Self-focusing type strong-field terahertz radiation source system

Abstract

The invention discloses a self-focusing strong-field terahertz radiation source system, and belongs to the technical field of terahertz application, the self-focusing strong-field terahertz radiation source system comprises a laser, a laser beam expanding system and a self-focusing terahertz conversion system which are sequentially arranged, the laser is a femtosecond pulse laser, the laser beam expanding system comprises a plano-concave lens and a plano-convex lens I which are sequentially arranged, and the self-focusing terahertz conversion system comprises a plano-convex lens II and a plano-convex lens II which are sequentially arranged. The self-focusing terahertz conversion system comprises a sample support, a spintronics terahertz source film and permanent magnets, the sample support is a copper sample support, the spintronics terahertz source film grows on the substrate so as to be installed on the sample support, and the permanent magnets are symmetrically arranged on the two sides of the sample support. By adopting the system, high-intensity terahertz radiation can be realized under the conditions that complex optical elements are not increased and the system cost is not increased.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz application, and in particular to a self-focusing strong-field terahertz radiation source system. Background Art

[0002] Terahertz waves are electromagnetic waves with a frequency range of 0.1-10THz (10 to the 12th power vibration cycles per second). Electromagnetic waves in this frequency band have many unique properties, for example: many material components have unique spectral characteristics in the terahertz frequency band; terahertz waves are not absorbed by common solid materials such as plastics, paper, ceramics, etc.; the photon energy of terahertz is equivalent to the vibration and rotation energy levels of molecules, etc. Therefore, terahertz technology has a wide range of applications in biology, chemistry, semiconductors, aerospace and military fields.

[0003] The main factor that has plagued the development of terahertz technology is the lack of convenient, stable, high-intensity, and high-conversion-efficiency terahertz sources. With the development of laser technology, the development of terahertz sources has also ushered in a breakthrough. Terahertz sources based on laser systems include: nonlinear crystals based on the optical rectification effect (such as ZnTe, GaP, LiNbO3 crystals, etc.), photoconductive antennas (based on GaAs, InGaAs, etc.), and spin electronics terahertz sources based on ferromagnetic-heavy metal thin film films. Among them, nonlinear crystals or photoconductive antennas have a high terahertz conversion efficiency and are commonly used to generate strong-field terahertz. However, these two terahertz sources have the disadvantages of complex excitation optical paths, high prices, poor stability, and only applicable to specific excitation wavelengths. Compared with the former two, spin electronics terahertz sources based on ferromagnetic-heavy metal thin film films have the advantages of lower cost, simpler configuration, good stability, and no dependence on specific excitation light source wavelengths. However, the limitation of this solution is that when a strong laser is applied to the spin electronics terahertz source based on the ferromagnetic-heavy metal film, the film layer is easily volatilized under the high temperature of the laser. Therefore, there is a threshold for the power of the laser applied to the film per unit area, which leads to a low power of terahertz radiation generated by the spin electronics terahertz source per unit area. One of the current methods to increase the power threshold is to increase the area of ​​the ferromagnetic-heavy metal film while keeping the excitation light power per unit area unchanged, thereby increasing the total terahertz radiation power. Therefore, a simple and efficient terahertz convergence method is needed to converge the terahertz beam with a large cross-sectional area at the desired position to increase the terahertz electric field intensity per unit space. Traditional convergence methods rely on gold-plated off-axis parabolic mirrors or terahertz lenses. These methods greatly increase the overall cost of the system, and the emitted terahertz waves need to go through additional reflection or transmission steps, which reduces the ease of use of the optical path, so they are not the optimal solution. Summary of the invention

[0004] The purpose of the present invention is to provide a self-focusing strong-field terahertz radiation source system to solve the problems in the background technology.

[0005] To achieve the above-mentioned purpose, the present invention provides a self-focusing high-field terahertz radiation source system, comprising a laser, a laser beam expansion system and a self-focusing terahertz conversion system which are arranged in sequence, the laser is a femtosecond pulse laser, the laser beam expansion system comprises a plano-concave lens and a plano-convex lens 1 which are arranged in sequence, the self-focusing terahertz conversion system comprises a sample holder, a spin electronics terahertz source film and a permanent magnet, the sample holder is a copper sample holder, the spin electronics terahertz source film is mounted on the sample holder, the permanent magnets are symmetrically arranged on both sides of the sample holder, a circular hole is arranged on the sample holder, a step is arranged in the middle of the circular hole, and the circular hole is divided into region 1 and region 2 by the step.

[0006] Preferably, the concave side of the plano-concave lens is coated with an anti-reflection optical film, and the flat side of the plano-convex lens is coated with an anti-reflection optical film. The material of the plano-concave lens and the plano-convex lens is fused quartz with a relatively low thermal expansion coefficient.

[0007] Preferably, the laser beam expansion system also includes a translation stage base 1 and a translation stage base 2, the plano-concave lens is fixed on the translation stage base 1, the plano-convex lens 1 is fixed on the translation stage base 2, and a translation stage base 3 is arranged at the bottom of the sample holder.

[0008] Preferably, the structure of the spin electronics terahertz source film is a heterojunction consisting of a ferromagnetic metal film layer grown on a heavy metal film layer, or a heavy metal film layer is grown outside the ferromagnetic metal film of the heterojunction to enhance the injection capability of the spin current.

[0009] Preferably, the spintronics terahertz source thin film is grown on a substrate.

[0010] Preferably, a plano-convex lens 2 is fixedly installed in region 1, a substrate is fixed in region 2, a plano-convex lens 2 with one side of a spin electronics terahertz source facing region 1 is grown on the substrate, and a distance of 1 mm between the substrate and the plano-convex lens 2 is provided.

[0011] Preferably, the area one is fixedly mounted with a plano-convex lens two and a substrate.

[0012] Preferably, a threaded hole is provided on the side of the sample holder, and the permanent magnet is mounted on the sample holder through the threaded hole.

[0013] Preferably, a heat dissipation device is provided on the sample holder, and the heat dissipation device includes a water cooling pipe and a pipe interface. The water cooling pipe is installed inside the sample holder, one end of the pipe interface is connected to the water cooling pipe, and the other end is connected to an external water cooler through a water pipe.

[0014] Therefore, the present invention adopts the above-mentioned self-focusing strong-field terahertz radiation source system, which has the following beneficial effects: the spin electronics terahertz source and the focusing system are integrated together to generate focused terahertz radiation, thereby making the entire system cost lower and the optical path simpler and easier to use without weakening the excitation power of the spin electronics terahertz source and the terahertz radiation field strength at the focusing point.

[0015] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a structural schematic diagram of a self-focusing strong-field terahertz radiation source system according to Embodiment 1 of the present invention; Figure 2 This is a schematic structural diagram of a self-focusing terahertz conversion system according to Embodiment 1 of the present invention; Figure 3 This is a schematic structural diagram of a self-focusing terahertz conversion system according to Embodiment 2 of the present invention; Reference numerals 100, laser beam expansion system; 101, plano-concave lens; 102, plano-convex lens 1; 200, self-focusing terahertz conversion system; 201, sample holder; 202, self-selected terahertz source thin film; 203, pipeline interface; 204, permanent magnet; 205, circular hole; 206, step; 207, area 1; 208, area 2; 209, plano-convex lens 2; 210, substrate; 211, threaded hole; 212, water-cooling pipeline; 110, laser beam; 120, parallel light; 130, terahertz radiation; 140, focus. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0018] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0019] Example 1 like Figure 1-2 As shown, the present invention provides a self-focusing strong field terahertz radiation source system, comprising a laser, a laser beam expansion system 100 and a self-focusing terahertz conversion system 200 arranged in sequence, the laser is used to generate laser to excite the spin electronics terahertz source; the laser beam expansion system 100 is used to expand the spot diameter of the laser beam 110 generated by the laser to match the spin electronics terahertz source with a larger area; The laser is a femtosecond pulse laser, which is used to generate a femtosecond pulse laser beam. By exciting a spin electronics terahertz source with a femtosecond pulse laser, a terahertz radiation pulse having the same repetition frequency as the femtosecond pulse can be obtained.

[0020] The laser beam expansion system 100 includes a plano-concave lens 101 and a plano-convex lens 102 which are arranged in sequence. The excitation light generated by the laser source is incident on the concave side of the plano-concave lens 101 and the plane side of the plano-convex lens 102 in sequence. The plano-concave lens 101 is used to convert the parallel laser beam to be expanded into a divergent beam. The concave side of the plano-concave lens 101 is coated with an anti-reflection optical film. The plano-convex lens 102 is used to convert the divergent laser beam back into a parallel beam. The plane side of the plano-convex lens 102 is coated with an anti-reflection optical film. The material of the plano-concave lens 101 and the plano-convex lens 102 is preferably fused quartz with a low thermal expansion coefficient. The focal length of the plano-concave lens 101 and the plano-convex lens 102 is used to determine the magnification of the laser beam expansion system 100. That is: The magnification of the laser beam expansion system 100 = the absolute value of the focal length of the plano-convex lens 102 / the absolute value of the focal length of the plano-concave lens 101.

[0021] The laser beam expansion system also includes a translation stage base 1 and a translation stage base 2, a plano-concave lens 101 is fixed on the translation stage base 1, and a plano-convex lens 102 is fixed on the translation stage base 2. The translation stage base 1 and the translation stage base 2 can make the position of the lens finely adjusted along the optical path and in a plane perpendicular to the optical path, thereby facilitating the optimization of the beam expansion laser. The translation stage base 1 and the translation stage base 2 are used to maintain the distance between the plano-concave lens 101 and the plano-convex lens 102 so that it satisfies: The distance between the plano-concave lens 101 and the plano-convex lens 102 = the absolute value of the focal length of the plano-convex lens 102 - the absolute value of the focal length of the plano-concave lens 101.

[0022] The laser beam 110 is directly emitted by a laser (not shown in the figure). In this embodiment, the initial spot diameter is about 15 mm. The laser beam 110 is expanded into a parallel light 120 with a spot diameter of about 48 mm by the laser beam expansion system 100.

[0023] The self-focusing terahertz conversion system 200 includes a sample holder 201, a spin electronics terahertz source film 202 and a permanent magnet 204. The spin electronics terahertz source film 202 is mounted on the sample holder 201 through a substrate 210, that is, the spin electronics terahertz source film 202 is grown on the substrate 210, and the substrate 210 is a single crystal silicon wafer. The structure of the spin electronics terahertz source film 202 is a heterojunction consisting of a ferromagnetic metal film layer grown on a heavy metal film layer, wherein the ferromagnetic metal is iron, and the heavy metal film can be selected from platinum or gold; or a heavy metal film is grown on the outside of the ferromagnetic metal film of the above heterojunction to enhance the injection capability of the spin current, and the material can be tungsten. The material of the substrate 210 is one of glass, quartz, sapphire, titanium oxide, zinc oxide, zirconium oxide, germanium oxide, lanthanum oxide, tin oxide or silicon.

[0024] In this embodiment, the sample holder 201 is a copper sample holder, which can dissipate the heat generated by the laser irradiation film in time, and a translation stage base 3 is arranged at the bottom of the sample holder 201. The translation stage base is a three-axis translation stage, which can be a manual threaded rod type translation stage or an electric motor type translation stage.

[0025] A circular hole 205 with a diameter of 50 mm is provided on the sample holder 201, a step 206 is provided in the middle of the circular hole 205, and the circular hole 205 is divided into a region 1 207 and a region 2 208 by the step 206, wherein a plano-convex lens 2 209 with a focal length of 60 mm is fixedly installed in the region 1 207, a substrate 210 is fixed in the region 208, a plano-convex lens 2 209 with one side of the spin electronics terahertz source film 202 facing the region 1 207 is grown on the substrate 210, and the substrate 210 and the plano-convex lens 2 209 are separated by 1 mm. The plano-convex lens 2 209 is a self-focusing lens.

[0026] A heat dissipation device is provided on the sample holder 201, and the heat dissipation device includes a water cooling pipe 212 and a pipe interface 203. The water cooling pipe 212 is installed inside the sample holder 201, one end of the pipe interface 203 is connected to the water cooling pipe 212, and the other end can be connected to an external water cooler (not shown in the figure) through a water pipe.

[0027] The permanent magnets 204 are symmetrically arranged on both sides of the sample holder 201 to apply a magnetic field to the spin electronics terahertz source film 202 to increase its conversion efficiency. The N pole of one of the permanent magnets 204 faces the S pole of the other permanent magnet 204, and the substrate 210 is located at the midpoint of the line connecting the two permanent magnets 204. A self-focusing lens (not shown in the figure) is arranged between the plano-convex lens 102 and the spin electronics terahertz source film 202. The sample holder 201 includes a fixed base 2 and a displacement stage 2, wherein the fixed base 2 is used to place the sample holder 201, and the displacement stage 2 is used to adjust the lateral position of the radiation source.

[0028] The parallel light 120 incident on the spin electronics terahertz source film 202 is converted into a focused terahertz radiation 130, and the strongest terahertz electric field is generated at the focus 140. The magnetic field strength can be selected to be 50-200 mT.

[0029] The generation process of self-focusing strong-field terahertz: the laser generates excitation light with good collimation; the excitation light is expanded into a pulse light beam with a larger spot diameter through a laser beam expansion system; the pulse light beam with a larger spot diameter is incident on the spin electronics terahertz source film 202 through the convex side of the plano-convex lens 102, and the film is excited to generate a convergent terahertz beam, and the convergence point of the terahertz beam is located near the focus of the plano-convex lens 102 closer to the plane side.

[0030] Example 2 Reference Figure 3 The difference between this embodiment and embodiment 1 is that the substrate 210 and the second plano-convex lens 209 are both installed in the area 1 207 , so the substrate 210 can be closely attached to the second plano-convex lens 209 .

[0031] In this embodiment, the self-focusing terahertz conversion system 200 includes a sample holder 201 and a permanent magnet 204. The sample holder 201 is provided with a heat dissipation device, which includes a water cooling pipe 212 and a pipe interface 203. The water cooling pipe 212 is installed inside the sample holder 201. One end of the pipe interface 203 is connected to the water cooling pipe 212, and an external water cooler (not shown in the figure) is connected through the pipe interface 203 to obtain a better heat dissipation effect, thereby extending the service life of the system. The sample holder 201 is provided with a threaded hole 211 on the side, and the permanent magnet 204 is installed on the sample holder 201 through the threaded hole 211.

[0032] In this embodiment, the sample holder 201 is a copper sample holder, which can dissipate the heat generated by the laser irradiation film in time. The sample holder 201 is provided with a circular hole 205 with a diameter of 50 mm, and a step 206 is provided in the middle of the circular hole 205. The circular hole 205 is divided into a region 1 207 and a region 2 208 by the step 206. The region 1 207 is installed with a substrate 210 and a plano-convex lens 2 209. The spin electronics terahertz source film 202 is grown on the substrate 210, and the substrate 210 is a single crystal silicon wafer.

[0033] One side of the substrate 210 is covered with at least one layer of the spin electronics terahertz source film 202 . The side of the substrate 210 covered with the spin electronics terahertz source film 202 is in close contact with the plane side of the plano-convex lens 209 and is mounted on the sample holder 201 together.

[0034] The expanded parallel light 120 is incident through one side of the plano-convex lens 209, and thus becomes convergent light before entering the spin electronics terahertz source, so that the terahertz wave converted by the spin electronics terahertz source naturally becomes a convergent state.

[0035] Therefore, the present invention adopts the above-mentioned self-focusing high-field terahertz radiation source system. The spin electronics terahertz source generates converged terahertz radiation through a self-focusing terahertz conversion system. The system is simple and efficient and can meet the needs of high-intensity terahertz radiation.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A self-focusing high-field terahertz radiation source system, characterized in that: The invention comprises a laser, a laser beam expansion system and a self-focusing terahertz conversion system which are arranged in sequence. The laser is a femtosecond pulse laser. The laser beam expansion system comprises a plano-concave lens and a plano-convex lens 1 which are arranged in sequence. The self-focusing terahertz conversion system comprises a sample holder, a spin electronics terahertz source film and a permanent magnet. The sample holder is a copper sample holder. The spin electronics terahertz source film is installed on the sample holder. The permanent magnets are symmetrically arranged on both sides of the sample holder. A circular hole is arranged on the sample holder. A step is arranged in the middle of the circular hole. The circular hole is divided into area 1 and area 2 by the step.

2. A self-focusing high-field terahertz radiation source system according to claim 1, characterized in that: The concave side of the plano-concave lens is coated with an anti-reflection optical film, and the flat side of the plano-convex lens is coated with an anti-reflection optical film. The material of the plano-concave lens and the plano-convex lens is fused quartz with a relatively low thermal expansion coefficient.

3. A self-focusing high-field terahertz radiation source system according to claim 2, characterized in that: The laser beam expansion system also includes a translation stage base 1 and a translation stage base 2, a plano-concave lens is fixed on the translation stage base 1, a plano-convex lens is fixed on the translation stage base 2, and a translation stage base 3 is arranged at the bottom of the sample holder.

4. A self-focusing high-field terahertz radiation source system according to claim 3, characterized in that: The structure of the spin electronics terahertz source film is a heterojunction consisting of a ferromagnetic metal film layer grown on a heavy metal film layer, or a heavy metal film layer is grown on the outside of the ferromagnetic metal film of the heterojunction.

5. A self-focusing high-field terahertz radiation source system according to claim 4, characterized in that: The spintronics terahertz source thin film is grown on a substrate.

6. A self-focusing high-field terahertz radiation source system according to claim 5, characterized in that: A plano-convex lens 2 is fixedly installed in region 1, a substrate is fixed in region 2, a plano-convex lens 2 with one side of a spin electronics terahertz source facing region 1 is grown on the substrate, and a distance of 1 mm between the substrate and the plano-convex lens 2 is 1 mm.

7. The self-focusing high-field terahertz radiation source system according to claim 5, characterized in that: Area one is fixedly mounted with a plano-convex lens two and a substrate.

8. A self-focusing high-field terahertz radiation source system according to claim 6 or 7, characterized in that: A threaded hole is arranged on the side of the sample holder, and the permanent magnet is installed on the sample holder through the threaded hole.

9. The self-focusing high-field terahertz radiation source system according to claim 8, characterized in that: The sample holder is provided with a heat dissipation device, which includes a water cooling pipe and a pipe interface. The water cooling pipe is installed inside the sample holder, one end of the pipe interface is connected to the water cooling pipe, and the other end is connected to an external water cooler through a water pipe.

Images