CN213071697U

CN213071697U - Wide-tuning high-efficiency terahertz source based on collinear phase matching difference frequency of zinc telluride crystals

Info

Publication number: CN213071697U
Application number: CN202022480142.6U
Authority: CN
Inventors: 钟凯; 李方杰; 乔鸿展; 张献中; 徐德刚; 姚建铨
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2020-10-30
Filing date: 2020-10-30
Publication date: 2021-04-27
Anticipated expiration: 2030-10-30

Abstract

The utility model discloses a wide tuning high-efficiency terahertz source based on zinc telluride crystal collinear phase matching difference frequency, which comprises a fixed wavelength laser, a polarization beam splitter prism, two metal electrodes and a beam splitter, wherein the fixed wavelength laser, the polarization beam splitter prism, the two metal electrodes and the beam splitter are arranged in sequence; the variable wavelength laser and the fixed reflector are respectively and correspondingly arranged on the same side of the fixed wavelength laser and the polarization beam splitter prism, the zinc telluride crystal is arranged between the two metal electrodes, the two metal electrodes are respectively connected with the positive electrode and the negative electrode of a voltage source, and the variable wavelength laser is adjusted to emit lightVariable laser wavelength λ₂A fixed wavelength laser λ emitted from a fixed wavelength laser₁With variable laser wavelength lambda₂The frequency difference is continuously adjustable within 0.1-2.2 THz; variable wavelength laser λ₂The light is reflected to the polarization beam splitter prism through the fixed reflector, and is transmitted along the direction of the angular bisector of the x axis and the y axis of the zinc telluride crystal after being reflected again; fixed wavelength laser λ₁After passing through the polarization beam splitter prism, the laser beam with variable wavelength is lambda₂Collinear difference frequency interaction occurs in the zinc telluride crystal.

Description

Wide-tuning high-efficiency terahertz source based on collinear phase matching difference frequency of zinc telluride crystals

Technical Field

The utility model belongs to the technical field of nonlinear optics frequency conversion, concretely relates to is based on linear electro-optic effect, is showing through applying direct current electric field to zinc telluride crystal and improves collineation phase matching condition to increase terahertz radiation's tuning bandwidth, conversion efficiency and output now, thereby realize the technical scheme in wide tuning high-efficient terahertz source now.

Background

The high-power generation of the terahertz wave can be realized by utilizing the nonlinear frequency conversion property of the infrared optical crystal, and the performances of the terahertz wave, such as beam quality, tuning range and the like, are determined by the performance of the pump wave, the nonlinearity and the absorption coefficient of the crystal and the three-wave phase matching mode. Among them, phase matching is one of the important conditions for realizing high-efficiency optical-terahertz conversion (Powers P E, Haus J w. fundamental of nonlinear optics. crc press, 2017). Due to the dispersive action of the material, the phase velocity of the light wave is a function of frequency, which results in that phase matching can only be achieved within a certain narrow band of frequencies. To compensate for the dispersion induced phase mismatch, a number of methods have been developed. In isotropic crystals, non-collinear phase matching satisfies the medium wave vector triangular closed structure of the crystal by tuning the incident wave angle (Aggarwave RL, Lax B, and Favrot G. nonlinear phase matching in GaAs [ J ]. Applied physics letters,1973,22(7): 329) and quasi-phase matching realizes the continuous gain of terahertz waves in the whole crystal length by designing the polarization domain structure with period reversal (Vodopyanov K. optical THz-wave generation with periodic inversion GaAs [ J ]. Laser & photomets Reviews,2008,2: 11-25). But the tolerance of the former to the incident wave angle tolerance is extremely limited, and single-mode laser with a very small beam divergence angle and a good angle focusing mode are required to be adopted; the latter, however, makes it difficult to ensure good optical uniformity in complex crystal preparations. Collinear phase matching, the simplest and most practical way to match, is also very important for use in isotropic crystals. For ZnTe, ZnSe, InP and other crystals, due to the excellent phase matching characteristics, continuous broadband tuning in the terahertz band can be realized by changing the wavelengths of two pump waves, and the terahertz wave band is usually applied to optical rectification to generate terahertz pulses with rich frequency spectrum (Blanchard F, Razzari L, et al. Generation of 1.5 μ J single-cycle terrestrial pulses by optical recovery from a large aperture ZnTe crystal [ J ]. Optics Express,2007,15: 13212-. However, for the difference frequency of a double-pump wave with a fixed specific wavelength, the terahertz wave can be generated only within a very narrow bandwidth by adopting a collinear phase matching mode, the part outside the bandwidth cannot meet the phase matching condition due to lack of a regulating and controlling means for the wavelength and the refractive index, and the crystal cannot be well applied even if other properties of the crystal are excellent.

ZnTe crystal has higher electro-optic coefficient (gamma 41 is 3.9pm/V) (Shishuxiang, nonlinear optics, Seian electronics university Press, 2012) and wide phase matching frequency band (response exceeds 4THz), has smaller absorption in near infrared and terahertz low frequency bands, is commonly used for optical rectification generation of terahertz pulse and terahertz wave electro-optic sampling detection based on linear electro-optic effect (Liu, spring, Happy, etc.. THz radiation generated by optical rectification in ZnTe crystal and electro-optic detection research thereof [ J ] Physics, 2004,53(4): 1217-. In the latter application, the terahertz radiation period generated by light rectification is far longer than the pulse width of the detection light, so that the terahertz radiation period is regarded as a direct current electric field, and the detection light in the crystal is modulated by utilizing the linear electro-optic effect. In the aspect of a broadband adjustable narrow-linewidth terahertz source, because a single-wavelength fixed dual-wavelength pump source lacks a corresponding control means for phase matching conditions in a ZnTe crystal, a terahertz frequency band output by a difference frequency is extremely narrow, and practical application cannot be achieved all the time.

SUMMERY OF THE UTILITY MODEL

The utility model aims at overcoming the not enough among the prior art, provide a high-efficient terahertz source of wide tuning based on zinc telluride crystal collineation phase matching difference frequency, utilize zinc telluride ZnTe crystal's linear electro-optic effect, adopt titanium precious stone single frequency laser and tunable optical parametric oscillator to produce the harmonious dual wavelength pumping of single wavelength, through the regulation and control of plus direct current electric field, realize the complete collineation phase matching and difference frequency in crystal inside and produce the terahertz output of narrow line width, its frequency tuning range is 0.1-2.2THz, receive the impressed voltage value, crystal geometry, influence such as pumping wavelength.

The utility model aims at realizing through the following technical scheme:

the wide-tuning high-efficiency terahertz source based on the collinear phase matching difference frequency of the zinc telluride crystal comprises a fixed wavelength laser, a polarization beam splitter prism, two metal electrodes and a beam splitter, which are sequentially arranged; the device is characterized in that a variable wavelength laser and a fixed reflector are respectively and correspondingly arranged on the same sides of the fixed wavelength laser and the polarization splitting prism, a zinc telluride crystal is placed between the two metal electrodes, the two electrodes of the two metal electrodes are respectively connected with the positive electrode and the negative electrode of a voltage source, and the variable wavelength laser is adjusted to emit variable laser wavelength lambda₂Making the fixed wavelength laser λ emitted by the fixed wavelength laser₁With variable laser wavelength lambda₂The frequency difference is continuously adjustable within 0.1-2.2 THz; variable wavelength laser λ₂The light is reflected to the polarization beam splitter prism by the fixed reflector, and is reflected again and then is normally incident to the zinc telluride crystal; fixed wavelength laser λ₁After penetrating through the polarization beam splitter prism, the zinc telluride crystal is normally incident and is matched with variable wavelength laser lambda₂Collinear difference frequency interaction occurs; the tuning of the induced refractive index in the zinc telluride crystal is realized by regulating and controlling the voltage value of the voltage source so as to achieve collinear phase matching conditions and generate terahertz radiation by difference frequency, and the terahertz radiation is reflected and output by the light splitting device.

Furthermore, the direction of a direct current electric field applied to the zinc telluride crystal by the two metal electrodes is along the z axis of the crystal; the polarization direction of the fixed wavelength laser participating in the interaction in the zinc telluride crystal is along the z-axis, and the propagation direction is along the z-axisThe angular bisector direction of the x axis and the y axis of the crystal is vertical to the z axis; the polarization directions of the variable-wavelength laser and the generated terahertz wave in the zinc telluride crystal are in a plane formed by an x axis and a y axis of the crystal, and the transmission direction is collinear with the fixed-wavelength laser; the common line phase matching difference frequency of the fixed wavelength laser and the variable wavelength laser in the zinc telluride crystal generates terahertz radiation, and the effective nonlinear coefficient calculation formula of the difference frequency process is

Wherein

The included angle between the propagation direction of the laser with the fixed wavelength and the x axis of the zinc telluride crystal is shown, and the included angle between the propagation direction of the laser with the fixed wavelength and the z axis of the zinc telluride crystal is shown as theta (90 degrees) under the incident angle,

effective nonlinear coefficient d_eff＝d₁₄(ii) a The voltage between the two metal electrodes can be changed by regulating and controlling the voltage source, so that the electric field intensity in the zinc telluride crystal is changed, the induced refractive index in the zinc telluride crystal is further changed, and the complete phase matching condition of a wide frequency band is realized;

the fixed wavelength laser, the variable wavelength laser and the terahertz wave satisfy the following relations:

Δk＝k₁-k₂-k₃＝0

wherein k is_i＝n_iω_iWhere,/c (i ═ 1,2,3) is the spatial angular frequency, ω, of the fixed wavelength laser, variable wavelength laser, and terahertz wave, respectively₁、ω₂And ω₃The angular frequencies, n, of fixed wavelength laser, variable wavelength laser and terahertz wave, respectively₁、n₂And n₃Respectively the induced refractive index, lambda, of the fixed wavelength laser, the variable wavelength laser and the terahertz wave in the zinc telluride crystal₁、λ₂And λ₃The wavelengths of the fixed wavelength laser, the variable wavelength laser and the terahertz wave in vacuum are respectively; when the voltage source is not applied with voltage, the refractive indexes of the fixed wavelength laser, the variable wavelength laser and the terahertz wave in the crystal meet the following requirements:

where i is 1,2,3, wavelength λ_iIs μm, for fixed wavelength lasers and variable wavelength lasers, a is 4.34, B is 2.95, C is 0.142, for terahertz waves, a is 7.44, B is 2.58, C is 3180; the height of the zinc telluride crystal in the z-axis direction is d, when a voltage source applies a voltage U, a direct current electric field is formed in the crystal through two metal electrodes, and the strength of the direct current electric field is E-U/d; the optical property of the zinc telluride crystal is changed into a biaxial crystal from isotropy, three main shafts of a refractive index ellipsoid of the zinc telluride crystal are obtained by rotating the three main shafts around a z axis by 45 degrees when a direct current electric field is not applied, and an x axis and a y axis are respectively changed into an x 'axis and a y' axis; according to the polarization configuration of the fixed wavelength laser, the variable wavelength laser and the terahertz wave in the zinc telluride crystal, the induced refractive indexes of the fixed wavelength laser, the variable wavelength laser and the terahertz wave and the electric field intensity E satisfy the following linear relationship:

n₁＝n_o,1

wherein gamma is₄₁Is an element in the zinc telluride crystal electro-optic coefficient matrix.

Furthermore, the fixed wavelength laser is generated by a titanium sapphire laser with high beam quality, the center wavelength is 800nm, the variable wavelength laser is generated by a tunable optical parametric oscillator, and the wavelength tuning range is 800-806 nm.

Further, the fixed reflector is a dielectric film reflector highly reflecting in the wavelength range of 800-806nm, the polarization splitting prism highly transmits the 800nm laser light emitted by the fixed wavelength laser, highly reflects the 800-806nm tunable laser light emitted by the variable wavelength laser, and can adjust the polarization state of the variable wavelength laser light, and the light splitting device highly reflects the terahertz wave in the 0.1-2.2THz frequency range and highly transmits the 800-806nm laser light.

Furthermore, the two metal electrodes are arranged on two sides of the zinc telluride crystal, the electrode distance is regarded as the thickness of the crystal, and a voltage source enables voltage to be generated between the two metal electrodes, so that a direct current electric field along the z axis is generated in the zinc telluride crystal.

Furthermore, the light passing direction of the zinc telluride crystal is vertical to the optical axis z axis, and theta is 90 degrees on the bisector of the angle of the x axis and the y axis,

the transmission direction of the generated terahertz waves in the range of 0.1-2.2THz is collinear with the light transmission direction, and the terahertz waves are finally reflected by a light splitting device at 90 degrees and output along the z-axis direction, wherein

The included angle between the propagation direction of the laser with the fixed wavelength and the x axis of the zinc telluride crystal is shown, and the included angle between the propagation direction of the laser with the fixed wavelength and the z axis of the zinc telluride crystal is shown as theta.

Compared with the prior art, the utility model discloses a beneficial effect that technical scheme brought is:

1. the utility model discloses a mode compensation three wave of voltage regulation and control is in the inside phase place mismatching volume of crystal to effectively realize wide band tuning, high conversion efficiency and high output's difference frequency terahertz source now. Compared with the collinear phase matching difference frequency mode of adopting the double-wavelength tunable, the utility model discloses a double-wavelength laser source with single wavelength fixed, wherein, the variable wavelength laser is continuously adjustable near 800nm, and the phase mismatch amount in the zinc telluride crystal is compensated through the voltage control system, so that the scheme of wide tuning terahertz radiation is realized, so the frequency tuning is more accurate and convenient, and the cost and the complexity of the device are reduced;

2. compare in adopting non-collinear phase matching difference frequency mode, the utility model discloses well triple wave collineation interact in zinc telluride crystal to but voltage control system real-time compensation phase mismatch volume, the event is great to the tolerance of pumping wave divergence angle tolerance, can adopt the many transverse mode laser pumping of high power, improves the difference frequency and produces terahertz radiation's power.

3. The utility model discloses based on linear electro-optical effect principle, phase matching's tuning speed is limited by voltage tuning speed and the linear electro-optical effect response rate of crystal, and wherein, zinc telluride crystal's linear electro-optical effect response is very fast, so phase matching's tuning speed mainly depends on voltage tuning speed; in addition, in the whole tuning bandwidth, the allowable parameters of the regulating voltage are large, and the voltage value is only required to be tuned to a proper interval and the variable-wavelength laser lambda is tuned₂The phase matching condition can be satisfied. Therefore, the method is beneficial to realizing the quick and flexible tuning of phase matching, and is expected to be applied to the fields of quick terahertz wave switching, quick terahertz imaging, terahertz frequency domain spectroscopy and the like.

Drawings

Fig. 1 is a schematic structural diagram of a terahertz source device of the present invention;

FIG. 2 is a schematic diagram of the zinc telluride crystal orientation, the external electric field orientation and the three-wave polarization configuration provided by the present invention;

fig. 3 is a schematic diagram of the rotation of three main axes of the refractive index ellipsoid after the direct current electric field is applied along the z-axis of the zinc telluride crystal.

Reference numerals: the device comprises a 1-fixed wavelength laser, a 2-variable wavelength laser, a 3-fixed reflector, a 4-polarization beam splitter prism, a 5-zinc telluride crystal, 6-two metal electrodes, a 7-voltage source and an 8-beam splitter.

Detailed Description

The present invention will be described in further detail with reference to the following drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

As shown in fig. 1, the utility model provides a wide tuning high-efficiency terahertz source based on zinc telluride crystal collinear phase matching difference frequency, which comprises a fixed wavelength laser 1, a polarization beam splitter prism 4, two metal electrodes 6 and a beam splitter 8 which are arranged in sequence; the same sides of the fixed wavelength laser 1 and the polarization splitting prism 4 are respectively provided with a variable wavelength laser 2 and a fixed reflector 3 correspondingly, a zinc telluride crystal 5 is arranged between two metal electrodes 6, two electrodes of the two metal electrodes are respectively connected with the positive electrode and the negative electrode of a voltage source 7, and the variable laser wavelength lambda emitted by the variable wavelength laser is adjusted₂A fixed wavelength laser λ emitted from a fixed wavelength laser₁With variable laser wavelength lambda₂The frequency difference is continuously adjustable within 0.1-2.2 THz; variable wavelength laser λ₂The light is reflected to the polarization beam splitter prism by the fixed reflector, and is transmitted along the direction of the angular bisector of the x axis and the y axis of the zinc telluride crystal after being reflected again; fixed wavelength laser λ₁After penetrating through the polarization beam splitter prism, the polarization beam splitter prism also propagates along the direction of the angular bisector of the x axis and the y axis of the zinc telluride crystal and is matched with variable-wavelength laser lambda₂Collinear normal incidence is carried out on the zinc telluride crystal to generate difference frequency interaction; the tuning of the induced refractive index in the zinc telluride crystal is realized by regulating and controlling the voltage value of the voltage source so as to achieve collinear phase matching conditions and generate terahertz radiation by difference frequency, and the terahertz radiation is reflected and output by the light splitting device.

Specifically, the fixed wavelength laser 1 is a high beam quality titanium sapphire laser, and generates fixed wavelength laser λ with center wavelength of 800nm₁After passing through the polarization splitting prism 4, the light propagates along the optical axis of the system. The variable wavelength laser 2 is a tunable optical parametric oscillator which is pumped after the frequency multiplication of the titanium sapphire laser and generates variable wavelength laser lambda within the wavelength tuning range of 800-₂Reflected to a polarization beam splitter prism 4 by a fixed reflector 3, and reflected again to the laser lambda with fixed wavelength₁Co-linearly propagating and normal incidence to the zinc telluride crystal 5. The fixed reflector 3 has high reflectivity in the 800-plus-806 nm wavelength rangeThe polarization beam splitter 4 has high transmittance to the 800nm laser emitted from the fixed wavelength laser 1, high reflectance to the 800-₂The polarization state of (c). The two metal electrodes 6 are respectively connected with the positive electrode and the negative electrode of a voltage source 7, and a direct current electric field along the z-axis direction is applied to the zinc telluride crystal 5 arranged between the electrodes. The light-splitting device 8 is highly transparent to the laser within the wavelength range of 800-806nm, and highly reflective to the generated terahertz wave within the 0.1-2.2THz frequency range, and the terahertz radiation is reflected by the light-splitting device 8 at an angle of 90 degrees and then output along the z-axis direction.

As shown in fig. 2, the zinc telluride crystal 5 is a rectangular thin plate with a thickness d of 1mm, and the light passing direction thereof is perpendicular to the optical axis z-axis, and is on the bisector of the x-axis and the y-axis (θ is 90 °,

). Fixed wavelength laser λ₁Polarization direction along z-axis, variable wavelength laser λ₂And the polarization direction of the terahertz wave is perpendicular to a plane formed by the z axis and the optical axis of the system. The induced refractive index in the zinc telluride crystal 5 is regulated and controlled by the voltage source 7, and the maximum voltage value which can be applied by the voltage source 7 is 3 kV. The three waves meet the collinear phase matching condition in the zinc telluride crystal 5 and generate terahertz radiation in the frequency range of 0.1-2.2 THz.

As shown in FIG. 3, after a direct current electric field is applied along the optical axis z-axis of the zinc telluride crystal 5, the optical property of the crystal is changed from isotropy to biaxial crystal, the three main axes of the refractive index ellipsoid are obtained by rotating the three main axes around the z-axis by 45 degrees when no direct current electric field is applied, and the x-axis and the y-axis are changed into an x '-axis and a y' -axis respectively.

To sum up, the utility model also relates to a method for utilizing extra direct current electric field to show improvement collineation phase place matching condition in zinc telluride crystal, this method has widened the tuning bandwidth that isotropic crystal collineation phase place matches greatly, is showing and is improving conversion efficiency and the output that produces terahertz radiation now. The method has simple principle, convenient design and good feasibility, and can be applied to other isotropic crystals.

The present invention is not limited to the above-described embodiments. The above description of the embodiments is intended to describe and illustrate the technical solutions of the present invention, and the above embodiments are merely illustrative and not restrictive. Without departing from the spirit of the invention and the scope of the appended claims, the person skilled in the art can make many changes in form and detail within the teaching of the invention.

Claims

1. The wide-tuning high-efficiency terahertz source based on the collinear phase matching difference frequency of the zinc telluride crystal is characterized by comprising a fixed wavelength laser (1), a polarization beam splitter prism (4), two metal electrodes (6) and a beam splitter (8) which are sequentially arranged; the device is characterized in that a variable wavelength laser (2) and a fixed reflector (3) are respectively and correspondingly arranged on the same side of the fixed wavelength laser (1) and the polarization beam splitter prism (4), a zinc telluride crystal (5) is arranged between the two metal electrodes (6), the two electrodes of the two metal electrodes (6) are respectively connected with the positive electrode and the negative electrode of a voltage source (7), and the variable laser wavelength lambda emitted by the variable wavelength laser (2) is adjusted₂Causing the fixed wavelength laser light λ emitted by the fixed wavelength laser (1)₁With variable laser wavelength lambda₂The frequency difference is continuously adjustable within 0.1-2.2 THz; variable wavelength laser λ₂The light is reflected to the polarization beam splitter prism (4) through the fixed reflector (3), and is reflected again and then is normally incident to the zinc telluride crystal (5); fixed wavelength laser λ₁After penetrating through the polarization beam splitter prism (4), the zinc telluride crystal (5) is normally incident and is matched with variable-wavelength laser lambda₂Collinear difference frequency interaction occurs; the tuning of the induced refractive index inside the zinc telluride crystal (5) is realized by regulating and controlling the voltage value of the voltage source (7), so that collinear phase matching conditions are achieved, terahertz radiation is generated by difference frequency, and the terahertz radiation is reflected and output by the light splitting device (8).

2. The wide-tuning high-efficiency terahertz source based on the collinear phase matching difference frequency of the zinc telluride crystal as claimed in claim 1, wherein the direction of a direct-current electric field applied to the zinc telluride crystal (5) by the two metal electrodes (6) is along the z-axis of the crystal; involving interactionThe polarization direction of the fixed wavelength laser in the zinc telluride crystal (5) is along the z axis, and the transmission direction is vertical to the z axis along the angular bisector direction of the x axis and the y axis of the crystal; the polarization directions of the variable-wavelength laser and the generated terahertz wave in the zinc telluride crystal (5) are in a plane formed by an x axis and a y axis of the crystal, and the transmission direction is collinear with the fixed-wavelength laser; the common-line phase matching difference frequency of the fixed wavelength laser and the variable wavelength laser in the zinc telluride crystal (5) generates terahertz radiation, and the effective nonlinear coefficient calculation formula of the difference frequency process is d_eff＝d₁₄sin θ sin2 φ, where d₁₄Is an element in a second-order nonlinear optical coefficient matrix of the zinc telluride crystal (5) under Kleinman symmetry approximation, phi is an included angle between a fixed wavelength laser propagation direction and an x axis of the zinc telluride crystal (5), theta is an included angle between the fixed wavelength laser propagation direction and a z axis of the zinc telluride crystal (5), and because the incident angle corresponds to theta-90 degrees, phi-45 degrees and an effective nonlinear coefficient d_eff＝d₁₄(ii) a The voltage between the two metal electrodes (6) can be changed by regulating the voltage source (7), so that the electric field intensity in the zinc telluride crystal (5) is changed, the induced refractive index in the zinc telluride crystal (5) is changed, and the complete phase matching condition of a wide frequency band is realized;

Δk＝k₁-k₂-k₃＝0

wherein k is_i＝n_iω_iWhere,/c (i ═ 1,2,3) is the spatial angular frequency, ω, of the fixed wavelength laser, variable wavelength laser, and terahertz wave, respectively₁、ω₂And ω₃The angular frequencies, n, of fixed wavelength laser, variable wavelength laser and terahertz wave, respectively₁、n₂And n₃Respectively the induced refractive index, lambda, of the fixed wavelength laser, the variable wavelength laser and the terahertz wave in the zinc telluride crystal (5)₁、λ₂And λ₃Respectively, fixed wavelength laser, variableThe wavelengths of the wavelength laser and the terahertz wave in vacuum; when no voltage is applied to the voltage source (7), the refractive indexes of the fixed wavelength laser, the variable wavelength laser and the terahertz wave in the crystal meet the following requirements:

where i is 1,2,3, wavelength λ_iIs μm, for fixed wavelength lasers and variable wavelength lasers, a is 4.34, B is 2.95, C is 0.142, for terahertz waves, a is 7.44, B is 2.58, C is 3180; the height of the zinc telluride crystal (5) in the z-axis direction is d, when a voltage source (7) applies a voltage U, a direct current electric field is formed in the crystal through the two metal electrodes (6), and the strength of the direct current electric field is E-U/d; the optical property of the zinc telluride crystal (5) is changed into a biaxial crystal from isotropy, three main shafts of a refractive index ellipsoid of the zinc telluride crystal (5) are obtained by rotating the three main shafts around a z-axis by 45 degrees when a direct current electric field is not applied, and an x-axis and a y-axis are respectively changed into an x '-axis and a y' -axis; according to the polarization configuration of the fixed wavelength laser, the variable wavelength laser and the terahertz wave in the zinc telluride crystal (5), the induced refractive indexes of the fixed wavelength laser, the variable wavelength laser and the terahertz wave and the electric field intensity E satisfy the following linear relationship:

n₁＝n_o，1

wherein gamma is₄₁Is an element in the electro-optic coefficient matrix of the zinc telluride crystal (5).

3. The wide-tuning high-efficiency terahertz source based on the collinear phase matching difference frequency of the zinc telluride crystal as claimed in claim 1, wherein the fixed wavelength laser (1) is generated by a titanium sapphire laser with high beam quality, the center wavelength is 800nm, the variable wavelength laser (2) is generated by a tunable optical parametric oscillator, and the wavelength tuning range is 800-806 nm.

4. The wide-tuning high-efficiency terahertz source based on the collinear phase matching difference frequency of the zinc telluride crystal as claimed in claim 1, wherein the fixed reflector (3) is a dielectric film reflector highly reflecting in the wavelength range of 800-.

5. The wide-tuning high-efficiency terahertz source based on the collinear phase matching difference frequency of the zinc telluride crystal as claimed in claim 1, wherein the two metal electrodes (6) are placed on two sides of the zinc telluride crystal (5), the electrode distance is regarded as the thickness of the crystal, and the voltage source (7) enables voltage to be generated between the two metal electrodes (6) so as to generate a direct current electric field along the z axis in the zinc telluride crystal (5).

6. The wide-tuning high-efficiency terahertz source based on the collinear phase matching difference frequency of the zinc telluride crystal as in claim 1 is characterized in that the light transmission direction of the zinc telluride crystal (5) is perpendicular to the optical axis z axis, theta is 90 degrees and phi is 45 degrees on the angular bisector of the x axis and the y axis, the generated terahertz wave in the range of 0.1-2.2THz is collinear with the light transmission direction, and finally the terahertz wave is reflected by the light splitting device (8) at 90 degrees and output along the z axis direction, wherein phi is the included angle between the fixed wavelength laser transmission direction and the x axis of the zinc telluride crystal (5), and theta is the included angle between the fixed wavelength laser transmission direction and the z axis of the zinc telluride crystal (5).