阅读说明：本技术 飞秒激光脉冲前沿及波前畸变的补偿装置方法 (Device and method for compensating femtosecond laser pulse front edge and wavefront distortion ) 是由 吴分翔 许毅 杨晓骏 冷雨欣 于 2019-10-28 设计创作，主要内容包括：本发明公开了一种飞秒激光脉冲前沿及波前畸变的补偿装置和方法,装置包括：薄膜偏振片、1/4波片、第一负透镜、第二负透镜、离轴抛面镜、可变形镜。激光脉冲经薄膜偏振片反射后沿轴方向依次经过1/4波片、第一负透镜、第二负透镜,再经离轴抛面镜反射后准直输出,输出脉冲经可变形镜零度反射后按原路返回,最后经薄膜偏振片透射输出。本发明不仅可以实现脉冲波前畸变的补偿,还能同时实现脉冲前沿畸变的动态补偿,在时域和空域上提高脉冲质量,使激光聚焦强度大大增强。具有调节方便、简单高效,实用性强的特点。(The invention discloses a device and a method for compensating the leading edge and wavefront distortion of a femtosecond laser pulse, wherein the device comprises: the lens comprises a thin-film polarizer, an 1/4 wave plate, a first negative lens, a second negative lens, an off-axis parabolic mirror and a deformable mirror. The laser pulse is reflected by the film polaroid, then sequentially passes through the 1/4 wave plate, the first negative lens and the second negative lens along the axial direction, is reflected by the off-axis parabolic mirror and then is output in a collimation manner, and the output pulse returns along the original path after being reflected by the deformable mirror at zero degree and finally is transmitted and output by the film polaroid. The invention can not only realize the compensation of the wave front distortion of the pulse, but also realize the dynamic compensation of the front distortion of the pulse, improve the pulse quality in a time domain and a space domain and greatly enhance the focusing intensity of the laser. Has the characteristics of convenient adjustment, simplicity, high efficiency and strong practicability.)

1. A device for compensating the front edge and wavefront distortion of femtosecond laser pulse comprises: the device comprises a thin film polarizer (1), an 1/4 wave plate (2), a first negative lens (3), a second negative lens (4), an off-axis parabolic mirror (5) and a deformable mirror (6); the first negative lens (3) and the second negative lens (4) are respectively placed on a high-precision translation table; laser pulses are reflected by the thin film polarizer (1), then sequentially pass through the 1/4 wave plate (2), the first negative lens (3) and the second negative lens (4) to enter the off-axis parabolic mirror (5) along the optical axis direction, are reflected by the off-axis parabolic mirror (5) and then are collimated and output, output pulses return according to the original path after being reflected at zero degree by the deformable mirror (6), are reflected by the off-axis parabolic mirror (5), then sequentially pass through the second negative lens (4), the first negative lens (3) and the 1/4 wave plate (2) for transmission, finally enter the thin film polarizer (1), and are transmitted and output through the thin film polarizer (1).

2. The apparatus for compensating the leading edge and wavefront distortion of femtosecond laser pulses according to claim 1, wherein the thin-film polarizer (1) and the 1/4 wave plate (2) are both broadband achromatic.

3. The apparatus for compensating for leading edge and wavefront distortion of femtosecond laser pulses according to claim 1, wherein the focal length of the second negative lens (4) is longer than that of the first negative lens (3), and they are disposed in a confocal manner.

4. The apparatus for compensating for pulse front and wavefront distortion of femtosecond laser according to claim 1, wherein the focal lengths of the first negative lens (3) and the second negative lens (4) are determined according to the total pulse front distortion in the femtosecond laser system.

5. The apparatus for compensating for the leading edge and wavefront distortion of femtosecond laser pulses according to claim 1, wherein the focal length of the off-axis parabolic mirror (5) is determined according to the focal lengths of the first negative lens (3) and the second negative lens (4) and the distance between the first negative lens and the second negative lens (4), which constitute the image transfer system.

6. The apparatus for compensating the leading edge and wavefront distortion of femtosecond laser pulses according to claim 1, wherein the positions of the first negative lens (3) and the second negative lens (4) can be finely adjusted by a high-precision translation stage, so as to dynamically compensate the leading edge distortion of the pulses.

7. A method for compensating the front edge and wavefront distortion of a femtosecond laser pulse is characterized by comprising the following steps:

① calculating total pulse front distortion T in femtosecond laser system_total；

② determining the radius r of the incident pulse of the device;

③, setting the focal length ratio m of the second negative lens (4) to the first negative lens (3);

④ according to T in step ①_totalAnd r in step ②, calculating the focal length f of the first negative lens (3)₁And the caliber d₁And the focal length f of said second negative lens (4)₂And the caliber d₂；

⑤ setting the distance L between the off-axis paraboloidal mirror (5) and the second negative lens (4), and then determining the focal length f of the off-axis paraboloidal mirror (5) according to the image transmission requirement₃And the caliber d₃；

⑥ determining the aperture d of the deformable mirror (6) according to the aperture of the off-axis parabolic mirror (5)₄；

⑦ the thin film polarizer (1), the 1/4 wave plate (2), the first negative lens (3), the second negative lens (4) and the off-axis paraboloidal mirror (5) are sequentially arranged according to the optical axis, wherein the first negative lens (3) and the second negative lens (4) are confocal and form an image transfer system with the off-axis paraboloidal mirror (5);

⑧ the deformable mirror (6) is installed behind the off-axis paraboloidal mirror (5), so that the pulse generates zero-degree reflection and returns according to the original path, and secondary compensation of pulse front edge distortion is realized;

⑨ correcting the wave front distortion of the pulse in real time by the deformable mirror (6);

⑩ the position of the first negative lens (3) and the second negative lens (4) is finely adjusted according to the focusing quality of the output pulse of the femtosecond laser system, and the dynamic compensation of the pulse front distortion is carried out.

Technical Field

The invention relates to femtosecond laser pulse front edge distortion and wavefront distortion, and a device and a method for compensating the pulse front edge distortion and the wavefront distortion by using a negative lens and a deformable mirror, in particular to dynamically compensating the pulse front edge distortion.

Background

The invention of Chirp Pulse Amplification (CPA) technology and the breakthrough of titanium gem growth technology lead the super-strong ultrashort laser technology to be rapidly developed, and the peak power thereof reachesOn the order of watts, pulse widths have also been achieved on the order of tens of femtoseconds. At present, multiple countries are competing to develop 10-watt-level ultrashort laser systems, and the corresponding laser pulse focusing intensity is expected to break through 10²³W/cm². Such high laser pulse focusing intensity can create unprecedented experimental means and extreme physical conditions for many subject studies, thereby promoting the development of a series of intense laser physics and related studies. Such as laser wake field electron acceleration, high energy proton and ion acceleration, solid higher harmonics, etc. In most intense field laser physics and related research, the focusing intensity of laser pulses is often one of the important factors determining the success or failure of the research. The laser pulse focusing intensity is closely related to its spatio-temporal quality, in addition to being dependent on the output energy of the laser pulse. However, limited by the growth technique of the laser gain medium and the damage threshold of the optical elements, the amplified energy of the laser pulse reaches a bottleneck. Therefore, improving the focusing intensity by optimizing the space-time quality of a high peak power femtosecond laser system is a core problem and research focus of the development of ultrashort laser. The spatio-temporal quality of a high peak power femtosecond laser system includes, in addition to pulse width and contrast, pulse front and wavefront quality.

The leading edge of a pulse, i.e. the energy leading edge of a pulse, can be understood as the plane or curved surface to which the peak of the wave packet corresponds. When the laser pulse passes through the lens, the dispersion effect causes the pulse front edge to generate delay relative to the pulse front edge, which depends on the spatial position of the light beam, so that the pulse front edge distortion is formed. And the distortion of the pulse front edge can be rapidly increased along with the increase of the aperture of the light beam. In addition, the tilt of the grating in the laser system also introduces chromatic aberration, which results in distortion of the pulse front. The pulse front distortion causes the time for the laser pulse to reach the focal region at different spatial positions during focusing to be different, thereby causing broadening of the pulse time width in the focal region, resulting in a decrease in the peak intensity of the true focused pulse. Especially for femtosecond pulses, the pulse front distortion tends to be much larger than the pulse width.

The wavefront of a pulse, i.e. the phase plane of the pulse, can be understood as the plane or curved surface to which the phase of the wave packet corresponds. The wavefront distortions of the pulses are mainly divided into static and dynamic wavefront distortions, the former arising from imperfections in the optical elements of the system themselves and mechanical clamping stresses, and the latter arising mainly from thermal and nonlinear effects of the system. The wavefront distortion of the pulse affects the focusing power of the laser pulse, thereby greatly reducing the focusing intensity of the laser.

Although some methods of compensating for the distortion of the leading edge of the pulse and the distortion of the wavefront have been proposed, they are independent. Since the leading edge and the wavefront are opposite, compensating for the distortion of the leading edge alone does not result in an ideal planar leading edge, and there is also distortion that is consistent with the wavefront of the pulse. In addition, the compensation of the distortion of the leading edge of the pulse is based on theoretical calculation results, and large errors can exist between the theoretical calculation results and actual results. Therefore, dynamic compensation for pulse front distortion is required. Moreover, only by compensating the pulse front edge and the wavefront distortion at the same time, the perfect plane pulse front edge can be obtained, so that the femtosecond laser pulse obtains the highest focusing intensity.

Disclosure of Invention

The invention aims to provide a device and a method for compensating the femtosecond laser pulse front edge and wavefront distortion, which can simultaneously improve the pulse quality in a time domain and a space domain, effectively improve the pulse focusing intensity and further promote the development of the physical and related researches of high-field laser. The invention breaks through the limitation of the existing compensation method, realizes the dynamic compensation of the pulse front edge distortion while realizing the pulse front distortion compensation, and has the characteristics of convenient adjustment, simplicity, high efficiency and strong practicability.

The technical scheme adopted by the invention for solving the technical problems is as follows:

a device for compensating the front edge and wavefront distortion of femtosecond laser pulse comprises: the high-precision optical lens comprises a thin film polarizer, an 1/4 wave plate, a first negative lens, a second negative lens, an off-axis parabolic mirror and a deformable mirror, wherein the first negative lens and the second negative lens are respectively arranged on a high-precision translation stage; laser pulse passes through film polaroid reflection back along the optical axis direction pass through 1/4 wave plate, first negative lens, second negative lens in proper order, the rethread off-axis paraboloid mirror reflection back collimation output, output pulse warp the deformable mirror zero degree reflection back return according to the original way, the warp after off-axis paraboloid mirror reflection, in proper order through second negative lens, first negative lens and 1/4 wave plate transmission, incide at last the film polaroid to through this film polaroid transmission output.

The thin film polarizer and the 1/4 waveplate were both broadband achromatic and thus did not limit the bandwidth of the femtosecond laser pulses nor introduce additional pulse front distortion.

The first negative lens can not only partially compensate the laser pulse front edge distortion, but also enable the laser pulse to diverge, thereby improving the compensation capability of the second negative lens for the laser pulse front edge distortion.

The focal length of the second negative lens is longer than that of the first negative lens and is placed in a confocal mode.

The focal lengths of the first negative lens and the second negative lens are determined according to the total pulse front distortion amount in the femtosecond laser system.

The focal length of the off-axis paraboloidal mirror is determined according to the focal lengths of the first negative lens and the second negative lens and the distance between the first negative lens and the second negative lens, and the first negative lens, the second negative lens and the second negative lens form an image transmission system.

The positions of the first negative lens and the second negative lens can be finely adjusted through the high-precision translation stage, so that dynamic compensation of pulse leading edge distortion is realized.

The deformable mirror not only realizes the correction of the pulse wavefront distortion, but also returns the pulse original path to realize the secondary compensation of the pulse front edge distortion.

Another technical solution adopted by the present invention to solve the above technical problems is:

a method for compensating the front edge and wavefront distortion of a femtosecond laser pulse is characterized by comprising the following steps:

① calculating total pulse front distortion T in femtosecond laser system_total；

② determining the radius r of the incident pulse of the device;

③ setting the focal length ratio m of the second negative lens to the first negative lens;

④ according to T in step ①_totalAnd r in step ②, calculating the focal length f of the first negative lens₁And the caliber d₁And a focal length f of said second negative lens₂And the caliber d₂；

⑤ setting the distance L between the off-axis paraboloidal mirror and the second negative lens, and determining the focal length f of the off-axis paraboloidal mirror according to the image transmission requirement₃And the caliber d₃；

⑥ determining the aperture d of the deformable mirror according to the aperture of the off-axis parabolic mirror₄；

⑦ the film polarizer, 1/4 wave plate, the first negative lens, the second negative lens and the off-axis paraboloidal mirror are sequentially installed according to the optical axis, wherein the first negative lens and the second negative lens are confocal and form an image transmission system with the off-axis paraboloidal mirror;

⑧ installing deformable mirror behind the off-axis paraboloid mirror to make pulse generate zero degree reflection and return back according to original path to realize secondary compensation of pulse front edge distortion;

⑨ correcting the wavefront distortion of the pulse in real time by the deformable mirror;

⑩ the positions of the first negative lens and the second negative lens are finely adjusted according to the focusing quality of the output pulse of the femtosecond laser system, and the dynamic compensation of the pulse front edge distortion is carried out.

The total pulse front distortion amount in the femtosecond laser system in the step ① is calculated as follows:

wherein r is_iThe incident pulse radius of the ith lens in the femtosecond laser system; c is the speed of light in vacuum; f. of_iIs the focal length of the ith lens; n and dn/d λ are the refractive index and dispersion of the lens material; λ is the central wavelength of the pulse to be measured.

The focal length f of the first negative lens in said step ④₁And second negative osmosisFocal length f of mirror₂Satisfies the following conditions:

the aperture d of the first negative lens and the second negative lens in the step ④₁>r，d₂>mr。

The focal length of the off-axis parabolic mirror in the step ⑤

Bore diameter

The aperture d of the deformable mirror in said step ⑥₄≥d₃。

Compared with the prior art, the invention has the following remarkable characteristics:

1. firstly, a negative lens is used for diffusing the pulse, and then a negative lens is used for compensating the distortion of the leading edge of the pulse instead of directly compensating the parallel light, so that the compensation capability of the device is greatly enhanced;

2. returning the original path of the pulse by using a deformable mirror, and realizing secondary compensation of the front edge distortion of the pulse while finishing wavefront correction;

3. meanwhile, the compensation of the pulse leading edge and the wave front distortion is realized, so that an ideal plane pulse leading edge is obtained in a real sense;

4. without being bound by theory, the pulse front distortion can be dynamically compensated according to the actual focus quality.

Drawings

FIG. 1 is a schematic diagram of the apparatus of the present invention;

FIG. 2 is a schematic structural diagram of an embodiment of the present invention;

Detailed Description

The invention is described in further detail below with reference to the accompanying examples.

Fig. 1 is a schematic structural diagram of a femtosecond laser pulse front edge and wavefront distortion compensation device of the present invention, and as can be seen from the figure, the device includes: the film polarizer 1, 1/4 wave plate 2, first negative lens 3, second negative lens 4, off-axis paraboloidal mirror 5 and deformable mirror 6, wherein the first negative lens 3 and the second negative lens 4 are respectively placed on a high-precision translation stage; the laser pulse is reflected by the film polaroid 1, then sequentially passes through the 1/4 wave plate 2, the first negative lens 3 and the second negative lens 4 along the axial direction, is reflected by the off-axis paraboloid 5 and then is collimated and output, the output pulse returns along the original path after being reflected at zero degree by the deformable mirror 6, is reflected by the off-axis paraboloid 5, is sequentially transmitted by the second negative lens 4, the first negative lens 3 and the 1/4 wave plate 2, then is incident to the film polaroid 1, and finally is transmitted and output by the film polaroid 1.

The device is used for compensating the femtosecond laser pulse front edge and wavefront distortion, and the method comprises the following steps:

① calculating total pulse front distortion T in femtosecond laser system_total；

② determining the radius r of the incident pulse of the device;

③, setting the focal length ratio m of the second negative lens 4 to the first negative lens (3);

④ according to T in step ①_totalAnd r in step ②, calculating the focal length f of the first negative lens 3₁And the caliber d₁And the focal length f of the second negative lens 4₂And the caliber d₂；

⑤ setting the distance L between the off-axis paraboloidal mirror 5 and the second negative lens 4, and determining the focal length f of the off-axis paraboloidal mirror 5 according to the image transmission requirement₃And the caliber d₃；

⑥ determining the aperture d of the deformable mirror 6₄，d₄≥d₃；

⑦ the thin film polarizer 1, the 1/4 wave plate 2, the first negative lens 3, the second negative lens 4 and the off-axis paraboloidal mirror 5 are sequentially arranged according to the optical axis, wherein the first negative lens 3 and the second negative lens 4 are confocal and form an image transmission system with the off-axis paraboloidal mirror 5;

⑧ installing the deformable mirror 6 behind the off-axis parabolic mirror 5 to make the pulse generate zero degree reflection and return back as before to realize the secondary compensation of pulse front distortion;

⑨ correcting the wavefront distortion of the pulse in real time by the deformable mirror 6;

⑩ the position of the first negative lens 3 and the second negative lens 4 is finely adjusted according to the focusing quality of the output pulse of the femtosecond laser system, and the dynamic compensation of the pulse front edge distortion is carried out.