CN112510352A - Terahertz wave radiation method and system of microstructure photoconductive antenna - Google Patents

Terahertz wave radiation method and system of microstructure photoconductive antenna Download PDF

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CN112510352A
CN112510352A CN202011214941.7A CN202011214941A CN112510352A CN 112510352 A CN112510352 A CN 112510352A CN 202011214941 A CN202011214941 A CN 202011214941A CN 112510352 A CN112510352 A CN 112510352A
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terahertz
electric field
time
radiation
field
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邓琥
尚丽平
苗建波
熊中刚
杨洁萍
武志翔
熊亮
屈薇薇
李占锋
何俊
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Inner Mongolia Synthetic Chemical Research Institute
Southwest University of Science and Technology
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Inner Mongolia Synthetic Chemical Research Institute
Southwest University of Science and Technology
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/36—Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith
    • H01Q1/364—Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith using a particular conducting material, e.g. superconductor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q23/00—Antennas with active circuits or circuit elements integrated within them or attached to them

Abstract

The invention discloses a terahertz wave radiation method and system of a microstructure photoconductive antenna. The method uses ultrashort laser pulse photons to irradiate the surface of a photoconductive antenna, and when the energy of the ultrashort laser pulse photons is larger than the energy gap width of a photoconductive material, electron-hole pairs are generated in the photoconductive material; applying external bias voltage to make the electron-hole pairs move along two ends of the electrode to form a transient electric field; and adjusting the conversion from the near field to the remote terahertz radiation in the transient electric field through a Green function to realize the far field radiation of the terahertz pulse signal. The invention makes the calculation process more perfect and the calculation result more accurate.

Description

Terahertz wave radiation method and system of microstructure photoconductive antenna
Technical Field
The invention relates to the technical field of terahertz, in particular to a terahertz wave radiation method and system of a microstructure photoconductive antenna.
Background
Terahertz waves are electromagnetic waves with a frequency between 0.1THz and 10THz, and the corresponding wavelength is 3 μm to 30 μm. The band is just between microwave and infrared optics with relatively mature scientific and technical development, is not completely suitable for an analysis method of an electromagnetic field microwave correlation theory based on electronics, is not completely suitable for a correlation theory analysis method based on photonics, and has no feasible terahertz wave generation method and detection means, so that the development of terahertz science and technology is greatly limited, and terahertz gaps exist.
The existing method has the following defects: the research of the simulation method of the photoconductive antenna is mainly theoretical calculation, the radiation characteristic simulation of the photoconductive antenna based on commercial software and the radiation characteristic simulation of the photoconductive antenna by self programming, and the method for theoretically simulating the radiation characteristic of the photoconductive antenna has the advantages that the influence of main parameters of photoconductive materials, laser pulse parameters, bias voltage and the like on the radiation characteristic of THz waves can be qualitatively simulated, but the defects are obvious, namely, the related simulation problem directly corresponding to the photoconductive antenna structure cannot be solved. The existing microwave electromagnetic simulation software, such as HFSS, CST, etc., can solve the problem of simulation of radiation characteristics directly corresponding to photoconductive antenna structures, but cannot simulate carrier transport of semiconductor devices in THz band, and the remote radiation characteristics and accuracy of the antenna are yet to be further confirmed. Semiconductor numerical simulation software, such as medical and cmos software, can effectively simulate the static field distribution of the photoconductive antenna, but cannot solve the simulation problem of the radiation characteristic directly corresponding to the photoconductive antenna structure.
Disclosure of Invention
The invention aims to provide a terahertz wave radiation method and a terahertz wave radiation system for a microstructure photoconductive antenna, which aim to solve the simulation effect directly corresponding to a photoconductive antenna structure, simultaneously adopt Maxwell equation to solve, simulate the carrier transport of a semiconductor device in THz wave band, improve the accuracy of the result, divide an electric field into an electrostatic field component and a time-varying electric field component by utilizing linear superposition theorem, and simultaneously give consideration to electromagnetic simulation and semiconductor numerical simulation for structural calculation of the photoconductive antenna, so that the calculation process is more perfect, and the calculation result is more accurate.
In order to achieve the purpose, the invention provides the following scheme:
a terahertz wave radiation method of a microstructure photoconductive antenna comprises the following steps:
irradiating the surface of the photoconductive antenna with ultrashort laser pulse photons, and generating electron-hole pairs inside the photoconductive material when the energy of the ultrashort laser pulse photons is larger than the energy gap width of the photoconductive material;
applying external bias voltage to make the electron-hole pairs move along two ends of the electrode to form a transient electric field;
and adjusting the conversion from the near field to the remote terahertz radiation in the transient electric field through a Green function to realize the far field radiation of the terahertz pulse signal.
Optionally, the electron-hole uses linear superposition theorem to divide the electric field into an electrostatic field component and a time-varying electric field component.
Optionally, solving for the electrostatic field component comprises:
solving the initial potential in the photoconductive material by using a semiconductor Poisson equation to obtain a semiconductor electrostatic field component;
and dispersing by adopting a central difference method and solving the electrostatic field of the 3D nonlinear Poisson equation by a Newton iteration method.
Optionally, solving for the time-varying electric field component comprises:
and solving a diffusion-drift equation and a continuity equation of the carrier by adopting a Maxwell equation.
Optionally, the adjusting, by the green function, the conversion of the terahertz radiation from the near field to the remote in the transient electric field specifically includes:
and performing near-far field transformation on the near-field terahertz time-domain data by using a time-domain finite difference method to obtain a far-field terahertz time-domain waveform.
The invention also provides a terahertz wave radiation system of the microstructure photoconductive antenna, which comprises:
the electronic hole pair generating module is used for irradiating ultrashort laser pulse photons to the surface of the photoconductive antenna, and when the energy of the ultrashort laser pulse photons is larger than the energy gap width of the photoconductive material, electronic hole pairs are generated inside the photoconductive material;
the electron hole pair forming module is used for applying bias voltage externally so that the electron hole pair moves along two ends of the electrode to form a transient electric field;
and the adjusting module is used for adjusting the conversion from the near field to the remote terahertz radiation in the transient electric field through the Green function so as to realize the far field radiation of the terahertz pulse signal.
Optionally, the electron-hole uses linear superposition theorem to divide the electric field into an electrostatic field component and a time-varying electric field component.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the method uses ultrashort laser pulse photons to irradiate the surface of a photoconductive antenna, and when the energy of the ultrashort laser pulse photons is larger than the energy gap width of a photoconductive material, electron-hole pairs are generated in the photoconductive material; applying external bias voltage to make the electron-hole pairs move along two ends of the electrode to form a transient electric field; and adjusting the conversion from the near field to the remote terahertz radiation in the transient electric field through a Green function to realize the far field radiation of the terahertz pulse signal. The invention makes the calculation process more perfect and the calculation result more accurate.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a flow chart of a terahertz wave radiation method of a microstructure photoconductive antenna according to an embodiment of the present invention;
FIG. 2 is a block diagram of a design of a terahertz wave radiation method of a microstructure photoconductive antenna according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a structural XY plane and an XZ plane of a terahertz wave radiation method of a microstructure photoconductive antenna according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of potential distribution of a structural XY plane and an XZ plane of a terahertz wave radiation method of a microstructure photoconductive antenna according to an embodiment of the present invention;
FIG. 5 is a schematic diagram showing the relationship between the change of current density vector with time in the microstructure photoconductive antenna according to the terahertz wave radiation method of the microstructure photoconductive antenna of the embodiment of the present invention;
fig. 6 is a schematic diagram of a terahertz wave far-field radiation waveform of a microstructure photoconductive antenna according to a terahertz wave radiation method of the microstructure photoconductive antenna according to the embodiment of the present invention;
fig. 7 is a far field radiation pattern of the microstructure photoconductive antenna according to the terahertz wave radiation method of the microstructure photoconductive antenna of the embodiment of the present invention;
fig. 8 is a structural block diagram of a terahertz wave radiation system of a microstructure photoconductive antenna according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
As shown in fig. 1, a terahertz wave radiation method of a microstructure photoconductive antenna includes:
step 101: and irradiating the surface of the photoconductive antenna by using ultrashort laser pulse photons, wherein when the energy of the ultrashort laser pulse photons is larger than the energy gap width of the photoconductive material, electron-hole pairs are generated in the photoconductive material.
Step 102: and applying external bias voltage to enable the electron-hole pairs to move along two ends of the electrode to form a transient electric field.
Step 103: and adjusting the conversion from the near field to the remote terahertz radiation in the transient electric field through a Green function to realize the far field radiation of the terahertz pulse signal. Specifically, a time domain finite difference method is applied to perform near-far field transformation on near-field terahertz time-domain data to obtain a far-field terahertz time-domain waveform.
Wherein the electron holes divide the electric field into an electrostatic field component and a time-varying electric field component using linear superposition theorem. Solving for the electrostatic field component includes: solving the initial potential in the photoconductive material by using a semiconductor Poisson equation to obtain a semiconductor electrostatic field component; and dispersing by adopting a central difference method and solving the electrostatic field of the 3D nonlinear Poisson equation by a Newton iteration method.
Solving for the time-varying electric field component includes: and solving a diffusion-drift equation and a continuity equation of the carrier by adopting a Maxwell equation.
The present invention is described in detail below:
free carriers (electron hole pairs) in the photoconductive material are separated into electrostatic field components and time-varying electric field components by using a linear superposition theorem because the bias voltage always exists in the radiation process of the photoconductive antenna, and after an initial potential in a semiconductor is solved by using a semiconductor Poisson equation, the potential is subjected to gradient calculation to obtain the electrostatic field components of the semiconductor; and performing dispersion by adopting a central difference method and performing electrostatic field solution on the 3D nonlinear Poisson equation by a Newton iteration method. The semiconductor electrostatic field component:
Figure BDA0002760052100000051
wherein n isD，nAFor normalized concentration of donor and acceptor ions relative to the intrinsic carrier, the electrostatic potential
Figure BDA0002760052100000052
k is the Boltzmann constant, q is the electron electric quantity, T is the absolute temperature, ε is the semiconductor dielectric constant, niIs the concentration of the intrinsic carrier(s),
Figure BDA0002760052100000053
the electrostatic potential is graded.
In a rectangular coordinate system, the partial differential form of the laplacian operator can be expressed as:
Figure BDA0002760052100000054
wherein the content of the first and second substances,
Figure BDA0002760052100000055
the partial derivatives of the electrostatic potential are solved in the directions of three-dimensional coordinates x, y and z respectively.
Consider a central difference approximation of a first order partial differential function:
Figure BDA0002760052100000056
the second order difference approximation of the potential function to x can be expressed as
Figure BDA0002760052100000057
Figure BDA0002760052100000058
Similarly, a second order central difference approximation of the potential pair y, z can be obtained, and the central difference approximation of the laplacian operation can be expressed as:
Figure BDA0002760052100000061
a solution to the electrostatic potential in the semiconductor can be obtained.
Figure BDA0002760052100000062
After the electrostatic potential of the semiconductor is obtained, the electrostatic field inside the semiconductor can be calculated by using the correlation between the electrostatic potential and the electrostatic field:
Figure BDA0002760052100000063
the difference form is:
Figure BDA0002760052100000064
wherein the above formula represents the relationship between the defined formula and the electric field when the electric potential changes in the x, y and z directions,
Figure BDA0002760052100000065
representing discrete expressions of electrostatic fields in the x, y, z directions, respectively, with discrete steps 1/2.
And aiming at the time-varying electric field solving part, solving a diffusion-drift equation and a continuity equation of the carrier by adopting a Maxwell equation. The maxwell equations are as follows: in a rectangular coordinate system, maxwell's equations can be written in the form of coupled components.
Figure BDA0002760052100000071
Figure BDA0002760052100000072
Where ε is the dielectric constant, μ is the magnetic dielectric constant, JnxAnd JpxPhotocurrent of electrons and holes, respectively, in the x-direction, JnyAnd JpyPhotocurrent of electrons and holes, respectively, in the y-direction, JnzAnd JpzRespectively the photocurrent of the electrons and holes in the y-direction,
Figure BDA0002760052100000073
is the partial derivative of the z-axis magnetic field strength component with respect to x,
Figure BDA0002760052100000074
is the partial derivative of the Z-axis magnetic field strength component with respect to y,
Figure BDA0002760052100000075
is the partial derivative of the z-axis direction electric field strength with respect to time t,
Figure BDA0002760052100000076
the partial derivative of the y-axis magnetic field strength with respect to x,
Figure BDA0002760052100000077
is the partial derivative of the y-axis magnetic field strength component with respect to z,
Figure BDA0002760052100000078
is the partial derivative of the y-axis magnetic field strength with respect to time t,
Figure BDA0002760052100000079
the partial derivative of the x-axis magnetic field strength with respect to y,
Figure BDA00027600521000000710
is the partial derivative of the magnetic field strength in the x-axis direction with respect to time t,
Figure BDA00027600521000000711
is the partial derivative of the electric field strength in the x-axis direction with respect to y,
Figure BDA00027600521000000712
is the partial derivative of the electric field strength in the x-axis direction with respect to z,
Figure BDA00027600521000000713
is the partial derivative of the electric field strength in the x-axis direction with respect to time t,
Figure BDA00027600521000000714
is the partial derivative of the electric field strength in the y-axis direction with respect to x,
Figure BDA0002760052100000081
is the partial derivative of the electric field strength in the y-axis direction with respect to time z,
Figure BDA0002760052100000082
is the partial derivative of the electric field strength in the x-axis direction with respect to time t,
Figure BDA0002760052100000083
is the partial derivative of the electric field strength in the x-axis direction with respect to time t.
The semiconductor continuity equation current expression can be transformed into:
Figure BDA0002760052100000084
Figure BDA0002760052100000085
wherein, JnIs the total current density including electron drift current and diffusion current, JpIs a current including a hole drift current and a diffusion current, munElectron mobility, μpIs hole mobility, E is the time varying electric field, EdcElectrostatic field, DnAnd DpEinstein diffusion coefficients for electrons and holes respectively,
Figure BDA0002760052100000086
and
Figure BDA0002760052100000087
are the gradient solutions for electrons and holes, respectively.
Therefore, four independent currents are generated in the semiconductor, namely electron drift current and diffusion current, hole drift current and diffusion current, and the total current density is the sum of the four currents.
Figure BDA0002760052100000088
Figure BDA0002760052100000089
The total current density equation is:
the time domain transmission Green function carries out terahertz radiation conversion from a near field to a remote place in a multilayer medium on near field data, a Yee grid is adopted for dispersion by applying a time domain finite difference method, electromagnetic field radiation is approximately calculated by applying first-order partial derivative central difference of time and space, and the conversion from the near field terahertz time domain data to a far field is realized to obtain a far field terahertz time domain waveform. The calculation equations for the electric and magnetic fields in the x-axis direction are as follows, and the y-axis and the z-axis can be obtained according to similar principles.
Figure BDA0002760052100000091
Figure BDA0002760052100000092
Wherein the content of the first and second substances,
Figure BDA0002760052100000093
where n +1 and (n +1/2) represent space steps, i +1/2, j +1/2, and k +1/2 represent time steps in the x, y, and z directions, respectively;
Figure BDA0002760052100000094
representing discrete sampling values of the electric field component along the x-axis direction according to a time step i +1/2 of a space step n + 1;
Figure BDA0002760052100000095
representing discrete sample values of a time step i +1/2 for the time of an electric field component space step n in the x-axis direction;
Figure BDA0002760052100000096
representing the time of a magnetic field component space step n +1/2 in the z-axis direction, and discretely sampling values in the x-axis direction and the y-axis direction according to a time step i + 1/2;
Figure BDA0002760052100000097
representing the time of a magnetic field component space step n +1/2 in the z-axis direction, and discretely sampling values at a time step i +1/2 after the point i in the x-axis direction and discretely sampling values at a time step j-1/2 before the point j in the y-axis direction;
Figure BDA0002760052100000098
representing discrete sampling values at the time of a magnetic field component in the z-axis direction according to a space step n +1/2, i point in the x-axis direction is followed by a time step i +1/2, and k point in the z-axis direction is followed by a time step k + 1/2;
Figure BDA0002760052100000101
representing the time of a magnetic field component space step n +1/2 in the z-axis direction, and discretely sampling values at a time step i +1/2 after the point i in the x-axis direction, and discretely sampling values at a time step k-1/2 before the point k in the z-axis direction;
Figure BDA0002760052100000102
represents the space step size n +1 of the electron density component in the x-axis directionTime/2, and discrete sampling value at time step i +1/2 after the point i in the x-axis direction;
Figure BDA0002760052100000103
representing discrete sampled values of the z-axis hole density component at a spatial step n +1/2 and at a time step i +1/2 after the x-axis i;
Figure BDA0002760052100000104
represents discrete sampling values of the dielectric constant at a time step i +1/2 after the point i in the x-axis direction; Δ t represents a time step; Δ x, Δ y, Δ z represent discrete steps in the x, y, z directions, respectively.
Figure BDA0002760052100000105
Representing the time of a magnetic field component space step n +1/2 in the x-axis direction, and discretely sampling values in the y-axis and z-axis directions according to time steps j +1/2 and k +1/2 respectively;
Figure BDA0002760052100000106
representing the time of a magnetic field component space step n-1/2 in the x-axis direction, and discretely sampling values in the y-axis and z-axis directions according to time steps j +1/2 and k +1/2 respectively;
Figure BDA0002760052100000107
representing the time of an electric field component space step n in the y-axis direction, and discretely sampling values according to time steps j +1/2 and k +1 in the y-axis direction and the z-axis direction respectively;
Figure BDA0002760052100000108
representing the time of an electric field component space step n in the y-axis direction, and discretely sampling values according to time steps j +1/2 and k +1 in the y-axis direction and the z-axis direction respectively;
Figure BDA0002760052100000109
representing the moment of an electric field component space step n in the z-axis direction, and discretely sampling values according to time steps j +1 and k +1/2 in the y-axis direction and the z-axis direction respectively;
Figure BDA00027600521000001010
representing the moment of an electric field component space step n in the z-axis direction, and discretely sampling values according to a time step k +1/2 in the z-axis direction;
Figure BDA00027600521000001011
indicating that the magnetic medium constant is respectively discretely sampled at a time step j +1/2 after the j point in the y-axis direction and at a time step k +1/2 after the k point in the z-axis direction.
In order to obtain a far-field terahertz time-domain waveform, near-field and far-field transformation must be carried out on near-field terahertz time-domain data, the microstructure light guide antenna is a multilayer dielectric structure, and the near-field and far-field transformation principle and method are as follows:
radiation electric field E in the air in the time domainr(r, t) can be expressed as a time domain surface current JtAnd MtThe integrals of (1) are superimposed.
Figure BDA0002760052100000111
Where c is the speed of light in vacuum, r is the observation distance to the radiation source, t is time, Fθ(theta, phi, t-r/c) and Fφ(theta, phi, t-r/c) represents the electric field force in the theta and phi angle plane directions at the time of t-r/c, respectively.
Figure BDA0002760052100000112
Wherein, the symbol
Figure BDA0002760052100000113
Representing the time convolution, trT + (x 'sin θ cos φ + y' sin θ sin φ)/c is the lateral delay time, vector
Figure BDA0002760052100000114
Expressed as:
Figure BDA0002760052100000115
Figure BDA0002760052100000116
Figure BDA0002760052100000117
Figure BDA0002760052100000118
wherein the content of the first and second substances,
Figure BDA0002760052100000119
is the impedance of the vacuum wave and is,
Figure BDA00027600521000001110
Vi p(t | z') is determined by the transmission line Green function in the time domain, and the superscript p represents e (TE polarization) or h (TM polarization), and the following represents the corresponding sub-expressions of the far-field transformed data storage array.
Figure BDA00027600521000001111
Figure BDA00027600521000001112
Figure BDA00027600521000001113
Figure BDA00027600521000001114
Wherein, alpha represents x or y, and p represents e or h. J. the design is a squarex,y,zAnd Mx,y,zRepresents the surface current JtAnd MtX, y and z components of (1), JαRepresents the surface current JtComponents in the x and y directions, JzDenotes JtComponent in the z direction.
Figure BDA0002760052100000121
And Vi p(t | z') is represented as z.
Figure BDA0002760052100000122
Figure BDA0002760052100000123
Wherein p represents e (TE polarization) or h (TM polarization),
Figure BDA0002760052100000124
representing an up-going wave travel time step function in medium 0,
Figure BDA0002760052100000125
represents a step function, V, of the transmission time of the downlink wave in the medium 0pExcitation voltage, v, representing the TE polarization mode0、v1And v2Respectively representing propagation velocities in different media, Γ01Denotes the reflection coefficient, Γ, of the media 0 to 112Denotes the reflection coefficient, γ, of the media 1 to 201Denotes the transmission coefficient, γ, of the medium 0 to 121Representing the transmission coefficient of medium 2 to medium 1,
Figure BDA0002760052100000126
representing the characteristic impedance in medium 0 in the TE polarization mode,
Figure BDA0002760052100000127
representing the characteristic impedance in the medium 1 in the TE polarization mode,
Figure BDA0002760052100000128
when indicating the TE polarization modeThe characteristic impedance in the medium 2 is,
Figure BDA0002760052100000129
and Vi p(t | z ') denotes the excitation voltage or current at the source point z', t ═ 0, respectively, at the observation point z0The voltage response generated at time t,
Figure BDA00027600521000001210
representing the propagating wave traveling upward to the observation point z ═ z0The direct contribution of the (c) to the (c),
Figure BDA00027600521000001211
representing the direct contribution of the upgoing wave, the remaining similar expressions have similar meanings, h representing the propagation depth from the source point z ', and z' representing the transport distance variable along the z-axis.
The invention adopts a transmission line Green function and time domain finite difference combined interpolation method, adopts a central difference format for dispersion, then adopts a Newton iteration method to carry out 3D nonlinear Poisson equation, solves the simulation effect directly corresponding to the photoconductive antenna structure, simultaneously adopts Maxwell equation for solution, simulates the carrier transport of a semiconductor device in THz wave band, improves the accuracy of the result, utilizes linear superposition theorem to divide an electric field into an electrostatic field component and a time-varying electric field component, and simultaneously considers the electromagnetic simulation and the semiconductor numerical simulation to carry out structural calculation on the photoconductive antenna, thereby leading the calculation process to be more perfect and leading the calculation result to be more accurate.
As shown in fig. 2, a block diagram of a design of a terahertz wave radiation method of a microstructure photoconductive antenna according to an embodiment of the present invention is shown. The generation of THz waves by a photoconductive antenna is a relatively complex process, and the whole process involves four main equations: nonlinear poisson's equation, carrier's diffusion drift equation, continuity equation, and maxwell's equation. Firstly, considering the influence of bias voltage on carrier current, because the bias voltage exists in the radiation process of the photoconductive antenna all the time, the bias voltage is simply not suitable as the initial value of a time-varying electric field, the field value of the electric field is divided into an electrostatic field component and a time-varying electric field component, the electrostatic field component does not change along with time, so the bias voltage is used as a constant to act on a semiconductor after the static electric field value is solved by a 3D nonlinear Poisson equation in initialization, when the photon energy of an incident ultrashort laser pulse is larger than the energy gap width of the photoconductive material, electron-hole pairs can be generated in the material, the electron-hole pairs are solved by a 3D diffusion drift equation, the time-varying electromagnetic field is further solved by a Maxwell equation, the time-varying electric field changes along with the change of the carrier current, and the 3D continuity equation is combined under the action of external bias voltage, the photon-generated carriers move along the direction of the electric field to form transient current, so that THz pulse is radiated outwards, an error threshold value is set, iterative calculation is carried out through FDTD time, the calculation is finished, and the operation is quitted, otherwise, the range is continuously executed.
As shown in fig. 3, schematic diagrams of the XOY plane and XOZ plane of the structure of the terahertz wave radiation method of the microstructure photoconductive antenna according to the embodiment of the present invention.
The photoconductive antenna structure is characterized in that the 2 pairs of micron-sized resonant ring microstructure photoconductive antenna structures are obtained through FDTD iterative simulation calculation by applying the previous algorithm and system design, the diagrams (a) and (b) respectively represent the top view full structure of an XOY plane and the left view structural diagram of an XOZ plane, the structure in the diagrams is formed by combining and designing a dipole and an open resonant ring, the width of a single-side structure is 80 mu m, the length of the single-side structure is 220 mu m, and the structure has the main advantage of being capable of generating high-power terahertz radiation.
As shown in fig. 4, a schematic diagram of potential distribution of a structure XY plane and an XZ plane of the terahertz wave radiation method of the microstructure photoconductive antenna according to the embodiment of the present invention.
The potential distribution diagram of the photoconductive antenna structure of the 2-pair micron-sized resonant ring microstructure obtained through simulation respectively represents XY section potential distribution and XZ section potential distribution, and the result shows that energy can be localized in the resonant ring, and college transient photocurrent is generated through resonance action, so that whether calculation iteration is complete or not can be known, and whether the calculation result accurately provides reference or not can be known.
As shown in fig. 5, a schematic diagram of a time-dependent change relationship of a current density vector in a microstructure photoconductive antenna according to the terahertz wave radiation method of the microstructure photoconductive antenna of the embodiment of the present invention is shown.
The graphs (a), (b) and (c) respectively show the current density along the x-axis, the y-axis and the z-axis which are generated transiently under the action of a strong electric field and change along the time, and the comparison shows that the current density along the x-axis of the graph (a) is the strongest, and the strongest current density reaches 0.35A/mum2And the carrier rise-to-fall duration is 1.5ps to 3.0 ps; the current density in the y-axis direction of graph (b) is up to 16 x 10 at the maximum-5A/μm2And the carrier rising-to-falling duration is substantially maintained at 1.5ps to 3.0ps, but the carrier density intensity is weak; the current density in the z-axis direction of graph (c) was the strongest, reaching-7.0 x 10-3A/μm2And the carrier rise-to-fall duration is substantially maintained at 1.5ps to 3.0ps, but the carrier density intensity is weaker; from this comparison, the duration of time during which the current density in the x-axis direction in graph (a) rises to fall and the maximum value of the rise determine the duration of time and the intensity of the generated photocurrent, respectively.
As shown in fig. 6, a schematic diagram of a terahertz wave far-field radiation waveform of a microstructure photoconductive antenna according to the terahertz wave radiation method of the microstructure photoconductive antenna provided by the embodiment of the present invention.
In the graph, (a) represents a terahertz time-domain signal of a far-field observation point in an angle theta direction in a spherical coordinate system, the duration of a main time-domain signal is 35.8-37ps, the strongest signal in the time domain is 0.6a.u, and an oscillation waveform generated due to resonance action is generated after 37 ps; (b) the graph is a frequency domain signal obtained after Fourier transform of the graph (a), and the graph (b) can show that the spectrum width is 0-2.0THz, the frequency value of the main peak with the strongest radiation is about 0.65THz, and the strongest value of the radiation power reaches 180000a.u.
As shown in fig. 7, a far field radiation pattern of a microstructure photoconductive antenna according to a terahertz wave radiation method of the microstructure photoconductive antenna provided by the embodiment of the present invention.
The results in the figure are (a) XZ planes, respectively; (b) a YZ plane; (c) the XY plane microstructure light guide antenna far field radiation pattern. The radiation intensity is far stronger than that of a dipole antenna, and the front-to-back ratio, the backward isolation degree or the interference capability of the microstructure XZ plane direction antenna are better. The antenna radiation performance is changed in the YZ plane direction of fig. 7(b), the main beam direction is obvious, and thus a directional radiation antenna can be designed, and partial power radiated in other directions of the directional radiation antenna is strengthened to the maximum radiation direction. Therefore, the main beam can be narrowed through optimizing the design structure, more power is strengthened to the maximum radiation direction, the direction coefficient of the antenna is larger, and reliable information is provided for follow-up research. Fig. 7(c), the main beam width of the microstructure antenna in the XY plane direction is widened, and the directivity is deteriorated.
As shown in fig. 8, the present invention further provides a terahertz wave radiation system of a microstructure photoconductive antenna, including:
the electron-hole pair generating module 1 is configured to irradiate a surface of the photoconductive antenna with ultrashort laser pulse photons, and when energy of the ultrashort laser pulse photons is greater than an energy gap width of the photoconductive material, electron-hole pairs are generated inside the photoconductive material.
And the electron-hole pair forming module 2 is used for applying bias voltage externally so that the electron-hole pair moves along two ends of the electrode to form a transient electric field.
And the adjusting module 3 is used for adjusting the conversion from the near field to the remote terahertz radiation in the transient electric field through the Green function, so as to realize the far field radiation of the terahertz pulse signal.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims (7)

1. A terahertz wave radiation method of a microstructure photoconductive antenna is characterized by comprising the following steps:
irradiating the surface of the photoconductive antenna with ultrashort laser pulse photons, and generating electron-hole pairs inside the photoconductive material when the energy of the ultrashort laser pulse photons is larger than the energy gap width of the photoconductive material;
applying external bias voltage to make the electron-hole pairs move along two ends of the electrode to form a transient electric field;
and adjusting the conversion from the near field to the remote terahertz radiation in the transient electric field through a Green function to realize the far field radiation of the terahertz pulse signal.
2. The method for terahertz wave irradiation of a microstructured photoconductive antenna according to claim 1, wherein the electron holes use a linear superposition theorem to divide an electric field into an electrostatic field component and a time-varying electric field component.
3. The method for radiating terahertz waves of the microstructure photoconductive antenna according to claim 2, wherein solving for the electrostatic field component comprises:
solving the initial potential in the photoconductive material by using a semiconductor Poisson equation to obtain a semiconductor electrostatic field component;
and dispersing by adopting a central difference method and solving the electrostatic field of the 3D nonlinear Poisson equation by a Newton iteration method.
4. The method for radiating terahertz waves of a microstructure photoconductive antenna according to claim 2, wherein solving for the time-varying electric field component comprises:
and solving a diffusion-drift equation and a continuity equation of the carrier by adopting a Maxwell equation.
5. The method for radiating the terahertz waves of the microstructure photoconductive antenna according to claim 1, wherein the adjusting of the conversion of the terahertz radiation from the near field to the remote in the transient electric field by the green's function specifically comprises:
and performing near-far field transformation on the near-field terahertz time-domain data by using a time-domain finite difference method to obtain a far-field terahertz time-domain waveform.
6. A terahertz wave radiation system of a microstructure photoconductive antenna is characterized by comprising:
the electronic hole pair generating module is used for irradiating ultrashort laser pulse photons to the surface of the photoconductive antenna, and when the energy of the ultrashort laser pulse photons is larger than the energy gap width of the photoconductive material, electronic hole pairs are generated inside the photoconductive material;
the electron hole pair forming module is used for applying bias voltage externally so that the electron hole pair moves along two ends of the electrode to form a transient electric field;
and the adjusting module is used for adjusting the conversion from the near field to the remote terahertz radiation in the transient electric field through the Green function so as to realize the far field radiation of the terahertz pulse signal.
7. The microstructured photoconductive antenna terahertz wave radiation system of claim 6, wherein the electron holes use a linear superposition theorem to divide an electric field into an electrostatic field component and a time-varying electric field component.
CN202011214941.7A 2020-11-04 2020-11-04 Terahertz wave radiation method and system of microstructure photoconductive antenna Pending CN112510352A (en)

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