CN117805060A - Terahertz radiation enhancement method based on radial asymmetric air plasma - Google Patents
Terahertz radiation enhancement method based on radial asymmetric air plasma Download PDFInfo
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- CN117805060A CN117805060A CN202311675558.5A CN202311675558A CN117805060A CN 117805060 A CN117805060 A CN 117805060A CN 202311675558 A CN202311675558 A CN 202311675558A CN 117805060 A CN117805060 A CN 117805060A
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- 238000000034 method Methods 0.000 title claims abstract description 20
- 230000005855 radiation Effects 0.000 title claims abstract description 17
- 230000010287 polarization Effects 0.000 claims abstract description 15
- 230000001965 increasing effect Effects 0.000 claims abstract description 8
- 239000013307 optical fiber Substances 0.000 claims abstract description 8
- 238000005086 pumping Methods 0.000 abstract description 7
- 238000002679 ablation Methods 0.000 abstract description 3
- 210000002381 plasma Anatomy 0.000 description 18
- 238000010586 diagram Methods 0.000 description 5
- 238000001514 detection method Methods 0.000 description 3
- 230000002708 enhancing effect Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
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- 230000002238 attenuated effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
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- 238000002474 experimental method Methods 0.000 description 1
- 238000003384 imaging method Methods 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000005693 optoelectronics Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
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Abstract
The invention belongs to the technical field of laser physics, and particularly discloses a terahertz radiation enhancement method based on radial asymmetric air plasma, which comprises the following steps: before the collimated femtosecond laser passes through the lens for focusing, the baffle is used for shielding the laser, the laser passes through the baffle and then is asymmetrically distributed in the radial direction, and then ionized air is focused to form light wires with asymmetrically distributed radial plasma density; and along with the unidirectional movement of the baffle, the area of the shielding laser light spot is increased, the radial asymmetry of the optical fiber is enhanced, the terahertz time-domain peak-to-peak values in the X and Y polarization directions are enhanced, and the terahertz intensity is enhanced. The method saves laser power and reduces the ablation of the lens; the structure is simple, and the cost is low; and is suitable for various terahertz systems of laser pumping radiation.
Description
Technical Field
The invention relates to the technical field of laser physics, in particular to a terahertz radiation enhancement method based on radial asymmetric air plasma.
Background
Terahertz waves generally refer to electromagnetic waves with frequencies between 0.1THz and 10 THz, are electromagnetic spectrums between far infrared and microwaves, and are one field of research and development under great force at present by combining a plurality of subjects of optoelectronics, semiconductor science, materials and the like.
The laser-induced air plasma is a powerful broadband terahertz source and has good application prospects, such as nondestructive detection, remote sensing, near-field imaging, ultra-fast switching, dynamic control and biological detection. However, the widespread use of plasma terahertz sources also presents some practical challenges, particularly the lack of effective enhancement methods. Since simply increasing the laser energy again mainly lengthens the filament length when the laser energy fully ionizes air molecules within the cross section, the plasma density can hardly be increased, and the terahertz output can be saturated or even absorbed and attenuated.
The existing terahertz signal enhancement means have a light wire array method, such as parallel double wires, cross double wires and the like, which all need to construct a more complex laser transmission light path before a terahertz source, so that not only is space occupied, but also the device is often complex in structure, so that the whole system is low in integration level and inconvenient to operate.
It should be noted that the information disclosed in the above background section is only for enhancing understanding of the background of the invention and thus may include information that does not form the prior art that is already known to those of ordinary skill in the art.
Disclosure of Invention
The invention aims to solve the technical problems in the background art, and provides a terahertz radiation enhancement method based on radial asymmetric air plasmas, which is used for shielding laser of pumping plasma optical fibers through a baffle plate to form asymmetric pumping laser so as to form optical fibers with asymmetric radial plasma density distribution, thereby enhancing terahertz waves radiated by the optical fibers, saving laser power and reducing ablation of lenses.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
a terahertz radiation enhancement method based on radial asymmetric air plasma comprises the following steps: before the collimated femtosecond laser passes through the lens for focusing, the baffle is used for shielding the laser, the laser passes through the baffle and then is asymmetrically distributed in the radial direction, and then ionized air is focused to form light wires with asymmetrically distributed radial plasma density; and along with the unidirectional movement of the baffle, the area of the shielding laser light spot is increased, the radial asymmetry of the optical fiber is enhanced, the terahertz time-domain peak-to-peak values in the X and Y polarization directions are enhanced, and the terahertz intensity is enhanced.
The following is a further defined technical solution of the present invention, where the moving direction of the baffle is parallel to the radial direction of the laser.
The following is a further defined technical scheme of the invention, wherein the baffle starts to move from one side vertex to the other side vertex of the laser transverse circular surface, and the moving distance of the baffle is a, wherein a is more than 0 and less than or equal to the radius of the laser transverse circular surface.
Compared with the prior art, the invention has the following technical effects:
terahertz radiation enhancement method based on radial asymmetric air plasma
According to the invention, the intensity of terahertz of air plasma radiation can be effectively enhanced by shielding pumping laser by using the baffle plate, the laser power is saved, and the ablation of the lens is reduced; the structure is simple, and the cost is low; and is suitable for various terahertz systems of laser pumping radiation. The terahertz strength enhancement realized by the method has important and positive significance for future research and practical application of air plasma radiation terahertz waves.
The invention will be further described with reference to the drawings and examples.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following description will briefly explain the embodiments or the drawings needed in the prior art, and it is obvious that the drawings in the following description are only some embodiments of the present invention and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a simplified structure diagram and a light spot shielding cross-section diagram of a device for generating plasma radiation terahertz wave by shielding laser by a baffle plate, and is an initial position of shielding the laser by the baffle plate;
FIG. 2 is a simplified view of the structure of the device after the baffle plate is displaced downwards by 3mm and a light spot shielding cross-section view;
FIG. 3 is a terahertz time-domain signal diagram respectively measured when the baffle is at the initial position and is displaced downward by 3mm, wherein FIG. 3 (a) is an X-polarization-direction terahertz time-domain signal diagram; 3 (b) is a terahertz time-domain signal diagram in the Y polarization direction;
FIG. 4 is a normalized graph of the peak-to-peak variation of the amplitude of the terahertz time-domain signal in the X, Y polarization direction measured in the process of completely shielding the laser from the initial position of the baffle plate in the invention;
fig. 5 is a normalized graph of the measured terahertz intensity variation of the baffle in the present invention from the initial position to the complete shielding of the laser.
Detailed Description
In order that the above objects, features and advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to the appended drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be embodied in many other forms than described herein and similarly modified by those skilled in the art without departing from the spirit of the invention, whereby the invention is not limited to the specific embodiments disclosed below.
As shown in fig. 1-5, there is provided a terahertz radiation enhancement method based on a radially asymmetric air plasma, comprising the steps of: before the collimated femtosecond laser 1 is focused by a lens 3, the laser 1 is shielded by a baffle plate 2, the laser 1 is asymmetrically distributed in the radial direction after passing through the baffle plate 2, and then ionized air is focused to form a light wire 5 with asymmetrically distributed radial plasma density; along with the unidirectional movement of the baffle plate 2, the area of the light spot of the shielding laser 1 is increased, the radial asymmetry of the optical fiber 5 is enhanced, the terahertz time domain peak value in the X and Y polarization directions is enhanced, and the terahertz intensity is enhanced, wherein the terahertz intensity is the square sum of terahertz amplitude in the X, Y polarization direction.
Wherein the direction of movement of the shutter 2 is parallel to the radial direction of the laser 1. The baffle plate 2 moves from one side vertex to the other side vertex of the transverse circular surface of the laser 1, and the moving distance of the baffle plate 2 is a, wherein a is more than 0 and less than or equal to the radius of the transverse circular surface of the laser.
Based on the above method, the working process of this embodiment will be further described:
as shown in fig. 1, first, a collimated femtosecond laser 1 with a section diameter of 13mm passes through a baffle plate 2, in the current initial state, the vertex on the spot circle of the laser 1 is tangent to the lower edge of the baffle plate 2, as shown in the right spot shielding sectional view of fig. 1, and at this time, the laser 1 is not shielded by the baffle plate 2. Then, the laser 1 passes through a focusing lens 3 with a focal length of 300mm, then passes through a frequency doubling crystal 4 arranged behind the lens to form bicolor laser, and finally ionizes air at the focal point of the focusing lens 3 to form a plasma light wire 5, wherein the light wire 5 is a plasma channel with a length of about 10mm and a diameter of about 0.1 mm; the terahertz waves 6 radiated by the optical fiber 5 are finally measured by a detection system respectively for the time domain signals of the terahertz waves in the X, Y polarization direction.
The shutter 2 starts to move in the y-axis forward direction (i.e., downward direction in the drawing), each time by 1mm. When the shutter 2 is moved to 3mm, as shown in fig. 2. After passing through the baffle plate 2, the laser 1 is in asymmetric distribution in the radial direction, then ionized air is focused again to form optical wires in asymmetric distribution in the radial direction, finally, the time domain signal of the terahertz wave in the X, Y polarization direction of the optical wire radiation is measured, and the time domain signal and the signal in the initial state are put together, as shown in fig. 3. The comparison shows that after the light spot of the laser 1 is blocked, the terahertz signal in the X polarization direction or the Y polarization direction is larger than the corresponding initial signal.
And then continuously moving the baffle plate 2 until the lower edge of the baffle plate 2 is tangent to the lower vertex of the spot circle of the laser 1 after 13 times of movement, namely, the laser spot is completely shielded. We moved baffle 2 to the measured X, Y polarization direction terahertz time-domain signal at different positions throughout the experiment, and took the peak-to-peak value of the amplitude and normalized the result as shown in fig. 4. Wherein the amplitude of the terahertz time-domain signal in the X polarization direction increases from 0.82 to 1 in the range of 0-3mm of the movement of the baffle 2, and the amplitude of the terahertz time-domain signal in the Y polarization direction increases from 0.2 to 0.75 in the range of 0-6mm of the movement of the baffle 2.
Furthermore, the present embodiment further calculates the sum of squares to obtain the terahertz intensity according to the terahertz amplitude peak values in the X and Y polarization directions in fig. 4, and normalizes the result as shown in fig. 5. One can see the following procedure: along with the movement of the baffle plate 2, the area for shielding the light spot of the laser 1 is increased, the radial asymmetry of the light wire pumped by the laser 1 is enhanced, and even if part of pumping energy is lost due to shielding part of laser, the terahertz intensity is obviously enhanced compared with that in the initial state. When the area of the light spot is blocked by nearly half, the baffle plate 2 is continuously moved, the pumping laser energy loss is increased, the terahertz intensity is reduced below the initial signal, and finally, the light wire disappears and the terahertz intensity is reset to zero along with the fact that the light spot is almost completely blocked.
The above description is only of the preferred embodiment of the present invention, and is not intended to limit the present invention in any way. Any person skilled in the art can make many possible variations and modifications to the technical solution of the present invention or modifications to equivalent embodiments using the methods and technical contents disclosed above, without departing from the scope of the technical solution of the present invention. Therefore, all equivalent changes according to the shape, structure and principle of the present invention are covered in the protection scope of the present invention.
Claims (3)
1. The terahertz radiation enhancement method based on the radial asymmetric air plasma is characterized by comprising the following steps of: before the collimated femtosecond laser passes through the lens for focusing, the baffle is used for shielding the laser, the laser passes through the baffle and then is asymmetrically distributed in the radial direction, and then ionized air is focused to form light wires with asymmetrically distributed radial plasma density; and along with the unidirectional movement of the baffle, the area of the shielding laser light spot is increased, the radial asymmetry of the optical fiber is enhanced, the terahertz time-domain peak-to-peak values in the X and Y polarization directions are enhanced, and the terahertz intensity is enhanced.
2. The terahertz radiation enhancement method based on radially asymmetric air plasma according to claim 1, wherein the moving direction of the baffle is parallel to the radial direction of the laser.
3. The terahertz radiation enhancement method based on radially asymmetric air plasma according to claim 2, wherein the baffle starts to move from one side vertex to the other side vertex of the laser cross-cut circular surface, and the moving distance of the baffle is a, wherein 0 < a is smaller than or equal to the radius of the laser cross-cut circular surface.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202311675558.5A CN117805060A (en) | 2023-12-07 | 2023-12-07 | Terahertz radiation enhancement method based on radial asymmetric air plasma |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202311675558.5A CN117805060A (en) | 2023-12-07 | 2023-12-07 | Terahertz radiation enhancement method based on radial asymmetric air plasma |
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| CN117805060A true CN117805060A (en) | 2024-04-02 |
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| CN202311675558.5A Pending CN117805060A (en) | 2023-12-07 | 2023-12-07 | Terahertz radiation enhancement method based on radial asymmetric air plasma |
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