CN207234145U - The system that double plasma adjustable in pitch produces high intensity THz wave - Google Patents

Abstract

The utility model discloses a system for generating high-intensity terahertz waves with adjustable distance between two plasmas, which comprises a laser, an optical parameter amplifier, a chopper, a climber, a laser beam expander, a space light Modulator, mirror, BBO crystal, first off-axis parabolic mirror, second off-axis parabolic mirror, filter and silicon wafer. The utility model can control the distance and spatial distribution between the two plasmas by adjusting the distance between the phase diagrams of the two Fresnel lenses loaded on the spatial light modulator and the rotation angle of the symmetry axis. It can also precisely control the energy and polarization state of the terahertz wave, making up for the gap in the technical field of high-intensity terahertz wave generation, and has strong scientific research and practical application value; the system structure of the utility model is simple, easy to build Low cost, easy maintenance, and high stability, the generated terahertz wave has strong energy and wide spectrum, which is beneficial for spectral measurement.

Description

A system for generating high-intensity terahertz waves from dual plasmons with adjustable spacing

technical field

The utility model relates to the technical field of terahertz wave generation, in particular to a system for generating high-intensity terahertz waves by dual plasmas with adjustable spacing.

Background technique

The technology of focusing ultrashort laser pulses in the surrounding air to directly generate terahertz has attracted widespread attention in recent years. This method can generate terahertz waves at a distance (up to several kilometers away), so the application prospect is very bright.

When a high-energy ultrashort laser pulse is focused in the air, the air at the focal point will ionize to form a plasma, and the resulting mass dynamics will form a large density difference between the ion charge and the electronic charge, and This charge separation process results in powerful electromagnetic transients that emit terahertz radiation.

In previous experiments, a femtosecond laser was generally used to excite a single air plasma through a single lens to generate terahertz waves. However, the intensity of the generated terahertz waves is not very large, which cannot meet the needs of use. In 2007, Y.Liu et al. discovered a method for generating terahertz waves by focusing double plasmons with a single lens, but the spacing and spatial distribution of the double plasmons cannot be precisely controlled. In 2016, Sun Wenfeng et al. invented a method of modulating the terahertz spectrum with front and rear dual optical filaments, but the intensity and generation efficiency of terahertz waves have not been significantly enhanced under this setting.

How to use air plasma to generate stronger terahertz waves is an important research direction for those skilled in the art.

Utility model content

The utility model provides a system for generating high-intensity terahertz waves by double plasmas with adjustable spacing, so as to generate terahertz waves with greater intensity by using air plasma.

In order to achieve the above purpose, the utility model provides a system for generating high-intensity terahertz waves with adjustable spacing of dual plasmas, which includes a laser, an optical parametric amplifier, a chopper, a climber, a laser Beam expander, spatial light modulator, mirror, BBO crystal, first off-axis parabolic mirror, second off-axis parabolic mirror, filter and silicon chip, wherein,

The laser emits laser light with a wavelength of 800nm and a vertical polarization direction, and then outputs signal light with a wavelength of 1300nm or 1550nm after passing through the optical parametric amplifier. After the signal light passes through the chopper, the polarization direction is changed to the horizontal direction by the climber. Then the beam is expanded by the laser beam expander and then enters the spatial light modulator. The spatial light modulator is loaded with two Fresnel lens phase maps, and the two Fresnel lens phase maps have the first focal point and the second focal point respectively. , so as to convert the incident light into two beams of parallel focused light and project them to the reflector and the BBO crystal, the two beams emitted by the BBO crystal are respectively focused at the first focus and the second focus to excite the air to generate plasma, and then form a solar Hertz radiation source, the terahertz wave emitted by the terahertz radiation source is reflected by the first off-axis parabolic reflector and the second off-axis parabolic reflector, and then passes through the filter and the silicon chip in sequence, thereby obtaining high-intensity terahertz wave.

In an embodiment of the present invention, the distance between two Fresnel lens phase diagrams is equal to the distance between two plasmas.

In one embodiment of the present invention, the phase diagrams of the two Fresnel lenses are axisymmetric about a symmetry axis, the connection line of the two plasma centers is perpendicular to the symmetry axis, and the connection line of the two plasma centers follows the symmetry The clockwise/counterclockwise rotation of the shaft rotates in the same direction and at the same angle.

In an embodiment of the present invention, the first focal point and the second focal point correspond to a first focal length and a second focal length respectively, and the first focal length and the second focal length are proportional to the length of the plasma and inversely proportional to the width.

In an embodiment of the present invention, the system for generating high-intensity terahertz waves with adjustable spacing between two plasmas further includes a terahertz wave intensity detector arranged at the back end of the silicon wafer.

In an embodiment of the present invention, the terahertz wave intensity detector is a pyroelectric detector or a Gouley detector.

In an embodiment of the present invention, the climber includes two metal mirrors.

In an embodiment of the present utility model, the frequency of the chopper is 15-20 Hz.

In an embodiment of the present utility model, the reflector is a metal mirror.

The system for generating high-intensity terahertz waves by dual plasmas with adjustable spacing provided by the utility model has the following advantages:

(1) By adjusting the spacing between the two Fresnel lens phase diagrams loaded on the spatial light modulator and the rotation angle of the symmetry axis, the spacing and spatial distribution between the two plasmons can be controlled, which is different from the existing terahertz wave Compared with the generation method, it not only improves the intensity of the terahertz wave, but also can precisely control the energy and polarization state of the terahertz wave, which makes up for the gap in the current high-intensity terahertz wave generation technology field, and has strong scientific research and practical application value;

(2) The system has simple structure, low construction cost, easy maintenance and high stability;

(3) The generated terahertz wave has strong energy and wide spectrum, which is beneficial to spectrum measurement.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are only some embodiments of the utility model, and those skilled in the art can also obtain other drawings based on these drawings without creative work.

Figure 1 is a schematic structural diagram of a system for generating high-intensity terahertz waves with adjustable spacing between dual plasmas provided by the present invention;

Fig. 2 is the schematic diagram that two Fresnel lens phase diagrams are axisymmetric about the symmetry axis;

Fig. 3 is the schematic diagram of climber;

Fig. 4 a is a single Fresnel lens phase diagram in the utility model;

Figure 4b is a Fresnel lens phase diagram with a center spacing of 60 microns;

Fig. 5 is a relationship diagram between the distance between two plasmas generated by a 1300nm laser and the terahertz energy ratio between two/single plasmas;

Fig. 6 is a graph showing the relationship between the distance between two plasmons generated by a 1550nm laser and the terahertz energy ratio between two/single plasmons.

Description of reference signs: 1-laser; 2-optical parametric amplifier; 3-chopper; 4-climber; 5-laser beam expander; 6-spatial light modulator; 7-mirror; 8-BBO crystal; 9-first off-axis parabolic mirror; 10-second off-axis parabolic mirror; 11-filter; 12-silicon wafer; 13-terahertz wave intensity detector; A, B-Fresnel lens phase diagram; L-axis of symmetry.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. example. Based on the embodiments of the present utility model, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the scope of protection of the present utility model.

Figure 1 is a schematic structural diagram of a system for generating high-intensity terahertz waves from dual plasmas with adjustable spacing provided by the present invention. The terahertz wave system includes a laser 1, an optical parametric amplifier 2, a chopper 3, a climber 4, a laser beam expander 5, a spatial light modulator 6, a mirror 7, a BBO crystal 8, and An off-axis parabolic reflector 9, a second off-axis parabolic reflector 10, a filter 11 and a silicon chip 12, wherein,

Laser 1 emits laser light with a wavelength of 800nm and a vertical polarization direction, and then outputs signal light with a wavelength of 1300nm or 1550nm after passing through an optical parametric amplifier 2, and after the signal light passes through a chopper 3, the polarization direction is changed by a climber 4 In the horizontal direction, the beam is expanded by the laser beam expander 5 and then incident to the spatial light modulator 6. The spatial light modulator 6 is loaded with two Fresnel lens phase diagrams A and B, and the two Fresnel lens phase diagrams Figures A and B respectively have a first focal point and a second focal point to convert the incident light into two bundles of parallel focused light rays and project them to the mirror 7 and the BBO crystal 8, and the two beams emitted through the BBO crystal 8 are respectively at the first Focusing and exciting the air at the focal point and the second focal point to generate plasma, and then forming a terahertz radiation source, the terahertz wave emitted by the terahertz radiation source is reflected by the first off-axis parabolic mirror 9 and the second off-axis parabolic mirror 10 and then sequentially After passing through the filter 11 and the silicon wafer 12, a high-intensity terahertz wave is obtained.

The laser 1 can be a femtosecond laser amplifier, such as the femtosecond laser amplifier Spitfire produced by Spectra-Physics Corporation of the United States.

Fig. 4a is a phase diagram of a single Fresnel lens in the present invention, and Fig. 4b is a phase diagram of a Fresnel lens whose center distance is 60 microns, and the focal lengths in Fig. 4a and Fig. 4b are both 160 millimeters.

In the utility model, as shown in Figure 1, the spacing between two plasmas is d, and the spacing between two Fresnel lens phase diagrams A, B is equal to the spacing d between the two plasmas, so , the distance between the two plasmas can be controlled by controlling the distance between the two Fresnel lens phase diagrams A and B. In addition, as shown in Figure 2, the two Fresnel lens phase diagrams A and B are axisymmetric about a symmetry axis L, the distance between the centers O ₁ and O ₂ of the two Fresnel lens phase diagrams is d, and the two centers The connecting line is perpendicular to the symmetry axis L. At this time, the connecting line of the two plasma centers formed by focusing rotates in the same direction and at the same angle as the symmetry axis L rotates clockwise/counterclockwise. It should be noted that the clockwise/counterclockwise mentioned in the utility model should be observed against the direction of the light path or observed along the direction of the light path.

In the present utility model, the first focal point and the second focal point respectively correspond to a first focal length and a second focal length, and the first focal length and the second focal length are respectively the optical path distances between the spatial light modulator 6 and the two plasmas, In the present utility model, it is the sum of the optical path distance from the spatial light modulator 6 to the reflector 7, the optical path distance from the reflector 7 to the BBO crystal 8, and the optical path distance from the BBO crystal 8 to the plasma, the first focal length and The second focal length is proportional to the length of the plasma and inversely proportional to the width.

As shown in Figure 1, the system for generating high-intensity terahertz waves with adjustable spacing between the dual plasmas provided by the present invention may further include a terahertz wave intensity detector 13 arranged at the rear end of the silicon wafer 12, the terahertz wave intensity The detector 13 may be a pyroelectric detector or a Colloid detector.

Fig. 3 is the schematic diagram of climber, as shown in Fig. 3, climber 4 comprises two metal reflectors M1, M2, and incident light is the laser light that polarization direction is vertical (z axis), passes through one side optical axis direction and x direction The mirror M1 with an angle of 45 degrees reflects the laser light to the z direction, and then passes through the mirror M2 whose optical axis direction is 45 degrees from the y axis on the second surface. The reflected beam propagates along the y direction, and the polarization direction is horizontal (x axis) .

The frequency of the chopper 3 used in the utility model can be between 15-20 Hz, and a chopper with other parameters can also be selected according to actual needs, and the utility model is not limited thereto. Reflecting mirror 7 can be selected metal mirror for use.

Fig. 5 is a graph showing the relationship between the distance between two plasmas generated by a 1300nm laser and the terahertz energy ratio between two/single plasmas. As shown in Fig. 5, when the distances between two plasmas are At 0 microns, 20 microns, 40 microns, 60 microns, and 80 microns, the corresponding terahertz energy ratios are 1, 0.99, 1.45, 0.15, and 0.14, respectively. where the spacing "0" represents the case where a single Fresnel lens phase map is used. It can be seen that when the laser wavelength is 1300nm, the distance between the two plasmas is controlled to be 40 microns, and the terahertz energy obtained is the largest, and the terahertz energy at this time is about the phase diagram produced by a single Fresnel lens when the distance is 0 1.45 times the terahertz energy.

Fig. 6 is a graph showing the relationship between the distance between two plasmas generated by a 1550nm laser and the terahertz energy ratio between two/single plasmas. As shown in Fig. 6, when the distances between two plasmas are At 0 micron, 20 micron, 40 micron, 60 micron, 80 micron and 120 micron, the corresponding terahertz energy ratios are 1, 1.01, 2.28, 2.3, 0.81, 0.22, respectively. where the spacing "0" represents the case where a single Fresnel lens phase map is used. It can be seen that when the laser wavelength is 1550nm, the distance between the two plasmas is controlled to be 60 microns, and the obtained terahertz energy is the largest, and the terahertz energy at this time is about the phase diagram produced by a single Fresnel lens when the distance is 0 2.3 times the energy of terahertz.

It can be seen that in the present utility model, when only the spacing between two Fresnel lens phase diagrams A and B changes (the line connecting the centers of the two Fresnel lens phase diagrams does not rotate with the axis of symmetry L), At this time, the polarization state of the terahertz wave does not change, and the terahertz energy will change with the distance between the two Fresnel lens phase diagrams A and B, and when the two Fresnel lens phase diagrams A and B A terahertz energy maximum is obtained when the distance between them reaches a certain value.

In addition, under different laser wavelengths, the distance between the two Fresnel lens phase diagrams A and B corresponding to the maximum terahertz energy is different, and the distance increases with the increase of the wavelength.

When only the line connecting the centers of the two Fresnel lens phase diagrams rotates with the symmetry axis L (the distance between the two Fresnel lens phase diagrams A and B does not change), the energy of the terahertz wave at this time does not change, the polarization state of the terahertz wave changes with the direction of the corresponding two plasmon lines, and the polarization direction is parallel to the direction of the two plasmon lines.

The system for generating high-intensity terahertz waves by dual plasmas with adjustable spacing provided by the utility model has the following advantages:

(1) By adjusting the spacing between the two Fresnel lens phase diagrams loaded on the spatial light modulator and the rotation angle of the symmetry axis, the spacing and spatial distribution between the two plasmons can be controlled, which is different from the existing terahertz wave Compared with the generation method, it not only improves the intensity of the terahertz wave, but also can precisely control the energy and polarization state of the terahertz wave, which makes up for the gap in the current high-intensity terahertz wave generation technology field, and has strong scientific research and practical application value;

(2) The system has simple structure, low construction cost, easy maintenance and high stability;

(3) The generated terahertz wave has strong energy and wide spectrum, which is beneficial to spectrum measurement.

Those of ordinary skill in the art can understand that: the accompanying drawing is only a schematic diagram of an embodiment, and the modules or processes in the accompanying drawing are not necessarily necessary for implementing the utility model.

Those of ordinary skill in the art can understand that: the modules in the device in the embodiment may be distributed in the device in the embodiment according to the description in the embodiment, or may be changed and located in one or more devices different from the embodiment. The modules in the above embodiments can be combined into one module, and can also be further split into multiple sub-modules.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present utility model, and are not intended to limit it; although the utility model has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: It is still possible to modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention .

Claims (9)

1. A system for generating high-intensity terahertz waves from two plasmas with adjustable spacing, characterized in that it includes lasers, optical parametric amplifiers, choppers, climbers, laser beam expanders, space Optical modulator, reflector, BBO crystal, first off-axis parabolic reflector, second off-axis parabolic reflector, filter and silicon chip, wherein, The laser emits laser light with a wavelength of 800nm and a vertical polarization direction, and then outputs signal light with a wavelength of 1300nm or 1550nm after passing through the optical parametric amplifier. After the signal light passes through the chopper, the polarization direction is changed to the horizontal direction by the climber. Then the beam is expanded by the laser beam expander and then enters the spatial light modulator. The spatial light modulator is loaded with two Fresnel lens phase maps, and the two Fresnel lens phase maps have the first focal point and the second focal point respectively. , so as to convert the incident light into two beams of parallel focused light and project them to the reflector and the BBO crystal, the two beams emitted by the BBO crystal are respectively focused at the first focus and the second focus to excite the air to generate plasma, and then form a solar Hertz radiation source, the terahertz wave emitted by the terahertz radiation source is reflected by the first off-axis parabolic reflector and the second off-axis parabolic reflector, and then passes through the filter and the silicon chip in sequence, thereby obtaining high-intensity terahertz wave. 2. The system for generating high-intensity terahertz waves by dual plasmas with adjustable spacing according to claim 1, wherein the spacing between two Fresnel lens phase diagrams and the spacing between two plasmas equal. 3. The system for generating high-intensity terahertz waves from adjustable dual plasmas according to claim 1, wherein the two Fresnel lens phase diagrams are axisymmetric about a symmetry axis, and the two plasma centers The line connecting the two plasma centers is perpendicular to the axis of symmetry, and the line connecting the two plasma centers rotates in the same direction and at the same angle as the axis of symmetry rotates clockwise/counterclockwise. 4. The system for generating high-intensity terahertz waves by dual plasmas with adjustable spacing according to claim 1, wherein the first focal point and the second focal point correspond to a first focal length and a second focal length respectively, and the first The focal length and the second focal length are directly proportional to the length of the plasma and inversely proportional to the width. 5 . The system for generating high-intensity terahertz waves by dual plasmas with adjustable spacing according to claim 1 , further comprising a terahertz wave intensity detector arranged at the back end of the silicon wafer. 6 . The system for generating high-intensity terahertz waves by dual plasmas with adjustable spacing according to claim 5 , wherein the terahertz wave intensity detector is a pyroelectric detector or a Goulet detector. 7. The system for generating high-intensity terahertz waves by dual plasmas with adjustable spacing according to claim 1, wherein the climber includes two metal mirrors. 8 . The system for generating high-intensity terahertz waves from dual plasmas with adjustable spacing according to claim 1 , wherein the frequency of the chopper is 15-20 Hz. 9. The system for generating high-intensity terahertz waves with adjustable spacing dual plasmas according to claim 1, wherein the reflector is a metal mirror.