Terahertz signal generation device based on parallel grating pair cooperative chirped beat frequency technology

Abstract

The utility model discloses parallel grating pair's terahertz signal generating device of cooperative chirp beat frequency technology, first optical signal processing branch in the device includes parallel grating pair, incident pulse generating branch and terahertz radiation source, first laser signal produces chirp pulse after parallel grating pair, and the initial incident pulse is produced by incident pulse generating branch and is incident to terahertz radiation source and produces multi -cycle terahertz pulse, second laser signal and multi -cycle terahertz pulse after the beam combination of second optical signal processing branch act on signal detector, and terahertz wave signal is generated by signal detector detection. Visible, the utility model can replace femtosecond laser with the longer chirp pulse beat frequency light energy in time, this greatly improved available pumping energy, and still can protect terahertz radiation source not by high -energy laser damage, thereby improved the terahertz energy and conversion efficiency of generation, namely: can efficiently and stably generate multi -cycle terahertz wave signal.

Description

Technical Field

[0001] This utility model relates to the field of optoelectronic technology, and in particular to a terahertz signal generation device using parallel grating pair cooperative chirping beat frequency technology. Background Technology

[0002] Compared to microwaves, terahertz waves offer higher frequency resolution; compared to infrared light, they have longer wavelengths and stronger penetrating power. These characteristics make terahertz waves an ideal tool for studying low-energy excitation processes, material spectral responses, and vibrational modes of biomolecules, attracting widespread attention in several cutting-edge fields in recent years. However, practical experience has shown that traditional terahertz wave generation methods, such as optical rectification using low-nonlinear crystals like ZnTe, typically produce terahertz waves with energy typically in the nJ range and limited tuning capabilities. In other words, traditional terahertz wave generation methods suffer from low energy conversion efficiency. Therefore, designing a terahertz radiation generation device to improve the energy conversion efficiency from laser to terahertz waves is essential. Utility Model Content

[0003] This invention provides a terahertz signal generation device using parallel grating pair cooperative chirped beat frequency technology, which can improve the energy conversion efficiency from laser to terahertz wave.

[0004] To address the aforementioned technical problems, the first aspect of this utility model discloses a terahertz signal generation device using a parallel grating pair cooperative chirped beat frequency technique, the device comprising: The system comprises a first optical signal processing branch, a second optical signal processing branch, and a signal detector; wherein the first optical signal processing branch includes a parallel grating pair, an incident pulse generation branch, and a terahertz radiation source. The first optical signal processing branch generates a chirped pulse after receiving the first laser signal; the chirped pulse generates an initial incident pulse after passing through the incident pulse generation branch; the initial incident pulse is incident on the terahertz radiation source and generates a multi-period terahertz pulse; the multi-period terahertz pulse and the second laser signal are combined in the second optical signal processing branch and then act on the signal detector, which detects and generates a terahertz wave signal; wherein the first laser signal and the second laser signal are obtained by splitting the initial laser pulse by a beam splitter, and the energy proportion of the first laser signal is higher than that of the second laser signal.

[0005] As an optional implementation, in the first aspect of this utility model, the first optical signal processing branch further includes: a first off-axis parabolic mirror disposed after the terahertz radiation source; wherein, the multi-period terahertz pulse enters the second optical signal processing branch after passing through the first off-axis parabolic mirror and is combined with the second laser signal; And / or, The second optical signal processing branch includes a second off-axis parabolic mirror; The multi-cycle terahertz pulse and the second laser signal are combined at the second off-axis parabolic mirror.

[0006] As an optional implementation, in the first aspect of this invention, the second optical signal processing branch further includes: an optical delay unit disposed before the second off-axis parabolic mirror; Furthermore, the second optical signal processing branch further includes a filter disposed between the optical delayer and the second off-axis parabolic mirror; Furthermore, the second optical signal processing branch further includes a first lens disposed between the filter and the second off-axis parabolic mirror.

[0007] As an optional implementation, in the first aspect of this invention, the signal detector includes: The electro-optic sampling crystal, quarter-wave plate, Wollaston prism, and two photodetectors are arranged sequentially. The electro-optic sampling crystal converts the electric field information of the multi-period terahertz pulse into the polarization information of the second laser signal; the quarter-wave plate converts the linearly polarized light of the second laser signal into circularly polarized light to adjust the polarization state of the second laser signal; the Wollaston prism splits the second laser signal after polarization adjustment into two linearly polarized beams with mutually perpendicular vibration directions; and the two photodetectors respectively detect the light intensity of the two linearly polarized beams.

[0008] As an optional implementation, in the first aspect of this invention, the incident pulse generation branch includes: The first chirped pulse processing sub-device and the reflective grating; The chirped pulse is processed by a first chirped pulse processing sub-device to form a first pulse signal. The first pulse signal is then processed by the reflective grating to generate a tilted wavefront pulse, which serves as the initial incident pulse incident on the terahertz radiation source.

[0009] As an optional implementation, in the first aspect of this invention, the incident pulse generation branch further includes: A first optical chopper is disposed between the first chirped pulse processing sub-device and the reflective grating; Furthermore, the incident pulse generation branch further includes: A first half-wave plate is disposed between the first optical chopper and the reflective grating.

[0010] As an optional implementation, in the first aspect of this invention, the incident pulse generation branch further includes: A second half-wave plate and an imaging system are sequentially arranged between the reflective grating and the terahertz radiation source; the imaging system includes a second lens and a third lens.

[0011] As an optional implementation, in the first aspect of this utility model, the first chirped pulse processing sub-device includes: a Michel interferometer, which splits the chirped pulse to generate two pulses with relative time delay and combines the two pulses to form a multi-period pulse, wherein the first pulse signal is the multi-period pulse; or, The first chirped pulse processing sub-device includes: a first Fabry-Perot cavity, wherein the chirped pulse generates two outgoing pulses with relative time delay after passing through the first Fabry-Perot cavity, and the two outgoing pulses overlap to form a quasi-sinusoidal light intensity envelope modulated electromagnetic wave pulse, and the first pulse signal is the electromagnetic wave pulse; wherein the first chirped pulse processing sub-device further includes: a third half-wave plate and a first polarizer.

[0012] As an optional implementation, in the first aspect of this utility model, the incident pulse generation branch includes: a second Fabry-Perot cavity; the chirped pulse generates two outgoing pulses with relative time delay after passing through the second Fabry-Perot cavity, and the two outgoing pulses overlap to form a quasi-sinusoidal light intensity envelope modulated electromagnetic wave pulse; Furthermore, the incident pulse generation branch further includes a fourth half-wave plate and a second polarizer, wherein the fourth half-wave plate and the second polarizer are sequentially disposed after the second Fabry-Perot cavity and before the terahertz radiation source.

[0013] As an optional implementation, in the first aspect of this invention, the incident pulse generation branch further includes: a second optical chopper disposed after the second polarizer and before the terahertz radiation source; Furthermore, the incident pulse generation branch further includes a fifth half-wave plate disposed after the second optical chopper and before the terahertz radiation source; Furthermore, the incident pulse generation branch also includes: a dual cylindrical telescope system disposed after the fifth half-wave plate and before the terahertz radiation source; Furthermore, the incident pulse generation branch further includes an aperture stop disposed after the dual cylindrical telescope system and before the terahertz radiation source.

[0014] Implementing this utility model has the following beneficial effects: The first optical signal processing branch of this invention includes a parallel grating pair, an incident pulse generation branch, and a terahertz radiation source. After the first laser signal generates a chirped pulse through the parallel grating pair, the incident pulse generation branch generates an initial incident pulse, which is then incident on the terahertz radiation source to generate multi-period terahertz pulses. The second laser signal and the multi-period terahertz pulses are combined in the second optical signal processing branch and then act on a signal detector, which detects and generates a terahertz wave signal. Therefore, this invention replaces the femtosecond laser with chirped pulse beat frequency light energy, which significantly increases the available pump energy and protects the terahertz radiation source from damage by high-energy lasers, thereby improving the generated terahertz energy and conversion efficiency. In other words, it can efficiently and stably generate multi-period terahertz wave signals. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the structure of a terahertz signal generation device using a parallel grating pair cooperative chirped beat frequency technology disclosed in an embodiment of this utility model; Figure 2 This is a schematic diagram of another terahertz signal generation device using parallel grating pair cooperative chirped beat frequency technology disclosed in this utility model embodiment; Figure 3 This is a schematic diagram of the structure of another terahertz signal generation device using parallel grating pair cooperative chirped beat frequency technology disclosed in this utility model embodiment; Figure 4 This is a schematic diagram of the structure of another terahertz signal generation device using parallel grating pair cooperative chirped beat frequency technology disclosed in this utility model embodiment. Detailed Implementation

[0017] To better understand and implement this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0018] It should be noted that, unless otherwise explicitly specified and limited, the term "electrical connection" in the specification, claims, and accompanying drawings of this utility model should be interpreted broadly. For example, it can refer to a fixed electrical connection, a detachable electrical connection, or an integral electrical connection; it can refer to a mechanical electrical connection or a mutually communicating connection; it can refer to a direct connection or an indirect connection through an intermediate medium; it can refer to the internal connection of two components or the interaction between two components. Furthermore, the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this utility model are used to distinguish different objects, not to describe a specific order. The terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0019] This invention discloses a terahertz signal generation device using a parallel grating pair with coordinated chirped beat frequency technology. It replaces femtosecond lasers with chirped pulse beat frequency light energy with a longer duration, significantly increasing the available pump energy and protecting the terahertz radiation source from damage by high-energy lasers. This improves the generated terahertz energy and conversion efficiency, meaning it can efficiently and stably generate multi-cycle terahertz wave signals. The following are based on... Figure 1-4 The structure of the terahertz signal generation device for the parallel grating pair coordinated chirped beat frequency technology is described in detail.

[0020] like Figure 1-4 As shown, the terahertz signal generation device for the parallel grating-coordinated chirped beat frequency technology may include: A first optical signal processing branch 101, a second optical signal processing branch 102, and a signal detector 103; wherein, the first optical signal processing branch 101 includes a parallel grating pair 1011, an incident pulse generation branch 1012, and a terahertz radiation source 1013.

[0021] The first optical signal processing branch 101 generates a chirped pulse after receiving the first laser signal; the chirped pulse generates an initial incident pulse after passing through the incident pulse generation branch 1012; the initial incident pulse is incident on the terahertz radiation source 1013 and generates a multi-period terahertz pulse; the multi-period terahertz pulse and the second laser signal are combined in the second optical signal processing branch 102 and then act on the signal detector 103, which detects and generates a terahertz wave signal.

[0022] In this embodiment of the invention, the first laser signal and the second laser signal are generated by a beam splitter (see reference). Figure 2-4The initial laser pulse (1042 in the original text) is obtained by splitting the initial laser pulse, and the energy proportion of the first laser signal is higher than that of the second laser signal. Furthermore, the initial laser pulse can be generated by a femtosecond laser (see [reference needed]). Figure 2-4 The first laser signal and the second laser signal are generated by the single-pulse femtosecond laser (i.e., the initial laser pulse) output by the femtosecond laser 1041 and then split by the beam splitter 1042.

[0023] Optionally, the beam splitter 1042 is a non-polarizing beam splitter. After the single-pulse femtosecond laser is split by the non-polarizing beam splitter, the incident beam is incident on the coated surface. Most of the incident light is reflected by the coated surface to form the first laser signal, while a small portion of the transmitted light forms the first laser signal for subsequent electro-optic sampling. The splitting ratio of the beam splitter 1042 can be adjusted or set according to actual needs. Optionally, the femtosecond laser 1041 can be a Ti:sapphire laser with a center wavelength of 800 nm, energy in the millijoule range, and pulse width in the hundreds of femtosecond range to output the single-pulse femtosecond laser. It can be seen that this embodiment of the invention can split the single-pulse femtosecond laser into two laser beams using the beam splitter 1042, improving the convenience and flexibility of laser beam splitting, and is simple in structure and easy to implement. Furthermore, outputting the single-pulse femtosecond laser using a Ti:sapphire laser with a center wavelength of 800 nm, energy in the millijoule range, and pulse width in the hundreds of femtosecond range helps to ensure the stable output of the high-intensity terahertz wave signal.

[0024] Optionally, in this embodiment of the invention, the parallel grating pair 1011 adjusts the position of each frequency component in the time domain of the first laser signal by introducing a frequency-related phase shift to generate a chirped pulse. This allows for the generation of a chirped pulse with a wider pulse width based on the parallel grating pair 1011. This not only reduces the peak power of the first laser signal, avoiding or minimizing damage to the terahertz radiation source 1031 and improving the energy injection ceiling, but also broadens the spectral coverage of the terahertz wave, thus adapting to wideband application requirements. Furthermore, it compensates for group velocity mismatch, extends the effective action length, improves terahertz conversion efficiency, and allows for the modulation of the time-domain characteristics of the terahertz pulse, generating a multi-period, stable terahertz signal. It also facilitates adaptation to high-power terahertz generation systems and compatibility with subsequent optical control stages.

[0025] As can be seen, the device described in this embodiment of the present invention can replace femtosecond laser with chirped pulse beat frequency light energy with a longer duration, which greatly increases the available pump energy and can also protect the terahertz radiation source from damage by high-energy laser, thereby improving the generated terahertz energy and conversion efficiency, that is: it can efficiently and stably generate multi-cycle terahertz wave signals.

[0026] In an optional embodiment, please refer to Figure 2-4 The first optical signal processing branch 101 further includes a first off-axis parabolic mirror 1014 disposed after the terahertz radiation source 1013; wherein, the multi-cycle terahertz pulse enters the second optical signal processing branch 102 after passing through the first off-axis parabolic mirror 1014 and is combined with the second laser signal.

[0027] In this optional embodiment, the first off-axis parabolic mirror 1014 acts as an off-axis reflector, which can convert the divergent conical multi-period terahertz pulse into a parallel-emitted multi-period terahertz pulse. This can reduce energy diffusion during transmission, thereby reducing energy waste and further improving the energy conversion rate.

[0028] In another alternative embodiment, please refer to Figure 2-4 The second optical signal processing branch 102 includes a second off-axis parabolic mirror 1021; the multi-period terahertz pulse and the second laser signal are combined at the second off-axis parabolic mirror 1021.

[0029] As can be seen, this optional embodiment, through the second off-axis parabolic mirror 1021, enables the beam combining of the second laser signal and the multi-period terahertz pulse to adapt to the "high absorption" characteristics of the terahertz band, achieving low-loss beam combining. In addition, it ensures that the second laser signal and the multi-period terahertz pulse can act precisely and synchronously on the signal detector 103. Furthermore, during the beam combining process of the second off-axis parabolic mirror 1021, the propagation paths of the two beams completely avoid the mirror itself, without any central obstruction, reducing energy loss and improving energy conversion efficiency.

[0030] In yet another alternative embodiment, please refer to Figure 2-4 The second optical signal processing branch 102 further includes an optical delay unit 1022 disposed before the second off-axis parabolic mirror 1021. The optical delay unit 1022 is used to adjust the time delay of the second laser signal.

[0031] In this optional embodiment, when the second laser signal passes through the optical delay unit 1022, the time delay of the second laser signal relative to the terahertz radiation is changed by finely adjusting the optical path. Typically, a time interval of 50 fs is used to ensure that the second laser signal and the multi-cycle terahertz pulse reach the second off-axis parabolic mirror 1021 synchronously for beam combining, which helps to ensure effective beam combining / superposition of the second laser signal and the multi-cycle terahertz pulse.

[0032] In this optional embodiment, the second optical signal processing branch 102 may further include a filter 1023 disposed between the optical delay unit 1022 and the second off-axis parabolic mirror 1021. The filter 1023 is used to reduce the light intensity of the second laser signal.

[0033] In this optional embodiment, the second laser signal is time-delayed by the optical delayer 1022 before passing through the filter 1023. This reduces the light intensity of the second laser signal, thereby reducing the possibility of damage to the optical element due to the light intensity exceeding the damage threshold of the optical element, which is beneficial to improving the safety and stability of the device.

[0034] In this optional embodiment, the second optical signal processing branch 102 may further include a first lens 1024 disposed between the filter 1023 and the second off-axis parabolic mirror 1021. The first lens 1024 is used to direct the second laser signal parallel to the second off-axis parabolic mirror 1021.

[0035] This optional embodiment can use the first lens 1024 to incident the second laser signal parallel to the second off-axis parabolic mirror 1021 and combine it with the multi-period terahertz pulse, which is beneficial to improving the energy conversion efficiency.

[0036] In yet another alternative embodiment, please refer to Figure 2-4 The aforementioned signal detector 103 includes: The system consists of an electro-optic sampling crystal 1031, a quarter-wave plate 1032, a Wollaston prism 1033, and two photodetectors 1034 arranged sequentially. The electro-optic sampling crystal 1031 converts the electric field information of the multi-period terahertz pulse into the polarization information of the second laser signal. The quarter-wave plate 1032 converts the linearly polarized light of the second laser signal into circularly polarized light to adjust the polarization state of the second laser signal. The Wollaston prism 1033 splits the second laser signal after the polarization state adjustment into two linearly polarized beams with mutually perpendicular vibration directions. The two photodetectors 1034 detect the light intensity of the two linearly polarized beams, respectively.

[0037] Optionally, the electro-optic sampling crystal 1031 can be a ZnTe crystal.

[0038] In this optional embodiment, the ZnTe crystal utilizes the electro-optic effect to detect terahertz waves. The second laser signal and a multi-period terahertz pulse are synchronously incident on the ZnTe crystal. The electric field of the multi-period terahertz pulse causes a change in the refractive index of the ZnTe crystal, which in turn changes the polarization state of the second laser signal. That is, the electric field of the multi-period terahertz pulse is converted into the polarization information of the second laser signal. A quarter-wave plate (QWP) converts the linearly polarized light of the second laser signal into circularly polarized light, preparing for the subsequent conversion of the polarization state change into a change in light intensity using a Wollaston prism. The Wollaston prism is a polarization beam splitter that can split the second laser signal, whose polarization state has changed after passing through the ZnTe crystal, into two beams of linearly polarized light with mutually perpendicular vibration directions. The light intensities of these two beams will differ due to the polarization state change caused by the terahertz wave, thereby converting the electric field information of the terahertz wave into a difference in the light intensity of the two beams, which is beneficial for the subsequent effective detection of useful terahertz wave signals.

[0039] In this optional embodiment, the signal detector 103 may further include a differential processor 1035 and a signal locker 1036 sequentially disposed after the photodetector 1034. The differential processor 1035 calculates the intensity difference between the two linearly polarized beams to obtain a differential signal; the signal locker 1036 detects and extracts a target terahertz wave signal of a specific frequency from the differential signal.

[0040] In this optional embodiment, the differential processor 1035 can be a balanced detector, which performs differential processing on the light intensity signals detected by the two photodetectors 1034, i.e., calculates the difference in light intensity between the two beams. This can effectively suppress common-mode noise such as laser intensity fluctuations and improve the signal-to-noise ratio of the detected laser signal. Furthermore, the signal locker 1036 can be a lock-in amplifier, used to extract the useful signal related to the terahertz wave frequency, i.e., the terahertz wave signal at a specific frequency, from the differential signal obtained from the balanced detection. Since terahertz wave detection is usually performed under modulation, such as modulation of a terahertz source, the lock-in amplifier can lock onto the modulation frequency, thereby filtering out irrelevant noise, accurately obtaining the terahertz wave signal, and improving the reliability of terahertz wave signal detection.

[0041] In this optional embodiment, the signal detector 103 may further include a lens 1037 disposed between the electro-optic sampling crystal 1031 and the quarter-wave plate 1032. The lens 1037 is used to focus the multi-period terahertz pulses and the second laser signal, enabling them to interact better within the ZnTe crystal, thereby improving signal detection efficiency and sensitivity.

[0042] In yet another alternative embodiment, please refer to [the relevant documentation]. Figure 2-3 The incident pulse generation branch 1012 includes: The first chirped pulse processing sub-device 10121 and the reflective grating 10122; The chirped pulse is processed by the first chirped pulse processing sub-device 10121 to form a first pulse signal. The first pulse signal is then processed by the reflection grating 10122 to generate a tilted wavefront pulse, which serves as the initial incident pulse to the terahertz radiation source 1013.

[0043] As can be seen, this optional embodiment can combine chirped beat frequency technology and tilted wavefront technology in a terahertz wave signal generation device, which significantly improves the conversion efficiency from laser to terahertz wave and is beneficial to increasing the generated terahertz energy.

[0044] In this optional embodiment, further options are available upon request. Figure 2-3 The incident pulse generation branch 1012 also includes: A first optical chopper 10123 is disposed between the first chirped pulse processing sub-device 10121 and the reflective grating 10122.

[0045] In this optional embodiment, the first optical chopper 10123 can modulate multi-period pulses into a fixed-frequency alternating light signal (such as a square wave or sine wave signal) through periodic blocking, while background stray light (a small amount of co-polarized light mixed in after non-target polarized light is scattered, and ambient light) remains a DC signal. Furthermore, the first optical chopper 10123 can also cause the corresponding pulses to illuminate a terahertz radiation source (such as a lithium niobate crystal) at a fixed frequency, and the second optical signal processing branch 102 synchronously acquires the terahertz wave signal, ensuring that each terahertz pulse excited by the terahertz radiation source 1013 can be accurately captured, avoiding or reducing signal misalignment in time.

[0046] Alternatively, the incident pulse generation branch 1012 may further include: A first half-wave plate 10124 is disposed between the first optical chopper 10123 and the reflective grating 10122. The first half-wave plate 10124 is used to adjust the direction of the continuous laser pulse to a horizontal direction.

[0047] As can be seen, in this optional embodiment, the beam direction is adjusted to a horizontal direction by the first half-wave plate 10124 before it is incident on the reflective grating 10122, which helps to improve the energy and stability of the tilted wavefront pulse generated by the reflective grating 10122.

[0048] In yet another alternative embodiment, please refer to [the relevant documentation]. Figure 2-3 The incident pulse generation branch 1012 also includes: A second half-wave plate 10125 and an imaging system 10126 are sequentially arranged between the reflective grating 10122 and the terahertz radiation source 1013; the imaging system 10126 includes a second lens 101261 ​​and a third lens 101262.

[0049] The first pulse signal, after passing through the reflection grating 10122, generates a tilted wavefront pulse that passes through the second half-wave plate 10125 and the imaging system 10126 and is then perpendicularly incident on the terahertz radiation source 1013 along the optical path.

[0050] In this optional embodiment, the second half-wave plate 10125 can not only correct the polarization offset and ensure that the pulse incident on the terahertz radiation source 1013 is "polarized matched" with the terahertz radiation source 1013, but also ensure that the tilted wavefront pulse is incident perpendicularly on the terahertz radiation source 1013 along the optical path. This not only ensures the quality of the terahertz signal, but also maximizes the nonlinear effect, thereby improving the energy conversion efficiency.

[0051] Furthermore, in this optional embodiment, the tilted wavefront pulse generated by the reflective grating 10122, when incident perpendicularly on the terahertz radiation source 1013, must satisfy the following: The distance from the reflective grating 10122 to the second lens 101261 ​​is f1; the distance from the second lens 101261 ​​to the third lens 101262 is f1+f2; and the distance from the third lens 101262 to the surface of the terahertz radiation source 1013 is f2. Here, f1 is the focal length of the second lens 101261, and f2 is the focal length of the third lens 101262. Both the second lens 101261 ​​and the third lens 101262 are convex lenses.

[0052] In this optional embodiment, the tilted wavefront pulse generated by the reflective grating 10122 is ensured to be perpendicularly incident on the terahertz radiation source 1013 by adjusting the distance between the reflective grating 10122, the second lens 101261, the third lens 101262 and the surface of the terahertz radiation source 1013. The adjustment method is simple, flexible and easy to implement.

[0053] In yet another alternative embodiment, please refer to Figure 2The first chirped pulse processing sub-device 10121 includes: a Michael interferometer 101211, which splits the chirped pulse to generate two pulses with relative time delay and combines the two pulses to form a multi-period pulse, wherein the first pulse signal is a multi-period pulse.

[0054] In this optional embodiment, the terahertz radiation source 1013 can be a lithium niobate crystal. More optionally, the lithium niobate crystal is doped with 5-6.2 mol% magnesium oxide, and the lithium niobate crystal has a triangular prism structure with a base angle of approximately 63 degrees and a apex angle of approximately 54 degrees. The polarization direction of the incident light is parallel to the crystal axis of the lithium niobate crystal, and the angle between the incident and exit surfaces is approximately 63 degrees. This is done to ensure that the generated terahertz radiation direction is perpendicular to the exit surface, thereby reducing energy loss due to reflection and improving energy conversion efficiency.

[0055] Optionally, the multi-period pulse generates a tilted wavefront pulse through the reflection grating 10122. The tilted wavefront pulse at a specific angle can be generated by finely adjusting the angle of the incident multi-period pulse relative to the reflection grating 10122 to meet the phase matching condition, thereby ensuring that the incident light incident on the terahertz radiation source 1013 is non-collinearly phase matched with the terahertz wave.

[0056] As can be seen, this optional embodiment achieves quasi-sinusoidal modulation of optical intensity by precisely controlling the time delay between two linearly chirped pulses using a Michel interferometer, thereby effectively converting it into frequency-tunable narrowband terahertz radiation in the terahertz source. This device not only avoids complex frequency-selective components but also allows for continuous adjustment of the center frequency while maintaining high terahertz output energy. Furthermore, the Michel interferometer, as the core component of the device, has advantages such as simple structure, wide adjustable delay range, and flexible operation, resulting in significant improvements in tuning accuracy, frequency selectivity, and stability. In other words, the synergistic effect of the parallel grating pair and the Michel interferometer optimizes the generation process of the terahertz wave signal, thereby optimizing the generated terahertz wave signal and facilitating the expansion of application scenarios for terahertz wave signals.

[0057] In yet another alternative embodiment, please refer to Figure 3 The first chirped pulse processing sub-device 10121 includes: a first Fabry-Perot cavity 101212, after the chirped pulse passes through the first Fabry-Perot cavity 101212, two outgoing pulses with relative time delay are generated and the two outgoing pulses overlap to form a quasi-sinusoidal light intensity envelope modulated electromagnetic wave pulse, and the first pulse signal is an electromagnetic wave pulse.

[0058] In this optional embodiment, the terahertz radiation source 1013 can be a lithium niobate crystal. More optionally, the lithium niobate crystal is doped with 5-6.2 mol% magnesium oxide, and the lithium niobate crystal has a triangular prism structure with a base angle of approximately 63 degrees and a apex angle of approximately 54 degrees. The polarization direction of the incident light is parallel to the crystal axis of the lithium niobate crystal, and the angle between the incident and exit surfaces is approximately 63 degrees. This is done to ensure that the generated terahertz radiation direction is perpendicular to the exit surface, thereby reducing energy loss due to reflection and improving energy conversion efficiency.

[0059] As can be seen, this optional embodiment can combine chirped beat frequency technology and tilted wavefront technology in a terahertz wave signal generation device, which significantly improves the conversion efficiency from laser to terahertz wave and is beneficial to increasing the generated terahertz energy. In addition, multi-cycle pulses can be controlled by adjusting the pulse width of the chirped pulse and the time delay between the two pulses, which improves the convenience and flexibility of multi-cycle pulse control and the structure is simple.

[0060] In this optional embodiment, the first chirped pulse processing sub-device 10121 may further include a third half-wave plate 101213 and a first polarizer 101214.

[0061] In this optional embodiment, the electromagnetic wave pulse, after its polarization direction is adjusted by the third half-wave plate 101213, enters the first polarizer 101214. The first polarizer 101214 splits the electromagnetic wave pulse according to the polarization direction and outputs a continuous laser beam. Optionally, the first polarizer 101214 can be a thin-film polarizer (TFP).

[0062] In this optional embodiment, the third half-wave plate HWP and the thin-film polarizer TFP can constitute a light intensity regulator. The thin-film polarizer TFP has different reflection and transmission characteristics for light with different polarization directions. By rotating the third half-wave plate HWP to change the polarization direction of the linearly polarized light incident on the thin-film polarizer, the splitting ratio can be continuously adjusted, thereby achieving precise control of the energy of the first laser signal light during the terahertz wave generation process, and thus optimizing the terahertz wave generation efficiency.

[0063] In yet another alternative embodiment, please refer to Figure 4 The incident pulse generation branch 1012 includes: a second Fabry-Perot cavity 10127; after the chirped pulse passes through the second Fabry-Perot cavity 10127, it generates two outgoing pulses with relative time delays, and the two outgoing pulses overlap to form a quasi-sinusoidal light intensity envelope modulated electromagnetic wave pulse.

[0064] In this optional embodiment, the terahertz radiation source 1013 is a lithium niobate crystal, or a periodically polarized lithium niobate crystal, i.e., a PPLN crystal, where PPLN is an abbreviation for Periodically Poled Lithium Niobate. More preferably, the terahertz radiation source 1013 is a PPLN crystal, which allows for adjustment of the frequency of multi-period terahertz pulses through the PPLN crystal structure. As can be seen, this optional embodiment allows for adjustment of the frequency of multi-period terahertz pulses through the PPLN crystal structure, and replaces the femtosecond laser with chirped pulse beat frequency light energy with a longer duration, greatly increasing the energy of the usable first laser signal, and also protecting the terahertz radiation source from damage by high-energy lasers, thereby improving the generated terahertz energy and conversion efficiency.

[0065] In this optional embodiment, the incident pulse generation branch 1012 may further include a fourth half-wave plate 10128 and a second polarizer 10129, which are sequentially disposed after the second Fabry-Perot cavity 10127 and before the terahertz radiation source 1013.

[0066] In this optional embodiment, the electromagnetic wave pulse, after its polarization direction is adjusted by the fourth half-wave plate 10128, enters the second polarizer 10129. The second polarizer 10129 splits the electromagnetic wave pulse according to the polarization direction and outputs a continuous laser beam. Optionally, the second polarizer 10129 can be a thin film polarizer (TFP).

[0067] In this optional embodiment, the fourth half-wave plate HWP and the thin-film polarizer TFP can constitute a light intensity regulator. The thin-film polarizer TFP has different reflection and transmission characteristics for light with different polarization directions. By rotating the third half-wave plate HWP to change the polarization direction of the linearly polarized light incident on the thin-film polarizer, the splitting ratio can be continuously adjusted, thereby achieving precise control of the energy of the first laser signal light during the terahertz wave generation process, and thus optimizing the terahertz wave generation efficiency.

[0068] In this optional embodiment, the incident pulse generation branch 1012 may further include a second optical chopper 101210 disposed after the second polarizer 10129 and before the terahertz radiation source 1013. The second optical chopper 101210 is used to modulate the continuous laser beam output from the polarizer.

[0069] In this optional embodiment, the polarization-modulated light after passing through the fourth half-wave plate 10128 and the second polarizer 10129 is continuously and stably linearly polarized light. The second optical chopper 101210 can modulate it into a fixed-frequency alternating light signal (such as a square wave or sine wave signal) by periodically blocking it, while the background stray light (a small amount of co-polarized light and ambient light mixed in after non-target polarized light is scattered) remains a DC signal. In addition, the second optical chopper 101210 causes the first laser signal to irradiate the crystal at a fixed frequency, and the second optical signal processing branch 102 synchronously acquires the terahertz wave signal, ensuring that each terahertz pulse excited by the terahertz radiation source 1013 can be accurately captured, avoiding or reducing signal misalignment in time.

[0070] Optionally, the incident pulse generation branch 1012 further includes a fifth half-wave plate 101220 disposed after the second optical chopper 101210 and before the terahertz radiation source 1013. The fifth half-wave plate 101220 is used to adjust the direction of the continuous laser beam to a horizontal direction.

[0071] As can be seen, in this optional embodiment, the beam direction is adjusted to a horizontal direction by the fifth half-wave plate 101220 before being incident on the terahertz radiation source 1013, which is beneficial to improving the energy and stability of the multi-cycle terahertz pulses radiated by the terahertz radiation source 1013.

[0072] Alternatively, the incident pulse generation branch 1012 may further include a dual cylindrical telescope system 101230 positioned after the fifth half-wave plate 101220 and before the terahertz radiation source 1013. The dual cylindrical telescope system 101230 is used to shape the continuous laser beam.

[0073] In this optional embodiment, the dual cylindrical telescope system 101230 is primarily used to shape the incident laser beam. More specifically, the tangential lens is used to adjust the size of the beam in the tangential direction (vertical direction), and the sagittal plane lens is used to adjust the size of the beam in the bending direction (horizontal direction), so that the laser can pass completely through the effective aperture of the PPLN crystal, improving conversion efficiency and avoiding or reducing beam clipping.

[0074] Alternatively, the incident pulse generation branch 1012 may further include an aperture stop 101240 disposed after the dual cylindrical telescope system 101230 and before the terahertz radiation source 1013. The aperture stop 101240 is used to filter the continuous laser beam.

[0075] In this optional embodiment, the light beam of the first optical signal processing branch 101 needs to pass through the aperture stop 101240 before entering the terahertz radiation source 1013 (such as a PPLN crystal). Since the actual laser beam may have edge stray light or irregular shape, the aperture stop 101240 plays a spatial filtering role, allowing only the central part of the beam to pass through. It ensures that the beam that finally enters the terahertz radiation source 1013 (such as a PPLN crystal) is controlled within the effective aperture range of the terahertz radiation source 1013 (such as a PPLN crystal), avoiding or reducing the occurrence of non-uniform phase matching, thermal damage or edge burning, terahertz instability or mode distortion caused by the laser beam hitting the edge of the crystal.

[0076] The foregoing has provided a detailed description of a terahertz signal generation device for a parallel grating-coordinated chirped beat frequency technology disclosed in the embodiments of this utility model. Specific embodiments have been used to illustrate the principle and implementation of this utility model. However, the above preferred embodiments are not intended to limit this utility model. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​this utility model. At the same time, for those skilled in the art, based on the idea of ​​this utility model, there will be changes in the specific implementation and application scope without departing from the spirit and scope of this utility model. Therefore, the protection scope of this utility model is determined by the scope defined in the claims.

Claims

1. A terahertz signal generation device using parallel grating pair cooperative chirped beat frequency technology, characterized in that, The device includes: A first optical signal processing branch (101), a second optical signal processing branch (102), and a signal detector (103); wherein, the first optical signal processing branch (101) includes a parallel grating pair (1011), an incident pulse generation branch (1012), and a terahertz radiation source (1013). The first optical signal processing branch (101) generates a chirped pulse after receiving the first laser signal; the chirped pulse generates an initial incident pulse after passing through the incident pulse generation branch (1012); the initial incident pulse is incident on the terahertz radiation source (1013) and generates a multi-period terahertz pulse; the multi-period terahertz pulse and the second laser signal are combined in the second optical signal processing branch (102) and then act on the signal detector (103), which detects and generates a terahertz wave signal; wherein the first laser signal and the second laser signal are obtained by splitting the initial laser pulse by a beam splitter, and the energy ratio of the first laser signal is higher than that of the second laser signal.

2. The terahertz signal generation device for parallel grating pair cooperative chirped beat frequency technology according to claim 1, characterized in that, The first optical signal processing branch (101) further includes: a first off-axis parabolic mirror (1014) disposed after the terahertz radiation source (1013); wherein, the multi-period terahertz pulse enters the second optical signal processing branch (102) after passing through the first off-axis parabolic mirror (1014) and is combined with the second laser signal; And / or, The second optical signal processing branch (102) includes a second off-axis parabolic mirror (1021); The multi-period terahertz pulse and the second laser signal are combined at the second off-axis parabolic mirror (1021).

3. The terahertz signal generation device for parallel grating pair cooperative chirped beat frequency technology according to claim 2, characterized in that, The second optical signal processing branch (102) further includes an optical delay unit (1022) disposed before the second off-axis parabolic mirror (1021). In addition, the second optical signal processing branch (102) further includes a filter (1023) disposed between the optical delay unit (1022) and the second off-axis parabolic mirror (1021). In addition, the second optical signal processing branch (102) further includes a first lens (1024) disposed between the filter (1023) and the second off-axis parabolic mirror (1021).

4. The terahertz signal generation apparatus for the parallel grating pair cooperative chirped beat frequency technology according to any one of claims 1-3, characterized in that, The signal detector (103) includes: The electro-optic sampling crystal (1031), quarter-wave plate (1032), Wollaston prism (1033), and two photodetectors (1034) are arranged in sequence. The electro-optic sampling crystal (1031) converts the electric field information of the multi-period terahertz pulse into the polarization information of the second laser signal; the quarter-wave plate (1032) converts the linearly polarized light of the second laser signal into circularly polarized light to adjust the polarization state of the second laser signal; the Wollaston prism (1033) splits the second laser signal after the polarization state adjustment into two linearly polarized beams with mutually perpendicular vibration directions; and the two photodetectors (1034) respectively detect the light intensity of the two linearly polarized beams.

5. The terahertz signal generation device for parallel grating pair cooperative chirped beat frequency technology according to claim 1, characterized in that, The incident pulse generation branch (1012) includes: The first chirped pulse processing sub-device (10121) and the reflective grating (10122); The chirped pulse is processed by the first chirped pulse processing sub-device (10121) to form a first pulse signal. The first pulse signal is then processed by the reflection grating (10122) to generate a tilted wavefront pulse, which serves as the initial incident pulse incident on the terahertz radiation source (1013).

6. The terahertz signal generation device for parallel grating pair cooperative chirped beat frequency technology according to claim 5, characterized in that, The incident pulse generation branch (1012) further includes: A first optical chopper (10123) is disposed between the first chirped pulse processing sub-device (10121) and the reflective grating (10122). Furthermore, the incident pulse generation branch (1012) further includes: A first half-wave plate (10124) is disposed between the first optical chopper (10123) and the reflective grating (10122).

7. The terahertz signal generation device for parallel grating pair cooperative chirped beat frequency technology according to claim 5, characterized in that, The incident pulse generation branch (1012) further includes: A second half-wave plate (10125) and an imaging system (10126) are sequentially arranged between the reflective grating (10122) and the terahertz radiation source (1013); the imaging system (10126) includes a second lens (101261) and a third lens (101262).

8. The terahertz signal generation apparatus for parallel grating pair cooperative chirped beat frequency technology according to any one of claims 5-7, characterized in that, The first chirped pulse processing sub-device (10121) includes: a Michel interferometer (101211), which splits the chirped pulse to generate two pulses with relative time delay and combines the two pulses to form a multi-period pulse, wherein the first pulse signal is the multi-period pulse; or, The first chirped pulse processing sub-device (10121) includes: a first Fabry-Perot cavity (101212), wherein the chirped pulse generates two outgoing pulses with relative time delay after passing through the first Fabry-Perot cavity (101212), and the two outgoing pulses overlap to form a quasi-sinusoidal light intensity envelope modulated electromagnetic wave pulse, and the first pulse signal is the electromagnetic wave pulse; wherein, the first chirped pulse processing sub-device (10121) further includes: a third half-wave plate (101213) and a first polarizer (101214).

9. The terahertz signal generation device for parallel grating pair cooperative chirped beat frequency technology according to claim 1, characterized in that, The incident pulse generation branch (1012) includes: a second Fabry-Perot cavity (10127); the chirped pulse generates two outgoing pulses with relative time delay after passing through the second Fabry-Perot cavity (10127), and the two outgoing pulses overlap to form a quasi-sinusoidal light intensity envelope modulated electromagnetic wave pulse; Furthermore, the incident pulse generation branch (1012) further includes a fourth half-wave plate (10128) and a second polarizer (10129), wherein the fourth half-wave plate (10128) and the second polarizer (10129) are sequentially disposed after the second Fabry-Perot cavity (10127) and before the terahertz radiation source (1013).

10. The terahertz signal generation device for parallel grating pair cooperative chirped beat frequency technology according to claim 9, characterized in that, The incident pulse generation branch (1012) further includes a second optical chopper (101210) disposed after the second polarizer (10129) and before the terahertz radiation source (1013). In addition, the incident pulse generation branch (1012) further includes a fifth half-wave plate (101220) disposed after the second optical chopper (101210) and before the terahertz radiation source (1013). In addition, the incident pulse generation branch (1012) further includes a dual cylindrical telescope system (101230) disposed after the fifth half-wave plate (101220) and before the terahertz radiation source (1013). In addition, the incident pulse generation branch (1012) further includes an aperture stop (101240) disposed after the dual cylindrical telescope system (101230) and before the terahertz radiation source (1013).

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