An efficient ultrastrong and ultrashort mid-infrared pulse system

Abstract

The present invention discloses an efficient ultra-strong and ultra-short mid-infrared pulse system, comprising: a vacuum chamber for providing a vacuum environment; a chirped optical pulse generator disposed outside the vacuum chamber for outputting an optical pulse with continuously adjustable chirp coefficient to the vacuum chamber; a plasma channel target disposed inside the vacuum chamber and having a plasma with an axially trapezoidal density distribution therein; and a beam focusing device disposed inside the vacuum chamber and on the incident optical path of the optical pulse for focusing the optical pulse and then making it incident along the axis of the plasma channel target into the plasma channel target. The present invention is applied to the field of lasers. By using a negatively chirped pulse as the driving laser for the interaction with the plasma, the rapid compression of the negatively chirped optical pulse in the plasma can effectively reduce the length of the plasma channel target used, accelerate the generation speed of the mid-infrared optical pulse and the energy conversion efficiency, and can also control the parameters of the mid-infrared pulse by adjusting the chirp coefficient of the negatively chirped optical pulse.

Description

Technical Field

[0001] The present invention relates to the technical field of lasers, and particularly to an efficient ultra-intense and ultra-short mid-infrared pulse system. Background Art

[0002] Since the birth of the laser in 1960, laser technology has developed rapidly and is now widely used in scientific research, material processing, medical treatment and other fields. Early lasers output continuously in time. By using the Q-switching method, the laser was changed to pulsed output, obtaining laser pulses with a pulse width in the nanosecond order of magnitude and a peak power in the megawatt order of magnitude. Subsequently, through the mode-locking technology, the laser pulse width was further reduced to the picosecond order of magnitude. On this basis, with the emergence of titanium sapphire and Kerr lens mode-locking technologies, ultra-short laser pulses with a pulse width of dozens of femtoseconds can already be obtained. In 1985, Strickland and Mourou proposed the chirped pulse amplification (CPA) technology, which greatly improved the output power and output intensity of the laser. The CPA technology increased the laser intensity to 10 14 -10 15 W / cm 2 , and the laser electric field strength has reached the same order of magnitude as the Coulomb field of the atom. At this time, the laser electric field can easily change the motion trajectory of electrons in the atom. When the laser intensity continues to increase to 10 18 W / cm 2 , the laser electric field is already much larger than the Coulomb field in the atom. The laser field will instantly ionize the matter into a plasma state and then interact with the plasma. At this time, the interaction between the laser and the plasma has entered the relativistic regime, and the laser electric field can accelerate electrons to relativistic speeds within one period.

[0003] In recent years, research on new radiation sources based on the interaction between lasers and plasmas has attracted extensive attention internationally. Currently, common ultra-intense lasers are all based on titanium sapphire (Ti:sapphire) or neodymium glass (Nd:glass) as the laser working medium. Due to the limitations of the energy level structure of the working medium, these two types of lasers can only directly output lasers with wavelengths of 0.8 μm and 1 μm, both of which belong to the near-infrared band. With the continuous deepening of scientific research, researchers are no longer satisfied with pulses with wavelengths of 0.8 μm and 1 μm. People expect to obtain relativistic intensity pulses in other bands to provide new methods and ideas for scientific research. Especially in the high-frequency X-ray and γ-ray parts, as well as the low-frequency terahertz wave and mid-infrared wave, the generation of these electromagnetic waves has opened new doors for the interaction between light and matter.

[0004] The mid-infrared wave lies between the terahertz wave and the near-infrared wave in the spectrum, with a wavelength range of 2μm - 20μm, which exactly corresponds to the absorption spectra of many biological or chemical molecules. Similarly, for research such as two-dimensional infrared vibrational spectroscopy, time-resolved imaging of molecular structures, and improving terahertz radiation efficiency, mid-infrared pulses are also very ideal tools. When mid-infrared pulses are boosted to relativistic intensities, new ideas and methods will be brought to the field of laser-plasma interactions. For example, research such as super-bright coherent X-ray high-order harmonic generation and charged particle acceleration. Therefore, ultra-intense and ultra-short mid-infrared pulses have important applications in frontier scientific fields such as physics, chemistry, medicine, semiconductors, and military applications.

[0005] Currently, although high-intensity mid-infrared pulses can be directly generated using a CO 2 laser, due to the energy level structure of the CO 2 laser, the CO 2 laser can only generate mid-infrared pulses with wavelengths of 9.4μm or 10.8μm and does not have tunability. Moreover, high-intensity CO 2 lasers are not of universal significance. Currently, there are only two terawatt picosecond CO 2 laser systems in the world, namely the 15TW Neptune system at UCLA and the 1TW ATF system at Brookhaven National Laboratory (BNL). To meet the need for broadband mid-infrared pulses, non-linear optical methods are usually used to generate ultra-intense and ultra-short mid-infrared pulses. The main ways to generate mid-infrared pulses by non-linear optical methods are: optical parametric amplification technology, difference frequency technology, and optical rectification technology. Although mid-infrared pulses can be generated based on the non-linear optical effects in optical crystals, due to the damage threshold limitations of optical crystals, it is difficult for these traditional methods to generate mid-infrared pulses with relativistic intensities. Plasma under ultra-intense laser conditions, as a substance composed entirely of electrons and ions, can withstand extremely high-intensity laser fields and has almost no damage threshold, which provides new ideas and approaches for the research of many radiation sources. Therefore, the method of generating mid-infrared pulses based on laser-plasma interactions has attracted great interest from researchers.

[0006] In the interaction between ultra-intense laser and plasma, photon deceleration technology can be used to achieve the generation of ultra-short and ultra-intense mid-infrared pulses. When ultra-intense and ultra-short laser pulses propagate in low-density plasma, plasma waves will be excited, also known as "laser tail waves". When the laser intensity exceeds the relativistic intensity, the mass power driving the laser will completely expel the electrons in the plasma, thus forming a nonlinear tail wave - a three-dimensional cavity structure, also known as a "cavitation" structure. The cavitation structure has an extremely high electric field acceleration gradient, which can be used to accelerate charged particles to extremely high energies within a centimeter or shorter scale. The stable cavitation structure is not only a good acceleration structure, but also has important applications in electromagnetic wave radiation, optical regulation, etc. In the past, researchers focused their attention on improving the energy and quality of electron beams, and did not pay much attention to the evolution of the laser itself. In fact, when the laser drives the tail wave field, it will undergo a frequency down-conversion (frequency reduction), which makes it possible to generate mid-infrared pulses or even terahertz waves when the laser drives the tail wave. This technology that reduces the frequency of light in the cavitation is called photon deceleration technology. The basic principle is: when an ultra-strong ultra-short laser pulse propagates in a plasma and excites a wake field, different density perturbations and longitudinal scalar potentials exist at different longitudinal positions in the wake field, resulting in different refractive indices (η) at different longitudinal positions. In the laser co-moving transmission coordinate ξ = x-ct, the position where the refractive index gradient is greater than zero The laser will blue shift (the wavelength will become shorter) at the position where the refractive index gradient is less than zero. The laser will undergo a red shift (the wavelength becomes longer), and this red shift phenomenon is called "photon deceleration".

[0007] The essence of photon deceleration is the result of the combined effects of self-phase modulation (SPM) and group velocity dispersion (GVD) of light. When the driving laser propagates in the plasma, the laser will be compressed due to nonlinear effects such as self-steepening effect, self-focusing effect, and asymmetric self-phase modulation. As the laser is compressed, the laser intensity is increased, and the mass motive force is enhanced, which causes the laser to excite a larger density disturbance, and the laser also feels a stronger refractive index gradient. The existence of the refractive index gradient changes the phase velocity of the laser, making its wavelength elongated to the mid-infrared band. Due to the group velocity dispersion effect, the group velocity of the mid-infrared pulse is less than that of the driving laser, and the movement speed of the cavitation is approximately equal to the driving laser group velocity, so the mid-infrared pulse slides backward into the cavitation and moves forward with the cavitation. There are almost no electrons in the cavitation, that is, the wavelength of light cannot be modulated inside the cavitation, so the mid-infrared pulse can be stored in the cavitation and guided out of the plasma.

[0008] At present, there are some methods that use photon deceleration technology to generate mid-infrared pulses. In 2010, Pai et al. first experimentally used ultra-strong ultrashort pulses to irradiate uniform low-density plasma to obtain mid-infrared pulses with a wavelength range of 2-6μm, with an energy conversion efficiency of 1.5%. This is the first experimental verification that mid-infrared band pulses can be obtained through the photon deceleration effect. Subsequently, Zhu et al. theoretically studied the influence of various parameters of the driving laser and plasma on the energy conversion efficiency. Studies have shown that when the laser power exceeds 20TW, the energy conversion efficiency of the generated mid-infrared pulse wavelength greater than 6μm is about 1%. In 2018, Nie et al. simulated the propagation of ultra-strong ultrashort lasers in plasma using the Particle-in-Cell (PIC) method and conducted in-depth research on the generation process of mid-infrared pulses. By dividing the plasma into a compression module, a generation module, and a coupling module, a near-single-cycle, relativistic intensity, carrier-envelope phase (CEP) locked mid-infrared pulse with a central wavelength of 13μm was finally obtained, with an energy conversion efficiency of about 1.7%. Subsequently, Nie et al. experimentally verified the feasibility of this method and successfully obtained mid-infrared pulses with a power of about 100GW, nearly single cycle, and tunable wavelength in the range of 3-20μm. Similarly, the photon deceleration method can not only use Gaussian pulses as driving lasers, but also use other structures of light fields to generate special structured mid-infrared pulses. Zhu et al. successfully obtained vortex mid-infrared pulses with a wavelength of 10μm and an energy conversion efficiency of 4.8% by using vortex light to drive annular plasma waves, and once again proved CEP locking. Recently, Zhu et al. successfully greatly improved the energy conversion efficiency of mid-infrared pulses by using two laser beams to propagate in the plasma in the same direction and coaxially. This method first uses a beam of ultra-strong ultrashort laser as the driving light to drive the nonlinear plasma wave, and then injects the second signal light into the front end of the second cavity. In this way, mid-infrared pulses with a wavelength of about 4μm and an energy conversion efficiency of up to 30% were successfully obtained.

[0009] In summary, although relativistic intensity and short-period mid-infrared pulses can be obtained based on the interaction between laser and plasma, there are still many problems that need to be solved. The existing long-wavelength (wavelength greater than 5 microns) photon-decelerated mid-infrared pulse radiation source uses a longer and more complex plasma as a wavelength conversion device, which causes a large amount of driving laser energy to be absorbed by the plasma, making the energy conversion efficiency of the driving laser to the mid-infrared pulse only about 1%. In the long-wavelength region greater than 5μm, the energy conversion efficiency of mid-infrared pulses is still relatively low. Secondly, this method currently requires a longer plasma, which not only consumes a large amount of driving laser energy, but also causes certain instabilities, and the customized density distribution greatly increases the difficulty of the experiment. How to effectively optimize the design of plasma density distribution also needs further research. Summary of the invention

[0010] In view of the above deficiencies in the prior art, the present invention provides an efficient ultra-intense and ultra-short mid-infrared pulse system, which can generate ultra-intense and ultra-short mid-infrared pulses with a high energy conversion efficiency. The system uses a negatively chirped pulse as the driving laser to interact with the plasma. The rapid compression of the negatively chirped optical pulse in the plasma can effectively reduce the length of the plasma channel target used, accelerate the generation speed and energy conversion efficiency of the mid-infrared optical pulse, and its energy conversion efficiency can be increased to 3%. Moreover, the parameters of the generated mid-infrared pulse can be controlled by adjusting the chirp coefficient of the negatively chirped optical pulse. And the plasma structure is simplified, with a simple and novel structure and reliable performance.

[0011] To achieve the above object, the present invention provides an efficient ultra-intense and ultra-short mid-infrared pulse system, comprising:

[0012] A vacuum chamber for providing a vacuum environment;

[0013] A chirped optical pulse generator disposed outside the vacuum chamber for outputting an optical pulse with a continuously adjustable chirp coefficient to the vacuum chamber;

[0014] A plasma channel target disposed inside the vacuum chamber, having a cylindrical structure and containing a plasma with a trapezoidal density distribution along the axis;

[0015] A beam focusing device disposed inside the vacuum chamber and on the incident optical path of the optical pulse for focusing the optical pulse and making it incident along the axis of the plasma channel target into the plasma channel target.

[0016] In one embodiment, the wavelength of the optical pulse is 0.8 - 1 μm, the duration is 52.8 - 66 fs, the peak intensity is 5×10 18 -20×10 18 W / cm 2 , and the spot radius is 15 - 20 μm. Preferably, the wavelength of the optical pulse is 0.8 μm, the duration is 52.8 fs, the peak intensity is 5.5×10 18 W / cm 2 , and the spot radius is 15 μm.

[0017] In one embodiment, the continuously adjustable range of the chirp coefficient of the optical pulse is -0.07 - 0.0.

[0018] In one embodiment, the plasma channel target is made by filling hydrogen into a capillary and then discharging.

[0019] In one embodiment, the plasma density in the axial direction of the plasma channel target is trapezoidally distributed. From the inlet to the outlet, the plasma density within the axis of the plasma channel target successively includes a rising edge, a plateau edge, and a falling edge.

[0020] On the axis of the plasma channel target, the plasma densities at the starting point of the rising edge and the ending point of the falling edge are both 0, and the plasma densities at the ending point of the rising edge, any point on the plateau edge, and the starting point of the falling edge are all N.

[0021] In one embodiment, the length of the rising edge in the axial direction of the plasma channel target is 50 - 500 μm, the length of the plateau edge in the axial direction of the plasma channel target is 2700 - 2800 μm, and the length of the falling edge in the axial direction of the plasma channel target is 50 - 200 μm. Preferably, the length of the rising edge in the axial direction of the plasma channel target is 100 μm, the length of the plateau edge in the axial direction of the plasma channel target is 2780 μm, and the length of the falling edge in the axial direction of the plasma channel target is 200 μm.

[0022] In one embodiment, the plasma density at any point on the same radial cross - section within the plasma channel target is: where n 0 is the plasma density at the axis point where the radial cross - section is located, r is the distance from the position where the plasma is located to the axis, and w 0 is the laser focal spot radius.

[0023] In one embodiment, the beam focusing device is composed of a plurality of reflectors and an off - axis paraboloid mirror.

[0024] The present invention provides the following beneficial technical effects:

[0025] 1. Using a negatively chirped optical pulse as the incident light to drive the plasma channel target, the negatively chirped optical pulse can be longitudinally compressed in the plasma, and its compression speed is faster than that of a non - chirped optical pulse, enabling the generation of an ultra - strong and ultra - short mid - infrared pulse more quickly.

[0026] 2. The negatively chirped optical pulse can be quickly compressed in the plasma, which means that a shorter plasma channel target can be used to generate an ultra - strong and ultra - short mid - infrared pulse, overcoming the instability caused by the long plasma and long laser propagation time.

[0027] 3. The shorter plasma can effectively reduce the absorption of laser energy by the plasma, enabling a large amount of energy to be retained during the propagation and longitudinal compression of the laser. This means that more energy can be transferred when the laser is converted into a mid - infrared pulse, improving the energy conversion efficiency of the mid - infrared pulse.

[0028] 4. The plasma channel target is characterized by a special radial density distribution, with a low central density and a high surrounding density, which can effectively suppress the lateral diffusion of the laser and also suppress the energy loss caused by the diffusion of the laser. Similarly, it can improve the energy conversion efficiency during the generation of mid-infrared pulses. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0030] Figure 1 It is a schematic structural diagram of the mid-infrared pulse system in the embodiment of the present invention;

[0031] Figure 2 It is a schematic diagram of the propagation and evolution of a negatively chirped optical pulse in a plasma and the generation of a mid-infrared pulse in the embodiment of the present invention;

[0032] Figure 3 It is a schematic diagram of the process of generating an ultra-strong and ultra-short mid-infrared pulse by using an ultra-strong and ultra-short negatively chirped optical pulse in the embodiment of the present invention, where T 0 = 2.64 fs is the laser period. Among them, (a) is a snapshot of the plasma and the laser at 396 femtoseconds after the negatively chirped optical pulse enters the plasma channel, and the line is the plasma density on the axis at this time. (b) is a snapshot of the plasma and the laser at 5940 femtoseconds after the negatively chirped optical pulse enters the plasma channel, and the line is the plasma density on the axis at this time; (c) is a snapshot of the plasma and the laser at 9504 femtoseconds after the negatively chirped optical pulse enters the plasma channel, and the line is the plasma density on the axis at this time; (d) is the spectral evolution of the negatively chirped optical pulse from the time of incidence to the time of completely leaving the plasma channel target; (e) is the spectral diagrams at 396 femtoseconds, 5940 femtoseconds, and 9504 femtoseconds; (f) is a schematic diagram of the result after filtering the laser;

[0033] Figure 4 It is a schematic diagram of the relationship between the carrier-envelope phase of the mid-infrared pulse and the carrier-envelope phase of the negatively chirped optical pulse in the embodiment of the present invention. Among them, (a) is a graph of the mid-infrared pulse intensity changing with the initial laser phase, and the inset is a schematic diagram of the mid-infrared pulse when the initial laser phase is 0, π / 2, and π; (b) is the relationship between the mid-infrared carrier-envelope phase and the initial laser carrier-envelope phase and the carrier-envelope phase difference.

[0034] Reference numerals in the drawings: chirped optical pulse generator 1, vacuum chamber 2, beam focusing device 3, plasma channel target 4.

[0035] The implementation, functional features and advantages of the present invention will be further described in conjunction with embodiments with reference to the accompanying drawings. Specific embodiments

[0036] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0037] It should be noted that all directional indications (such as up, down, left, right, front, back...) in the embodiments of the present invention are only used to explain the relative positional relationship and movement conditions between components in a specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indications will also change accordingly.

[0038] In addition, in the present invention, descriptions such as "first" and "second" are only for descriptive purposes, and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0039] In the present invention, unless otherwise clearly defined and limited, terms such as "connection" and "fixation" should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection, an electrical connection, a physical connection or a wireless communication connection; it can be directly connected, or indirectly connected through an intermediate medium, and can be the communication inside two elements or the interaction relationship between two elements, unless otherwise clearly defined. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0040] In addition, the technical solutions between various embodiments of the present invention can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0041] This embodiment discloses an efficient ultra-intense and ultra-short mid-infrared pulse system. This system can effectively generate ultra-intense and ultra-short mid-infrared pulses while ensuring a relatively high energy conversion efficiency (about 3%) by the interaction of negatively chirped optical pulses with a plasma channel target. Refer to Figure 1, the system mainly includes a vacuum chamber, a chirped optical pulse generator, and a beam focusing device. Among them, the vacuum chamber is used to provide a vacuum environment; the chirped optical pulse generator is arranged outside the vacuum chamber and is used to generate femtosecond Gaussian optical pulses with negative chirp and inject the optical pulses into the vacuum chamber; the plasma channel target is arranged in the vacuum chamber and is made by filling hydrogen into a capillary with a cylindrical structure and discharging it. The density of the plasma in the plasma channel target is trapezoidally distributed along the axial direction; the beam focusing device is arranged in the vacuum chamber and on the incident optical path of the optical pulse, and is used to focus the optical pulse and then inject it along the axis of the plasma channel target into the entrance of the plasma channel target.

[0042] In the specific implementation process, the chirped optical pulse generator outputs an optical pulse with a wavelength of 0.8 μm, a duration of 52.8 fs, a peak intensity of 5.5×10 18 W / cm 2 , and a spot radius of 15 μm, and the chirp coefficient of the optical pulse can be continuously adjusted, and the adjustment range is from -0.07 to 0.0.

[0043] In the specific implementation process, the plasma density in the plasma channel target is trapezoidally distributed along the axial direction, that is, from the entrance to the exit of the plasma channel target, the plasma density in the axis of the plasma channel target is the rising edge, the plateau edge, and the falling edge in sequence; on the axis of the plasma channel target, the plasma densities at the starting point of the rising edge and the ending point of the falling edge are both 0, and the plasma densities at the ending point of the rising edge, any point on the plateau edge, and the starting point of the falling edge are all N, N = 3×10 18 cm -3 . Further specifically, the length of the rising edge in the axial direction of the plasma channel target is 100 μm, the length of the plateau edge in the axial direction of the plasma channel target is 2780 μm, and the length of the falling edge in the axial direction of the plasma channel target is 200 μm. The plasma density at any point on the same radial cross-section in the plasma channel target is: Among them, n 0 ∈0~N is the plasma density at the axis point where the radial cross-section is located, r is the distance from the position where the plasma is located to the axis, and w 0 is the laser focal spot radius. For example, the plasma density at any point on the plateau edge is: cm -3 .

[0044] In the specific implementation process, the beam focusing device is composed of multiple reflectors and an off-axis paraboloid mirror.

[0045] In this embodiment, the principle of generating mid-infrared pulses is as Figure 2As shown, when a negatively chirped optical pulse enters the plasma, it will excite a nonlinear wakefield. The nonlinear wakefield has a bubble structure and a negative refractive index gradient at the front end of the bubble. The generation process of the mid-infrared pulse is divided into three stages: (a), (b), and (c). Stage (a) is the incident stage. In this stage, the laser is introduced into the plasma by the rising edge of the density, and the rising edge of the density hardly consumes the laser energy. Stage (b) is the compression stage. In this stage, the laser causes photon acceleration and deceleration due to the change in plasma density, resulting in rapid longitudinal compression of the laser and a significant increase in the laser peak intensity. Stage (c) is the generation stage. After passing through stage (b), the laser has a very high peak intensity. At this time, the large peak intensity causes an increase in the refractive index gradient, resulting in intense photon deceleration. The laser wavelength is stretched to the mid-infrared band. And due to the group velocity dispersion of light, the mid-infrared pulse velocity is slower than the driving laser velocity and falls into the bubble. Since there are almost no electrons in the bubble, the mid-infrared pulse can be stored in the bubble and finally guided out of the plasma by the bubble.

[0046] In this embodiment, the generation process of the ultra-strong and ultra-short mid-infrared pulse is as Figure 3 (a)-(c) shown. The negatively chirped optical pulse undergoes a photon deceleration process in the plasma to generate an ultra-strong and ultra-short mid-infrared pulse. Figure 3 (d) It can be seen that the laser wavelength gradually stretches from 0.8 μm to about 8 μm over time, generating a mid-infrared pulse. Figure 3 (e) It can be seen that there is an intensity peak in the long-wavelength spectral region, indicating that a mid-infrared pulse has been generated. The central wavelength of this mid-infrared pulse is 0.8 μm. Figure 3 (f) is the result after filtering the laser. The result shows that the mid-infrared pulse has only about 2 optical cycles, which is a few-cycle optical pulse. The duration of this mid-infrared pulse is 105.6 femtoseconds, and its peak intensity can reach 1.8×10 17 W / cm 2 , so the obtained mid-infrared pulse is an ultra-strong and ultra-short mid-infrared pulse.

[0047] Figure 4 It is a schematic diagram of the relationship between the carrier-envelope phase of the infrared pulse and the carrier-envelope phase of the negatively chirped optical pulse. Figure 4 It can be seen that there is a stable carrier-envelope phase difference (Δ MIR ) between the carrier-envelope phase (CEP 0 ) of the mid-infrared pulse and the carrier-envelope phase (CEP CEP ) of the negatively chirped optical pulse, that is, the system of the present invention can generate mid-infrared pulses with a stable carrier-envelope phase difference. Figure 4 (a) The inset in it is the filtered result of the mid-infrared pulse generated by negatively chirped optical pulses with different CEP 0 .

[0048] Table 1 shows the relationship between the chirp coefficient and the mid-infrared pulse parameters in this embodiment. It can be seen from Table 1 that as the chirp coefficient changes, the parameters of the mid-infrared pulse will change accordingly. b = 0 represents a chirpless laser pulse. As the chirp coefficient decreases, the energy conversion efficiency of the mid-infrared pulse increases from 1.8% to 3%, successfully achieving an improvement in the energy conversion efficiency.

[0049] Table 1

[0050]

[0051] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made under the inventive concept of the present invention by using the content of the specification and drawings of the present invention, or any direct / indirect application in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. An efficient ultra-intense and ultra-short mid-infrared pulse system, characterized in that, comprising: a vacuum chamber for providing a vacuum environment; a chirped optical pulse generator disposed outside the vacuum chamber for outputting an optical pulse with continuously adjustable chirp coefficient to the vacuum chamber; a plasma channel target disposed inside the vacuum chamber, having a cylindrical structure and having a plasma with an axially trapezoidal density distribution therein; a beam focusing device disposed inside the vacuum chamber and on the incident optical path of the optical pulse for focusing the optical pulse and then injecting it into the plasma channel target along the axis of the plasma channel target; The wavelength of the optical pulse is 0.8 - 1 μm, the duration is 52.8 - 66 fs, the peak intensity is 5×10 18 - 20×10 18 W / cm 2 , and the spot radius is 15 - 20 μm.

2. The efficient ultra-intense and ultra-short mid-infrared pulse system according to claim 1, characterized in that, the continuously adjustable range of the chirp coefficient of the optical pulse is -0.07 to 0.

0.

3. The efficient ultra-intense and ultra-short mid-infrared pulse system according to claim 1, characterized in that, the plasma channel target is made by filling a capillary with hydrogen and then discharging.

4. The efficient ultra-intense and ultra-short mid-infrared pulse system according to any one of claims 1 to 3, characterized in that, the plasma density in the axial direction of the plasma channel target is trapezoidally distributed. From the inlet to the outlet, the plasma density inside the axis of the plasma channel target is successively the rising edge, the plateau edge, and the falling edge; On the axis of the plasma channel target, the plasma densities at the starting point of the rising edge and the ending point of the falling edge are both 0 cm -3 , and the plasma densities at the ending point of the rising edge, any point on the plateau edge, and the starting point of the falling edge are all N cm -3 .

5. The efficient ultra-intense and ultra-short mid-infrared pulse system according to claim 4, characterized in that, the length of the rising edge in the axial direction of the plasma channel target is 50 - 500 μm, the length of the plateau edge in the axial direction of the plasma channel target is 2700 - 2800 μm, and the length of the falling edge in the axial direction of the plasma channel target is 50 - 200 μm.

6. The efficient ultra-intense and ultra-short mid-infrared pulse system according to claim 4, characterized in that, The plasma density at any point on the same radial cross-section within the plasma channel target is: cm -3 , where is the plasma density at the axis point where the radial cross-section is located, is the distance from the point where the plasma is located to the axis, is the laser focal spot radius.

7. The efficient ultra-intense and ultra-short mid-infrared pulse system according to any one of claims 1 to 3, characterized in that, the beam focusing device is composed of a plurality of reflectors and an off-axis paraboloid mirror.

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