Ultra-wideband terahertz excess current detection system based on gas-phase medium ionization

Abstract

The present application relates to the technical field of terahertz detection, and particularly relates to a super-wideband terahertz residual current detection system based on gas-phase medium ionization, which comprises: a femtosecond laser for emitting femtosecond laser; a beam splitter for splitting the femtosecond laser into two beams, one of which is used as a detection light, and the other of which is focused by a parabolic mirror to generate terahertz radiation, and the terahertz radiation light transmits through a silicon wafer, becomes a parallel light beam through a parabolic mirror, and is focused again by a parabolic mirror; a thin film beam splitter, the two beams are finally focused by the thin film beam splitter; and an electrode for detecting the residual current formed by the accelerated free electrons of the to-be-detected terahertz electric field after the pulse ends. The present application can reconstruct the to-be-detected terahertz electric field, and further can realize the detection of a narrow-pulse-width to-be-detected pulse by a wide-pulse-width detection pulse.

Description

Technical Field

[0001] This invention relates to the field of terahertz detection technology, and more specifically, to a detection system for ultra-wideband terahertz residual current based on gaseous medium ionization. Background Technology

[0002] Current terahertz detection technology is mainly divided into coherent detection technology and incoherent detection technology. The detection technology involved in this patent belongs to air breakdown coherent detection technology. The gaseous medium is tunneled and ionized by femtosecond laser and terahertz pulse. Electrons undergo variable speed motion under the action of the combined field and radiate electromagnetic waves. The electromagnetic waves generated by ionization at different times are coherently superimposed, and then the terahertz electric field is reconstructed based on the field-induced second harmonic.

[0003] However, existing detection technologies have high requirements for the width of the detection pulse, often requiring the detection pulse to be narrower than the pulse to be measured. Summary of the Invention

[0004] In view of this, the present invention proposes an ultra-wideband terahertz residual current detection system based on gas phase medium ionization, mainly to solve the problem that existing detection technologies have high requirements for the detection pulse width, often requiring the detection pulse to be narrower than the pulse to be measured.

[0005] This invention proposes a detection system for ultra-wideband terahertz residual current based on gaseous medium ionization, the system comprising: Femtosecond lasers are used to emit femtosecond laser beams. A beam splitter is used to split the femtosecond laser into two beams. One beam is used as a probe beam. After a time delay is introduced by a high-reflection mirror, it is converged by a plano-convex lens. The other beam is used as the fundamental frequency beam. After passing through a BBO crystal, it is doubled. The fundamental frequency beam and the doubled frequency beam are focused and ionized by a first parabolic mirror to generate gas-phase plasma, which in turn generates terahertz radiation. The terahertz radiation passes through a silicon wafer, becomes a parallel beam by a second parabolic mirror, and is adjusted to horizontal polarization by a metal wire grid polarizer. It is then converged by a third parabolic mirror. The two beams of light split by the beam splitter pass through the thin-film beam splitter again, undergo terahertz transmission, femtosecond laser reflection, and are finally focused and ionized. Electrodes are used to detect the residual current formed after the pulse ends when free electrons accelerated by the terahertz electric field under test are discharged.

[0006] In some embodiments of this application, the femtosecond laser is a horizontally polarized femtosecond laser with a wavelength of 800 nm, a frequency of 1 kHz, and a pulse width of 35 fs.

[0007] In some embodiments of this application, when a beam of light, used as a probe beam, is converged by a plano-convex lens after a time delay introduced by a high-reflectivity mirror, the process further includes: A beam of light is used as a probe beam. After a time delay is introduced by a high-reflectivity mirror, it is converted from horizontal polarization to vertical polarization by a half-glass plate, and then converged by a plano-convex lens.

[0008] In some embodiments of this application, the other beam of light is used as the fundamental frequency light. After passing through a BBO crystal, the light is doubled. When the fundamental frequency light and the doubled light are focused and ionized by the first parabolic mirror to generate gas-phase plasma, and then terahertz radiation is generated, the terahertz radiation is on the picosecond scale.

[0009] Compared with the prior art, the present invention has the following beneficial effects: The ultra-wideband terahertz residual current detection system based on gas phase medium ionization of the present invention, based on terahertz detection technology, can realize the reconstruction of the electric field to be measured, and thus realize the detection of narrow pulse width test pulses by wide pulse width detection pulses. The horizontally polarized femtosecond laser is split into two beams by a beam splitter. One beam is used as the detection beam. The time delay is introduced by a high reflection mirror and it is converged by a plano-convex lens. The other beam is used as the fundamental frequency beam. The frequency-doubled beam is obtained by passing through a BBO crystal. The fundamental frequency beam and the frequency-doubled beam are focused by a first parabolic mirror to ionize the gas, generate gas phase plasma, and then generate terahertz radiation. The terahertz light passes through the silicon wafer, becomes a parallel beam by a second parabolic mirror, and the polarization state of the terahertz light is adjusted to horizontal polarization by a metal wire grid polarizer. It is then converged by a third parabolic mirror. The two beams pass through a thin film beam splitter. The terahertz light is transmitted and the femtosecond laser is reflected, and they act together on the sample. Finally, the femtosecond laser is focused on the gaseous medium to generate free electrons. The terahertz electric field to be measured accelerates the free electrons, and after the pulse ends, they form a residual current, which is detected by the electrode. The electrons are ionized by the combined field of femtosecond laser and terahertz, and under its drive, they undergo variable speed motion and radiate electromagnetic waves. The electromagnetic waves generated at different ionization times are coherently superimposed to obtain a time-domain waveform. When different time delays are introduced, the superimposed time-domain waveforms are different, and thus the residual current detected is different, thereby realizing the reconstruction of the electric field to be measured. Attached Figure Description

[0010] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. In the drawings: Figure 1 This is a schematic diagram of the structure of an ultra-wideband terahertz residual current detection system based on gas phase medium ionization provided in an embodiment of the present invention.

[0011] In the diagram: 1. Femtosecond laser; 2. Beam splitter; 3. High-reflection mirror; 4. Half glass plate; 5. Plano-convex lens; 6. BBO crystal; 7. First parabolic mirror; 8. Silicon wafer; 9. Metal wire grid polarizer; 10. Thin-film beam splitter; 11. Electrode; 12. Second parabolic mirror; 13. Third parabolic mirror. Detailed Implementation

[0012] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0013] See Figure 1 As shown, this invention proposes an ultra-wideband terahertz residual current detection system based on gaseous medium ionization. The system includes: Femtosecond laser 1, used to emit femtosecond lasers; Beam splitter 2 is used to split the femtosecond laser into two beams. One beam is used as a probe beam. After a time delay is introduced by high-reflectivity mirror 3, it is converged by plano-convex lens 5. The other beam is used as the fundamental frequency beam. After passing through BBO crystal 6, it is used to obtain frequency-doubled light. The fundamental frequency beam and the frequency-doubled light are focused and ionized by first parabolic mirror 7 to generate gas phase plasma, which in turn generates terahertz radiation. The terahertz radiation light passes through silicon wafer 8, passes through second parabolic mirror 12 to become a parallel beam, and is adjusted to horizontal polarization by metal wire grid polarizer 9. Then it is converged by third parabolic mirror 13. The two beams of light split by the beam splitter 2 pass through the thin-film beam splitter 10 again, undergo terahertz transmission, femtosecond laser reflection, and are finally focused and ionized. Electrode 11 is used to detect the residual current formed after the terahertz electric field accelerates free electrons to be measured ends the pulse.

[0014] In one specific embodiment of this application, the femtosecond laser is a horizontally polarized femtosecond laser with a wavelength of 800 nm, a frequency of 1 kHz, and a pulse width of 35 fs.

[0015] In one specific embodiment of this application, when a beam of light, used as a probe beam, is converged by a plano-convex lens 5 after a time delay introduced by the high-reflection mirror 3, it further includes: A beam of light is used as a probe beam. After a time delay is introduced by the high-reflection mirror 3, it is converted from horizontal polarization to vertical polarization by the half-glass plate 4, and then converged by the plano-convex lens 5.

[0016] In one specific embodiment of this application, the other beam of light is used as the fundamental frequency light. After passing through the BBO crystal 6, the frequency-doubled light is obtained. When the fundamental frequency light and the frequency-doubled light are focused and ionized by the first parabolic mirror 7 to generate gas phase plasma, and then generate terahertz radiation, the terahertz radiation is on the picosecond level.

[0017] Understandably, in this embodiment, the horizontally polarized femtosecond laser is split into two beams by the beam splitter 2. One beam is used as the probe beam, which is delayed by the high-reflection mirror 3 and converged by the plano-convex lens 5. The other beam is used as the fundamental frequency beam, which is doubled by the BBO crystal 6. The fundamental frequency beam and the doubled frequency beam are focused by the first parabolic mirror 7 to ionize the gas, generating gaseous plasma, which in turn generates terahertz radiation. The terahertz radiation passes through the silicon wafer 8, becomes a parallel beam by the second parabolic mirror 12, and is adjusted to horizontal polarization by the metal wire grid polarizer 9. It is then converged by the third parabolic mirror 13. The two beams then pass through the thin-film beam splitter 10, where the terahertz is transmitted and the femtosecond laser is reflected. Finally, they are focused and ionized. The residual current formed by the accelerated free electrons in the terahertz electric field after the pulse ends is detected by the electrode 11.

[0018] Furthermore, an 800nm ​​femtosecond laser is used for ionization, and a picosecond-level terahertz field is equivalent to a quasi-static electric field. Electrons are ionized by the combined field of the femtosecond laser and the terahertz field and undergo variable-speed motion under its drive, radiating electromagnetic waves. The electromagnetic waves generated at different ionization times are coherently superimposed to obtain a time-domain waveform. When different time delays are introduced, the superimposed time-domain waveforms are different, and thus the residual current detected is different, thereby realizing the reconstruction of the electric field to be measured.

[0019] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0020] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0021] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0022] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable apparatus for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0023] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A detection system for ultra-wideband terahertz residual current based on ionization of a gaseous medium, characterized in that, include: Femtosecond lasers are used to emit femtosecond laser beams. A beam splitter is used to split the femtosecond laser into two beams. One beam is used as a probe beam. After a time delay is introduced by a high-reflection mirror, it is converged by a plano-convex lens. The other beam is used as the fundamental frequency beam. After passing through a BBO crystal, it is doubled. The fundamental frequency beam and the doubled frequency beam are focused and ionized by a first parabolic mirror to generate gas-phase plasma, which in turn generates terahertz radiation. The terahertz radiation passes through a silicon wafer, becomes a parallel beam by a second parabolic mirror, and is adjusted to horizontal polarization by a metal wire grid polarizer. It is then converged by a third parabolic mirror. The two beams of light split by the beam splitter pass through the thin-film beam splitter again, undergo terahertz transmission, femtosecond laser reflection, and are finally focused and ionized. Electrodes are used to detect the residual current formed after the terahertz electric field accelerates free electrons to be measured ends.

2. The detection system for ultra-wideband terahertz residual current based on gaseous medium ionization according to claim 1, characterized in that, The femtosecond laser is a horizontally polarized femtosecond laser with a wavelength of 800 nm, a frequency of 1 kHz, and a pulse width of 35 fs.

3. The detection system for ultra-wideband terahertz residual current based on gaseous medium ionization according to claim 2, characterized in that, A beam of light, used as a probe beam, after being delayed by a high-reflectivity mirror and converged by a plano-convex lens, also includes: A beam of light is used as a probe beam. After a time delay is introduced by a high-reflectivity mirror, it is converted from horizontal polarization to vertical polarization by a half-glass plate, and then converged by a plano-convex lens.

4. The detection system for ultra-wideband terahertz residual current based on gaseous medium ionization according to claim 3, characterized in that, The other beam of light serves as the fundamental frequency light. After passing through a BBO crystal, it is doubled to produce frequency-doubled light. When the fundamental frequency light and the frequency-doubled light are focused and ionized by the first parabolic mirror to generate gas-phase plasma, and then terahertz radiation is generated, the terahertz radiation is on the picosecond scale.

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