Detection method of flexible magnetic-field-free terahertz ultrafast light source and spin terahertz equipment

Abstract

The invention provides a detection method of a flexible magnetic-field-free terahertz ultrafast light source and spin terahertz equipment. The detection method comprises the following steps: exciting an ultrafast terahertz light source device to generate an ultrafast terahertz pulse through a near-infrared ultrafast laser pulse, and detecting through a terahertz ultrafast spectrum. Meanwhile, a spinning THz source based on a transition metal oxide heterojunction without an external magnetic field, a flexible ultrafast spinning THz source based on inorganic substrate mica and a new method for widening the THz ultrafast pulse frequency domain width are achieved, and the spinning THz source which is low in energy consumption and practical is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of electromagnetic waves, and particularly relates to a detection method for a flexible non-magnetic terahertz ultrafast light source and a spin terahertz device. Background Art

[0002] THz (terahertz) waves are electromagnetic waves with frequencies in the range of 0.1 - 10 THz. Ultrafast THz pulses have extensive applications and demands in fields such as THz imaging, THz spectroscopy, and THz communication. In order to pursue a more reliable, wider frequency domain width, faster response speed, lower cost, lower excitation power, and more flexible structural design of THz ultrafast light sources, THz emitters based on spintronics (ultrafast spin THz sources) are the focus of current research.

[0003] In existing research and technologies, the initial ultrafast spin THz source consists of a heterojunction interface composed of a ferromagnetic material and a heavy metal with strong spin-orbit coupling. Under the excitation of a femtosecond pulsed laser, THz pulses are emitted. The pulse width of the femtosecond pulsed laser used to excite the heterojunction is generally 100 fs, the wavelength is 800 nm, and the repetition frequencies include kHz lasers with a relatively high power density and MHz lasers with a relatively low power density. Generally speaking, lower requirements for the excitation light mean a greater possibility of achieving widespread applications. For example, an ultrafast spin THz source that can emit THz pulses under the irradiation of a femtosecond laser is fabricated by forming a heterojunction with ferromagnetic metals such as Fe and Co and heavy metals such as Pt, Ru, Ta, and W with strong spin-orbit coupling.

[0004] The basic principle of THz pulse generation is that the laser excites a spin current from the ferromagnetic layer, and the spin current is injected into the heavy metal layer. Due to the strong spin-orbit coupling effect, spin-charge conversion occurs, enabling the spin current to drive the generation of a charge current, which in turn radiates THz ultrafast pulsed electromagnetic waves. Therefore, later research found that double-layer or multi-layer heterojunctions composed of ferromagnetic alloys such as CoFeB, CoFe, and NiFe and heavy metals such as Ta, Pt, and W can also be used to prepare ultrafast spin THz sources. Further research shows that forming heterojunctions with other non-magnetic materials with strong spin-orbit coupling and ferromagnetic materials can also achieve ultrafast THz emission. For example, ferromagnetic and topological insulators: Co|Bi2Se3, Fe3GeTe2|Bi2Te3, ferromagnetic and wide-bandgap semiconductors: n-GaN / NiFe.

[0005] The first important technology is to achieve ultrafast THz pulse emission without external magnetic field. In order to achieve more convenient control of the emitted THz pulses and get rid of the external conditions that require an external magnetic field, studies have shown that ultrafast THz emission can be achieved by introducing antiferromagnetic materials to replace ferromagnetic materials to construct heterojunctions. For example, antiferromagnetic materials and heavy metals: Mn3Sn|Pt (external magnetic field), NiO|Pt, W, Cu (no magnetic field), antiferromagnetic materials and ferromagnetic materials: IrMn3|Co 20 Fe 60 B 20 (No magnetic field).

[0006] The second important technology is to achieve "flexible (wearable) ultrafast THz pulse emission on inorganic substrates". Most of the existing ultrafast spin THz sources use hard substrates such as glass, MgO, and SiO2, which cannot be made flexible, thus limiting the possible application of such ultrafast spin THz sources in wearable or soft devices in the future. Some studies have grown heterojunction films on organic substrate polyester resin (PET). Although the demand for flexible THz sources can be met, the growth of films on organic substrates can only be carried out at slightly higher than room temperature or even at room temperature, which greatly limits the types of flexible films that can be prepared, thereby reducing the range of optional materials for flexible ultrafast spin THz sources. Many heterojunction materials that can only be synthesized at high temperatures cannot be bent. Fortunately, growing oxides on inorganic substrate mica is a new method for synthesizing flexible oxide films developed in recent years. Bending can be achieved by thinning the mica.

[0007] The third important technology is to achieve ultrafast THz pulse emission with a "wider THz frequency domain". The effective frequency domain width of ultrafast THz pulse emission generated by the optical rectification effect of traditional semiconductors such as GaAs and ZnTe crystals will not exceed 2THz. The frequency domain width of THz pulses emitted by ultrafast spin THz sources based on metal heterojunctions can be significantly improved compared to GaAs and ZnTe crystals, which can be increased to 3THz, 5THz, 8THz, and even 30THz. However, the frequency domain width of existing ultrafast THz pulses that can be emitted in the absence of an external magnetic field still does not exceed 2.5THz. In addition, in the existing flexible ultrafast spin THz sources, an external magnetic field is still required to emit ultrafast THz pulses. Therefore, for flexible ultrafast spin THz sources, being able to emit ultrafast THz pulses in an environment without an external magnetic field is one of the urgent problems to be solved.

[0008] The fourth important technology is to achieve low - energy - consumption and practical ultrafast THz pulse emission. Most of the existing ultrafast spin THz sources use ultrafast lasers with a repetition rate of 1 kHz as the excitation light, and another part uses ultrafast lasers with a repetition rate of 80 MHz or 76 MHz as the excitation light. The cost of kHz lasers is higher than that of MHz lasers. And the THz ultrafast pulses generated by MHz lasers have a better signal - to - noise ratio than those of kHz lasers. Therefore, the spin THz source excited by MHz lasers has lower cost and practicality.

[0009] So far, there has been no method of using oxides to construct heterojunctions to achieve ultrafast spin THz sources in previous studies. Transition metal oxides also have a strong spin - orbit coupling effect. Existing studies have also achieved the mutual conversion of charge current and spin current in transition metal oxides such as SrRuO3. However, there are still some research challenges: Can an ultrafast spin THz source based on transition metal oxides be realized? What role will transition metal oxides play in the ultrafast THz emission process? What advantages will the heterojunction based on oxides have in the application of ultrafast spin THz sources? These questions remain to be solved. Summary of the Invention

[0010] Therefore, the object of the present invention is to overcome the defects in the prior art and provide a detection method for a flexible magnetic - field - free terahertz ultrafast light source and a spin terahertz device. At the same time, it realizes an "external - magnetic - field - free" ultrafast spin THz source based on metal - oxide heterojunctions, a flexible ultrafast spin THz source based on an inorganic substrate, a new method for broadening the frequency domain width of ultrafast THz pulses, and an ultrafast spin THz source with low energy consumption and practicality.

[0011] Before elaborating on the content of the present invention, the terms used in this article are defined as follows:

[0012] The term "terahertz (THz)" refers to: electromagnetic waves with frequencies in the range of 0.1 - 10 THz.

[0013] The term "ultrafast light source" refers to: a light - emitting source that can generate pulsed lasers with pulse widths on the order of picoseconds (ps) or femtoseconds (fs). 。

[0014] The term "ultrafast spectroscopy" refers to: the time - evolution relationship of optical pulse signals obtained by using ultrafast laser pulses to control the "pump - probe" process through a time - delay device.

[0015] The term "ultrafast laser pulse" refers to: a laser pulse with an ultrashort pulse width on the order of picoseconds (ps) or even femtoseconds (fs).

[0016] The term "near-infrared" refers to: Near-infrared light is an electromagnetic wave with a wavelength in the range of 780 - 2526 nm.

[0017] The term "transition metal" refers to: Metal elements located in Groups IIIB - VIII of the periodic table.

[0018] The term "Mica" refers to: The English expression for mica, which refers to mica in the specification.

[0019] To achieve the above object, a first aspect of the present invention provides a detection method for a flexible magnetic-field-free terahertz ultrafast light source. The detection method uses a near-infrared ultrafast laser pulse to excite an ultrafast terahertz light source device and performs detection through terahertz ultrafast spectroscopy; wherein,

[0020] The ultrafast terahertz light source device includes a multi-layer heterojunction of transition metal oxides, and the multi-layer heterojunction includes:

[0021] A ferromagnetic layer;

[0022] A first single-crystal thin film layer;

[0023] A second single-crystal thin film layer made of transition metal oxide; and

[0024] A flexible substrate.

[0025] According to the detection method of the first aspect of the present invention, wherein the detection method includes the following steps:

[0026] (1) Without being additionally placed in a magnetic field, the ultrafast terahertz light source device is irradiated with a near-infrared ultrafast laser pulse. The ultrafast terahertz light source device emits an ultrafast terahertz pulse on the back surface irradiated by the near-infrared ultrafast laser pulse. After being focused by a parabolic mirror, it is detected by a terahertz detector. Among them, the parabolic mirror is preferably an off-axis parabolic mirror; and

[0027] (2) The terahertz detector converts the terahertz pulse into an electrical signal and outputs the signal via a lock-in amplifier, thereby realizing the generation and detection of ultrafast terahertz pulses at room temperature and in a magnetic-field-free environment;

[0028] Preferably, in step (1), the ultrafast terahertz light source device is placed in an optical cryostat and emits ultrafast terahertz pulses at low temperature. The optical window of the optical cryostat more preferably transmits electromagnetic waves in the terahertz and 800 nm infrared light bands; wherein, the temperature of the low temperature is preferably 4 - 300 K, more preferably 80 - 300 K, and further preferably 180 - 300 K.

[0029] The detection method according to the first aspect of the present invention, wherein in the step (1), it further includes: the near-infrared ultrafast laser pulse is split into two pulses by a beam splitter, where: the first pulse passes through a mirror to excite the ultrafast terahertz light source device to generate a terahertz pulse, and the second pulse passes through a mirror, is attenuated and then introduced into the terahertz detector to detect the generated terahertz pulse;

[0030] Preferably, the first pulse passes through a time delay device, and by controlling the optical path of the light generating the first pulse passing through the beam splitter, the time-domain waveform of the generated terahertz pulse is detected; and the delay device preferably includes: two mutually perpendicular mirrors and a micrometer-level electric translation stage, and the two mutually perpendicular mirrors are more preferably combined on the micrometer-level electric translation stage.

[0031] The detection method according to the first aspect of the present invention, wherein in the step (1), it further includes: a half-wave plate and a polarizer are arranged in front of the ultrafast terahertz light source device to control the polarization direction and power of the first pulse.

[0032] The detection method according to the first aspect of the present invention, wherein in the step (1):

[0033] The off-axis parabolic mirror is an aluminum-based off-axis parabolic mirror;

[0034] The size of the off-axis parabolic mirror is 1.5 to 4 inches, preferably 3 inches, and most preferably 3 inches;

[0035] The near-infrared ultrafast laser pulse passes through a chopper before irradiating the sample to improve the signal-to-noise ratio of the detection signal;

[0036] The laser power of the near-infrared ultrafast laser pulse before beam splitting is 0 mw to 1000 mw, preferably 400 mw to 500 mw, and most preferably 500 mw;

[0037] The laser power of the first pulse after beam splitting of the near-infrared ultrafast laser pulse is 0 to 500 mW, preferably 200 to 250 mW, and most preferably 250 mW;

[0038] The laser power of the first pulse after beam splitting of the near-infrared ultrafast laser pulse before passing through the chopper and reaching the sample is 0 to 250 mW, preferably 0 to 125 mW;

[0039] The laser power of the second pulse after beam splitting of the near-infrared ultrafast laser pulse after attenuation is 0 to 25 mW, most preferably 23 mW; and / or

[0040] The wavelength of the near-infrared ultrafast laser pulse is 760 to 840 nm, preferably 770 to 830 nm, and most preferably 800 nm.

[0041] According to the detection method of the first aspect of the present invention, in the step (1), the terahertz detector is a low-temperature-grown GaAs photoconductive antenna. The laser generated by the oscillator is divided into two beams. One beam is incident perpendicularly on the sample surface, and the other beam is used to excite the GaAs photoconductive antenna for detecting terahertz pulses;

[0042] Preferably, the low temperature is 4 - 300K, more preferably 80 - 300K, and further preferably 180 - 300K.

[0043] The second aspect of the present invention provides a spin terahertz device, which includes a multi-layer heterojunction with the following structure;

[0044] The multi-layer heterojunction is a multi-layer heterojunction of transition metal oxides, including:

[0045] A ferromagnetic layer;

[0046] A first single-crystal thin film layer;

[0047] A second single-crystal thin film layer made of transition metal oxides; and

[0048] A flexible substrate.

[0049] According to the detection method of the first aspect of the present invention or the spin terahertz device of the second aspect, the chemical formula of the multi-layer heterojunction except for the flexible substrate is: E u F v |A x B y C z |SrTiO3; where E is Ni, Co, and most preferably Ni;

[0050] F is Fe;

[0051] A is selected from one or more of the following metal elements: Sr, Ca, La, Bi, preferably Sr or Ca, and most preferably Sr;

[0052] B is selected from one or more of the following elements: Ru, Ir, O, Al, preferably the transition metal Ru or the transition metal Ir, and most preferably the transition metal Ru;

[0053] C is O or Se, and most preferably O;

[0054] x is 1 - 2, and most preferably 1;

[0055] y is 0 - 2, preferably 0 - 1, and more preferably 1;

[0056] z is 1 - 3, and most preferably 3;

[0057] u is 20 - 80, and most preferably 80;

[0058] v is from 20 to 80, and most preferably 20.

[0059] According to the detection method of the first aspect of the present invention or the spin terahertz device of the second aspect, the flexible substrate is an inorganic flexible substrate, and most preferably mica.

[0060] According to the spin terahertz device of the second aspect of the present invention, wherein the spin terahertz device is selected from one or more of the following: terahertz ultrafast lasers, terahertz emitters, terahertz-band spintronic devices, flexible wearable spin terahertz devices;

[0061] Preferably, the terahertz emitter is selected from one or more of the following: terahertz emitters for terahertz imaging, terahertz emitters for terahertz spectroscopy, terahertz emitters for terahertz communication, more preferably selected from one or more of the following: terahertz emitters for terahertz imaging, terahertz emitters for terahertz spectroscopy, terahertz emitters for terahertz communication, and further preferably selected from one or more of the following: terahertz emitters for terahertz imaging, terahertz emitters for terahertz spectroscopy, terahertz emitters for terahertz communication.

[0062] According to a specific embodiment of the present invention, a multilayer heterojunction based on the transition metal oxide SrRuO3 is constructed. The complete chemical formula including the mica substrate is: Ni 80 Fe 20 |SrRuO3|SrTiO3|Mica. First, a single-crystal SrTiO3 thin film with a thickness of 15 nm was epitaxially grown on the mica substrate by the van der Waals interaction between the oxide and mica at a temperature of 800 °C and an oxygen partial pressure of 0.1 mbar. Using a KrF excimer laser with a wavelength of 248 nm, a single-crystal SrRuO3 thin film with a thickness of 20 nm was deposited on the SrTiO3 substrate with a lattice orientation of (001) by the method of laser pulse deposition, and the energy density of the laser spot was 2.45 J / cm 2 . After the growth of SrRuO3, the thin film was cooled to room temperature at a rate of 10 °C / min in an oxygen atmosphere of 1 mbar. Subsequently, a 7-nm Ni -7 layer was in-situ deposited on SrRuO3 under high vacuum conditions (2.2 × 10 80 Fe 20 layer.

[0063] The finished product is a square sample with a size of 1 cm × 1 cm. The sample is irradiated with femtosecond pulsed laser with a pulse width of 100 fs, a wavelength of 800 nm, and a repetition frequency of 80 MHz generated by a titanium:sapphire oscillator. THz pulses will be emitted on the back side of the sample irradiated by the laser. The emitted THz pulses are focused by an off-axis parabolic mirror (OAP) and detected by a THz detector. The THz detector is a low-temperature grown GaAs photoconductive antenna. The laser generated by the titanium:sapphire oscillator is split into two beams. One beam is incident perpendicularly on the sample surface, and the other beam is used to excite the GaAs photoconductive antenna for detecting THz pulses. The laser power for exciting GaAs is about 23 mW. The THz detector converts the THz pulses into electrical signals and outputs the signals via a lock-in amplifier. The pulsed laser used to excite the sample needs to pass through a chopper to improve the signal-to-noise ratio of the detected signal. The laser power for exciting the sample is adjustable between 10 mW and 120 mW. A half-wave plate for 800 nm light is placed in front of the sample to control the polarization direction of the excitation light. The sample can emit THz waves at room temperature in a magnetic-field-free environment. Applying a constant static magnetic field in the plane of the sample can enhance the THz emission intensity of the sample. By changing the direction of the magnetic field, the polarization direction of the emitted THz electric field can be manipulated. Thinning the mica substrate to 19 μm can achieve bending of the sample, thus realizing a flexible spin THz source.

[0064] The detection method includes the following steps:

[0065] (1) Place the ultrafast THz light source device under the irradiation of a near-infrared ultrafast laser pulse. It is not necessary to place the sample in an additional magnetic field. The ultrafast THz light source device emits THz pulses on the back side irradiated by the near-infrared ultrafast laser pulse. After being focused by a parabolic mirror, they are detected by a THz detector. In addition, the THz light source device of the present invention can be placed in an optical cryostat to emit ultrafast THz pulses at low temperature. The optical window of the cryostat can transmit electromagnetic waves in the THz and 800 nm infrared light bands;

[0066] (2) The THz detector converts the ultrafast THz pulses into electrical signals and outputs the signals via a lock-in amplifier, so that ultrafast THz pulses can be generated and detected in a room-temperature and magnetic-field-free environment.

[0067] The flexibility of the ultrafast THz light source device of the present invention is based on a mica substrate, aiming to protect the method of realizing flexibility using an inorganic substrate. The magnetic-field-free is realized based on a heterojunction composed of a specific "ferromagnet|spin-orbit coupling material". In the present invention, the following materials are taken as examples to illustrate the technical effects of the present invention: The ferromagnetic material used in the present invention is Ni 80 Fe 20The alloy thin film, and the spin-orbit coupling material is a single-crystal thin film of transition metal oxide SrRuO3. In addition, the role of SrTiO3 is to achieve lattice matching with SrRuO3 for growth on a mica substrate. The present invention is based on the above materials to fabricate a device for laser-induced generation of ultrafast THz pulses. Among them, the heterojunction can be replaced with other materials.

[0068] According to another specific embodiment of the present invention, the present invention provides a flexible ultrafast spin THz source.

[0069] 1. As a THz source:

[0070] (1) For the fabrication of a THz ultrafast laser, as a crystal for generating ultrafast THz pulses.

[0071] (2) A THz emitter for fields such as THz imaging, THz spectroscopy, and THz communication.

[0072] 2. As a spin THz device:

[0073] (1) For the design of spin electronic devices in the THz frequency band.

[0074] 3. As a flexible device:

[0075] (1) For spin THz devices in soft and wearable scenarios.

[0076] (2) For a flexible ultrafast THz source.

[0077] The detection method of the flexible field-free ultrafast terahertz pulse of the present invention can have but is not limited to the following beneficial effects:

[0078] (1) An ultrafast spin THz source based on transition metal oxides is realized, expanding the range of materials that can be used for spin THz sources.

[0079] (2) Ultrafast spin THz emission under low power, field-free, and room temperature conditions is realized, verifying that an externally applied magnetic field can manipulate the THz electric field, and this spin THz source has practical value.

[0080] (3) A flexible spin THz source based on an inorganic substrate is realized, expanding the application potential of wearable and soft spin THz devices. Description of the Drawings

[0081] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings, wherein:

[0082] Figure 1 Shows a schematic structural diagram of the ultrafast terahertz light source device of the present invention.

[0083] Figure 2The optical path diagram when the ultrafast terahertz light source device of the present invention laser-excites a sample to emit THz is shown.

[0084] Figure 3 The spectrum of the heterojunction sample emitting THz waves and the comparison diagram of the THz spectrum emitted by a single ferromagnetic layer are shown.

[0085] Figure 4 The physical diagram of the flexible sample pasted on the surface of the curved copper block is shown.

[0086] Figure 5 The schematic structural diagram of the flexible terahertz light source device emitting THz when excited by a near-infrared ultrafast laser pulse is shown. Specific embodiments

[0087] The present invention will be further described below through specific embodiments. However, it should be understood that these embodiments are only used for more detailed and specific description, and should not be construed as limiting the present invention in any form.

[0088] This part generally describes the materials and test methods used in the experiments of the present invention. Although many materials and operation methods used to achieve the purpose of the present invention are well known in the art, the present invention still describes them in as much detail as possible here. Those skilled in the art are aware that in the context, if not specifically stated, the materials and operation methods used in the present invention are well known in the art.

[0089] Example 1

[0090] This embodiment is used to illustrate the flexible magnetic-field-free terahertz light source device and the detection method of terahertz ultrafast pulses of the present invention.

[0091] In this embodiment, a multi-layer heterojunction based on the transition metal oxide SrRuO3 is constructed. The complete chemical formula including the mica substrate is: Ni 80 Fe 20 |SrRuO3|SrTiO3|Mica.

[0092] First, through the van der Waals interaction between the oxide and mica, a single-crystal SrTiO3 thin film with a thickness of 15 nm was epitaxially grown on the mica substrate at a temperature of 800 °C and an oxygen partial pressure of 0.1 mbar. Using a KrF excimer laser with a wavelength of 248 nm, a single-crystal SrRuO3 thin film with a thickness of 20 nm was deposited on the SrTiO3 substrate with a lattice orientation of (001) by the method of laser pulse deposition. The energy density of the laser spot was 2.45 J / cm 2 . After the growth of SrRuO3, the thin film was cooled to room temperature at a rate of 10 °C / min in an oxygen atmosphere of 1 mbar. Subsequently, under high vacuum conditions (2.2ⅹ10 -7A 7-nm Ni layer was deposited in situ on SrRuO₃ at mbar. 80 Fe 20 layer.

[0093] The finished product is a square sample with a size of 1 cm × 1 cm, and the structure of the sample is as Figure 1 shown.

[0094] The femtosecond pulsed laser generated by a titanium:sapphire oscillator, with a pulse width of 100 fs, a wavelength of 800 nm, and a repetition frequency of 80 MHz, is split into two beams by a beam splitter. The first beam of pulses sequentially passes through a delay device and a chopper to reduce the signal-to-noise ratio, and then passes through a half-wave plate for 800-nm light and a polarizer to control the polarization state and power of the first beam of pulses. The first beam of pulses is finally guided and irradiated on the front surface of the sample. As Figure 2 shown, the sample will emit THz pulses on the back surface irradiated by the laser. The emitted THz pulses are focused by an off-axis parabolic mirror (OAP) and detected by a THz detector. The THz detector is a low-temperature-grown GaAs photoconductive antenna. The second beam of pulses after the beam splitter is guided into the THz detector to excite the GaAs photoconductive antenna for detecting THz pulses. The laser power of the second beam of pulses is generally controlled at 23 mW. The THz detector converts the THz pulses into electrical signals and outputs the signals via a lock-in amplifier. The pulsed laser used to excite the sample needs to pass through a chopper to improve the signal-to-noise ratio of the detected signal. The laser power used to excite the sample is adjustable between 10 mW and 120 mW. The sample can emit THz waves at room temperature in a magnetic-field-free environment. To further illustrate its function, a constant static magnetic field can be applied to the sample plane through an electromagnet, which can enhance the THz emission intensity of the sample. By changing the direction of the magnetic field, the polarization direction of the emitted THz pulses can be manipulated. Thinning the mica substrate to 19 μm can achieve bending of the sample, thus realizing a flexible spin THz source, as Figures 2-4 shown. The thinned sample is pasted on a bent bracket (a bent copper bracket is used in this embodiment), and a practical flexible ultrafast spin THz device is realized.

[0095] Examples 2 to 6

[0096] This embodiment is used to illustrate the flexible magnetic-field-free terahertz light source device of the present invention.

[0097] The preparation methods of Examples 2 - 6 are the same as those of Example 1, and all realize flexible spin THz sources. The difference lies in the different second single-crystal thin film layers, as shown in Table 1:

[0098] Table 1 Preparation of terahertz light source devices in Examples 2 - 6

[0099] Example Second single crystal thin film layer 2 <![CDATA[SrIrO3]]> 3 <![CDATA[CaRuO3]]> 4 Bi 5 <![CDATA[Bi2O2Se]]> 6 <![CDATA[LaAlO3]]>

[0100] Comparative Examples 1 to 12

[0101] This comparative example is used to compare the ultrafast terahertz light source device of the present invention with heterojunctions of other components.

[0102] Table 2 Heterojunctions of the ultrafast terahertz light source device of the present invention and other components

[0103]

[0104]

[0105]

[0106] Compared with the prior art, the ultrafast terahertz light source device of the present invention can achieve ultrafast laser-induced THz emission in a wider frequency domain under the condition of no external magnetic field, can achieve ultrafast THz emission under low-power pulsed laser, can achieve a curved spin THz source, and for the first time realizes a flexible THz source based on the inorganic substrate mica.

[0107] Although the present invention has been described to a certain extent, obviously, appropriate changes can be made to various conditions without departing from the spirit and scope of the present invention. It can be understood that the present invention is not limited to the described embodiments, but falls within the scope of the claims, which includes equivalent replacements of each factor described.

Claims

1. A detection method for a flexible magnetic-field-free terahertz ultrafast light source, characterized in that, The detection method excites an ultrafast terahertz light source device with a near-infrared ultrafast laser pulse and performs detection through terahertz ultrafast spectroscopy. Among them, the ultrafast terahertz light source device includes a multi-layer heterojunction of transition metal oxides, and the multi-layer heterojunction includes: a ferromagnetic layer; a first single-crystal thin film layer; a second single-crystal thin film layer made of transition metal oxides; and a flexible substrate.

2. The detection method according to claim 1, characterized in that, The detection method includes the following steps: (1) Without being additionally placed in a magnetic field, the ultrafast terahertz light source device is irradiated with a near-infrared ultrafast laser pulse. The ultrafast terahertz light source device emits an ultrafast terahertz pulse on the back surface irradiated by the near-infrared ultrafast laser pulse, which is converged by a parabolic mirror and detected by a terahertz detector. Among them, the parabolic mirror is preferably an off-axis parabolic mirror; and (2) The terahertz detector converts the terahertz pulse into an electrical signal and outputs the signal via a lock-in amplifier, thereby realizing the generation and detection of ultrafast terahertz pulses at room temperature and in a magnetic-field-free environment; Preferably, in step (1), the ultrafast terahertz light source device is placed in an optical cryostat and emits ultrafast terahertz pulses at low temperature. The optical window of the optical cryostat more preferably transmits electromagnetic waves in the terahertz and 800 nm infrared light bands. Among them, the temperature of the low temperature is preferably 4 - 300 K, more preferably 80 - 300 K, and further preferably 180 - 300 K.

3. The detection method according to claim 2, wherein Step (1) also includes: The near-infrared ultrafast laser pulse is split into two pulses by a beam splitter. Among them: The first pulse passes through a mirror to excite the ultrafast terahertz light source device to generate a terahertz pulse, and the second pulse passes through a mirror, is attenuated and then introduced into the terahertz detector to detect the generated terahertz pulse; Preferably, the first pulse passes through a time delay device, and by controlling the optical path of the first pulse generated by the beam splitter, the time-domain waveform of the generated terahertz pulse is detected; and the delay device preferably includes: two mutually perpendicular mirrors and a micrometer-level electric translation stage, and the two mutually perpendicular mirrors are more preferably combined on the micrometer-level electric translation stage.

4. The detection method according to claim 2 or 3, characterized in that Step (1) also includes: A half-wave plate and a polarizer are arranged in front of the ultrafast terahertz light source device to control the polarization direction and power of the first pulse.

5. The detection method according to any one of claims 2 to 4, characterized in that In step (1): the off-axis parabolic mirror is an aluminum-based off-axis parabolic mirror; the size of the off-axis parabolic mirror is 1.5 - 4 inches, preferably 3 inches, and most preferably 3 inches; the near-infrared ultrafast laser pulse passes through a chopper before irradiating the sample to improve the signal-to-noise ratio of the detection signal; the laser power of the near-infrared ultrafast laser pulse before beam splitting is 0 mw - 1000 mw, preferably 400 mw - 500 mw, and most preferably 500 mw; the laser power of the first pulse after beam splitting of the near-infrared ultrafast laser pulse is 0 - 500 mW, preferably 200 - 250 mW, and most preferably 250 mW; the laser power of the first pulse after beam splitting of the near-infrared ultrafast laser pulse before passing through the chopper and reaching the sample is 0 - 250 mW, preferably 0 - 125 mW; After the near-infrared ultrafast laser pulse is split, the laser power of the second pulse after attenuation is 0 to 25 mW, most preferably 23 mW; and / or The wavelength of the near-infrared ultrafast laser pulse is 760 to 840 nm, preferably 770 to 830 nm, and most preferably 800 nm.

6. The detection method according to any one of claims 2 to 5, characterized in that, In step (1): The terahertz detector is a low-temperature grown GaAs photoconductive antenna. The laser generated by the oscillator is split into two beams. One beam is incident perpendicularly on the sample surface, and the other beam is used to excite the GaAs photoconductive antenna to detect terahertz pulses. Preferably, the temperature of the low temperature is 4 to 300 K, more preferably 80 to 300 K, and further preferably 180 to 300 K.

7. A spin terahertz device, characterized in that, The spin terahertz device includes a multi-layer heterojunction with the following structure; The multi-layer heterojunction is a multi-layer heterojunction of transition metal oxides, including: A ferromagnetic layer; A first single-crystal thin film layer; A second single-crystal thin film layer made of transition metal oxide; and A flexible substrate.

8. The detection method according to any one of claims 1 to 6 or the terahertz spin device according to claim 7, characterized in that, The chemical formula of the multi-layer heterojunction except for the flexible substrate is: E u F v |A x B y C z |SrTiO3; where, E is Ni, Co, and most preferably Ni; F is Fe; A is selected from one or more of the following metal elements: Sr, Ca, La, Bi, preferably Sr or Ca, and most preferably Sr; B is selected from one or more of the following elements: Ru, Ir, O, Al, preferably transition metal Ru or transition metal Ir, and most preferably transition metal Ru; C is O or Se, and most preferably O; x is 1 to 2, and most preferably 1; y is 0 to 2, preferably 0 to 1, and more preferably 1; z is 1 to 3, and most preferably 3; u is 20 to 80, and most preferably 80; v is 20 to 80, and most preferably 20.

9. The detection method according to any one of claims 1 to 6 or the spin terahertz device according to claim 7, characterized in that, The flexible substrate is an inorganic flexible substrate, and most preferably mica.

10. The spin terahertz device according to any one of claims 7 to 9, characterized in that, The spin terahertz device is selected from one or more of the following: terahertz ultrafast lasers, terahertz emitters, terahertz-band spintronic devices, flexible wearable spin terahertz devices; Preferably, the terahertz emitter is selected from one or more of the following: terahertz emitters for terahertz imaging, terahertz emitters for terahertz spectroscopy, terahertz emitters for terahertz communication, more preferably selected from one or more of the following: terahertz emitters for terahertz imaging, terahertz emitters for terahertz spectroscopy, terahertz emitters for terahertz communication, and further preferably selected from one or more of the following: terahertz emitters for terahertz imaging, terahertz emitters for terahertz spectroscopy, terahertz emitters for terahertz communication.

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