Terahertz directional radiation source and implementation method thereof

Abstract

The invention relates to a terahertz directional radiation source and an implementation method thereof, the terahertz directional radiation source is formed by arranging four plasma filaments in a pairwise orthogonal mode, and each plasma filament is formed by ionizing air after laser pulses with the same power are focused. The terahertz source is dominated by directional terahertz radiation perpendicular to the plane where the four light filaments are located, the radiation intensity is increased along with the increase of the length of the light filaments, and meanwhile the directional performance of the terahertz radiation is kept all the time. The terahertz radiation generation method solves the problems of large divergence angle, poor directionality, difficulty in splitting in common-beam transmission with laser filaments and the like of common single-filament radiation terahertz waves, and is expected to promote the development of technologies such as terahertz imaging and the like.

Description

Technical Field

[0001] The invention relates to the field of laser physics, and in particular to a terahertz directional radiation source and a realization method thereof. Background Art

[0002] Terahertz waves usually refer to electromagnetic waves with frequencies between 0.1THz-10 THz, which is an electromagnetic spectrum between far infrared and microwaves. It combines multiple disciplines such as optoelectronics, semiconductors and materials science, and is a field that people are currently vigorously researching and developing.

[0003] Laser ionized air plasma filaments are a powerful broadband terahertz source, which refers to the process of focusing femtosecond lasers using optical devices such as lenses or parabolic mirrors, ionizing air at the focus to form plasma filaments, which then radiate terahertz waves. This terahertz source has good application prospects, such as non-destructive testing, remote sensing, near-field imaging, ultrafast switching, dynamic control and biological detection.

[0004] However, the application of terahertz sources based on plasma filaments also faces some practical challenges, especially the lack of effective methods to make terahertz radiation directional. This is because the terahertz wave radiated by a single filament diverges in a forward cone image, and the main direction is co-beamed with the laser filament, so the terahertz wave is bound to be mixed with the laser for transmission, which brings many inconveniences to the further application of terahertz waves. Although terahertz waves and lasers can be separated by devices such as beam splitters, the separation process will introduce losses, resulting in a huge loss of terahertz energy. Summary of the invention

[0005] In order to solve the problem that the terahertz waves radiated by the above-mentioned laser plasma filaments are transmitted in the same beam as the laser in direction and are difficult to separate, a terahertz directional radiation source and its implementation method are proposed. The method is simple and effective. By constructing a four-filament array with four filaments orthogonal to each other, the terahertz waves can be directional-radiated perpendicular to the plane of the four-filaments, so that the terahertz waves can be better separated from the laser in direction, which is convenient for the subsequent terahertz applications.

[0006] The technical solution of the present invention is:

[0007] A terahertz directional radiation source based on orthogonal four-filaments, which is composed of four plasma filaments arranged orthogonally in pairs, that is, the angle between adjacent filaments is 90°, the four filaments are in the same plane, and each filament is formed by focusing laser pulses of the same power to ionize the air.

[0008] A method for realizing a terahertz directional radiation source based on orthogonal four-filaments, wherein a laser pulse Laser first passes through a beam splitter BS1, partially transmitted and partially reflected; the reflected pulse then passes through a beam splitter BS2, also partially transmitted and partially reflected; the pulse reflected by BS2 is focused by a lens L1, and the pulse transmitted by BS2 is focused by a lens L4 after being reflected twice by mirrors M1 and M2; at the same time, the pulse transmitted by BS1 passes through a beam splitter BS3, partially transmitted and partially reflected; the pulse reflected by BS3 is focused by a lens L3, and the pulse transmitted by BS3 is focused by a lens L2 after being reflected twice by mirrors M3 and M4; finally, four laser pulses of the same power are focused by lenses L1, L2, L3 and L4 respectively, and ionize air near the focus to form four plasma filaments, which are arranged orthogonally in pairs, and the terahertz waves radiated by the four filaments mainly generate directional terahertz radiation perpendicular to the plane where the four filaments are located.

[0009] The beneficial effects of the present invention are:

[0010] The terahertz directional radiation source based on orthogonal four-filaments is dominated by directional terahertz radiation perpendicular to the plane where the four-filaments are located, and the radiation intensity increases with the increase of the length of the filaments, while the directional performance of the terahertz radiation is always maintained. This terahertz radiation generation method solves the problems of large divergence angle, poor directivity, and poor separation of terahertz waves in common single-filament radiation and laser filament co-beam transmission, and is expected to promote the development of technologies such as terahertz imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 Schematic diagram of the experimental device structure and terahertz radiation of a single laser plasma filament; (a) is a diagram of the experimental device of a single filament; (b) is a 3D diagram of the terahertz wave radiated by a single filament;

[0012] Figure 2 The schematic diagram of the structure of the experimental device of the orthogonal four-wire and the terahertz radiation of the present invention; (a) is a diagram of the experimental device of the four-wire; (b) is a 3D diagram of the terahertz wave radiated by the four-wire;

[0013] Figure 3 This is a comparison diagram of the terahertz radiation directivity of a single filament and orthogonal four filaments when the length of the filament gradually increases from 0 mm to 2.5 mm. For a single filament, each value in the diagram is equal to the maximum terahertz radiation intensity perpendicular to the filament axis divided by the maximum terahertz radiation intensity along the filament axis; for four filaments, each value in the diagram is equal to the maximum terahertz radiation intensity perpendicular to the filament plane divided by the maximum terahertz radiation intensity in the filament plane. DETAILED DESCRIPTION

[0014] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0015] A terahertz directional radiation source based on orthogonal four-filaments, which is composed of four plasma filaments arranged orthogonally in pairs, that is, the angle between adjacent filaments is 90°, the four filaments are in the same plane, and each filament is formed by focusing laser pulses of the same power to ionize the air.

[0016] We conducted single filament and four filament terahertz radiation experiments. The experimental setup and terahertz radiation results are shown in the figure. Figure 1 , 2 shown.

[0017] First, if Figure 1 As shown in (a), the laser pulse (Laser) is focused by lens L1, ionizing the air near the focus to produce a single plasma filament, which radiates terahertz waves, which is a forward cone-shaped radiation along the filament axis, such as Figure 1 (b)

[0018] Secondly, if Figure 2 As shown in (a), the laser pulse (Laser) first passes through the beam splitter BS1, which is partially transmitted and partially reflected. The reflected pulse then passes through the beam splitter BS2, which is also partially transmitted and partially reflected. The pulse reflected by BS2 is focused by lens L1, and the pulse transmitted by BS2 is focused by lens L4 after being reflected twice by mirrors M1 and M2. At the same time, the pulse transmitted by BS1 passes through the beam splitter BS3, which is partially transmitted and partially reflected. The pulse reflected by BS3 is focused by lens L3, and the pulse transmitted by BS3 is focused by lens L2 after being reflected twice by mirrors M3 and M4. Finally, four laser pulses of the same power are focused by lenses L1, L2, L3 and L4 respectively, and ionize the air near the focus to form four plasma filaments. These filaments are arranged orthogonally in pairs. The terahertz waves radiated by the four filaments mainly produce directional terahertz radiation perpendicular to the plane where the four filaments are located, as shown in Figure 2. Figure 2 (b) as shown.

[0019] Then, we gradually increased the laser input energy to gradually lengthen the single filament until it reached 2.5 mm. In this process, we calculated the ratio of the maximum terahertz radiation intensity of the single filament perpendicular to the filament axis to the maximum terahertz radiation intensity along the filament axis, and the ratio of the maximum terahertz radiation intensity of the four filaments perpendicular to the filament plane to the maximum radiation intensity in the plane, as indicators of the terahertz radiation directionality. The results are shown in Figure 2. Figure 3 As shown in the figure, it can be seen that at different single-filament lengths, the four-filament designed by us is better than the single-filament in the terahertz radiation directionality. However, as the length of the single-filament increases further, the directionality of the four-filament gradually weakens.

[0020] Nevertheless, as the length of a single filament increases, the intensity of the terahertz radiation increases, and the four filaments we designed still mainly produce directional terahertz radiation perpendicular to the filament plane, and maintain good directionality. This not only solves the problems of large divergence angle, poor directionality, and difficulty in separating the common beam transmission with the laser filament from the ordinary single filament, but also has the potential to promote the development of terahertz imaging and other technologies.

[0021] The above-mentioned embodiment only expresses one implementation mode of the present invention, and its description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A terahertz directional radiation source, characterized in that: It consists of four plasma filaments arranged orthogonally in pairs, that is, the angle between adjacent filaments is 90°, the four filaments are in the same plane, and each filament is formed by focusing laser pulses of the same power to ionize the air.

2. A method for realizing a terahertz directional radiation source, characterized in that: The laser pulse Laser first passes through the beam splitter BS1, partially transmitted and partially reflected; the reflected pulse then passes through the beam splitter BS2, also partially transmitted and partially reflected; the pulse reflected by BS2 is focused by lens L1, and the pulse transmitted by BS2 is focused by lens L4 after being reflected twice by mirrors M1 and M2; at the same time, the pulse transmitted by BS1 passes through the beam splitter BS3, partially transmitted and partially reflected; the pulse reflected by BS3 is focused by lens L3, and the pulse transmitted by BS3 is focused by lens L2 after being reflected twice by mirrors M3 and M4; Finally, four laser pulses of the same power are focused by lenses L1, L2, L3 and L4 respectively, and ionize the air near the focus to form four plasma filaments. These filaments are arranged orthogonally in pairs. The terahertz waves radiated by the four filaments mainly produce directional terahertz radiation perpendicular to the plane where the four filaments are located.

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