A Co / Ru heterojunction terahertz pulse width-based regulation method

Abstract

The application discloses a kind of based on Co / Ru heterojunction terahertz pulse width's regulation and control method, belong to terahertz optoelectronic technical field.The method includes: substrate processing, Co / Ru heterojunction film preparation, terahertz emission and detection optical path establishment, signal acquisition processing and pulse width regulation and control.Co layer and the Ru layer of adjustable thickness are sequentially deposited on substrate by magnetron sputtering, and Co / Ru heterojunction is formed;Terahertz pulse is generated by using femtosecond laser excitation heterojunction, time-domain signal is collected by electro-optic sampling system, and pulse width and delay time are extracted by using Hilbert transform;Based on the monotonic correspondence between Ru layer thickness and terahertz pulse width, the pulse width is continuously adjustable in the range of 100-500fs by adjusting the thickness of Ru layer, while the spectral bandwidth and peak delay time are simultaneously regulated.

Description

Technical Field

[0001] This invention relates to the field of orbital electronics technology, and more particularly to a method for controlling the terahertz pulse width based on a Co / Ru heterojunction. Background Technology

[0002] The terahertz (THz) band, located between microwaves and infrared, possesses unique physical properties and broad application prospects, including bioimaging, spectral analysis, security detection, and high-speed wireless communication. The pulse width, peak time delay, and spectral bandwidth of a terahertz pulse are key parameters determining its application performance. However, most commercially available or researched THz generation technologies currently suffer from significant limitations in pulse width modulation capabilities.

[0003] Existing methods for changing the pulse width of terahertz pulses mainly fall into three categories:

[0004] In photoconductive antenna (PCA) structures, terahertz pulse widths can be modulated by changing the bias voltage, carrier lifetime, or using different bandgap materials. These methods rely on an external high-voltage electric field or special semiconductor material systems, resulting in fragile devices, unstable responses, and limited controllability, making it difficult to achieve continuously adjustable picosecond-level pulse width variations.

[0005] Phase-matching modulation based on nonlinear optical crystals. The pulse width can be adjusted by changing the incident angle, crystal thickness, or pump wavelength. However, the pulse width adjustment range is limited by the crystal dispersion relation, and most nonlinear crystals are highly sensitive to the pump wavelength, which limits their application in wide-band systems.

[0006] These methods rely on external optical path control, such as using delay lines, pulse stretchers, and bandpass filters. While these methods offer high precision, they involve external system control, increasing the complexity of the device and making it impossible to "control the pulse width internally through the structure of the emission source," thus limiting their application to compact terahertz sources.

[0007] The closest prior art to this invention is the terahertz pulse width modulation technology disclosed in Chinese patent CN105116565A. This technology employs a light-controlled terahertz modulation structure based on a high-resistivity silicon wafer, controlling the transmission and blocking of terahertz waves through an external pump laser to achieve external modulation of the terahertz pulse width. However, this technology is essentially a "light-controlled shutter" method, modulating the THz transmission process rather than the intrinsic waveform of terahertz radiation itself. It cannot directly control the shape, width, or spectral composition of the THz pulse; the modulation speed is limited by the carrier lifetime of the semiconductor material, making high-speed, fine-tuning difficult; and the modulation efficiency depends on parameters such as laser power and silicon wafer resistivity, resulting in a complex and costly system that is difficult to integrate on-chip and miniaturize.

[0008] In summary, existing technologies cannot solve the problem of tunable terahertz pulse width within metal thin-film heterojunction systems. There is no technology that can achieve engineered controllable adjustment of terahertz pulse width within the same device system by adjusting the thickness of the metal layer, which cannot meet the needs of modern terahertz communication, ultrafast optoelectronics, and on-chip THz integrated devices. Summary of the Invention

[0009] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for controlling the terahertz pulse width based on a Co / Ru heterojunction.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] This invention first proposes a method for controlling the terahertz pulse width based on a Co / Ru heterojunction, comprising the following steps:

[0012] S1. Substrate treatment: Select an electrically insulating substrate with good optical transmittance and perform cleaning and drying treatment;

[0013] S2. Preparation of Co / Ru heterojunction thin film: On the treated substrate, a Co layer and a Ru layer are sequentially deposited by magnetron sputtering to form a Co / Ru heterojunction thin film. The thickness d of the Ru layer is adjusted. Ru The range is 0-50nm;

[0014] S3. Establishing the terahertz emission and detection optical path: Femtosecond laser is used as the excitation source. The detection system is divided into a pump optical path and a detection optical path. After the pump light is focused, it irradiates the metal layer side of the Co / Ru heterojunction thin film.

[0015] The probe light passes through an adjustable delay line and an electro-optic crystal to form a terahertz electro-optic sampling system.

[0016] An external magnetic field sufficient to fully magnetize the sample is applied in the planar direction of the Co / Ru heterojunction film, with the magnetic field direction perpendicular to the polarization direction of the femtosecond laser.

[0017] S4. Terahertz signal acquisition and processing: Scan the adjustable delay line to acquire the terahertz time-domain signal emitted by the Co / Ru heterojunction film, perform multiple repeated acquisitions, averaging and baseline correction on the time-domain signal, and extract the peak width and delay time of the terahertz pulse.

[0018] S5. Terahertz pulse width control: Select or adjust the thickness dRu of the Ru layer according to the target terahertz pulse width to achieve adjustable control of the terahertz pulse width in the range of 100-500fs.

[0019] The core of the terahertz pulse width modulation mechanism lies in the intrinsic long-distance angular momentum transport and the inverse orbital Hall effect (IOHE) mechanism of the Co / Ru heterostructure, breaking through the physical limitation of traditional spin terahertz emitters that rely on spin diffusion. Co, as a ferromagnetic layer, generates both spin-polarized charge carriers and orbital angular momentum currents upon femtosecond laser excitation. The latter achieves efficient conversion of angular momentum current to charge current in Ru through IOHE, thereby radiating terahertz waves. Crucially, the diffusion length of the orbital angular momentum current in the Ru layer can reach tens of nanometers, far exceeding the spin diffusion length (1-3 nm), providing a physical basis for controlling the transport process through the Ru layer thickness.

[0020] The temporal characteristics of terahertz radiation can be directly modulated by altering the angular momentum transport path length and relaxation efficiency through the Ru layer thickness. When the Ru layer is thin (0-3 nm), the transport time of the angular momentum current from the Co layer to the adjacent Ru layer is extremely short, the charge conversion process is concentrated, and the temporal pulse of terahertz radiation is compact, with a pulse width maintained at 100-200 fs. As the Ru layer thickens (10-50 nm), the propagation distance of the angular momentum current in the Ru layer increases, and the relaxation time of the entire conversion process increases, leading to temporal broadening of terahertz radiation, with the pulse width increasing to 300-500 fs. Simultaneously, the longer transport path prolongs the residence time of the angular momentum current in the Ru layer, making the cumulative effect of the relaxation process more significant. Since high-frequency components correspond to short-timescale oscillations, they are more sensitive to relaxation dissipation, and their energy is rapidly dissipated; while low-frequency components have longer timescales and are less affected by relaxation, thus being retained. Ultimately, this results in a significant reduction in the proportion of high-frequency components in the spectrum, and a corresponding narrowing of the spectral bandwidth. The peak delay time is essentially a direct manifestation of the angular momentum transport delay, forming a monotonic correspondence between "thickness-transport-time-frequency characteristics", ultimately achieving structured and engineerable terahertz pulse width modulation.

[0021] Preferably, in step S1, the substrate is a glass, Al2O3, or MgO substrate, and the size of the substrate is 10mm×10mm×1mm or selected according to actual needs;

[0022] The cleaning and drying process specifically includes: ultrasonically cleaning the substrate sequentially in anhydrous ethanol and deionized water, with each ultrasonic cleaning step lasting 5-15 minutes; after cleaning, drying at 80-120℃ for 10-30 minutes, or naturally drying in a nitrogen stream; optionally, plasma cleaning is performed on the dried substrate for 1-5 minutes.

[0023] Preferably, in step S2, the magnetron sputtering deposition conditions are: a base vacuum better than 5 × 10⁻⁶. -5 The working pressure is stable at 0.1-0.5 Pa. The working gas is high-purity argon with a purity ≥99.999% and a flow rate of 40 sccm. The deposition process is carried out at room temperature.

[0024] The Co layer has a thickness of 0.5-3 nm, and the magnetron sputtering RF power during Co layer deposition is 50-100 W. The target thickness of the Co layer is obtained by controlling the deposition time.

[0025] Preferably, in step S2, the Ru layer thickness is adjusted in one of the following two ways:

[0026] a) Prepare a series of Co / Ru heterojunction samples with different Ru layer thicknesses, wherein the typical thicknesses of the Ru layer include 0 nm, 1 nm, 3 nm, 5 nm, 8 nm, 12 nm, 20 nm, 30 nm and 50 nm;

[0027] b) Using a wedge deposition method, a Ru layer with a continuously varying thickness along one direction is formed on the same substrate.

[0028] The magnetron sputtering RF power during Ru deposition is 20-40W; optionally, after deposition, annealing is performed at 150-300℃ for 10-60min in an inert atmosphere or vacuum to reduce interface defects and stabilize the Co / Ru interface structure.

[0029] Preferably, in S3, the center wavelength of the femtosecond laser system is 800nm ​​and the repetition frequency is 70-100MHz; the average power of the pump light is controlled within the range of 10-200mW to ensure that the Co / Ru heterojunction film is in the linear optical response range.

[0030] The electro-optic crystal is ZnTe or GaP; the strength of the external magnetic field is 1000 Oe, provided by a permanent magnet or electromagnet, and the direction of the magnetic field is arranged in a preset geometric relationship with the terahertz detection direction to obtain the maximum terahertz signal.

[0031] Preferably, in step S4, the envelope of the terahertz time-domain signal is extracted using Hilbert transform, the time corresponding to the peak of the envelope is defined as the delay time, and the time-domain width between the two peaks of the time-domain signal is defined as the peak width; a fast Fourier transform is performed on the time-domain signal to obtain the corresponding frequency-domain spectrum, which is used to analyze the trend of the spectrum width with the Ru layer thickness.

[0032] In S5, when the Ru layer thickness is 0-3nm, the terahertz pulse width is 100-200fs, which is suitable for broadband spectroscopy scenarios; when the Ru layer thickness is 10-50nm, the terahertz pulse width is 300-500fs, which is suitable for narrowband imaging or communication scenarios.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] 1. For the first time, a structured and continuously tunable terahertz pulse width was achieved in a metallic heterostructure terahertz emission system. Experimental results show that the pulse width can be structurally and continuously tunable in Co(1.5nm) / Ru(d Ru In the bilayer film, when the Ru layer thickness increases from 0 nm to 30-50 nm, the peak width of the terahertz time-domain pulse increases continuously from about 100 fs to about 500 fs. The pulse width change has a good monotonic correspondence with the Ru layer thickness. It can be engineered through material structure parameters, which solves the problem that the terahertz pulse width is basically unadjustable in the existing technology.

[0035] 2. This invention achieves synchronous and controllable adjustment of the terahertz emission delay time and spectral structure. As the Ru layer thickness increases, a repeatable time delay appears at the peak position of the terahertz pulse, the high-frequency components in the frequency domain spectrum gradually attenuate, and the spectral bandwidth narrows accordingly. This invention not only allows for the control of the pulse width but also enables overall control of the time-frequency structure of the terahertz wave, providing selectable pulse forms for different application scenarios (such as broadband spectroscopy, narrowband imaging, or communication). This is something that traditional optically controlled absorption modulators and spin terahertz transmitters cannot achieve.

[0036] 3. This invention overcomes the limitations of traditional spin transport on layer thickness. The pulse width modulation of this invention originates from the long-distance propagation characteristics of the angular momentum flow within the Co / Ru heterojunction, with a diffusion length reaching tens of nanometers, far exceeding the spin diffusion length (typically only 1-3 nm). In experiments, even with a Ru layer thickness of 30 nm, significant terahertz signal output can still be observed, ensuring the effectiveness and stability of pulse width modulation from a physical mechanism perspective.

[0037] 4. Simple structure, high stability, and easy integration. This invention does not rely on external bias voltage, high-power optical shutter, or complex optical path systems. Control can be achieved solely through thin-film structure parameters, resulting in low energy consumption and high system stability. Experiments show that under varying pump light power and laser polarization angle conditions, the terahertz pulse width and delay time remain essentially constant. The contribution of nonlinear optical effects to the terahertz signal is less than 10%, and the pulse width control effect mainly originates from the intrinsic angular momentum flow-charge flow conversion process of the material, exhibiting good repeatability and anti-interference capabilities.

[0038] 5. Broad application prospects. This invention provides an all-optical driving scheme for terahertz pulse width tunable without the need for an external modulator. It is suitable for building compact and integrable terahertz source modules and can play an important role in terahertz time-domain spectroscopy, imaging systems, high-speed communications, and programmable terahertz devices. It has good technical promotion value and industrialization potential. Attached Figure Description

[0039] Figure 1 A comparison of the spectral lines of the terahertz signal and the Hilbert transform;

[0040] Figure 2 Terahertz signal spectrum of Co / Ru bilayer films with different Ru thicknesses;

[0041] Figure 3 The graph shows the dependence of the terahertz signal intensity of the Co / Ru bilayer film on the Ru thickness.

[0042] Figure 4 The spectrum of terahertz signals for Co / Ru bilayer films with different Ru thicknesses is shown.

[0043] Figure 5 This is a graph showing the relationship between the terahertz signal delay time and the Ru thickness.

[0044] Figure 6 This is a graph showing how the peak width of the terahertz signal varies with the Ru thickness. Detailed Implementation

[0045] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0046] This embodiment fabricates Co / Ru bilayer heterojunctions with varying Ru layer thicknesses, excites their terahertz emission behavior using femtosecond lasers, and achieves controllable adjustment of the terahertz pulse width, peak delay time, and spectral structure by changing the Ru layer thickness. This method does not rely on external optical modulators or electrical biases; it achieves terahertz pulse width modulation entirely based on material structure parameters.

[0047] Thin film preparation:

[0048] A glass substrate with dimensions of 10mm × 10mm × 1mm was selected as the substrate. The substrate was ultrasonically cleaned sequentially in anhydrous ethanol and deionized water, with each cleaning step lasting 10 minutes. After cleaning, it was dried at 100℃ for 15 minutes to remove organic residues and moisture from the surface.

[0049] The treated substrate was placed in a magnetron sputtering system with a base vacuum better than 5 × 10⁻⁶. -5 Thin film deposition was performed under the following conditions: First, a Co film was deposited on the substrate surface with a thickness controlled at 1.5 nm. The sputtering RF power was 50 W, the working gas was high-purity argon at a pressure of 0.2 Pa, and the argon flow rate was 40 sccm. Subsequently, a Ru film was deposited on the Co layer surface with a sputtering RF power of 20 W. The Ru layer thickness d was controlled by adjusting the deposition time. Ru d were prepared respectively RuSamples were deposited at wavelengths of 0 nm, 1 nm, 3 nm, 5 nm, 8 nm, 12 nm, 20 nm, 30 nm, and 50 nm. To ensure interface quality, the entire deposition process was carried out continuously at room temperature without exposure to air.

[0050] Terahertz emission experiment:

[0051] A femtosecond laser system was used as the pump source, with a center wavelength of 800 nm and a repetition rate of 80 MHz. After beam splitting, one beam was used as the pump light, focused onto the surface of the sample's metal layer, with the average power controlled within the range of 10-200 mW to ensure the experiment was conducted within the linear optical response range. The other beam was used as the probe light for terahertz electro-optic sampling.

[0052] An external magnetic field of approximately 1000 Oe was applied along the plane of the sample to saturate the Co layer with magnetization. Furthermore, dry air was circulated within the measurement system during the measurement process to maintain an ambient humidity of ≤5%, minimizing the absorption of terahertz waves by water vapor. The sample was measured under the same laser power, optical path configuration, and magnetic field conditions to eliminate the influence of non-structural factors on the experimental results. The terahertz waves emitted by the sample were collected by a parabolic mirror and then introduced into an electro-optic crystal for time-domain sampling, yielding the terahertz time-domain waveform.

[0053] Data processing:

[0054] The acquired terahertz time-domain signal was averaged multiple times to improve the signal-to-noise ratio, and the baseline was corrected. The terahertz time-domain signal was processed using the Hilbert transform to obtain the envelope, and the time corresponding to the peak value of the envelope was defined as the peak delay time of the terahertz pulse. The time between two peak values ​​of the time-domain signal was set as its peak width (THz width), serving as a quantitative indicator of pulse width.

[0055] Simultaneously, a Fast Fourier Transform (FFT) is performed on the time-domain signal to obtain the corresponding frequency-domain spectrum, which is used to analyze the variation of the spectral bandwidth with the Ru layer thickness and to verify the results with the time-domain pulse width variation.

[0056] Data Analysis:

[0057] Figure 1 The comparison between the original terahertz time-domain signal and the spectrum after Hilbert transform is presented. The original signal has slight fluctuations due to noise interference, while the spectrum after Hilbert transform smoothly extracts the pulse envelope, accurately delineating the peak position and contour boundary of the pulse. The transformed spectrum not only eliminates redundant noise, but also clarifies the effective time domain range of the pulse.

[0058] Figure 2The effect of Ru layer thickness (0 nm, 1 nm, 3 nm, 9 nm, 20 nm, 50 nm, etc.) on terahertz time-domain signals was demonstrated. When the Ru layer thickness was thin (e.g., 1 nm, 3 nm), the spectral peaks were sharp, the pulse leading edge was steep, and the time-domain width was narrow. As the Ru layer thickness increased (e.g., 20 nm, 50 nm), the spectral lines broadened significantly, the peak position shifted (delayed) towards the positive time axis, and the peak shape tended to be flatter. This intuitive correlation of "increased thickness - pulse broadening - peak delay" directly verifies the modulating effect of Ru layer thickness on terahertz pulse width.

[0059] Figure 3 The study revealed the relationship between signal intensity and Ru layer thickness. As the Ru layer thickness increased from 0 nm to 50 nm, the signal intensity, while exhibiting slight fluctuations, remained within the effective detection range without significant attenuation. Even at a Ru layer thickness of 30 nm (far exceeding the traditional spin diffusion length of 1-3 nm), significant signal intensity was still observed, strongly demonstrating the long-distance propagation characteristics of angular momentum flow in Co / Ru heterostructures. This breakthrough overcomes the traditional layer thickness limitation of spin transport and provides stable support for pulse width modulation under thick Ru layers.

[0060] Figure 4 The study revealed the modulatory effect of Ru layer thickness on the spectral structure of terahertz signals. When the Ru layer thickness is thin (0-3 nm), the high-frequency components (such as above 3 THz) in the spectrum are abundant, and the spectral bandwidth is wide, which is suitable for broadband spectral scenarios. As the Ru layer thickness increases (10-50 nm), the high-frequency components gradually attenuate, the spectral peak shifts to lower frequencies, and the bandwidth narrows significantly, which meets the needs of narrowband imaging and communication.

[0061] Figure 5 The delay time exhibits a monotonically increasing trend with the Ru layer thickness. From 0 nm to 50 nm, the delay time gradually increases from an initial short delay, and the change curve is smooth without abrupt changes, showing good linear correlation characteristics. This trend stems from the extension of the angular momentum flow transport path in the Ru layer: the thicker the Ru layer, the longer the transport time of the angular momentum flow from the Co layer to the Ru layer, resulting in a more significant delay in the terahertz pulse peak.

[0062] Figure 6 This invention demonstrates the continuously adjustable terahertz pulse width. When the Ru layer thickness is between 0-3 nm, the peak width stabilizes within a narrow pulse width range of 100-200 fs. As the thickness increases to 10-50 nm, the peak width gradually and continuously expands to 300-500 fs, with a smooth and uninterrupted overall change, achieving continuous control across the entire range of 100-500 fs. This figure provides direct quantitative evidence of the core technical effect of this invention, clearly proving that the terahertz pulse width can be precisely controlled by adjusting the Ru layer thickness. This solves the pain point of the non-adjustable pulse width in existing technologies and demonstrates the technical advantages of a wide controllability range, good continuity, and strong controllability.

[0063] Experimental results show that the terahertz pulse width emitted by the Co / Ru heterojunction exhibits a significant tunable trend with increasing Ru layer thickness. When the Ru layer thickness is 0-3 nm, the terahertz pulse is relatively sharp, with a pulse width of approximately 200 fs. When the Ru layer thickness increases to 10-20 nm, the pulse width gradually increases, reaching approximately 300-350 fs. When the Ru layer thickness further increases to over 30 nm, the pulse width can extend to approximately 420 fs. Simultaneously, the peak time of the terahertz pulse gradually delays with increasing Ru thickness, the high-frequency components in the frequency domain spectrum gradually attenuate, and the spectral bandwidth narrows accordingly. Even when the Ru layer thickness reaches 40-50 nm, a significant terahertz signal output can still be observed, indicating that this method is not limited by the traditional spin diffusion length and verifying the feasibility of using angular momentum transport to achieve terahertz pulse width modulation.

[0064] The Co / Ru heterojunction terahertz pulse width modulation method employed in this embodiment directly influences the terahertz emission formation process through material structural parameters (Ru layer thickness), avoiding the modulation methods in existing technologies that rely on semiconductor optical absorption control or external optical shutters. This method features a simple structure, direct modulation, a wide pulse width modulation range, good repeatability, and insensitivity to pump light power and polarization changes. The contribution of nonlinear optical effects to the terahertz signal is less than 10%, indicating that its pulse width modulation effect mainly originates from the intrinsic angular momentum-charge conversion mechanism of the material, demonstrating good stability and practicality.

[0065] 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 equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for controlling the terahertz pulse width based on a Co / Ru heterojunction, characterized in that, Includes the following steps: S1. Substrate treatment: Select an electrically insulating substrate with good optical transmittance and perform cleaning and drying treatment; S2, preparing Co / Ru wedge-shaped heterojunction film: on the treated substrate, Co layer and wedge-shaped Ru layer are deposited by magnetron sputtering to form Co / Ru wedge-shaped heterojunction film, the thickness d of the grown Ru layer is 0-50 nm Ru is continuous 0-50 nm; so that different pulse width outputs can be realized without changing the structure or re-preparing the sample; S3. Establishing the terahertz emission and detection optical path: Femtosecond laser is used as the excitation source. The detection system is divided into a pump optical path and a detection optical path. After the pump light is focused, it irradiates the metal layer side of the Co / Ru heterojunction thin film. The probe light passes through an adjustable delay line and an electro-optic crystal to form a terahertz electro-optic sampling system. An external magnetic field sufficient to fully magnetize the sample is applied in the planar direction of the Co / Ru heterojunction film, with the magnetic field direction perpendicular to the polarization direction of the femtosecond laser. S4. Terahertz signal acquisition and processing: Scan the adjustable delay line to acquire the terahertz time-domain signal emitted by the Co / Ru heterojunction film, perform multiple repeated acquisitions, averaging and baseline correction on the time-domain signal, and extract the peak width and delay time of the terahertz pulse. S5. Terahertz pulse width modulation: Based on the target terahertz pulse width, the excitation position of the laser pulse in the Ru layer is adjusted to change the Ru layer thickness dRu, thereby achieving continuous adjustable control of the terahertz pulse width in the range of 100-500 fs.

2. The continuous control method according to claim 1, characterized in that, In S1, the substrate is a glass, Al2O3 or MgO substrate, and the size of the substrate is 10mm×10mm×1mm or selected according to actual needs; The cleaning and drying process specifically includes: ultrasonically cleaning the substrate sequentially in anhydrous ethanol and deionized water, with each ultrasonic cleaning step lasting 5-15 minutes; after cleaning, drying at 80-120℃ for 10-30 minutes, or naturally drying in a nitrogen stream; optionally, plasma cleaning is performed on the dried substrate for 1-5 minutes.

3. The continuous control method according to claim 1, characterized in that, In S2, the deposition conditions for magnetron sputtering are: a base vacuum better than 5 × 10⁻⁶. -5 The working pressure is stable at 0.1-0.5 Pa. The working gas is high-purity argon with a purity ≥99.999% and a flow rate of 40 sccm. The deposition process is carried out at room temperature. The Co layer has a thickness of 0.5-3 nm, and the magnetron sputtering RF power during Co layer deposition is 50-100 W. The target thickness of the Co layer is obtained by controlling the deposition time.

4. The continuous control method according to claim 1, characterized in that, In S2, the Ru layer thickness can be adjusted in one of the following two ways: a) Prepare a series of Co / Ru heterojunction samples with different Ru layer thicknesses, wherein the typical thicknesses of the Ru layer include 0 nm, 1 nm, 3 nm, 5 nm, 8 nm, 12 nm, 20 nm, 30 nm and 50 nm; b) A Ru layer with a continuously varying thickness along one direction is formed on the same substrate using a wedge deposition method; The magnetron sputtering RF power during Ru layer deposition is 20-40W; After deposition, annealing is performed at 150-300℃ for 10-60 minutes in an inert atmosphere or vacuum to reduce interface defects and stabilize the Co / Ru interface structure.

5. The continuous control method according to claim 1, characterized in that, In S3, the center wavelength of the femtosecond laser system is 800 nm, and the repetition frequency is 70-100 MHz; the average power of the pump light is controlled within the range of 10-200 mW to ensure that the Co / Ru heterojunction film is in the linear optical response range. The electro-optic crystal is ZnTe or GaP; the strength of the external magnetic field is 1000 Oe, provided by a permanent magnet or electromagnet, and the direction of the magnetic field is arranged in a preset geometric relationship with the terahertz detection direction to obtain the maximum terahertz signal.

6. The continuous control method according to claim 1, characterized in that, In step S4, the envelope of the terahertz time-domain signal is extracted using Hilbert transform. The time corresponding to the peak of the envelope is defined as the delay time, and the time-domain width between the two peaks of the time-domain signal is defined as the peak width. The time-domain signal is then subjected to fast Fourier transform to obtain the corresponding frequency-domain spectrum, which is used to analyze the trend of the spectrum width with the Ru layer thickness.

7. The continuous control method according to claim 1, characterized in that, In S5, when the Ru layer thickness is 0-3nm, the terahertz pulse width is 100-200fs, which is suitable for broadband spectroscopy scenarios; when the Ru layer thickness is 10-50nm, the terahertz pulse width is 300-500fs, which is suitable for narrowband imaging or communication scenarios.

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