A polarization-tunable ultrashort and ultra-intense mid-infrared pulse system

Abstract

This invention relates to a polarization-tunable ultrashort, ultra-intense mid-infrared pulse system, comprising: a laser source for generating an incident laser beam, wherein the incident laser beam is a linearly polarized laser; a plasma unit for providing a plasma environment for the transmission of the incident laser; and a magnetic field generating unit for providing a unidirectional magnetizing magnetic field to the plasma environment. The polarization direction of the incident laser is set at an angle to the magnetization direction of the magnetic field. The incident laser, based on the unidirectionally magnetized plasma environment, generates a circularly polarized mid-infrared pulse using relativistic magnetic birefringence or the Faraday effect. This scheme generates polarization-tunable, relativistically intense, short-period, long-wavelength mid-infrared pulses through the interaction of linearly polarized laser and unidirectionally magnetized plasma. It maintains high pulse quality while achieving precise control of the mid-infrared pulse polarization state.

Description

Technical Field

[0001] This invention relates to the field of laser plasma technology, and in particular to a polarization-tunable ultrashort and ultra-intense mid-infrared pulse system. Background Technology

[0002] Mid-infrared light is a band of light in the electromagnetic spectrum, with wavelengths between terahertz and near-infrared waves, typically defined as 2 to 20 μm. Compared to visible light, this band has a longer wavelength and lower frequency, and corresponds to many biological and chemical absorption spectra. Polarization-tunable ultrashort, ultra-intense mid-infrared waves play a crucial role in various fields such as molecular spectroscopy, strong-field physics, and attosecond science due to their unique physical properties. In molecular spectroscopy, polarization-tunable mid-infrared pulses are primarily used for the structural analysis of chiral molecules. The chiral structure of biomolecules directly affects their function; however, traditional spectroscopy cannot distinguish their mirror isomers. By utilizing the selective interaction between circularly polarized mid-infrared light and chiral molecules, the left-handed and right-handed configurations of molecules can be directly identified. Furthermore, short-period mid-infrared pulses can capture transient processes of chemical bond breaking and formation, providing ultra-high temporal resolution. In addition, in strong-field physics, when linearly polarized lasers drive electron oscillations, electrons tend to return to the parent nucleus and collide, while circularly polarized light can suppress electron return, achieving directional acceleration. For example, in the acceleration of electrons in a wakefield, relativistically strong circularly polarized mid-infrared light can improve electron injection efficiency and quantity, suppress the divergence angle of the electron beam, and enhance acceleration stability. In the generation of higher harmonics, circularly polarized mid-infrared pulses can increase the distance between the electron and the nucleus, and longer-wavelength driving light can possess higher-energy manifold potentials, thus obtaining higher harmonics with higher cutoff energies. In attosecond science, the energy of an attosecond pulse is limited by the incident laser wavelength. Long-wavelength, strong mid-infrared light sources can extend the cutoff energy of higher harmonics, and the higher the cutoff energy of higher harmonics, the wider the spectral bandwidth, making it easier to shorten the pulse width to obtain shorter attosecond pulses. Furthermore, circularly polarized mid-infrared light can be used to generate vortex attosecond pulses, enabling the resolved measurement of electron angular momentum. Therefore, polarization-tunable ultrashort and ultra-intense mid-infrared pulse technology not only plays an important role in basic scientific research but also demonstrates broad application prospects in practical applications.

[0003] Although CO2 lasers can currently directly generate high-intensity mid-infrared pulses, their energy level structure limits them to producing fixed wavelengths of 9.4 μm or 10.8 μm, making wavelength tuning impossible. To meet the urgent need for broadband mid-infrared pulses, several new schemes for generating ultrashort mid-infrared pulses using nonlinear optical methods have emerged. Common nonlinear optical methods include optical parametric chirped pulse amplification (OPCPA), difference frequency generation, and optical rectification. However, nonlinear optical crystals typically have damage threshold limitations, preventing the intensity of the input light from being increased indefinitely to obtain strong mid-infrared pulses.

[0004] Plasma, a substance composed of charged particles, has virtually no damage threshold, allowing powerful lasers to propagate within it. This advantage makes the study of laser-plasma interaction physics a crucial branch of plasma physics. When an ultrashort, ultra-intense laser propagates in a low-density plasma, the driving force of the laser completely displaces electrons from the plasma, creating a nonlinear wake—a three-dimensional cavity structure, also known as a "cavitation" structure. The cavity front has a positive density gradient, resulting in a negative refractive index gradient, causing the laser to redshift (wavelength increase), or "photon deceleration." Due to group velocity dispersion, the group velocity of the long-wavelength mid-infrared pulse is lower than that of the driving laser. Therefore, the mid-infrared pulse recedes rapidly relative to the driving laser into the cavity and moves forward with it. Since the cavity contains almost no or very few electrons, it does not drastically modulate the mid-infrared pulse. Thus, the cavity can act as a container for storing the mid-infrared pulse until it leaves the plasma. However, this approach lacks a polarization modulation mechanism and can only generate mid-infrared pulses with fixed polarization states.

[0005] It is evident that CO2 lasers, due to limitations in their energy level structure, can only generate mid-infrared light of specific wavelengths, failing to meet the demand for broadband mid-infrared pulses. Nonlinear crystals, limited by their damage threshold, cannot generate mid-infrared pulses of relativistic intensity, and their phase-matching conditions force polarization locking, making polarization tunability impossible. Plasma self-modulation can generate ultrashort, ultra-intense mid-infrared pulses, but polarization cannot be controlled. Therefore, how to generate an ultrashort, ultra-intense mid-infrared pulse with tunable polarization has become a pressing problem to be solved. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a polarization-tunable ultrashort and ultra-intense mid-infrared pulse system.

[0007] To achieve the above-mentioned objectives, this invention provides a polarization-tunable ultrashort, ultra-intense mid-infrared pulse system, comprising:

[0008] A laser source for generating an incident laser beam, wherein the incident laser beam is a linearly polarized laser beam;

[0009] A plasma unit is used to provide a plasma environment for the transmission of the incident laser.

[0010] A magnetic field generating unit is used to provide a magnetic field that magnetizes the plasma environment in one direction.

[0011] The polarization direction of the incident laser is set at an angle to the magnetization direction of the magnetic field;

[0012] The incident laser is based on a plasma environment magnetized in one direction and generates a circularly polarized mid-infrared pulse using the relativistic magnetic birefringence effect or the Faraday effect.

[0013] According to one aspect of the invention, the angle between the polarization direction of the incident laser and the magnetization direction of the magnetic field is 45°.

[0014] According to one aspect of the invention, the incident laser is synthesized from O-rays parallel to the magnetization direction of the magnetic field and X-rays perpendicular to the magnetization direction of the magnetic field.

[0015] According to one aspect of the invention, the plasma density in the plasma environment is less than 0.01 times the critical density.

[0016] According to one aspect of the invention, the plasma unit comprises, along the input-to-output direction, an input segment, a conversion segment, and an output segment connected in sequence.

[0017] In the input section, the incident laser enters the plasma environment and drives the plasma to generate a cavitation structure;

[0018] In the conversion section, the incident laser generates a mid-infrared pulse at the front end of the cavitation structure, and the mid-infrared pulse enters the cavitation structure and moves forward together with the cavitation structure.

[0019] In the output section, the cavitation structure moves forward in the output section and gradually expands until the mid-infrared pulse in the cavitation structure leaves the plasma environment.

[0020] According to one aspect of the invention, along the input-to-output direction of the plasma unit, the plasma electron number density in the input segment is configured to gradually increase, the plasma electron number density in the conversion segment is configured to remain constant, and the plasma electron number density in the output segment is configured to gradually decrease.

[0021] According to one aspect of the invention, along the input-to-output direction of the plasma unit, the plasma electron number density in the input segment is set to increase linearly, and the plasma electron number density in the output segment is set to decrease linearly.

[0022] According to one aspect of the invention, along the input-to-output direction of the plasma unit, the length of the conversion section is greater than the lengths of the input section and the output section.

[0023] According to one aspect of the invention,

[0024] If a circularly polarized mid-infrared pulse is generated using the relativistic magnetic birefringence effect, then the magnetic field generating unit is used to provide a transversely magnetized magnetic field to the plasma environment.

[0025] If the Faraday effect is used to generate circularly polarized mid-infrared pulses, then the magnetic field generating unit is used to provide a longitudinally magnetizing magnetic field for the plasma environment.

[0026] According to one aspect of the present invention, the magnetic field strength of the magnetic field generated by the magnetic field generating unit is adjustable, and the magnetic field strength is set to 1200T to 1600T.

[0027] According to one aspect of the present invention, this method generates mid-infrared pulses with tunable polarization, relativistic intensity, few periods, and long wavelengths through the interaction of linearly polarized laser with unidirectional magnetized plasma. This maintains high pulse quality while achieving precise control of the mid-infrared pulse polarization state.

[0028] According to one aspect of the present invention, this aspect creatively proposes a relativistic magnetic birefringence theory, which enables polarization modulation while generating mid-infrared light of relativistic intensity.

[0029] According to one aspect of the present invention, the high-quality mid-infrared light source generated by this approach has the characteristics of adjustable polarization, relativistic intensity, few periods, and long wavelength.

[0030] According to one aspect of the present invention, in terms of polarization control, the polarization can be precisely adjusted by changing the magnitude of the magnetic field; in terms of pulse intensity, a mid-infrared pulse with relativistic intensity can be generated in magnetized plasma; and in terms of pulse characteristics, a short-period, long-wavelength circularly polarized mid-infrared pulse can be generated within a wide range of parameters.

[0031] According to one aspect of the present invention, this approach can stably generate ultra-short, ultra-intense mid-infrared pulses with adjustable polarization over a wide parameter range. Attached Figure Description

[0032] Figure 1 This is a structural block diagram of a polarization-tunable ultrashort and ultra-intense mid-infrared pulse system according to one embodiment of the present invention.

[0033] Figure 2 This is a schematic diagram of a structure in one embodiment of the present invention;

[0034] Figure 3 In one embodiment of the present invention, the distribution of electric field and electron density, refractive index variation and refractive index gradient variation, and Wigner spectrum of the input section, conversion section, and output section of the plasma unit are shown, wherein... Figure 3 (a) shows the laser electric field distribution, electron density distribution, and refractive index variation at different locations in a portion of the input segment. Figure 3 (b) shows the laser electric field distribution, electron density distribution, and refractive index variation at different locations in the partial conversion segment. Figure 3 (c) shows the laser electric field distribution, electron density distribution, and refractive index variation at different locations in a portion of the output segment. Figure 3 (d) shows the refractive index gradient changes and Wigner spectra at different locations in a portion of the input segment. Figure 3 (e) shows the refractive index gradient changes and Wigner spectra at different locations in a portion of the transformation segment. Figure 3 (f) shows the refractive index gradient changes and Wigner spectra at different positions in a portion of the output segment;

[0035] Figure 4 This is a quality map of a simulated mid-infrared pulse in one embodiment of the present invention, wherein... Figure 4 (a) shows the generated mid-infrared pulse pattern. Figure 4 (b) shows a comparison of the spectra at the initial and final moments. Figure 4 (c) shows the trend changes of the V component of the infrared pulse in a portion of the output segment, the trend changes of the phase difference between the O-beam and the X-beam, and the trend changes of the electric field components of the O-beam and the X-beam.

[0036] Figure 5 In one embodiment of the present invention, Lissajous figures and Stokes parametric plots of mid-infrared pulses simulated under different magnetic field strengths are shown, wherein... Figure 5 (a) The figure shows the Lissajous figure of a mid-infrared pulse with a magnetic field strength of 800T. Figure 5 (b) The Lissajous figure represents a mid-infrared pulse with a magnetic field strength of 1200T. Figure 5 (c) represents the Lissajous figure of a mid-infrared pulse under a magnetic field strength of 1600T. Figure 5 (d) shows the Stokes parametric plot of a mid-infrared pulse under a small magnetic field strength. Figure 5 (e) shows the Stokes parametric plot of the mid-infrared pulse under medium magnetic field strength. Figure 5 (f) shows the Stokes parametric plot of a mid-infrared pulse under a large magnetic field strength;

[0037] Figure 6 In one embodiment of the present invention, a graph showing the change in the quality of a simulated mid-infrared pulse as the intensity of the incident laser increases is provided. Figure 6 (a) shows a comparison of the spectra of the incident laser at the initial and final moments. Figure 6 (b) shows the Lissajous figure representing the generated mid-infrared pulse. Figure 6 (c) shows the quality parameters of the mid-infrared pulse under different incident laser intensities. Figure 6 (d) shows the Stokes parameters of mid-infrared pulses under different incident laser intensities;

[0038] Figure 7 This is a quality map of a simulated mid-infrared pulse generated under different plasma background densities, conversion section lengths, and output section lengths in one embodiment of the present invention. Figure 7 (a) represents the Stokes parameters of mid-infrared pulses under different plasma background densities. Figure 7 (b) Stokes parameters of mid-infrared pulses under different conversion segment lengths Figure 7 (c) represents the Stokes parameters of the mid-infrared pulse under different output segment lengths. Figure 7 (d) represents the quality parameters of the mid-infrared pulse under different plasma background densities. Figure 7 (e) represents the quality parameters of the mid-infrared pulse under different conversion segment lengths. Figure 7 (f) represents the quality parameters of the mid-infrared pulse under different output segment lengths. Detailed Implementation

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0040] When describing embodiments of the present invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer" express orientations or positional relationships based on the orientations or positional relationships shown in the relevant drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limitations on the present invention.

[0041] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The embodiments cannot be described in detail here, but the embodiments of the present invention are not limited to the following embodiments.

[0042] like Figure 1As shown, according to one embodiment of the present invention, a polarization-tunable ultrashort and ultra-intense mid-infrared pulse system includes: a laser source 1, a plasma unit 2, and a magnetic field generating unit 3; wherein, the laser source 1 is used to generate an incident laser beam, and the incident laser beam is a linearly polarized laser beam; the plasma unit 2 is arranged opposite to the laser source 1, thereby providing a plasma environment for the transmission of the incident laser, wherein the provided plasma environment is filled with plasma; further, the magnetic field generating unit 3 is arranged around the plasma unit 2 to provide a unidirectional magnetized magnetic field to the plasma environment, thereby allowing the incident laser to propagate in the magnetized plasma environment. In this embodiment, the polarization direction of the incident laser is set at an angle to the magnetization direction of the magnetic field; thereby, the incident laser generates a circularly polarized mid-infrared pulse based on the unidirectionally magnetized plasma environment and utilizing the relativistic magnetic birefringence effect or the Faraday effect.

[0043] According to one embodiment of the present invention, the angle between the polarization direction of the incident laser and the magnetization direction of the magnetic field is 45°.

[0044] The above settings effectively ensure the accurate and reliable generation of circularly polarized infrared pulses.

[0045] According to one embodiment of the present invention, the incident laser is synthesized from O-rays parallel to the magnetization direction of the magnetic field and X-rays perpendicular to the magnetization direction of the magnetic field. In this embodiment, the wavelength formula of the incident laser can be expressed as:

[0046] ;

[0047] in, This indicates the laser wavelength of the mid-infrared pulse. Indicates the incident laser wavelength. Represents the speed of light. Indicates refractive index, Indicates the coordinates of the co-motion transmission. Represents the time integral element. Indicates the interaction time.

[0048] According to one embodiment of the present invention, the plasma density in the plasma environment is low; specifically, the plasma density in the plasma environment is set within a range less than 0.01 times the critical density. In this embodiment, the plasma density in the plasma environment is preferably much less than 0.01 times the critical density, i.e., it is set within a range of ×10. 18 cm -3 The magnitude range is [not specified]. Based on the above settings, the stable generation of cavitation structures in plasma unit 2 is effectively guaranteed, providing a reliable guarantee for the stable operation of this scheme.

[0049] According to one embodiment of the present invention, along the input-to-output direction of the plasma unit 2, the plasma unit 2 includes an input segment, a conversion segment, and an output segment connected in sequence. In this embodiment, in the input segment, the incident laser enters the plasma environment and drives the plasma to generate a cavitation structure. The plasma electron number density in the input segment is gradually increased along the input-to-output direction of the plasma unit. Specifically, according to the one-dimensional nonlinear wakefield theory, the cavitation structure generated by the incident laser entering the plasma environment and driving the plasma is a nonlinear wakefield with a cavitation shape. Furthermore, the formation of the nonlinear wakefield leads to changes in the refractive index and its gradient, thereby causing a change in the local frequency of the incident laser.

[0050] In this embodiment, in the conversion section, the incident laser generates a mid-infrared pulse at the front end of the cavitation structure, and the mid-infrared pulse enters the cavitation structure and moves forward with it. The plasma electron number density in the conversion section is kept constant. Because the plasma density in the plasma environment is relatively low in the conversion section, the incident laser undergoes a mild frequency down-conversion, i.e., photon deceleration. Specifically, based on the aforementioned wavelength formula for laser wavelength, it can be seen that at the front end of the cavitation structure, a positive density gradient leads to a negative refractive index gradient, i.e. Therefore, the laser wavelength becomes longer, thus generating a mid-infrared pulse. Since the mid-infrared pulse has a smaller group velocity than the driving laser pulse, it lags behind the driving laser pulse (i.e., the incident laser) and enters the cavitation structure. At this point, because the cavitation structure contains almost no or very few electrons, it acts as an ideal container for the mid-infrared pulse, effectively preserving it until it leaves the plasma environment.

[0051] In this embodiment, in the output section, the cavitation structure moves forward and gradually expands until the mid-infrared pulse within the cavitation structure leaves the plasma environment. Furthermore, the plasma electron number density in the output section is gradually reduced. Specifically, the generated mid-infrared pulse must be extracted from the plasma, and the extraction process must not result in attenuation due to absorption or dispersion diffusion. Therefore, gradually reducing the plasma electron number density in the output section can increase the wake size; it is known that the size of the cavitation structure is inversely proportional to the plasma density, i.e. , The characteristic length used to characterize the size of the cavitation structure. For plasma frequency, As the normalized intensity of the laser decreases, the plasma density decreases, the frequency decreases, and the cavitation structure increases accordingly. This ensures that the mid-infrared pulse has no energy loss or further frequency change within the cavitation structure. Furthermore, as the cavitation structure gradually increases with the decreasing plasma density, it creates a dynamic output channel for the mid-infrared pulse, directly reaching the position of minimum plasma density. This not only better enables the storage of mid-infrared pulses but also allows for lossless output of mid-infrared pulses as the plasma gradually disappears.

[0052] According to one embodiment of the present invention, along the input-to-output direction of the plasma unit 2, the plasma electron number density in the input segment is set to increase linearly, and the plasma electron number density in the output segment is set to decrease linearly.

[0053] By setting the plasma electron number density linearly in the input segment, the incident laser is made more reliable and stable in the process of forming a cavitation structure. In the output segment, the plasma electron number density is set linearly to decrease, so that the trend of increasing cavitation structure during the output process changes linearly. This ensures that the cavitation structure is kept stable during the output process until the minimum plasma electron number density is reached, so as to achieve reliable output of mid-infrared pulse.

[0054] According to one embodiment of the present invention, along the input-to-output direction of the plasma unit 2, the length of the conversion segment is greater than the lengths of the input segment and the output segment. The lengths of the input segment and the output segment can be the same or different; for example, the length of the input segment is less than the length of the output segment. Based on this, the stroke and transport process of the mid-infrared pulse can be flexibly controlled by flexibly controlling the length of each segment. In particular, by adjusting the length of the output segment, the efficiency and extent of cavitation structure expansion during the output process can be flexibly controlled, thereby providing more favorable conditions for the storage and lossless output of the mid-infrared pulse, and further improving the working performance of this solution.

[0055] According to one embodiment of the present invention, a magnetic field generating unit is used to provide a transversely magnetizing or longitudinally magnetizing magnetic field to a plasma environment; specifically, if a circularly polarized mid-infrared pulse is generated using the relativistic magnetic birefringence effect, the magnetic field generating unit is used to provide a transversely magnetizing magnetic field to the plasma environment; if a circularly polarized mid-infrared pulse is generated using the Faraday effect, the magnetic field generating unit is used to provide a longitudinally magnetizing magnetic field to the plasma environment. In this embodiment, the magnetic field strength generated by the magnetic field generating unit is adjustable, and the magnetic field strength is from 1200T to 1600T.

[0056] With the above settings, this scheme, by setting the magnetic field generation unit with adjustable magnetic field strength, can achieve flexible and accurate adjustment of the plasma environment in the plasma unit. Thus, the different polarization states of the output mid-infrared pulse can be adjusted by changing the magnitude of the magnetic field strength.

[0057] Based on the aforementioned setup, the incident laser used is a combination of O-rays (parallel to the magnetization direction of the magnetic field) and X-rays (perpendicular to the magnetization direction of the magnetic field). Therefore, according to the relativistic magnetic birefringence effect, the O-rays and X-rays have different dispersion relations:

[0058] ;

[0059] ;

[0060] in, This represents the angular frequency of the incident laser. Indicates the wavenumber of the incident laser. Indicates the background plasma density. Represents the plasma electron number density. Represents the relativistic factor. and These represent the plasma frequency and the electron cyclotron frequency, respectively. Indicates the amount of charge on an electron. Represents the dielectric constant. Indicates electron mass, Indicates magnetic field strength. and These are the phase velocities of the O-ray and X-ray, respectively. Due to the difference in phase velocities, a phase difference will occur. :

[0061] ;

[0062] when At that time, linearly polarized light is converted into circularly polarized light, where The propagation length of the incident laser in the plasma. The wavelength of the incident laser light. When and At that time, the phase difference can be simplified to:

[0063] .

[0064] Therefore, when the incident laser is a linearly biased laser, its phase difference is 0. Based on the aforementioned settings of this scheme, the phase difference can be precisely adjusted to convert it into the circularly polarized mid-infrared pulse of this scheme.

[0065] To further illustrate this plan, further examples will be provided.

[0066] Example 1

[0067] like Figure 2 As shown, a three-dimensional PIC simulation of this scheme is performed. In the simulation environment, a relativistic intensity laser beam is incident from left to right along the x-axis. The simulation box is set to have a length of 50 μm and a width and height of 70 μm. The spatial resolution in the x-direction of the three-dimensional simulation is [missing information]. The spatial resolution in the y and z directions is The total length of the plasma unit is 1700 μm, the rising edge length of the input section and the falling edge length of the output section are both 400 μm, and the platform length of the conversion section is 900 μm.

[0068] In this embodiment, the normalized intensity of the incident laser is The pulse width (FWHM) is 23.1 fs, and the pulse envelope uses... Shape, size of the foci .

[0069] In this embodiment, the control magnetic field generating unit applies a transverse magnetic field to the plasma unit, and the magnetic field strength of the transverse magnetic field is... .

[0070] In this embodiment, a moving window technique is used to acquire the distribution of electric field and electron density, refractive index changes and refractive index gradient changes, and Wigner spectra in the input, conversion, and output sections, and to... Figure 3 Display. For example... Figure 3 (a)- Figure 3 As shown in (c), when a relativistically strong incident laser enters the plasma, the mass dynamics of the incident laser displace electrons, forming a stable cavitation structure. Different plasma density perturbations occur at different longitudinal positions within the cavitation structure, resulting in different refractive indices. η) In the coordinate system that propagates in sync with the incident laser, the position where the refractive index gradient is greater than zero. Laser light undergoes a blue shift (wavelength shortening) at locations where the refractive index gradient is less than zero. Laser light undergoes a redshift (wavelength increase), a phenomenon known as "photon deceleration." For example... Figure 3 (d)- Figure 3 As shown in (f), with the compression of the laser, the laser intensity is further increased, the mass dynamics are enhanced, the electron perturbation density in the plasma increases, and the laser pulse also senses a stronger refractive index gradient, thus generating mid-infrared pulses faster.

[0071] Furthermore, by Figure 3(c) As can be seen, due to the group velocity dispersion effect, the group velocity of the mid-infrared pulse with a long wavelength is less than that of the driving laser. Therefore, the mid-infrared pulse recedes rapidly into the cavitation structure relative to the driving laser and moves forward with the cavitation structure. Since there are almost no or very few electrons in the cavitation, the mid-infrared pulse is not drastically modulated inside. Therefore, the cavitation structure can serve as a container for storing the mid-infrared pulse until it leaves the plasma.

[0072] Based on the above initial parameter settings, the center wavelength of the mid-infrared pulse is 8.33 μm, the wavelength range is 6.25 μm to 16.67 μm, and the normalized intensity of the mid-infrared pulse is... a =0.84, pulse width is 66.4 fs, and number of cycles is 2.4. For example... Figure 4 (a) and Figure 4 As shown in (b), a strong mid-infrared pulse with a long wavelength, short period, and circular polarization was successfully generated. Therefore, the polarization of the generated mid-infrared pulse can be explained using the Stokes parameters, which include: I , Q , U , V Four parameters, , , , ,in, Indicates mid-infrared pulse in y Electric field components in the direction, Indicates mid-infrared pulse in z Electric field components in the direction, express The complex conjugate, Indicates taking the real part, This indicates taking the imaginary part. I Indicates an intensity independent of polarization. Q express y (+) or z Linearly polarized light along the (-) axis, U Indicates and y Linearly polarized light with its axis at +45° (+) or -45° (-) V This indicates right-handed (+) or left-handed (-) circular polarization.

[0073] For ease of comparison, all parameters are normalized to the initial peak intensity, and then... Figure 4 (c) It can be seen that under the influence of a magnetic field, V Gradually reaching -0.99, Gradually reach Mid-infrared pulse in y and zThe phase difference of the components along the axial direction is exactly one-quarter of a period. Calculations show that the theoretical formula yields a phase difference of -4.74, which is close to... The results are highly consistent with the simulation results, indicating that this scheme can generate infrared pulses in circular polarization.

[0074] As mentioned earlier, this scheme can generate infrared pulses in circular polarization, and as... Figure 5 (a) and Figure 5 As shown in (d), when the magnetic field strength is small, the circular polarization component of the mid-infrared pulse is relatively small. Most of it is still linearly polarized light. For example... Figure 5 (b) and Figure 5 As shown in (e), with the increase of magnetic field strength, the circular polarization component of the infrared pulse increases. V =-0.7, linear polarization component Q and U Reduced, the overall polarization is elliptically oriented. For example... Figure 5 (c) and Figure 5 As shown in (f), the linear polarization component of the mid-infrared pulse Q and U The value is almost zero, and the circular polarization component is almost equal to the total intensity. V =-0.99. As can be seen from the magnetostrictive birefringence effect, the magnetic field plays a crucial role in regulating the polarization state of the generated mid-infrared pulses. Different magnetic field strengths result in different phase differences between the O-ray and X-rays, thus producing mid-infrared pulses with different polarization states. Therefore, this scheme can achieve the regulation of mid-infrared pulses with different polarization states by setting up a magnetic field generating unit with adjustable magnetic field strength.

[0075] Furthermore, to obtain relativistically strong mid-infrared pulses, a direct and effective method is to increase the intensity of the incident laser. See also Figure 6 It demonstrates the change in the quality of the generated mid-infrared pulses as the intensity of the incident laser increases, among which... N This indicates the number of cycles of the mid-infrared pulse. This indicates the center wavelength of the mid-infrared pulse. R Indicates mid-infrared pulse in y and z The ratio of the electric field components in the direction, i.e. E y / E z , R The closer the value is to 1, the more rounded the mid-infrared pulse is. This represents the normalized intensity of the mid-infrared pulse. Figure 6 (a) and Figure 6 (b) shows the normalized intensity of the incident laser. The magnetic field strength of the applied transverse magnetic field is In this case, the center wavelength of the generated mid-infrared pulse is 10 μm, and the normalized intensity of the mid-infrared pulse is... This reaches a relativistic intensity. As shown in the Lissajous figure, this mid-infrared pulse is still light that is very close to circularly polarized. Figure 6 As shown in (c), the normalized intensity of the incident laser is further increased to... The magnetic field strength of the applied transverse magnetic field is The center wavelength of the generated mid-infrared pulse continues to increase, and the normalized intensity of the mid-infrared pulse also continues to increase. The wavelength of the mid-infrared pulse increases with increasing incident laser intensity because higher incident light intensity results in a larger absolute value of the refractive index gradient. Since this gradient is negative, the refractive index gradient is smaller. Therefore, the wavelength of the mid-infrared pulse will become longer, and the number of cycles will increase. N It will naturally become smaller. For example... Figure 6 As shown in (d), even under different incident light intensities, it is still possible to generate near-circularly polarized mid-infrared pulses, with the linear polarization component not exceeding 0.5 and the circular polarization component remaining close to -1. In this embodiment, if it is desired to obtain circularly polarized mid-infrared pulses even when the incident light intensity is increased, the phase difference between the O-ray and X-ray remains close to 0.5. The applied magnetic field strength needs to be reduced, which is controlled based on the aforementioned phase difference formula, i.e. When the intensity of the incident laser increases, the wavelength... With relativistic factor Both will increase, and the increase will be almost the same, so the effect on the phase difference is almost negligible. However, a stronger incident light intensity will excite a larger density gradient, i.e. It will increase, if you still want to make Then it is necessary to reduce the magnetic field to make The intensity decreases. Furthermore, this scheme can obtain relativistically intense, short-period, long-wavelength, circularly polarized mid-infrared pulses by increasing the intensity of the incident light.

[0076] Furthermore, Figure 7 Displaying plasma densities with different backgrounds Length of the transformation section Output segment length The quality of the mid-infrared pulses is shown. It can be seen that, within a relatively wide parameter range, near-relativistic intensity, short period, long wavelength, and circularly polarized mid-infrared pulses can be generated. For example... Figure 7 (a) – Figure 7 As shown in (c), although the linear polarization component Q and U It will change with the initial parameters, but the circular polarization component VThe value remains close to -1, indicating that the generated mid-infrared pulses are all nearly circularly polarized. For example... Figure 7 As shown in (d), the background plasma density The larger the density, the longer the wavelength of the generated mid-infrared pulse. This is because as the density increases, the density gradient of laser excitation is larger, resulting in a smaller refractive index gradient and thus a longer wavelength for the mid-infrared pulse. For example... Figure 7 (e) and Figure 7 As shown in (f), the length of the transformation segment and output segment length There is no effect on the mid-infrared pulse wavelength because the wavelength of the mid-infrared pulse is mainly related to the refractive index gradient and the cavitation size, both of which are closely related to the plasma density. If the density remains unchanged, the wavelength remains the same. However, the number of cycles in the mid-infrared pulse will increase with the length of the conversion section. and output segment length It increases with the increase of [something], because of the longer transition segment length. and output segment length This will cause more photons at the front end of the cavitation structure to be converted into mid-infrared pulses, thus increasing the period of the mid-infrared pulses. Therefore, this scheme can fully guarantee its robustness and stability by flexibly arranging the plasma environment and the length of each segment of the plasma unit.

[0077] The above description is merely an example of a specific solution of the present invention. For any devices and structures not described in detail herein, it should be understood that they are implemented using common devices and methods already available in the art.

[0078] The above description is merely one embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A polarization-tunable ultrashort, ultra-intense mid-infrared pulse system, characterized in that, include: A laser source for generating an incident laser beam, wherein the incident laser beam is a linearly polarized laser beam; wherein the incident laser beam is composed of O-rays parallel to the magnetization direction of the magnetic field and X-rays perpendicular to the magnetization direction of the magnetic field; A plasma unit is used to provide a plasma environment for the transmission of the incident laser. A magnetic field generating unit is used to provide a magnetic field that magnetizes the plasma environment in one direction. The polarization direction of the incident laser is set at an angle to the magnetization direction of the magnetic field; The incident laser is based on a plasma environment magnetized in one direction and uses the relativistic magnetic birefringence effect to generate a circularly polarized mid-infrared pulse. The magnetic field generating unit is adjustable, and the polarization state of the output mid-infrared pulse can be adjusted by changing the magnitude of the magnetic field strength. By utilizing the relativistic magnetic birefringence effect to generate circularly polarized mid-infrared pulses, the O-ray and X-ray exhibit different dispersion relations. Therefore, adjusting the phase difference based on the different phase velocities of the O-ray and X-ray is necessary. To convert circularly polarized infrared pulses; where the phase difference Expressed as: in, The value is The propagation length of the incident laser in the plasma. The incident laser wavelength is denoted as . Indicates the background plasma density. Represents the plasma electron number density. Represents the relativistic factor. and These represent the plasma frequency and the electron cyclotron frequency, respectively. Indicates the amount of charge on an electron. Represents the dielectric constant. Indicates electron mass, Indicates magnetic field strength. It represents the speed of light.

2. The polarization-tunable ultrashort and ultra-intense mid-infrared pulse system according to claim 1, characterized in that, The angle between the polarization direction of the incident laser and the magnetization direction of the magnetic field is 45°.

3. The polarization-tunable ultrashort and ultra-intense mid-infrared pulse system according to claim 2, characterized in that, The plasma density in the plasma environment is less than 0.01 times the critical density.

4. The polarization-tunable ultrashort and ultra-intense mid-infrared pulse system according to claim 3, characterized in that, Along the input-to-output direction of the plasma unit, the plasma unit includes: an input section, a conversion section, and an output section connected in sequence; In the input section, the incident laser enters the plasma environment and drives the plasma to generate a cavitation structure; In the conversion section, the incident laser generates a mid-infrared pulse at the front end of the cavitation structure, and the mid-infrared pulse enters the cavitation structure and moves forward together with the cavitation structure. In the output section, the cavitation structure moves forward in the output section and gradually expands until the mid-infrared pulse in the cavitation structure leaves the plasma environment.

5. The polarization-tunable ultrashort and ultra-intense mid-infrared pulse system according to claim 4, characterized in that, Along the input-to-output direction of the plasma unit, the plasma electron number density in the input segment is set to gradually increase, the plasma electron number density in the conversion segment is set to remain constant, and the plasma electron number density in the output segment is set to gradually decrease.

6. The polarization-tunable ultrashort and ultra-intense mid-infrared pulse system according to claim 5, characterized in that, Along the input-to-output direction of the plasma unit, the plasma electron number density in the input segment is set to increase linearly, and the plasma electron number density in the output segment is set to decrease linearly.

7. The polarization-tunable ultrashort and ultra-intense mid-infrared pulse system according to claim 6, characterized in that, Along the input-to-output direction of the plasma unit, the length of the conversion section is greater than the lengths of the input section and the output section.

8. The polarization-tunable ultrashort and ultra-intense mid-infrared pulse system according to claim 7, characterized in that, By utilizing the relativistic magnetic birefringence effect to generate circularly polarized mid-infrared pulses, the magnetic field generating unit is used to provide a transversely magnetizing magnetic field to the plasma environment.

9. The polarization-tunable ultrashort and ultra-intense mid-infrared pulse system according to claim 8, characterized in that, The magnetic field strength generated by the magnetic field generating unit is adjustable, and the magnetic field strength is set from 1200T to 1600T.

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