Terahertz wave pulse emitter based on ferromagnetic heterojunction

Abstract

The invention discloses a terahertz wave pulse emitter based on a ferromagnetic heterojunction. The terahertz wave pulse emitter mainly comprises a substrate, a reflecting layer, the ferromagnetic heterojunction, a spacing layer, microspheres, a conductive layer, a rear cover and an anti-reflection layer. In addition, the invention further provides a manufacturing method of the terahertz wave pulse transmitter based on the ferromagnetic heterojunction. By irradiating the terahertz wave pulse emitter based on the ferromagnetic heterojunction with femtosecond laser, terahertz pulses with high peak field intensity can be generated. The terahertz wave pulse emitter provided by the invention has the advantages of simple structure and large spectral bandwidth, and is suitable for the fields of terahertz wave imaging, security and protection and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of terahertz emission devices, and particularly relates to a terahertz wave pulse emitter based on a ferromagnetic heterojunction. BACKGROUND

[0002] Terahertz waves are electromagnetic waves between millimeter waves and infrared rays, with a frequency range of 0.1-10 terahertz. Terahertz waves have advantages such as low radiation energy, high penetration, and large bandwidth. In the field of communication, terahertz waves are expected to become a key technology for realizing 6G and high-speed wireless communication, providing people with faster data transmission speed and more stable communication experience. In the field of security inspection, terahertz waves can effectively penetrate most insulating materials, and their low photon energy does not cause harmful radiation to the human body like X-rays, so they can be used for human security inspection and identification of dangerous items hidden under clothes, effectively ensuring the safety of public places. In the field of materials science, terahertz spectroscopy can complement near-infrared spectroscopy and Raman spectroscopy, helping researchers to better understand the characteristics of materials and promote the research and application of new materials. In the field of biomedicine, terahertz waves are close to the vibration and rotation frequencies of biological macromolecules, so they can be used for qualitative and quantitative analysis of biological molecules according to their fingerprint peaks in the terahertz wave band. At present, researchers have applied terahertz technology to the early diagnosis of skin cancer.

[0003] However, the current commercial terahertz sources based on photoconductive antennas or nonlinear crystals (such as zinc telluride and gallium phosphide) are relatively expensive, which to some extent limits the popularization and application of terahertz technology. At the same time, the emission intensity of existing commercial terahertz sources is relatively weak, which is difficult to meet the increasingly complex and diverse application requirements. Therefore, it is particularly important to strengthen the development of terahertz source-related technologies to improve their performance. SUMMARY

[0004] The present application provides a terahertz wave pulse emitter based on a ferromagnetic heterojunction, which comprises a substrate, a reflective layer, a ferromagnetic heterojunction, a spacer layer, a microsphere, a conductive layer, a back cover, and an antireflection layer. The reflective layer is made on the substrate and is used to transmit terahertz pulses and reflect femtosecond laser; the ferromagnetic heterojunction is made on the reflective layer, and when the ferromagnetic heterojunction is irradiated by femtosecond laser, it will radiate terahertz pulses in both forward and backward directions; the microsphere is embedded in the spacer layer to control the thickness of the spacer layer; the spacer layer is located between the ferromagnetic heterojunction and the conductive layer; the ferromagnetic heterojunction and the back cover are fixed; and the conductive layer and the antireflection layer are respectively made on both sides of the back cover.

[0005] Further, the substrate can be made of high-resistance silicon wafer, germanium wafer, sapphire wafer, quartz wafer and other materials with small absorption to terahertz waves; the substrate is polished on both sides, with a thickness of 200 microns to 10000 microns and a diameter of 4 mm to 400 mm.

[0006] Further, the reflective layer is composed of multi-component and multi-period medium materials, which can be one of silicon dioxide / titanium dioxide, silicon dioxide / tantalum oxide, silicon dioxide / niobium oxide or silicon dioxide / hafnium oxide, with a period number of 5 to 40 layers and a total thickness of 500 nm to 8000 nm.

[0007] Further, the ferromagnetic heterojunction is composed of multiple layers of ferromagnetic metal and heavy metal, and the ferromagnetic metal can be one of iron, cobalt, nickel, iron-nickel alloy, cobalt-iron-boron alloy and the like; the heavy metal can be one or more of tungsten, platinum, tantalum, gold, ruthenium and the like, with a total thickness of 4 nm to 40 nm.

[0008] Further, the spacer layer is used to separate the ferromagnetic heterojunction and the conductive layer, and the material of the spacer layer can be one or more of air, liquid, liquid crystal, inorganic oxide and organic polymer material, with a thickness of 1 micron to 1000 microns.

[0009] Further, the microspheres are embedded in the spacer layer to control the thickness of the spacer layer, and the material of the microspheres can be one or more of silicon oxide, titanium oxide, titanium oxide, tantalum oxide and the like, with a diameter of 1 micron to 1000 microns.

[0010] Further, the material of the conductive layer can be transparent conductive oxide such as tin-doped indium oxide or fluorine-doped tin oxide, with a thickness of 10 nm to 4000 nm.

[0011] Further, the back cover can be made of a material transparent in the visible-near infrared band, including sapphire, quartz and various optical glasses, with a thickness of 0.2 mm to 10 mm.

[0012] Further, the antireflection layer is used to increase the transmittance of femtosecond laser, and can be one or more of titanium oxide, silicon oxide, magnesium oxide and magnesium fluoride, with a thickness of 10 nm to 4000 nm.

[0013] The present application also discloses a manufacturing method of a terahertz wave pulse emitter based on ferromagnetic heterojunction, comprising the following steps: (1) cleaning the substrate with ultrapure water and alcohol; (2) using a chemical vapor deposition device to make a reflective layer on the substrate; (3) using a magnetron sputtering device to make a ferromagnetic heterojunction on the reflective layer; (4) using a chemical vapor deposition device to make a conductive layer on one side of the back cover; (5) using a chemical vapor deposition device to make an anti-reflection layer on the other side of the back cover; (6) injecting microspheres into the spacer layer; (7) using a physical fixing or adhesive fixing method to fix the substrate and the back cover.

[0014] Advantages: The ferromagnetic heterojunction-based terahertz wave pulse emitter has the advantages of wide spectrum and large emission intensity, and can meet the application requirements of terahertz scientific research or imaging. Meanwhile, the manufacturing process of the ferromagnetic heterojunction-based terahertz wave pulse emitter can meet the requirements of large-area and industrial batch manufacturing, and greatly reduces the production cost. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 FIG. 1 is a structural schematic diagram of a ferromagnetic heterojunction-based terahertz wave pulse emitter according to an embodiment of the present application; Figure 2 FIG. 2 is a terahertz wave pulse time-domain waveform diagram measured by an embodiment of the present application; Figure 3 FIG. 3 is a terahertz wave pulse spectrum measured by an embodiment of the present application.

[0016] FIG. 4 is a structural schematic diagram of a ferromagnetic heterojunction-based terahertz wave pulse emitter according to an embodiment of the present application. DETAILED DESCRIPTION

[0017] The present application will be further illustrated below in conjunction with the drawings and specific embodiments, but it should be understood that these embodiments are only used to more specifically illustrate the present application, and should not be understood as limiting the present application in any form. After reading the present application, those skilled in the art can modify various equivalent forms of the present application, which fall within the scope defined by the appended claims of the present application.

[0018] As Figure 1As shown, we use femtosecond laser pulses with a pulse width of 50 femtoseconds and a center wavelength of 800 nanometers to irradiate the terahertz wave pulse emitter from the side of the antireflection layer 1. The role of the antireflection layer 1 is to increase the transmittance of femtosecond laser and reduce the Fresnel loss at the interface. The femtosecond laser pulses pass through the antireflection layer 1, the back cover 2, the conductive layer 3 and the spacer layer 4, and reach the ferromagnetic heterojunction 6. Most of the laser energy is absorbed by the ferromagnetic heterojunction 6, and the electrons in the ferromagnetic heterojunction are heated and radiate terahertz pulses in both forward and backward directions. The ferromagnetic heterojunction 6 used in this embodiment is tungsten (1.8 nanometers) / iron (1.8 nanometers) / platinum (1.8 nanometers), and the thickness of the metal film is in the parentheses. The structure of the reflective layer 7 used in this embodiment is: [titanium dioxide (95 nanometers) | tantalum oxide (135 nanometers)] 11 , the thickness of the metal film is in the parentheses, and the number outside the square brackets represents 11 periods, and the total thickness of the reflective layer 7 is 2530 nanometers. The reflective layer 7 has high reflectivity to femtosecond laser but high transmittance to terahertz pulses, which is used to block a small part of femtosecond laser that is not absorbed by the ferromagnetic heterojunction 6 from entering the silicon substrate 8.

[0019] The material of the conductive layer 3 in this embodiment is indium tin oxide, and the thickness is 200 nanometers. The conductive layer is almost transparent to femtosecond laser but provides an emissivity of more than 95% to terahertz pulses, which can reflect the backward radiated terahertz pulses to make them propagate in the same direction as the forward radiated terahertz pulses.

[0020] When the time delay between the two terahertz pulses radiated in the forward and backward directions is appropriate, the two pulses will exhibit superposition enhancement. In this embodiment, the time delay between the two pulses is determined by the diameter of the silica microspheres 5 in the spacer layer 4, and the diameter of the silica microspheres is 26 micrometers.

[0021] The ferromagnetic heterojunction 6 and the back cover 2 can be fixed by physical fixation, bonding, adhesion or exposure, etc. In this embodiment, the back cover 2 is 1 millimeter of fused quartz, and the material of the spacer layer 4 is ultraviolet glue. The silica microspheres 5 are injected between the ferromagnetic heterojunction 6 and the back cover 2, and after being pressed, ultraviolet light is irradiated on the side of the back cover 2 to solidify the spacer layer 4, thereby realizing the fabrication of the device.

[0022] Figure 2 The waveform of the terahertz pulse emitted by the sample provided in the embodiment of the present application is shown, and compared with a control sample containing only the silicon substrate 8, the reflective layer 7 and the ferromagnetic heterojunction 6. From Figure 2It can be clearly seen that the peak field strength (maximum value) of the terahertz pulse emitted by the sample of the embodiment is increased by 1.2 times. At the same time, the pulse width emitted by the sample of the embodiment is narrower and the energy is more concentrated. The full width at half maximum of the sample of the embodiment is 196 femtoseconds, and the pulse energy within the full width at half maximum accounts for 62%. The full width at half maximum of the control sample is 220 femtoseconds, and the pulse energy within the full width at half maximum accounts for only 39%.

[0023] Figure 3 The spectrum of the terahertz pulse emitted by the sample provided in the embodiment of the application is shown, and the bandwidth is as high as 8 THz, which can well support high-speed and high-capacity wireless communication applications.

Claims

1. A terahertz wave pulse emitter based on a ferromagnetic heterojunction, characterized by, It comprises a substrate, a reflective layer, a ferromagnetic heterojunction, a spacer layer, microspheres, a conductive layer, a back cover and an antireflection layer, the reflective layer is made on the substrate for transmitting terahertz pulses and reflecting femtosecond laser; the ferromagnetic heterojunction is made on the reflective layer, when the ferromagnetic heterojunction is irradiated by femtosecond laser, it will radiate terahertz pulses in front and back directions at the same time; the microspheres are located inside the spacer layer, the spacer layer is located between the ferromagnetic heterojunction and the conductive layer; the ferromagnetic heterojunction and the back cover are fixed; the conductive layer and the antireflection layer are made on both sides of the back cover respectively. The reflective layer is composed of multi-component and multi-period medium materials.

2. The terahertz wave pulse emitter based on a ferromagnetic heterojunction according to claim 1, characterized in that, The ferromagnetic heterojunction is composed of nano-thickness multi-layer ferromagnetic metal and heavy metal.

3. The terahertz wave pulse emitter based on ferromagnetic heterojunction according to claim 1, characterized in that, The microspheres are embedded in the spacer layer, and the microspheres are used to control the thickness of the spacer layer.

4. The terahertz wave pulse emitter based on ferromagnetic heterojunction according to claim 1, characterized in that, The ferromagnetic heterojunction and the back cover are fixed by physical fixation or adhesive fixation.

5. The terahertz wave pulse emitter based on ferromagnetic heterojunction according to claim 1, characterized in that, The conductive layer is used to transmit femtosecond laser and reflect back-radiation terahertz wave pulses.

6. The terahertz wave pulse emitter based on ferromagnetic heterojunction according to claim 1, characterized in that, 7. A preparation method of a terahertz wave pulse emitter based on a ferromagnetic heterojunction, comprising the following steps: (1) cleaning the substrate with ultrapure water and alcohol; (2) using a chemical vapor deposition device to make a reflective layer on the substrate; (3) using a magnetron sputtering device to make a ferromagnetic heterojunction on the reflective layer; (4) using a chemical vapor deposition device to make a conductive layer on one side of the back cover; (5) using a chemical vapor deposition device to make an antireflection layer on the other side of the back cover; (6) injecting microspheres into the spacer layer; (7) using physical fixation or adhesive fixation method to fix the substrate and the back cover. ​

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