A nanosecond terahertz pulse sequence generation system

Abstract

The present application discloses a system for generating a nanosecond terahertz pulse sequence, comprising: a wave source for generating a terahertz wave in the form of a Gaussian beam; a beam splitting optical path for dividing the terahertz wave into n terahertz waves, where n≥2; n single pulse generating optical paths, where the n terahertz waves are timed to generate n terahertz single pulses with amplified wave source power through the corresponding single pulse generating optical paths; a beam combining optical path for sequentially combining the n terahertz single pulses into one terahertz wave pulse sequence with amplified output power; and a laser driving component for controlling the generation timing of the n terahertz single pulses and the synthesis order of the n terahertz single pulses. The present application can generate a high-power terahertz pulse sequence with controllable timing.

Description

Technical Field

[0001] The present application belongs to the field of terahertz, and more specifically, to a system for generating a nanosecond terahertz pulse sequence. Background Art

[0002] Electron spin resonance spectrometer, also known as ESR spectrometer, is the main analytical instrument for studying the electron spin resonance phenomenon of matter. According to the type of wave source, ESR spectrometers are divided into continuous wave spectrometers and pulsed wave spectrometers. Among them, for pulsed wave ESR, high frequency can improve the polarization intensity, spectral resolution and sensitivity of the spectrometer; high power can shorten the π / 2 time of the spectrometer, improve the time resolution, and make many substances that cannot be detected at low power detectable. The difficulty of pulsed wave ESR compared to continuous wave is that it requires a wave source to generate a pulse sequence composed of multiple microwave pulses with a pulse width of several to hundreds of nanoseconds. The higher the power, the shorter the pulse width. At kilowatt-level power, the pulse width only needs 5ns. Therefore, the development of nanosecond-level, terahertz-band, and high-power pulse sequence generation technology is of great significance to improving the performance of pulsed wave ESR spectrometers.

[0003] At present, the most commonly used methods for generating terahertz wave pulse sequences include the following two: one is to directly generate pulse sequences through solid-state wave sources. The power generated by this method is relatively small, usually only in the hundreds of milliwatts level; the other is to amplify low-frequency, low-power microwave pulses into high-power terahertz pulses through vacuum devices such as cyclotron amplifiers and traveling wave amplifiers. The frequency and power of this method are also limited. When the frequency exceeds 200GHz, the power level will drop significantly. In addition, vacuum devices such as cyclotrons have the ability to generate high-frequency, high-power terahertz pulses, but the pulse width of the pulse waves they generate is usually in the millisecond level, which does not meet the requirements of pulse ESR and needs to be further processed with the subsequent optical path.

[0004] Therefore, how to generate high-power terahertz pulse sequences is an urgent problem to be solved. Summary of the invention

[0005] In view of the defects of the prior art, the purpose of the present application is to provide a nanosecond terahertz pulse sequence generation system, aiming to solve the problem that traditional terahertz wave pulse sequence generation systems are difficult to generate high-power terahertz pulse sequences.

[0006] To achieve the above objectives, the present application provides a system for generating a nanosecond terahertz pulse sequence, comprising:

[0007] a wave source for generating terahertz waves in the form of Gaussian beams;

[0008] A beam splitting optical path, used for splitting the terahertz wave into n terahertz waves, where n≥2;

[0009] n single pulse generating optical paths, n terahertz waves pass through corresponding single pulse generating optical paths to generate n terahertz single pulses with amplified wave source power in a timely manner;

[0010] A beam combining optical path, used to sequentially combine n terahertz single pulses into one, outputting a terahertz wave pulse sequence with amplified output power;

[0011] The laser driving component is used to control the generation timing of n-channel terahertz single pulses and the synthesis order of n-channel terahertz single pulses.

[0012] The nanosecond terahertz pulse sequence generation system provided in the present application generates n terahertz single pulses with amplified wave source power through n single pulse generation optical paths, and then combines them into one pulse in sequence through a beam combining optical path, and controls the output timing with a laser driving component, thereby generating a high-power and timing-controllable terahertz pulse sequence.

[0013] As a further preferred embodiment, the single pulse generating optical path includes a Fabry-Perot resonant cavity, a first beam splitter and a first semiconductor chip driven by laser, each terahertz wave is reflected and coupled into the Fabry-Perot resonant cavity through the corresponding first beam splitter to resonate, and the first semiconductor chip reflects all the electromagnetic energy accumulated in the resonant cavity under the irradiation of the first laser, thereby generating a terahertz single pulse whose power is amplified by dozens of times relative to the wave source power;

[0014] The laser driving component is used to emit n first lasers and n-1 second lasers in a time sequence;

[0015] The beam combining optical path includes n-1 second semiconductor chips driven by lasers, which are used to sequentially combine n terahertz single pulses into one under the control of n-1 second lasers to output a terahertz wave pulse sequence with amplified output power; wherein the second laser irradiated to the i-th second semiconductor chip irradiates after the i-th terahertz single pulse is generated.

[0016] As a further preferred embodiment, the Fabry-Perot resonant cavity uses two spherical reflectors facing each other with an adjustable spacing;

[0017] In each single pulse generating optical path, the first beam splitter and the first semiconductor chip are arranged between two spherical reflectors, the axis of the spherical reflector is orthogonal to the optical axis of the terahertz wave incident into the single pulse generating optical path, the axis of the first beam splitter and the axis of the spherical reflector are 45 degrees, and the axis of the first semiconductor chip is 45 degrees to the axis of the first beam splitter and is orthogonal to the first beam splitter.

[0018] As further preferred, the single pulse generating optical path further includes a first laser beam expander and a first laser reflecting mirror, which are used to control the optical axis of the first laser of the first semiconductor wafer and the axis of the first laser beam expander to be located in the XOY plane and to have a certain angle with the axis of the first semiconductor wafer;

[0019] The first laser reflecting mirror is used to reflect the laser for controlling the first semiconductor chip to the first laser beam expander, and the first laser beam expander is used to enlarge the light spot of the reflected laser and make the center of the light spot located at the center of the first semiconductor chip.

[0020] As a further preference, the single pulse generating optical path further comprises a displacement platform, and the displacement platform is used to adjust the distance between the two spherical reflectors so as to match the frequency of the terahertz wave incident on the single pulse generating optical path.

[0021] As a further preferred embodiment, the beam splitting optical path includes n-1 second beam splitters with a certain splitting ratio and n-1 first off-axis parabolic reflectors, the optical axis of the terahertz wave incident into the beam splitting optical path is parallel to the Y axis, the axis of the second beam splitter is at an angle of 45 degrees to the X axis, the first off-axis parabolic reflector is installed parallel to the X axis and the Y axis, and the incident center of the first off-axis parabolic reflector and the axis of the second beam splitter are both located in the XOY plane; the n-1 first off-axis parabolic reflectors and the n-1 second beam splitters are spaced at a distance d s Alternately arranged along the X and Y axes, the spacing d s It is determined by the focal length of the first off-axis parabolic reflector and the frequency and waist radius of the terahertz wave incident into the split beam path, and is used to ensure that each second beam splitter is located at the waist of the Gaussian beam.

[0022] As a further preferred embodiment, the beam combining optical path further comprises n-1 second off-axis parabolic reflectors, the optical axis of the terahertz single pulse incident into the beam combining optical path is parallel to the X-axis, the second off-axis parabolic reflectors are installed parallel to the X-axis and the Y-axis, the axis of the second semiconductor wafer is located in the XOY plane and is 45 degrees to the X-axis; the n-1 second off-axis parabolic reflectors and the n-1 second semiconductor wafer are spaced at a distance d o Alternately arranged along the X and Y axes, the spacing d o It is determined by the focal length of the second off-axis parabolic reflector and the frequency and waist radius of the terahertz single pulse entering the combined beam path, and is used to ensure that each second semiconductor wafer is located at the waist of the Gaussian beam.

[0023] As further preferred, the beam combining optical path further includes a second laser beam expander and a second laser reflector, which are used to control the optical axis of the second laser of the second semiconductor wafer and the axis of the second laser beam expander to be located in the XOY plane, and there is a certain angle between the axis of the second semiconductor wafer;

[0024] The second laser reflector is used to reflect the laser for controlling the second semiconductor chip to the second laser beam expander; the second laser beam expander is used to enlarge the light spot of the reflected laser so that the center of the light spot is located at the center of the second semiconductor chip.

[0025] As a further preferred embodiment, the laser driving component includes an arbitrary sequence generator and n lasers; the arbitrary sequence generator is used to drive each laser to emit laser in a time sequence, and the laser emitted by each laser is divided into two beams by a laser beam splitter, one beam is irradiated to the first semiconductor chip in the i-th single pulse generation optical path, and the other beam is irradiated to the i-th second semiconductor chip, and the second laser irradiated to the i-th second semiconductor chip is irradiated after the i-th terahertz single pulse is generated by means of an optical path difference.

[0026] As a further preference, the wave source is a continuous wave source or a pulse wave source with a pulse width above microsecond level; when the wave source is a pulse wave source, the wave source sends an electrical signal to an arbitrary sequence generator when outputting terahertz waves. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a structural diagram of a system for generating a nanosecond terahertz pulse sequence provided in one embodiment of the present application;

[0028] Figure 2 is a structural diagram of a beam splitting optical path provided in an embodiment of the present application;

[0029] Figure 3 is a structural diagram of a single pulse generating optical path provided by an embodiment of the present application;

[0030] Figure 4 is a structural diagram of a beam combining optical path provided in an embodiment of the present application;

[0031] Figure 5 The specific embodiments of the present application provide a theoretical calculation result (a) of a time domain variation curve of the power in the resonant cavity in the single pulse generation optical path, a simulation calculation result (b) of a variation curve of the power received by the detector in the single pulse generation optical path with the distance between the reflectors, and a theoretical calculation result (c) of a single pulse waveform generated by the single pulse generation optical path;

[0032] Figure 6 The timing waveform diagram of the voltage pulse signal, laser signal and four-pulse sequence provided in the specific embodiment of the present application. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0034] It should be understood that, in the description of the present application, the term "several" means at least one, such as one, two, etc., unless otherwise clearly and specifically defined; the term "plurality" means two or more, unless otherwise clearly and specifically defined; the terms "first" and "second" etc. are used to distinguish different objects rather than to describe a specific order of objects; the term "and / or" includes any and all combinations of one or more related listed items.

[0035] In addition, references throughout this specification to "one embodiment"; "one embodiment", "an example" or similar language indicate that a particular feature, structure, or characteristic described in conjunction with the embodiment is included in at least one embodiment of the present application. Thus, appearances of the phrase "in one embodiment"; "in one embodiment" and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0036] In order to generate a power-amplified terahertz pulse sequence, the present application provides a system for generating a nanosecond terahertz pulse sequence, such as Figure 1 As shown, the generating system includes a wave source, a beam splitting optical path, n single pulse generating optical paths, a laser driving component and a beam combining optical path.

[0037] Among them, for the wave source, its function is to generate terahertz waves.

[0038] Specifically, the wave source provided in this embodiment can be a continuous wave source or a pulse wave source with a pulse width above microsecond level, and the output wave needs to be transformed into a Gaussian beam that can be transmitted over long distances.

[0039] The function of the beam splitting optical path is to split the terahertz wave output by the wave source into n terahertz waves with a certain power ratio, where n≥2.

[0040] Specifically, Figure 2 As shown, the beam splitting optical path provided in this embodiment can use a beam splitter with a certain splitting ratio to split a beam of terahertz waves into two beams of terahertz waves with corresponding power ratios, and use a multi-stage beam splitter to split the terahertz waves emitted by the wave source into multiple terahertz waves with a certain power ratio. In addition, the terahertz wave generated by the wave source is a Gaussian beam, and an off-axis parabolic reflector is used to transmit the terahertz wave to avoid its divergence during transmission, and the beam splitter is always located at the waist of the Gaussian beam, thereby obtaining a higher beam splitting efficiency.

[0041] For n single pulse generating optical paths, each terahertz wave passes through the corresponding single pulse generating optical path to generate n terahertz single pulses with amplified wave source power in a timely manner.

[0042] Specifically, the single pulse generation optical path provided in this embodiment can adopt a Fabry-Perot resonant cavity, a beam splitter and a semiconductor chip driven by a laser. Each terahertz wave is reflected and coupled into the resonant cavity through the corresponding beam splitter to resonate. Under the irradiation of the laser, the semiconductor chip reflects all the electromagnetic energy accumulated in the resonant cavity, generating a terahertz single pulse whose power is amplified dozens of times relative to the wave source power.

[0043] like Figure 3 As shown, the Fabry-Perot resonant cavity in each single pulse generation optical path can use two spherical reflectors with opposite sides and adjustable spacing. In each single pulse generation optical path, the beam splitter and the semiconductor chip are arranged between the two spherical reflectors, and the axis of the spherical reflector is orthogonal to the optical axis of the incident terahertz wave (here is a Gaussian beam). The incident wave is coupled into the resonant cavity through a low-reflectivity beam splitter, and the axis of the beam splitter and the axis of the reflector are at a 45-degree angle. The distance L between the two spherical reflectors can be adjusted using a displacement platform. When the distance L matches the frequency of the incident wave, the resonant cavity resonates, and the frequency of the incident wave is the resonant frequency. The wave coupled into the resonant cavity is continuously reflected and accumulated in the resonant cavity, reaching saturation within a few microseconds, and its internal power is also amplified by dozens of times relative to the wave source. The semiconductor chip, whose reflectivity rises rapidly when irradiated by laser, reflects all the electromagnetic energy accumulated in the resonant cavity within a few nanoseconds, generating a terahertz pulse that is amplified dozens of times relative to the source power. The axis of the semiconductor chip forms an angle of 45 degrees with the axis of the beam splitter and is orthogonal to the beam splitter.

[0044] The function of the beam combining optical path is to combine multiple terahertz pulses in sequence into one path to obtain a terahertz pulse sequence.

[0045] Specifically, Figure 4 As shown, the beam combining optical path includes n-1 semiconductor chips whose reflectivity is driven by laser. For the beam combining optical path, when there is no laser irradiation, the i-th semiconductor chip fully transmits the terahertz single pulse Ai (i=1, 2, ..., n-1). When there is laser irradiation, its reflectivity toward the laser surface rises rapidly, and it fully reflects the single pulses Ai+1, Ai+2, ..., An, thereby achieving the beam combining of the terahertz single pulses Ai~An. Therefore, the laser irradiating the i-th semiconductor chip must be irradiated after the single pulse Ai is generated. The laser used in the optical path for generating the single pulse Ai can be emitted by the same laser, divided into two beams by a laser beam splitter, and then the time of irradiating the semiconductor chip is adjusted by the optical path difference.

[0046] The laser driving component is used to control the generation timing and synthesis order of n terahertz single pulses, that is, to send laser to the semiconductor chips in the single pulse generation optical path and the beam combining optical path according to the timing.

[0047] Specifically, the laser driving component may include an arbitrary sequence generator and n lasers. The arbitrary sequence generator is used to drive each laser to emit laser in a time sequence, and the laser emitted by each laser is divided into two beams by a laser beam splitter, one beam is irradiated to the semiconductor chip in the i-th single pulse generation optical path through a laser reflector and a laser beam expander, and the other beam is irradiated to the i-th semiconductor chip in the beam combining optical path through a laser reflector and a laser beam expander, and the laser irradiated to the i-th semiconductor chip in the beam combining optical path is irradiated after the single pulse i is generated by means of an optical path difference.

[0048] It should be noted that the laser reflector provided in this embodiment is used to reflect the laser for controlling the semiconductor wafer to the laser beam expander, and the laser beam expander is used to enlarge the spot of the reflected laser so that the center of the spot is located at the center of the semiconductor wafer.

[0049] The entire working principle of the system for generating a nanosecond terahertz pulse sequence provided in this embodiment is as follows: the terahertz wave generated by the wave source is divided into multiple terahertz waves with a certain power ratio through a beam splitting optical path, each terahertz wave is timed to generate n terahertz single pulses through n single pulse generating optical paths driven by a laser, and finally, the n terahertz pulses are sequentially synthesized into one path through a beam combining optical path also driven by a laser to obtain a terahertz pulse sequence. Among them, the laser that controls the single pulse generating optical path and the beam combining optical path is generated by the same laser and is divided into two beams by a laser beam splitter. The laser can be controlled by a voltage pulse signal sequence generated by any sequence generator, and the moment of laser driving is controlled by the voltage pulse signal to control the moment of generating the terahertz single pulse.

[0050] The system for generating a nanosecond terahertz pulse sequence provided in this embodiment divides the terahertz wave generated by a wave source into multiple paths through a beam splitting optical path, and uses a Fabry-Perot resonant cavity to increase the power of the terahertz pulse on the one hand, and on the other hand, utilize the energy storage function of the resonant cavity to make the timing of the pulse sequence controllable, thereby generating a power-amplified and timing-controllable terahertz pulse sequence and reducing the burden on the wave source; in addition, since a laser-driven semiconductor chip is used to interrupt the terahertz wave, this method can be used to generate terahertz pulse sequences with higher frequency (6THz) and higher power (MW level).

[0051] The system for generating a nanosecond terahertz pulse sequence provided by the present application is described in detail below in conjunction with specific embodiments.

[0052] The generation system provided in this specific embodiment includes:

[0053] n sets of single pulse generation optical path modules, n is the number of pulses required, each set of single pulse generation optical path includes two spherical reflectors SM1, SM2, a beam splitter S i, i = 1, 2, ..., n, i represents the ith single pulse in the pulse sequence, and a Fabry-Perot resonant cavity composed of a displacement platform DP, a semiconductor chip W i , a laser beam expander E and a laser reflecting mirror FM. In addition, the n sets of single pulse generation optical paths share a terahertz power meter D.

[0054] A set of beam splitting optical path modules for splitting terahertz waves into multiple paths, including n-1 beam splitters S S1 ~S Sn-1 , n-1 off-axis parabolic reflectors PM.

[0055] A beam combining optical path module for combining multiple terahertz pulses into one, including n-1 semiconductor chips W O1 ~W On-1 , n-1 off-axis parabolic mirrors PM, n-1 laser beam expanders E and n-1 laser reflectors FM.

[0056] The laser driving component includes n lasers and an arbitrary sequence generator.

[0057] A series of off-axis terahertz parabolic mirrors and laser flat mirrors are used to build the terahertz and laser transmission optical paths between modules.

[0058] Taking a four-pulse pulse sequence as an example (n=4), the installation relationship of each component in each optical path module in this application, the terahertz wave transmission path, the working process, and the connection relationship and timing control flow between each module are as follows:

[0059] First, the terahertz Gaussian beam emitted by the wave source is used as the incident wave to input into the beam splitting optical path module, such as Figure 2 As shown in the figure, the XOY plane is a horizontal plane, and the incident wave optical axis is parallel to the Y axis. The four off-axis parabolic reflectors PM are installed parallel to the X axis and the Y axis. They can reflect the terahertz wave at 90 degrees. The axes of the three beam splitters are at an angle of 45 degrees to the X axis. The incident center of the off-axis parabolic reflector PM and the axis of the beam splitter are both located in the XOY plane. The off-axis parabolic reflector PM and the beam splitter are spaced at a distance d. s , arranged alternately along the X and Y axes with a spacing of d s The focal length of the off-axis parabolic reflector, the frequency of the incident wave, and the beam waist radius are determined to ensure that the three beam splitters are located at the beam waist of the Gaussian beam. For the transmission path of the terahertz wave in the splitting optical path, the incident wave is reflected by the off-axis parabolic reflector and passes through the first beam splitter S S1 , part of the light is transmitted as the first outgoing wave, and the other part is reflected and reflected again by the off-axis parabolic reflector and passes through the second beam splitter S S2The transmitted part serves as the second outgoing wave, and the remaining reflected part is further divided into multiple paths by the subsequent beam splitter, and finally multiple outgoing waves are generated, which will serve as the incident wave of the single pulse generating optical path.

[0060] Secondly, the four outgoing waves of the split beam path enter the corresponding four single pulse generating light paths as incident waves. Figure 3 As shown in the figure, the XOY plane is the horizontal plane, the Y axis is the optical axis of the incident wave, the two spherical reflectors SM1 and SM2, the beam splitter S i , semiconductor wafer W i The axes of the mirrors SM1 and SM2 are all in the XOY plane. The axes of the mirrors SM1 and SM2 coincide with the X axis. i and semiconductor wafer W i The axis of the laser beam expander E is at an angle of 45 degrees and -45 degrees to the X-axis respectively, and the center is on the X-axis. The center of the beam splitter coincides with point O in the figure. The optical axis of the laser used to control the semiconductor wafer and the axis of the laser beam expander E are also located in the XOY plane, and there is a small angle between them and the axis of the semiconductor wafer. This is to prevent the laser reflected by the semiconductor wafer from damaging the laser.

[0061] The resonance principle of this resonant cavity is as follows: the incident wave passes through the beam splitter S i , a small part is reflected and coupled into the resonant cavity, and reflected between the two mirrors. As time accumulates, the terahertz waves coupled into the resonant cavity at different times are superimposed on each other. If they have the same phase, they are superimposed on each other. The resonant frequency of the resonant cavity is consistent with the incident wave, and resonance occurs. In this state, the time domain change curve of the power of the terahertz wave reflected between the mirrors in the resonant cavity is as follows: Figure 5 As shown in part (a), saturation is reached within a few microseconds, and the power amplification is about 30 times the incident wave power, which means that the resonant cavity can be used not only for continuous waves, but also for power storage and amplification of terahertz pulse waves with a pulse width exceeding a few microseconds. The phase relationship is determined by the distance between the reflectors. The distance between the reflectors when resonance occurs can be roughly estimated as L = c(q+0.5) / (2f), where f is the frequency of the incident terahertz wave, c is the speed of light, and q is the number of longitudinal modes, which is an integer. In actual work, the resonant frequency of the resonant cavity is mainly determined by the distance between the reflectors, but it will also be interfered by other factors, so it needs to be tuned by fine-tuning the distance between the reflectors. In this process, the spherical reflector SM2 and the semiconductor chip W i , beam splitter S i The positions of the laser and the laser beam expander are fixed relative to the incident wave. The spherical reflector SM1 is installed on the displacement platform DP so that it can move along the X-axis. At the same time, the terahertz power meter D is installed so that its axis coincides with the Y-axis. The power of the terahertz wave emitted from the beam splitter is observed during the movement of SM1. If the following occurs: Figure 5The power spike shown in part (b) indicates that the resonant cavity has reached a resonant state.

[0062] After the resonance of the resonant cavity is established, the laser emits a laser, which enlarges the light spot through a laser beam expander and irradiates the semiconductor wafer located on the optical path of the resonant cavity. When there is no laser irradiation, the semiconductor wafer is almost completely transparent to the terahertz wave through appropriate thickness design, so it has almost no effect on the establishment of resonance. When irradiated by laser, the reflectivity of the semiconductor wafer rises rapidly within nanoseconds until it is fully reflected, which destroys the resonant state of the resonant cavity. The terahertz waves reflected back and forth between the reflectors are reflected through the semiconductor wafer, releasing the accumulated electromagnetic energy. This process is basically completed after the terahertz wave is reflected back and forth between the reflectors once, and all the energy is released, thereby generating a single terahertz pulse with a power amplified dozens of times and a pulse width of nanoseconds. The pulse waveform is as follows Figure 5 The power amplification factor is equivalent to the amplification factor when the resonant cavity accumulates energy, and the pulse width is given by Figure 3 It is determined by L1, which is approximately L1 / c, where L1 is the distance between the semiconductor chip and the left spherical mirror.

[0063] Finally, the generated multi-channel terahertz pulses are combined into one channel through the beam combining optical path module. Figure 4 As shown in the figure, the XOY plane is a horizontal plane, and the incident wave optical axis is parallel to the X axis. The three-sided off-axis parabolic reflector PM is installed parallel to the X axis and the Y axis, and the semiconductor wafer W O1 ~W O3 The axis of the off-axis parabolic reflector is located in the XOY plane and is at an angle of 45 degrees to the X axis. o , arranged alternately along the X and Y axes, with the same spacing as in the beam splitting optical path, to ensure that the three semiconductor chips are located at the waist of the Gaussian beam. The optical axis of the laser used to control the semiconductor chip and the axis of the laser beam expander E are also located in the XOY plane, with a small angle between them and the axis of the semiconductor chip. The beam combining process of multiple terahertz single pulses in this optical path is as follows:

[0064] At the beginning, there is no laser irradiation on the three sides of the semiconductor wafer, and the terahertz single pulse A1 is generated first (A1, A2, A3, A4 are the pulse generation order), W O1 It is completely transmitted. When the single pulse A1 passes through completely (according to Figure 5 In part (c), the pulse duration is a few nanoseconds), the laser irradiates W O1 , its reflectivity rises rapidly. According to the characteristics of semiconductors, the high reflectivity state can last for tens of microseconds. O1 When W is irradiated, it is almost totally reflected, thus realizing the beam combination of single pulse A1 and single pulse A2. O1The laser needs to be driven with lag to generate the single pulse A1. The laser in the optical path lags by more than a few nanoseconds. This is achieved by the optical path difference, that is, they are generated by the same laser, and the optical path they take to reach the semiconductor wafer differs by 2 to 3 meters. After that, the combined pulse of single pulses A1 and A2 and the further combination of single pulses A3 and A4 are achieved in the same way.

[0065] Regarding the connection relationship and timing control process between the three modules of the beam splitting optical path, the single pulse generating optical path and the beam combining optical path, such as Figure 1 As shown. If the terahertz wave source is a continuous wave source, the wave source and the beam splitting optical path do not need to be controlled. The terahertz wave output by the wave source is divided into four paths through the beam splitting optical path, and then enters four tuned terahertz single pulse generation optical paths through the terahertz transmission system composed of off-axis parabolic reflectors. After a period of energy accumulation, the arbitrary sequence generator sends pulse electrical signals to the four lasers in sequence. The lasers emit lasers in sequence and are transmitted to the semiconductor chip through the laser transmission optical path composed of plane reflectors. The timing of arriving at the semiconductor chip is: W1-W O1 -W2-W O2 -W3-W O3 After laser irradiation of W1~4, terahertz single pulses A1~A4 are generated, which enter the beam combining path through the terahertz transmission system composed of off-axis parabolic reflectors, and finally form a terahertz pulse sequence, which can be input into the subsequent ESR spectrometer for scientific experiments.

[0066] If the terahertz wave source is a pulse wave source, then the wave source needs to send an electrical signal to the arbitrary sequence generator when it outputs. After receiving the signal, it waits for tens of microseconds, and the energy accumulation of the four resonant cavities is basically completed. The arbitrary pulse sequence sends pulse electrical signals to the four lasers respectively, and the rest of the working process is the same as that of the continuous wave source.

[0067] The device parameters and equipment model selected in this specific embodiment are used to achieve the generation of a four-pulse terahertz pulse sequence. The frequency of the terahertz wave is 240 GHz, the pulse width of each pulse is 3.3 ns, the interval between adjacent pulses is 50 ns, the power of each pulse is equal, and the power amplification factor is 32.

[0068] In terms of equipment, the terahertz wave source uses a solid-state wave source model FT18230250-22 produced by VDI, which can generate terahertz waves with a frequency of 230 to 260 GHz and a power of 100 milliwatts. After passing through a corrugated horn, it can be transformed into a Gaussian beam with a waist radius of about 10 mm. The laser uses a nanosecond laser model Q-smart450 produced by Quantel laser, which can output a pulse width of 6 ns, a single pulse energy of more than 220 mJ, and a strong laser with a wavelength of 532 nm, which is enough to drive any semiconductor switch. The arbitrary pulse sequence generator model ASG8005 produced by Guoyi Quantum was selected, which has a time resolution of 50 ps and a pulse width of 7.5 ns to 2.6 s, meeting the driving requirements of the laser Q-smart 450. The terahertz power meter D uses a power meter of model 3A-Fs produced by Ophir, which can measure a power range of 8μW to 3W and a frequency range of 190GHz to 20THz.

[0069] For the beam splitting path, an off-axis parabolic reflector with an effective focal length of 250 mm is used. The material is hard aluminum plated with gold. The interval between the beam splitter and the reflector is 250 mm (d in the figure). s ≈250mm), so that it is always located at the waist of the Gaussian beam, and the beam radius is 10mm. The beam splitter is made of multiple layers of fused quartz wafers stacked together, with air between the layers. S1 By stacking three layers of quartz sheets with a thickness of 0.7mm and a spacing of 1.2mm between the layers, a reflectivity of 75% and a splitting ratio of 1:3 can be achieved; S S2 By stacking two layers of quartz sheets with a thickness of 0.7 mm and a layer spacing of 1.3 mm, a reflectivity of 66% and a splitting ratio of 1:2 can be achieved; S S1 By stacking two layers of quartz sheets with a thickness of 0.7 mm and a layer spacing of 1.1 mm, a reflectivity of 50% and a splitting ratio of 1:1 can be achieved. After passing through these three beam splitters, the incident terahertz wave can be divided into four paths with the same power.

[0070] For the single pulse generation optical path, SM1 and SM2 use gold-plated spherical mirrors with a curvature radius of 500mm. The distance between the two mirrors is adjusted around 1m (L≈1m in the figure). The displacement platform uses LS90-25C1 produced by Lubang Company, which can achieve an adjustment accuracy of 10μm. The beam splitter uses a single-layer 0.9mm thick fused quartz sheet with a reflectivity of about 6%; the semiconductor chip uses a 0.372mm high-resistance silicon wafer. When there is no laser irradiation, the reflectivity for 240GHz terahertz waves is almost 0. For 220mJ laser irradiation, its reflectivity can rise to 95% within 1ns. The beam expander uses VBE-532-2-10X produced by Lubang Company, which can achieve 2 to 10 times amplification of the 532nm laser spot. The laser reflector uses LPM10-532P-HP produced by Lubang Company, which can achieve a reflectivity of up to 99% for 532nm lasers. Based on the above parameters, according to the resonant cavity electromagnetic wave theory and semiconductor theory and the calculation results of the simulation software COMSOL, the time domain variation curve of the power in the cavity during the resonance establishment process is as follows: Figure 5 As shown in part (a) of the figure, during the tuning process, the power received by the detector changes with the distance between the reflectors. Figure 5 As shown in part (b); the single pulse waveform generated after laser irradiation is as follows Figure 5 As shown in part (c), a single pulse with a pulse width of 3.3ns and a power amplification factor of 32 times can be generated.

[0071] For the beam combining path, the off-axis parabolic reflector adopts the same result as the beam splitting path, with an equivalent focal length of 250mm. The semiconductor wafer is also the same as the single pulse generating path, using a 0.372mm high-resistance silicon wafer, and the distance between the silicon wafer and the reflector is 250mm (d in the figure o ≈250mm). The model of laser reflector and laser beam expander is the same as that of single pulse generation optical path. For the transmission system of laser and terahertz wave, the structure and model of off-axis parabolic reflector and laser reflector are consistent with that of beam splitting optical path and single pulse generation optical path. Oi The laser optical path ratio reaches W i The laser optical path length is 1.5m, which can achieve a 5ns turn-on hysteresis, and thus can achieve the generation of a four-pulse sequence with an interval between adjacent pulses greater than 5ns. According to the above parameters and equipment selection, the timing relationship between the voltage pulse signal emitted by any sequence generator, the laser irradiated to the semiconductor wafer, and the generated terahertz pulse sequence in this embodiment is as follows: Figure 6 shown.

[0072] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A system for generating a nanosecond terahertz pulse sequence, characterized in that: include: a wave source for generating terahertz waves in the form of Gaussian beams; A beam splitting optical path, used for splitting the terahertz wave into n terahertz waves, where n≥2; n single pulse generating optical paths, n terahertz waves pass through corresponding single pulse generating optical paths to generate n terahertz single pulses with amplified wave source power in a timely manner; A beam combining optical path, used to sequentially combine n terahertz single pulses into one, outputting a terahertz wave pulse sequence with amplified output power; A laser driving component, used for controlling the generation timing of n-channel terahertz single pulses and the synthesis order of n-channel terahertz single pulses; The single pulse generating optical path includes a Fabry-Perot resonant cavity, a first beam splitter and a first semiconductor chip driven by laser. Each terahertz wave is reflected and coupled into the Fabry-Perot resonant cavity through the corresponding first beam splitter to resonate. The first semiconductor chip reflects all the electromagnetic energy accumulated in the resonant cavity under the irradiation of the first laser, generating a terahertz single pulse that is amplified dozens of times relative to the wave source power. The laser driving component is used to emit n first lasers and n-1 second lasers in a time sequence; The beam combining optical path includes n-1 second semiconductor chips driven by lasers, which are used to sequentially combine n terahertz single pulses into one under the control of n-1 second lasers to output a terahertz wave pulse sequence with amplified output power; wherein the second laser irradiated to the i-th second semiconductor chip irradiates after the i-th terahertz single pulse is generated.

2. The system for generating nanosecond terahertz pulse sequences according to claim 1, characterized in that: The Fabry-Perot resonant cavity uses two spherical reflectors facing each other with adjustable spacing; In each single pulse generating optical path, the first beam splitter and the first semiconductor chip are arranged between two spherical reflectors, the axis of the spherical reflector is orthogonal to the optical axis of the terahertz wave incident into the single pulse generating optical path, the axis of the first beam splitter and the axis of the spherical reflector are 45 degrees, and the axis of the first semiconductor chip is 45 degrees to the axis of the first beam splitter and is orthogonal to the first beam splitter.

3. The system for generating nanosecond terahertz pulse sequences according to claim 2, characterized in that: The single pulse generating optical path further includes a first laser beam expander and a first laser reflecting mirror, which are used to control the optical axis of the first laser of the first semiconductor wafer and the axis of the first laser beam expander to be located in the XOY plane and to have a certain angle with the axis of the first semiconductor wafer; The first laser reflecting mirror is used to reflect the laser for controlling the first semiconductor chip to the first laser beam expander, and the first laser beam expander is used to enlarge the light spot of the reflected laser and make the center of the light spot located at the center of the first semiconductor chip.

4. The system for generating a nanosecond terahertz pulse sequence according to claim 2, characterized in that: The single pulse generating optical path further comprises a displacement platform, and the displacement platform is used to adjust the distance between the two spherical reflectors so as to match the frequency of the terahertz wave incident on the single pulse generating optical path.

5. The system for generating nanosecond terahertz pulse sequences according to claim 1, characterized in that: The beam splitting optical path comprises n-1 second beam splitters with a certain splitting ratio and n-1 first off-axis parabolic reflectors, the optical axis of the terahertz wave incident into the beam splitting optical path is parallel to the Y axis, the axis of the second beam splitter is at an angle of 45 degrees to the X axis, the first off-axis parabolic reflector is installed parallel to the X axis and the Y axis, and the incident center of the first off-axis parabolic reflector and the axis of the second beam splitter are both located in the XOY plane; the n-1 first off-axis parabolic reflectors and the n-1 second beam splitters are spaced at a distance d s Alternately arranged along the X and Y axes, the spacing d s It is determined by the focal length of the first off-axis parabolic reflector and the frequency and waist radius of the terahertz wave incident into the split beam path, and is used to ensure that each second beam splitter is located at the waist of the Gaussian beam.

6. The system for generating nanosecond terahertz pulse sequences according to claim 1, characterized in that: The beam combining optical path further comprises n-1 second off-axis parabolic reflectors, the optical axis of the terahertz single pulse incident into the beam combining optical path is parallel to the X-axis, the second off-axis parabolic reflectors are installed parallel to the X-axis and the Y-axis, the axis of the second semiconductor wafer is located in the XOY plane and is 45 degrees to the X-axis; the n-1 second off-axis parabolic reflectors and the n-1 second semiconductor wafer are spaced at a distance d o Alternately arranged along the X and Y axes, the spacing d o It is determined by the focal length of the second off-axis parabolic reflector and the frequency and waist radius of the terahertz single pulse entering the combined beam path, and is used to ensure that each second semiconductor wafer is located at the waist of the Gaussian beam.

7. The system for generating a nanosecond terahertz pulse sequence according to claim 6, characterized in that: The beam combining optical path further includes a second laser beam expander and a second laser reflector, which are used to control the optical axis of the second laser of the second semiconductor wafer and the axis of the second laser beam expander to be located in the XOY plane, and there is a certain angle between the axis of the second semiconductor wafer; The second laser reflector is used to reflect the laser for controlling the second semiconductor chip to the second laser beam expander; the second laser beam expander is used to enlarge the light spot of the reflected laser so that the center of the light spot is located at the center of the second semiconductor chip.

8. The system for generating nanosecond terahertz pulse sequences according to claim 1, characterized in that: The laser driving component includes an arbitrary sequence generator and n lasers; the arbitrary sequence generator is used to drive each laser to emit laser in a time sequence, and the laser emitted by each laser is divided into two beams by a laser beam splitter, one beam is irradiated to the first semiconductor chip in the i-th single pulse generation optical path, and the other beam is irradiated to the i-th second semiconductor chip, and the second laser irradiated to the i-th second semiconductor chip is irradiated after the i-th terahertz single pulse is generated by means of an optical path difference.

9. The system for generating nanosecond terahertz pulse sequences according to claim 1, characterized in that: The wave source is a continuous wave source or a pulse wave source with a pulse width above microsecond level; when the wave source is a pulse wave source, the wave source sends an electrical signal to an arbitrary sequence generator when outputting terahertz waves.

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