump light and the probe light is 1:9.

[0031] Optionally, the beam splitter 2 and the beam expander module form the pump light path, and a first interval reflector 10 is disposed between the beam splitter 2 and the beam expander module. The pump light exits from the beam splitter and enters the beam expander module through the first interval reflector 10. Preferably, the beam expander module is a 10x beam expander module.

[0032] Optionally, the beam expander module includes a concave mirror 11 and a convex mirror 12. The concave lens 11 is disposed between the beam splitter 2 and the convex lens 12. Further, the concave lens 11 is disposed between the first interval reflector 10 and the convex lens 12.

[0033] Optionally, the spin terahertz emission module is disposed on the light-emitting side of the convex mirror 12; the spin terahertz emission module is provided with multiple spin terahertz emitters, which are arranged in parallel at a preset distance. Preferably, three spin terahertz emitters are provided: a first spin terahertz emitter 13, a second spin terahertz emitter 14, and a third spin terahertz emitter 15. The pump light generates a terahertz wave 19 through the spin terahertz emission module.

[0034] Furthermore, the three spin terahertz emitters are arranged in parallel at a preset distance, with air as the gap between them. Preferably, the gap between the first spin terahertz emitter 13 and the second spin terahertz emitter 14 is a first preset distance, and the gap between the second spin terahertz emitter 14 and the third spin terahertz emitter 15 is a second preset distance, so as to realize cascaded emission, generate multiple terahertz waves, and realize the reuse of femtosecond laser.

[0035] The expressions for the first and second set distances are:

[0036] △d=(△t*c) / △n;

[0037] △n=n 环 -n THz ;

[0038] Where Δd is the distance between two adjacent spin terahertz emitters; Δt is the time difference between the terahertz wave generated by the spin terahertz emitter and the laser; Δn is the refractive index difference; c is the speed of light; n 环 n is the refractive index of the laser in the environment. THzThe refractive index of terahertz light in the environment.

[0039] In one embodiment, for the interval between the first spin terahertz emitter 13 and the second spin terahertz emitter 14, the laser amplifier emits a femtosecond laser with a center frequency of 800 nm, the femtosecond laser having an ambient refractive index n in air. 环 The refractive index n at a wavelength of 1 THz is 1.00027. THz Since 1.00006, Δn = 0.00021. To ensure full utilization of the laser energy, the pump light undergoes four reflections between the first spin terahertz emitter 13 and the second spin terahertz emitter 14. Therefore, the time difference generated by each reflection should be less than 125 fs. According to the above formula, Δd < 17.8 cm.

[0040] Each time the femtosecond laser is reflected at the interface, it loses 50% of its energy. By utilizing the linear relationship between the energy of the femtosecond laser and the terahertz efficiency of the spin terahertz emitter, the pump light is reflected four times between the first spin terahertz emitter 13 and the second spin terahertz emitter 14. This ensures full utilization of the incident femtosecond laser energy and avoids the insignificant terahertz gain effect caused by too many reflections.

[0041] Regarding the spacing between the second spin terahertz emitter 14 and the third spin terahertz emitter 15, the refractive index difference increases due to the SiO2 substrate of the spin terahertz emitter, resulting in a larger refractive index n in the SiO2 substrate. 环 The refractive index n of terahertz waves with a wavelength of 1 THz in SiO2 is 1.45. THz Since the intensity of the light transmitted to the third spin terahertz emitter 15 is only 25% of the incident light, the pump light undergoes two reflections between the second spin terahertz emitter 14 and the third spin terahertz emitter 15, thus fully utilizing the laser energy. Therefore, the time difference between each reflection should be less than 250 fs; according to the above formula, Δd < 0.714 mm. Therefore, the second spin terahertz emitter 14 and the third spin terahertz emitter 15 should, on the premise of being in close contact (without air gaps), have a substrate thickness of less than 0.714 mm for the second spin terahertz emitter 14.

[0042] In another aspect of the present invention, a detection system for a non-magnetic spin terahertz emitting device includes a spin terahertz emitting device, a delay unit 7, ITO glass (tin oxide glass) 16, a parabolic mirror assembly, a detector crystal 21, and an electro-optic sampling detector 22. The spin terahertz emitting device utilizes the aforementioned spin terahertz emitting device.

[0043] Optionally, the parabolic mirror, the detector crystal 21, and the delay unit 7 in the parabolic mirror group constitute the detector light path. Multiple second interval reflectors are set between the beam splitter 2 and the delay unit 7. After the detector light is emitted from the beam splitter, it passes through multiple first interval reflectors 3 and 4 and enters the delay unit 7. Then, it is reflected by multiple third interval reflectors 8 and 9 and enters the parabolic mirror to be emitted towards the detector crystal 21.

[0044] Optionally, the delay unit 7 includes a first reflection module 5 and a second reflection module 6. The second reflection module 5 receives the probe light incident from the second interval reflector 4 and reflects the probe light back to the second reflection module 6. The third reflection module 6 receives the probe light incident from the first reflection module 5 and reflects the probe light into the second interval reflector 8. Both the first reflection module 5 and the second reflection module 6 can be moved. The travel distance of the probe light can be controlled by moving the positions of the first reflection module 5 and the second reflection module 6 simultaneously.

[0045] Optionally, the spin terahertz emission module, ITO glass 16, and parabolic mirror group are sequentially arranged in the pump light path between the convex mirror 12 and the detector crystal 21; the pump light generates terahertz wave 19 through the spin terahertz emission module; the parabolic mirror group is provided with multiple parabolic mirrors, preferably three parabolic mirrors: a first parabolic mirror 17, a second parabolic mirror 18, and a third parabolic mirror 20.

[0046] Furthermore, a through hole is provided on the third parabolic mirror 20, through which the probe light passes and together with the terahertz wave 19 of the parabolic mirror group after being emitted from the spin hertz emitter group and reflected by the ITO glass 16, is focused onto the probe crystal 21.

[0047] Optionally, the electro-optic sampling detector 22 is disposed at the rear of the detector crystal 21 to receive the terahertz wave 19 and the detector light emitted from the detector crystal 21; by adjusting the positions of the first reflection module 5 and the second reflection module 6, the detector light is time-synchronized with the terahertz light, and then the intensity change of the detector light is detected by the electro-optic sampling detector 22 to obtain the terahertz wave waveform. Preferably, the electro-optic sampling detector 22 includes a detector crystal ZnTe, a quarter-wave plate, a Wöhlerston prism, and a photodetector.

[0048] Optionally, the spin terahertz transmitter is a 4-inch non-magnetic spin terahertz transmitter; the parabolic mirrors in the parabolic mirror assembly are larger than 4 inches to cover the terahertz cross section.

[0049] A third aspect of the present invention discloses a method for fabricating a 4-inch non-magnetic spin terahertz transmitter, the specific steps of which are as follows:

[0050] The substrate is ultrasonically cleaned; the substrate is 3-5 inches in size and 0.5-1.2 mm thick, preferably 4 inches in size and 1 mm thick; preferably, the substrate material is SiO2 and / or MgO.

[0051] Dry the moisture on the substrate surface with nitrogen gas;

[0052] Magnetron sputtering of the substrate: The vacuum level of the processing chamber is set to be higher than 5 × 10⁻⁶. -6 A magnetic field of 180 Oe (i.e., an external magnetic field) is applied to both ends of a substrate. IrMn, CoFeB, and W (tungsten) coatings are sequentially sputtered onto the substrate to form a non-magnetic spin terahertz emitter. The thickness ratio of IrMn, CoFeB, and W is 0.5–1.5:0.5–1.5:0.5–1.5. Preferably, the thickness ratio of IrMn, CoFeB, and W is 1:1:1. This ratio improves the terahertz emission reduction effect. Simultaneously, CoFeB induces an exchange bias effect in IrMn, enabling the terahertz spin generator to produce terahertz radiation even without an external magnetic field. Preferably, W:CoFeB:IrMn = 2 nm:2 nm:2 nm.

[0053] In this process, argon gas is introduced into the processing chamber as the sputtering gas at the start of sputtering. A preset negative bias voltage is applied to the target to form the cathode, and the substrate is grounded to form the anode. When the bias voltage exceeds the preset value, the cathode emits electrons, which move towards the anode substrate under the action of an accelerating voltage. During their movement, the electrons collide with argon molecules in the processing chamber, generating argon ions and new electrons. The argon ions bombard the surface of the target under the action of the accelerating voltage, and some target atoms are deposited on the substrate surface to form a dense thin film.

[0054] Among them, such as Figure 2 The coating of the first spin terahertz emitter is sputtered on the exit surface of the light after it passes through the substrate, the coating of the second spin terahertz emitter is sputtered on the incident surface of the light incident substrate, and the coating of the third spin terahertz emitter is sputtered on the incident surface of the light incident substrate.

[0055] The spin terahertz emitter utilizes sputtered IrMn, CoFeB, and W coatings to form antiferromagnetic, ferromagnetic, and nonferromagnetic materials, generating terahertz radiation in the absence of an external magnetic field. The radiation principle is primarily due to the exchange coupling effect between the antiferromagnetic and ferromagnetic materials. Under this exchange coupling, the spin arrangement of the antiferromagnetic material influences the spin arrangement of the ferromagnetic material, aligning their directions. This transforms the disordered spins in the ferromagnetic material into an ordered arrangement. This exchange coupling effect is equivalent to applying a spatially uniform magnetic field to the ferromagnetic material. Secondly, after the femtosecond laser excitation pump light enters the spin terahertz emitter, the spin electrons from the ferromagnetic layer form a spin current that is injected into the antiferromagnetic and nonferromagnetic layers. Under the influence of the inverse spin Hall effect, this spin current is converted into a charge current, generating terahertz radiation.

[0056] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A non-magnetic spin terahertz transmitting device, characterized in that, Includes laser amplifiers, beam splitters, beam expanders, and spin terahertz emission modules; A beam splitter is placed at the output end of the laser amplifier to separate the pump light from the laser generated by the laser amplifier. The beam expander module includes a concave mirror and a convex mirror, with the concave lens positioned between the beam splitter and the convex lens; The spin terahertz emission module is located on the light-emitting side of the convex mirror; the spin terahertz emission module is equipped with multiple spin terahertz emitters, which are arranged in parallel at a preset distance; the pump light generates terahertz waves through the spin terahertz emission module. The expression for the preset distance is: △ d =（△ t*c ） / △ n ； △ n = n 环 - n THz ； Among them, △ d The distance between two adjacent spin terahertz transmitters; △ t The time difference between the terahertz wave generated by the spin terahertz emitter and the laser; △ n The difference in refractive index; c The speed of light; n 环 The refractive index of the laser in the environment; n THz The refractive index of terahertz light in the environment.

2. The non-magnetic spin terahertz transmitting device according to claim 1, characterized in that, Three spin terahertz transmitters are set up: a first spin terahertz transmitter, a second spin terahertz transmitter, and a third spin terahertz transmitter; the three spin terahertz transmitters are set up in parallel at a preset distance.

3. A detection system for a non-magnetic spin terahertz transmitter, characterized in that, It includes a spin terahertz emitting device, a delay unit, ITO glass, a parabolic mirror assembly, a detector crystal, and an electro-optic sampling detector; wherein the spin terahertz emitting device uses the aforementioned spin terahertz emitting device; wherein the spin terahertz emitting device uses the spin terahertz emitting device of any one of claims 1-2.

4. A method for preparing a non-magnetic spin terahertz transmitter using any one of claims 1-2, comprising the following steps: The substrate is ultrasonically cleaned; Dry the moisture on the substrate surface with nitrogen gas; A non-magnetic spin terahertz emitter was obtained by magnetron sputtering of a substrate: IrMn, CoFeB, and W coatings were sequentially sputtered onto the substrate to obtain a non-magnetic spin terahertz emitter; the thickness ratio of IrMn, CoFeB, and W was: 0.5～1.5:0.5~1.5:0.5~1.5。

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