Terahertz wave frequency spectrum regulation and control method and device based on plasma transient time boundary

Abstract

The invention provides a plasma transient time boundary-based terahertz wave spectrum regulation and control method and device, and the method comprises the steps: obtaining femtosecond laser and terahertz waves, and enabling the femtosecond laser and the terahertz waves to enter a terahertz wave transmission space through beam combination; when the femtosecond laser and the terahertz wave synchronously pass through a first position point, the terahertz wave after frequency spectrum regulation and control is obtained; the first position point is located in the terahertz wave transmission space, a time boundary caused by medium transient refractive index sudden change is formed at the first position point when the femtosecond laser ionizes gas to obtain plasma, and frequency shift occurs when terahertz waves pass through the time boundary. According to the invention, the modulation effect on the terahertz wave frequency demand can be realized according to the abrupt change of the refractive index caused by the transient generation of the plasma.

Description

Technical Field

[0001] This invention relates to the field of terahertz technology, and in particular to a method and apparatus for terahertz wave spectrum modulation based on plasma transient time boundary. Background Technology

[0002] Terahertz waves typically refer to electromagnetic waves in the frequency range of 0.1-10 THz, falling between infrared and microwaves. They have a very broad application prospect in fields such as biomedicine, high-speed communication, and sensing imaging. Currently, terahertz wave technology is mainly limited by the scarcity of sources, detection methods, and control methods in the terahertz band. In particular, regarding the control methods of terahertz waves, the current lack of control media, slow control rates, and low control efficiency severely restricts the development and application of terahertz wave technology.

[0003] Current mainstream terahertz wave manipulation technologies mainly include optical, electrical, and metasurface methods, each with its own bottlenecks. For existing optical terahertz wave manipulation methods, such as in-situ optical generation and manipulation or the use of nonlinear crystals, the manipulation effect is limited by the damage threshold of the manipulation material. For existing electrical terahertz wave manipulation methods, the influence of electrically controlled carrier mobility limits manipulation speeds to GHz levels, making it difficult to meet the ultrafast manipulation requirements of picosecond-level terahertz waves. While existing metasurface manipulation methods offer advantages such as high Q-values, their fixed structure, once designed and fabricated, leads to limited manipulation functionality and makes it difficult to reuse across multiple frequencies and application scenarios. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides an ultrafast, efficient, and low-threshold terahertz wave spectrum modulation method and device based on the plasma transient time boundary.

[0005] This invention provides a method for terahertz wave spectrum manipulation based on plasma transient time boundary, comprising: Obtain femtosecond laser and terahertz wave, and combine the femtosecond laser and the terahertz wave into the terahertz wave transmission space; When the femtosecond laser and the terahertz wave pass through the first position point synchronously, a spectrally modulated terahertz wave is obtained. The first position point is located within the terahertz wave transmission space. At the first position point, when the femtosecond laser ionizes the gas to obtain plasma, a time boundary is formed due to the transient refractive index change of the medium. Then, when the terahertz wave passes through the time boundary, a frequency shift occurs.

[0006] According to the present invention, a terahertz wave spectrum manipulation method based on plasma transient time boundary is provided, the method further comprising: Determine the blue-shift and red-shift frequencies after the frequency shift occurs; Based on the blue shift frequency and the red shift frequency, determine the relative permittivity of the corresponding blue shift frequency and the relative permittivity of the corresponding red shift frequency, respectively. Based on the relative permittivity of the blue-shift frequency and the relative permittivity of the red-shift frequency, the real part of the refractive index of the corresponding blue-shift frequency and the real part of the refractive index of the red-shift frequency are determined respectively. Based on the relative permittivity of the blue-shift frequency, the relative permittivity of the red-shift frequency, the real part of the refractive index of the blue-shift frequency, and the real part of the refractive index of the red-shift frequency, the transmission coefficient of the terahertz wave at the transient time boundary of the medium is determined. The amplitude of the terahertz wave after spectral modulation is determined based on the transmission coefficients of the blue-shifted frequency and the red-shifted frequency.

[0007] According to the present invention, a method for terahertz wave spectrum modulation based on plasma transient time boundary is provided, wherein determining the transmission coefficient of the terahertz wave at the blue-shift frequency and the red-shift frequency at the transient time boundary of the medium based on the relative permittivity of the blue-shift frequency, the relative permittivity of the red-shift frequency, the real part of the refractive index of the blue-shift frequency, and the real part of the refractive index of the red-shift frequency includes: Based on the relative permittivity of the blue-shift frequency, the relative permittivity of the red-shift rate, the real part of the refractive index of the blue-shift frequency, and the real part of the refractive index of the red-shift frequency, the transmission coefficients of the terahertz wave at the time boundary are determined using the following calculation method. in, and These are the transmission coefficients at the blue-shifted frequency and the red-shifted frequency, respectively. and These are the real parts of the refractive index at the blue-shifted frequency and the real parts of the refractive index at the red-shifted frequency, respectively. and These are the relative permittivity at the blue-shift frequency and the relative permittivity at the red-shift frequency, respectively. and These are the blue shift frequency and the red shift frequency, respectively.

[0008] According to the present invention, a terahertz wave spectrum manipulation method based on plasma transient time boundary is provided, the method further comprising: Determine the blue shift or red shift frequency after the frequency shift occurs; Based on the blue shift frequency and the red shift frequency, determine the relative permittivity of the corresponding blue shift frequency or the relative permittivity of the red shift frequency; Based on the relative permittivity of the blue-shifted frequency or the relative permittivity of the red-shifted frequency, determine the real part of the refractive index of the corresponding blue-shifted frequency or the real part of the refractive index of the red-shifted frequency. Based on the refractive index of the blue-shifted frequency or the refractive index of the red-shifted frequency, the transmission coefficient of the terahertz wave at the time boundary is determined using the following calculation formula. in, For frequency The corresponding transmission coefficient, For frequency The corresponding real part of the refractive index; The amplitude of the terahertz wave after spectral modulation is determined based on the blue-shift transmission coefficient or the red-shift transmission coefficient.

[0009] According to the present invention, a terahertz wave spectrum manipulation method based on plasma transient time boundary is provided, wherein obtaining femtosecond laser and terahertz wave includes: Acquire an initial femtosecond laser beam and split the initial femtosecond laser beam into two beams; one of these beams is used as the femtosecond laser beam. The terahertz wave is generated by passing another beam of light through the first zinc telluride crystal.

[0010] According to the present invention, a terahertz wave spectrum manipulation method based on plasma transient time boundary is provided, the method further comprising: The initial femtosecond laser is further split into a third beam for electro-optic sampling and detection of terahertz wave waveform; The spectrally modulated terahertz wave is combined with the third beam, reflected by an off-axis parabolic mirror, and then collinearly injected into a second zinc telluride crystal for electro-optic sampling measurement. The beam is then split using a quarter-glass slide and a Wollaston prism, and the additional ellipsometric signal introduced into the zinc telluride crystal by the terahertz wave is detected and output by a balanced detector.

[0011] The present invention also provides a terahertz wave spectrum manipulation device based on plasma transient time boundary, comprising a light generation unit and a light propagation unit, wherein: The light generation unit is used to obtain femtosecond lasers and terahertz waves; An optical propagation unit is used to combine the femtosecond laser and the terahertz wave and introduce them into the terahertz wave transmission space, so that when the femtosecond laser and the terahertz wave synchronously pass through the first position point, a spectrally modulated terahertz wave is obtained; the first position point is located in the terahertz wave transmission space, and at the first position point, when the femtosecond laser ionizes the gas to obtain plasma, a time boundary is formed caused by the transient refractive index change of the medium, and the frequency shift occurs when the terahertz wave passes through the time boundary.

[0012] According to the present invention, a terahertz wave spectrum modulation device based on plasma transient time boundary is provided, wherein the optical propagation unit comprises indium tin oxide (ITO) glass and a first off-axis parabolic mirror, wherein: The indium tin oxide (ITO) glass is used to combine the femtosecond laser and the terahertz wave. The first off-axis parabolic mirror is used to converge the combined femtosecond laser and the terahertz wave to a first position point within the terahertz wave transmission space.

[0013] According to the present invention, a terahertz wave spectrum modulation device based on plasma transient time boundary is provided, wherein the light generation unit includes a femtosecond laser, a first zinc telluride crystal, and a reflector, wherein: The femtosecond laser is used to generate an initial femtosecond laser and split the initial femtosecond laser into two beams, one of which is used as the femtosecond laser. The first zinc telluride crystal is used to generate the terahertz wave after penetrating another beam of light; The reflector is used to propagate the terahertz wave to the indium tin oxide (ITO) glass and combine it with the femtosecond laser beam.

[0014] According to the present invention, a terahertz wave spectrum manipulation device based on plasma transient time boundary is provided. The device further includes an optical detection unit, which comprises a second off-axis parabolic mirror, a second zinc telluride crystal, a quarter-glass slide, a Wollaston prism, and a balanced detector, specifically used for: The spectrally modulated terahertz wave is combined with the third beam split from the initial femtosecond laser. After being reflected by an off-axis parabolic mirror, it is collinearly injected into a second zinc telluride crystal for electro-optic sampling measurement. Then, a quarter-glass slide and a Wollaston prism are used for beam splitting. The additional ellipsometric signal introduced into the zinc telluride crystal by the terahertz wave is detected and output by a balanced detector.

[0015] According to the present invention, a terahertz wave spectrum modulation device based on plasma transient time boundary is provided, wherein the optical detection unit further includes a silicon wafer and a third off-axis parabolic mirror, specifically used for: The regulated terahertz wave is transmitted through the silicon wafer, and then the third off-axis parabolic mirror combines the terahertz wave with the third beam.

[0016] This invention provides a terahertz wave spectrum modulation method and device based on plasma transient time boundary. By combining a femtosecond laser and a terahertz wave into a terahertz wave transmission space, and simultaneously passing through a point within the terahertz wave transmission space, a time boundary is formed by the transient refractive index change of the medium when the femtosecond laser ionizes the gas to obtain plasma. This causes the terahertz wave to shift its frequency when passing through the time boundary, thereby achieving the desired modulation effect of the terahertz wave frequency based on the refractive index change caused by the transient plasma generation. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a schematic flowchart of the terahertz wave spectrum control method based on plasma transient time boundary provided by the present invention.

[0019] Figure 2 This is a schematic diagram of the control process at a certain location in the terahertz wave transmission space provided by the present invention.

[0020] Figure 3 The original frequency provided by this invention and the new frequency after frequency shift The change graph.

[0021] Figure 4 The present invention provides a schematic diagram of the spectral changes caused by frequency shift at the transient plasma time boundary, as experimentally measured.

[0022] Figure 5 This is a schematic diagram of the terahertz wave spectrum control device based on plasma transient time boundary provided by the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0024] The following is combined with Figures 1-5The present invention describes a terahertz wave spectrum modulation method and apparatus based on plasma transient time boundary.

[0025] Figure 1 This invention provides a schematic flowchart of a terahertz wave spectrum modulation method based on plasma transient time boundary. (See attached diagram.) Figure 1 The method includes the following steps: Step 11: Obtain femtosecond laser and terahertz wave, and combine the femtosecond laser and terahertz wave into the terahertz wave transmission space.

[0026] Step 12: When the femtosecond laser and the terahertz wave pass through the first position point synchronously, the terahertz wave with spectrum modulation is obtained. The first position point is located in the terahertz wave transmission space. At the first position point, when the femtosecond laser ionizes the gas to obtain plasma, a time boundary is formed caused by the transient refractive index change of the medium. Then, when the terahertz wave passes through the time boundary, the frequency shift occurs.

[0027] Regarding steps 11 and 12, it should be noted that terahertz waves generally refer to electromagnetic waves in the frequency range of 0.1-10 THz, falling between infrared and microwaves, and have very broad application prospects in fields such as biomedicine, high-speed communication, and sensing imaging. Currently, terahertz wave technology is mainly limited by the scarcity of sources, detection methods, and modulation techniques in the terahertz band. Particularly in terms of terahertz wave modulation techniques, the current lack of modulation media, slow modulation rates, and low modulation efficiency severely restricts the development and application of terahertz wave technology. Therefore, this invention uses transient plasma generation to form a time boundary, causing a transient refractive index change at this boundary position within the terahertz wave transmission space, thereby achieving spectral modulation of the incident terahertz wave. By customizing the refractive index of the transient plasma, the frequency of the terahertz wave can be shifted to meet the desired modulation effect.

[0028] In this invention, since the object of frequency modulation is a terahertz wave, it is necessary to obtain the terahertz wave to be modulated. Because the transient generation of plasma is required to create the time boundary caused by the transient refractive index change of the medium, a femtosecond laser that ionizes the gas is needed. Since the frequency modulation of the terahertz wave needs to be achieved at a specific point within the terahertz wave transmission space, the femtosecond laser and the terahertz wave are combined and then enter the terahertz wave transmission space.

[0029] In this invention, plasma is generated by ionizing terahertz waves through a space containing gas (such as air) using a femtosecond laser. A time boundary is formed at the point where the refractive index of the plasma changes abruptly compared to the original air medium. When the terahertz waves that propagate synchronously to this point pass through this transient time boundary, their frequency shifts, thereby achieving the control of the terahertz wave spectrum.

[0030] See Figure 2 During the transmission of terahertz waves to a specific point in space, a femtosecond laser focuses on that location, ionizing the air to generate plasma and causing an instantaneous change in refractive index. From a temporal and spatial perspective, assuming space is a continuous homogeneous medium, at a certain instant, after the air ionizes to generate plasma, the refractive index undergoes a sudden change over time. The refractive index of that region changes from the air refractive index... abrupt change to plasma refractive index Based on the conservation of incident electromagnetic wave quantity, the following conditions are satisfied: At this time, for the original frequency in the air The frequency will shift and change to a new frequency. The frequency change is determined by the change in refractive index. The new frequency after the frequency shift... Satisfying the expression: According to this formula, when > At that time, the frequency after frequency shift The frequency decreases, resulting in a frequency redshift; when < At that time, the frequency after frequency shift As the frequency increases, a blue shift occurs. It's important to note that since this process is not a traditional nonlinear process, the frequency change does not need to meet a threshold requirement; a considerable change in the refractive index is sufficient for a frequency shift to occur, allowing for frequency shifts even at low incident terahertz wave energies.

[0031] The terahertz wave spectrum modulation method based on plasma transient time boundary provided by this invention combines a femtosecond laser and a terahertz wave into the terahertz wave transmission space. When the femtosecond laser and the terahertz wave synchronously pass through a position point in the terahertz wave transmission space, the plasma generated by the ionization of gas by the femtosecond laser forms a time boundary caused by a transient refractive index change in the medium. This causes the terahertz wave to shift its frequency when passing through the time boundary, thereby achieving the desired modulation effect of the terahertz wave frequency based on the refractive index change caused by the transient plasma generation.

[0032] In a further step of the above method, it should also be noted that, see [link to relevant documentation]. Figure 3 Provided raw frequency and the new frequency after frequency shift The refractive index used in the graph was calculated. The refractive index exhibits resonant absorption characteristics near the resonant frequency within the plasma, resulting in a Lorentz linearity and causing the frequency change to resemble a bistable structure. Figure 3In the multi-frequency conversion region, for amplitudes near 1THz with a strong terahertz wave intensity distribution, there will be a characteristic of frequency shift towards both ends, resulting in terahertz wave frequency shift and spectrum broadening.

[0033] A femtosecond laser ionizes at a certain location in the terahertz wave transmission space, transiently forming plasma. At this instant, during the interaction of the femtosecond laser, a large number of electrons are generated through tunneling ionization. Assume the electron density after ionization is... .

[0034] In the terahertz wave transmission region, plasma is generated due to the abrupt change of the medium from air. The relative permittivity of the plasma in this region can be written as: in, For the new frequency after transformation, It is an imaginary number. For electron collision relaxation, The plasma frequency is primarily determined by the electron density. Represents electron density, Represents the vacuum permittivity. The amount of electron charge. Let the electron mass be denoted as . Here, the plasma is calculated and the formulas are derived using a uniform cylindrical electron column. The cylindrical structure causes the terahertz waves to have different frequencies. The vicinity exhibits resonant properties, thus introducing a Lorentz dispersion structure. Due to the transiently generated plasma, for terahertz waves transmitted through this region of space, the real part of the refractive index abruptly changes from that in air to that in plasma, as expressed mathematically: in, For frequency The corresponding refractive index, For the real algorithm, For frequency The corresponding relative medium constant.

[0035] Terahertz waves are transmitted through a plasma region experiencing a transient refractive index change. Due to time-domain refraction and reflection, the frequency of the terahertz wave changes based on momentum conservation. At this point, the frequency change at the time interface is as follows: When the value is greater than 1, the transient time boundary causes a decrease in the frequency of the terahertz wave, resulting in a redshift; for When the refractive index is less than 1, the refractive index frequency corresponding to the terahertz wave increases, resulting in a blue shift. Due to the Lorentz linearity, the real part of the refractive index undergoes a transition from greater than 1 to less than 1 within the terahertz wave frequency range. The corresponding terahertz wave frequencies exhibit a red shift in the low-frequency range and a blue shift in the high-frequency range.

[0036] Under the influence of plasma transient time boundaries, broadband incident terahertz waves undergo redshift and blueshift, causing the frequency to shift towards higher or lower frequencies. Due to time refraction, the frequency conversion direction satisfying the time boundary conditions can shift the terahertz wave spectrum according to a preset target, achieving modulation and broadening of the terahertz wave spectrum. When a single-frequency change occurs at the time boundary (i.e.,...) Figure 3 In the single-conversion frequency region of the electromagnetic field, the transmission coefficient under time refraction can be obtained from the boundary conditions of the electromagnetic field as follows: in, For frequency The corresponding transmission coefficient, For frequency The corresponding refractive index.

[0037] In this invention, the transmission coefficient corresponding to a single frequency can be calculated based on the above formula, thereby estimating the amplitude after spectral transformation.

[0038] As described above, this method estimates the amplitude after spectral transformation as a representation of the modulation broadening of the terahertz wave spectrum, and specifically includes the following steps: Determine the blue shift or red shift frequency after the frequency shift occurs; Determine the relative permittivity of the corresponding blue-shift frequency or red-shift frequency based on the blue-shift frequency or red-shift frequency. Based on the relative permittivity of the blue-shifted frequency or the relative permittivity of the red-shifted frequency, determine the real part of the refractive index of the corresponding blue-shifted frequency or the real part of the refractive index of the red-shifted frequency. Based on the real part of the refractive index at the blue-shift frequency or the real part of the refractive index at the red-shift frequency, the transmission coefficient of the terahertz wave at the blue-shift frequency or the red-shift frequency at the time boundary is determined using the above calculation formula. The amplitude of the terahertz wave after spectral modulation is determined based on the transmission coefficient at the blue-shift frequency or the red-shift frequency.

[0039] When there are multiple conversion frequency points ( Figure 3 In the multi-frequency range (e.g., the quasi-bistable structure from 0.8 to 1.1 THz), the transformation law satisfies: in, and These are the transmission coefficients at the blue-shifted frequency and the red-shifted frequency, respectively. and These are the real parts of the refractive index at the blue-shifted frequency and the real parts of the refractive index at the red-shifted frequency, respectively. and These are the relative permittivity at the blue-shift frequency and the relative permittivity at the red-shift frequency, respectively. and These are the blue shift frequency and the red shift frequency, respectively.

[0040] In this invention, the transmission coefficients corresponding to the blue-shift and red-shift frequencies can be calculated based on the above formula, thereby estimating the amplitude after spectral transformation.

[0041] As described above, this method estimates the amplitude after spectral transformation as a representation of the modulation broadening of the terahertz wave spectrum, and specifically includes the following steps: Determine the blue-shift and red-shift frequencies after the frequency shift occurs; Based on the blue-shift frequency and the red-shift frequency, determine the relative permittivity of the corresponding blue-shift frequency and the relative permittivity of the corresponding red-shift frequency, respectively; Based on the relative permittivity of the blue-shift frequency and the relative permittivity of the red-shift frequency, determine the real part of the refractive index of the corresponding blue-shift frequency and the real part of the refractive index of the corresponding red-shift frequency, respectively. Based on the relative permittivity of the blue-shift frequency, the relative permittivity of the red-shift frequency, the real part of the refractive index of the blue-shift frequency, and the real part of the refractive index of the red-shift frequency, determine the transmission coefficient of the terahertz wave at the blue-shift frequency and the red-shift frequency at the time boundary. The amplitude of the terahertz wave after spectral modulation is determined based on the transmission coefficients at the blue-shift and red-shift frequencies.

[0042] See Figure 4 The experimentally measured spectral changes caused by frequency shifts at the transient plasma time boundary are presented. In the figure, the horizontal axis represents the corresponding frequency point, and the vertical axis represents the relative change in amplitude (ΔA / A). Black represents the effect of time boundary modulation, and gray represents the resonant absorption effect of the spatial boundary. As shown in the figure, the time boundary, represented by the black lines, achieves an increase in the amplitude of both the low-frequency and high-frequency terahertz waves, which is consistent with… Figure 3 The results of shifting the mid-frequency range to both low and high frequencies are consistent, demonstrating the frequency shifting properties and spectral broadening effect under the time boundary characteristics. In contrast, the gray line in the figure shows the interaction between the plasma and the terahertz wave after plasma generation, where the plasma acts as a spatial boundary. It can be observed that only broadband absorption leads to amplitude suppression across the entire spectrum. The figure clearly illustrates the frequency changes caused by the time boundary effect and the resulting amplitude changes in the terahertz wave, demonstrating how frequency shifting and spectral broadening of the terahertz wave spectrum are achieved through frequency conversion.

[0043] Further methods described above primarily explain the processing steps for obtaining femtosecond lasers and terahertz waves, specifically including: An initial femtosecond laser beam is acquired and split into two beams; one beam serves as the femtosecond laser beam, while the other beam passes through a first zinc telluride crystal to generate terahertz waves. In other words, in this invention, terahertz waves are generated by converting the femtosecond laser beam, while the other femtosecond laser beam is used to ionize air to obtain plasma.

[0044] In a further step of the above method, the initial femtosecond laser is split into a third beam for electro-optic sampling and detection of the terahertz wave waveform; the spectrally modulated terahertz wave is combined with the third beam, reflected by an off-axis parabolic mirror, and collinearly injected into a second zinc telluride crystal for electro-optic sampling and measurement; then, a quarter-glass slide and a Wollaston prism are used for beam splitting, and a balanced detector detects and outputs the additional ellipsometric signal introduced into the zinc telluride crystal by the terahertz wave.

[0045] The terahertz wave spectrum control device based on plasma transient time boundary provided by the present invention will be described below. The terahertz wave spectrum control device based on plasma transient time boundary described below can be referred to in correspondence with the terahertz wave spectrum control method based on plasma transient time boundary described above.

[0046] Figure 5 A schematic diagram of a terahertz wave spectrum manipulation device based on plasma transient time boundary provided by the present invention is shown. See also: Figure 5 The device includes a light generating unit and a light propagation unit, wherein: The light generation unit is used to obtain femtosecond lasers and terahertz waves; The optical propagation unit is used to combine the femtosecond laser and the terahertz wave and introduce them into the terahertz wave transmission space so that when the femtosecond laser and the terahertz wave pass through the first position point synchronously, the terahertz wave with spectrum modulation is obtained. The first position point is located in the terahertz wave transmission space. At the first position point, when the femtosecond laser ionizes the gas to obtain plasma, a time boundary is formed caused by the transient refractive index change of the medium. Then, when the terahertz wave passes through the time boundary, the frequency shift occurs.

[0047] In a further embodiment of the above-described apparatus, the light propagation unit comprises indium tin oxide (ITO) glass and a first off-axis parabolic mirror, wherein: Indium tin oxide (ITO) glass is used to combine femtosecond lasers and terahertz waves. The first off-axis parabolic mirror is used to converge the combined femtosecond laser and terahertz wave to a first position point within the terahertz wave transmission space.

[0048] In a further embodiment of the above-described device, the light-generating unit includes a femtosecond laser, a first zinc telluride crystal, and a mirror, wherein: A femtosecond laser is used to generate an initial femtosecond laser and split the initial femtosecond laser into two beams, one of which is used as the femtosecond laser. The first zinc telluride crystal is used to generate terahertz waves after penetrating another beam of light. A reflector is used to propagate terahertz waves onto indium tin oxide (ITO) glass for beam combining with a femtosecond laser.

[0049] In a further embodiment of the aforementioned device, the device also includes a light detection unit, which comprises a second off-axis parabolic mirror, a second zinc telluride crystal, a quarter-glass slide, a Wollaston prism, and a balanced detector, specifically used for: The spectrally modulated terahertz wave is combined with the third beam split from the initial femtosecond laser. After being reflected by an off-axis parabolic mirror, it is collinearly injected into a second zinc telluride crystal for electro-optic sampling measurement. Then, a quarter-glass slide and a Wollaston prism are used for beam splitting. The additional ellipsometric signal introduced into the zinc telluride crystal by the terahertz wave is detected and output by a balanced detector.

[0050] In a further embodiment of the aforementioned apparatus, the photodetector unit also includes a silicon wafer and a third off-axis parabolic mirror, specifically used for: The regulated terahertz wave is transmitted through the silicon wafer, and then the third off-axis parabolic mirror combines the terahertz wave with the third beam.

[0051] Since the apparatus of this embodiment is based on the same principle as the method of the above embodiment, more detailed explanations will not be repeated here.

[0052] The terahertz wave spectrum modulation device based on plasma transient time boundary provided by this invention combines a femtosecond laser and a terahertz wave into the terahertz wave transmission space. When the femtosecond laser and the terahertz wave synchronously pass through a position point in the terahertz wave transmission space, the plasma generated by the ionization of gas by the femtosecond laser forms a time boundary caused by a transient change in the refractive index of the medium. This causes the terahertz wave to shift its frequency when passing through the time boundary, thereby achieving the modulation effect of the required terahertz wave frequency based on the change in the real part of the refractive index caused by the transient plasma generation.

[0053] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0054] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for terahertz wave spectrum manipulation based on plasma transient time boundary, characterized in that, include: Obtain femtosecond laser and terahertz wave, and combine the femtosecond laser and the terahertz wave into the terahertz wave transmission space; When the femtosecond laser and the terahertz wave pass through the first position point synchronously, a spectrally modulated terahertz wave is obtained. The first position point is located within the terahertz wave transmission space. At the first position point, when the femtosecond laser ionizes the gas to obtain plasma, a time boundary is formed due to the transient refractive index change of the medium. Then, when the terahertz wave passes through the time boundary, a frequency shift occurs.

2. The terahertz wave spectrum manipulation method based on plasma transient time boundary according to claim 1, characterized in that, The method further includes: Determine the blue-shift and red-shift frequencies after the frequency shift occurs; Based on the blue shift frequency and the red shift frequency, determine the relative permittivity of the corresponding blue shift frequency and the relative permittivity of the corresponding red shift frequency, respectively. Based on the relative permittivity of the blue-shift frequency and the relative permittivity of the red-shift frequency, the real part of the refractive index of the corresponding blue-shift frequency and the real part of the refractive index of the red-shift frequency are determined respectively. Based on the relative permittivity of the blue-shift frequency, the relative permittivity of the red-shift frequency, the real part of the refractive index of the blue-shift frequency, and the real part of the refractive index of the red-shift frequency, the transmission coefficient of the terahertz wave at the transient time boundary of the medium is determined. The amplitude of the terahertz wave after spectral modulation is determined based on the transmission coefficients of the blue-shifted frequency and the red-shifted frequency.

3. The terahertz wave spectrum manipulation method based on plasma transient time boundary according to claim 2, characterized in that, The step of determining the transmission coefficients of the terahertz wave at the transient time boundary of the medium at the blue-shift frequency and the red-shift frequency, based on the relative dielectric constant of the blue-shift frequency, the relative dielectric constant of the red-shift frequency, the real part of the refractive index of the blue-shift frequency, and the real part of the refractive index of the red-shift frequency, includes: Based on the relative permittivity of the blue-shifted frequency, the relative permittivity of the red-shifted frequency, the real part of the refractive index of the blue-shifted frequency, and the real part of the refractive index of the red-shifted frequency, the transmission coefficients of the terahertz wave at the time boundary are determined using the following calculation method. in, and These are the transmission coefficients at the blue-shifted frequency and the red-shifted frequency, respectively. and These are the real parts of the refractive index at the blue-shifted frequency and the real parts of the refractive index at the red-shifted frequency, respectively. and These are the relative permittivity at the blue-shift frequency and the relative permittivity at the red-shift frequency, respectively. and These are the blue shift frequency and the red shift frequency, respectively.

4. The terahertz wave spectrum manipulation method based on plasma transient time boundary according to claim 1, characterized in that, The method further includes: Determine the blue shift or red shift frequency after the frequency shift occurs; Based on the blue shift frequency and the red shift frequency, determine the relative permittivity of the corresponding blue shift frequency or the relative permittivity of the red shift frequency; Based on the relative permittivity of the blue-shifted frequency or the relative permittivity of the red-shifted frequency, determine the real part of the refractive index of the corresponding blue-shifted frequency or the real part of the refractive index of the red-shifted frequency. Based on the real part of the refractive index of the blue-shifted frequency or the real part of the refractive index of the red-shifted frequency, the transmission coefficient of the terahertz wave at the time boundary is determined using the following calculation formula. in, For frequency The corresponding transmission coefficient, For frequency The corresponding real part of the refractive index; The amplitude of the terahertz wave after spectral modulation is determined based on the transmission coefficient of the blue-shifted frequency or the transmission coefficient of the red-shifted frequency.

5. The terahertz wave spectrum manipulation method based on plasma transient time boundary according to claim 1, 3, or 4, characterized in that, The acquisition of femtosecond lasers and terahertz waves includes: Acquire an initial femtosecond laser beam and split the initial femtosecond laser beam into two beams; one of these beams is used as the femtosecond laser beam. The terahertz wave is generated by passing another beam of light through the first zinc telluride crystal.

6. The terahertz wave spectrum manipulation method based on plasma transient time boundary according to claim 5, characterized in that, The method further includes: The initial femtosecond laser is further split into a third beam for electro-optic sampling and detection of terahertz wave waveform; The spectrally modulated terahertz wave is combined with the third beam, reflected by an off-axis parabolic mirror, and then collinearly injected into a second zinc telluride crystal for electro-optic sampling measurement. The beam is then split using a quarter-glass slide and a Wollaston prism, and the additional ellipsometric signal introduced into the zinc telluride crystal by the terahertz wave is detected and output by a balanced detector.

7. A terahertz wave spectrum manipulation device based on plasma transient time boundary, characterized in that, It includes a light-generating unit and a light-propagating unit, wherein: The light generation unit is used to obtain femtosecond lasers and terahertz waves; An optical propagation unit is used to combine the femtosecond laser and the terahertz wave and introduce them into the terahertz wave transmission space, so that when the femtosecond laser and the terahertz wave synchronously pass through the first position point, a spectrally modulated terahertz wave is obtained; the first position point is located in the terahertz wave transmission space, and at the first position point, when the femtosecond laser ionizes the gas to obtain plasma, a time boundary is formed caused by the transient refractive index change of the medium, and the frequency shift occurs when the terahertz wave passes through the time boundary.

8. The terahertz wave spectrum control device based on plasma transient time boundary according to claim 7, characterized in that, The light propagation unit includes indium tin oxide (ITO) glass and a first off-axis parabolic mirror, wherein: The indium tin oxide (ITO) glass is used to combine the femtosecond laser and the terahertz wave. The first off-axis parabolic mirror is used to converge the combined femtosecond laser and the terahertz wave to a first position point within the terahertz wave transmission space.

9. The terahertz wave spectrum control device based on plasma transient time boundary according to claim 8, characterized in that, The light-generating unit includes a femtosecond laser, a first zinc telluride crystal, and a mirror, wherein: The femtosecond laser is used to generate an initial femtosecond laser and split the initial femtosecond laser into two beams, one of which is used as the femtosecond laser. The first zinc telluride crystal is used to generate the terahertz wave after penetrating another beam of light; The reflector is used to propagate the terahertz wave to the indium tin oxide (ITO) glass and combine it with the femtosecond laser beam.

10. The terahertz wave spectrum control device based on plasma transient time boundary according to claim 9, characterized in that, The device further includes a light detection unit, which comprises a second off-axis parabolic mirror, a second zinc telluride crystal, a quarter-glass slide, a Wollaston prism, and a balanced detector, specifically used for: The spectrally modulated terahertz wave is combined with the third beam split from the initial femtosecond laser. After being reflected by an off-axis parabolic mirror, it is collinearly injected into the second zinc telluride crystal for electro-optic sampling measurement. Then, a quarter glass slide and a Wollaston prism are used for beam splitting. The additional ellipsoid signal introduced into the zinc telluride crystal by the terahertz wave is detected and output by a balanced detector. The optical detection unit also includes a silicon wafer and a third off-axis parabolic mirror, specifically used for: The regulated terahertz wave is transmitted through the silicon wafer, and then the third off-axis parabolic mirror combines the terahertz wave with the third beam.

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