A reflective high peak power femtosecond laser post-compression device

Abstract

A reflective high-peak power femtosecond laser post-compression device mainly includes a nonlinear spectrum broadening module composed of a coated reflector and a dispersion compensation module composed of a broadband chirped mirror. The high-peak power femtosecond laser is guided and transmitted through the coated reflector while completing nonlinear spectrum broadening, and then the dispersion compensation is completed through the broadband chirped mirror to achieve further compression of the pulse width. The present invention uses coating technology to solve the process problem of difficult preparation of high-quality large-caliber thin slices required in the high-peak power femtosecond laser post-compression process, and has the characteristics of flexibility, high efficiency and strong practicality.

Description

Technical Field

[0001] The present invention relates to laser post-compression technology, in particular to a thin-film post-compression of a high-peak power femtosecond laser, which is used to reduce the pulse width of the high-peak power femtosecond laser, thereby increasing the laser peak power and focusing intensity. 15 W or above, femtosecond means the laser pulse width is less than 100 femtoseconds. Background Art

[0002] Due to its important applications in major frontier scientific research such as high-energy particle acceleration, astrophysics, and laser plasma physics, high peak power femtosecond lasers have achieved rapid development in recent years. At present, many petawatt (10 15 W) or even 10 petawatt-level femtosecond laser systems, and the corresponding laser focusing intensity has reached 10 22 W / cm 2 Such high laser focusing intensity can provide unprecedented experimental means and extreme physical conditions for many disciplines, thereby promoting the development of a series of strong-field laser physics and related research. In addition, higher laser focusing intensity is also expected to be used in cutting-edge quantum effects and electrodynamic quantum mechanics research.

[0003] In order to improve the laser focusing intensity, scientists have proposed laser post-compression technology in recent years. Laser post-compression technology can be simply divided into two processes, namely, first achieving pulse spectrum broadening through nonlinear effects, and then removing chirp through dispersion compensation optical elements, and finally obtaining shorter pulse output. It can not only effectively increase the peak power of the laser, but also has the characteristics of high stability, simple maintenance, and low cost. For high-peak power femtosecond lasers, multi-thin slice nonlinear spectrum broadening is usually used. The solid medium is generally a fused silica slice. The laser intensity on the slice is 10 12 W / cm 2level. In order to overcome the reduction in energy transfer efficiency and beam quality caused by the self-focusing effect, the thickness of the thin sheet is generally around 0.1mm to 0.5mm. Based on this method, researchers from the Russian Institute of Applied Physics have achieved 3x and 4x pulse compression based on 0.2 and 0.25 petawatt femtosecond laser systems. Recently, researchers from the Korean Center for Relative Laser Science also achieved 2.1x pulse compression based on laser post-compression technology on a 0.1 petawatt / 23 femtosecond titanium sapphire laser system. In addition, G. Mourou et al. theoretically simulated the post-compression of a 1 petawatt / 27 femtosecond laser. The results show that the pulse width can be shortened from 27 femtoseconds to ~2 femtoseconds through two-stage post-compression, corresponding to a laser peak power increase ratio of ~10. Among them, the diameter of the thin sheet in the first and second stage post-compression processes is 200mm, and the thickness is 0.5mm and 0.1mm, respectively. AAVoronin et al. also simulated the post-compression of 13 PW / 120 fs laser, using 9 400 mm diameter and 0.27 mm thick fused silica sheets as the nonlinear medium. Their simulation results showed that after the spectrally broadened pulse was dispersed and compensated, the output pulse width was ~5 fs, corresponding to a peak power of up to 350 PW.

[0004] It can be seen that for the post-compression of high-peak power femtosecond lasers, as the laser peak power increases, the thickness of the required nonlinear medium decreases, while the aperture increases rapidly. When the laser peak power reaches the petawatt level, the aperture of the required nonlinear medium is usually greater than 200mm and the thickness is less than 0.5mm. In addition, the unevenness of the thin slice will directly affect the wavefront quality of the laser, thereby reducing its focusing intensity. However, for such a size, it is currently difficult to achieve high-quality processing of silicon-containing solid optical components, which has become a key issue restricting the development of high-peak power femtosecond laser post-compression. It is for this reason that the current laser post-compression has not been experimentally verified on petawatt-level femtosecond lasers. Therefore, how to achieve high-quality, large-aperture, and thin-thickness nonlinear media is an important link in promoting the development of high-peak power femtosecond laser post-compression technology, and is of great significance to the development of high-peak power femtosecond lasers. Summary of the invention

[0005] The purpose of the present invention is to overcome the limitations of the above-mentioned high peak power femtosecond laser post-compression technology due to the difficulty in preparing high-quality, large-caliber, and thin-thickness nonlinear media, and to provide a reflective high peak power femtosecond laser post-compression device. By using coating technology, the high peak power femtosecond laser can achieve nonlinear spectral broadening while completing transmission guidance and nonlinear interaction with the nonlinear medium film coated on the reflector.

[0006] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0007] A reflective high-peak power femtosecond laser post-compression device includes a nonlinear spectrum broadening module and a dispersion compensation module, wherein the nonlinear spectrum broadening module is composed of N coated reflectors placed in sequence along the optical path, and the coated reflectors are coated with a high-reflection film and a nonlinear dielectric film in sequence on a glass substrate. The laser first transmits through the nonlinear dielectric film, then is reflected by the high-reflection film, and finally transmits through the nonlinear dielectric film again for output. While the laser completes the guided transmission through the coated reflector, it interacts nonlinearly with the nonlinear dielectric film to achieve nonlinear spectrum broadening.

[0008] The reflectivity of the nonlinear medium film to the laser is less than 0.5%, and the reflectivity of the high-reflective film to the laser is greater than 99.5%.

[0009] The distance between two adjacent coated reflectors can suppress the small-size self-focusing during the laser post-compression process. The minimum distance L f Satisfies the following formula:

[0010]

[0011] In the formula, θ v is the transmission angle of the most unstable noise in the laser, and R is the radius of the laser beam.

[0012] The number N of the coated reflectors, the thickness d of the nonlinear dielectric film, and the laser incident angle θ satisfy the following formula:

[0013]

[0014] Where L is the total thickness of the nonlinear dielectric film on the N coated mirrors.

[0015] Compared with the prior art, the present invention has the following significant features:

[0016] 1. It can realize nonlinear media with larger diameter-to-thickness ratio (aperture / thickness), and support higher peak power of 10 PW or even 100 PW femtosecond laser post-compression;

[0017] 2. Compared with thin films, nonlinear dielectric films are flatter and more uniform, and the post-compression output laser quality is higher;

[0018] 3. The laser completes nonlinear spectrum broadening while transmitting and guiding, which greatly simplifies the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 : A schematic structural diagram of the present invention;

[0020] Figure 2 : Schematic diagram of the structure of the coated reflector;

[0021] Figure 3 : A schematic diagram of the structure of an application embodiment of the present invention;

[0022] Figure 4 : The spectrum and time domain shape before and after laser post-compression of the application embodiment of the present invention. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention should not be limited thereto.

[0024] Figure 1 1 is a schematic diagram of the structure of a reflective high peak power femtosecond laser post-compression device of the present invention. As can be seen from the figure, the device includes: a nonlinear spectrum broadening module 1 composed of coated reflectors 1-1, 1-2, ..., 1-N, and a dispersion compensation module 2 composed of broadband chirped mirror pairs 2-1, 2-2, ..., 2-K. The structures of the coated reflectors 1-1, 1-2, ..., 1-N are as follows: Figure 2 As shown, it includes a glass substrate 3, a high reflection film 4, and a nonlinear dielectric film 5. After the laser passes through the nonlinear dielectric film 5, it is reflected by the high reflection film 4, and then passes through the nonlinear dielectric film 5 again before being output.

[0025] The high-peak power femtosecond laser is reflected in sequence by the coated mirrors 1-1, 1-2, ..., 1-N, completing the laser transmission guidance while obtaining nonlinear spectrum broadening; the laser after spectrum broadening is then reflected by the broadband chirped mirror pairs 2-1, 2-2, ..., 2-K to complete dispersion compensation and achieve further compression of the pulse width.

[0026] The number N of the coated reflectors, the thickness d of the nonlinear dielectric film 5 and the laser incident angle θ satisfy the following formula:

[0027]

[0028] Wherein, L is the total thickness of the nonlinear dielectric film 5 required for the spectrum broadening process calculated based on the laser parameters and the spectrum broadening requirements;

[0029] The distance between two adjacent coated reflectors can suppress the small-size self-focusing during the laser post-compression process. The minimum distance L f Satisfies the following formula:

[0030]

[0031] In the formula, θ v is the transmission angle of the most unstable noise in the laser, and R is the radius of the laser beam.

[0032] The number K of broadband chirped mirror pairs in the dispersion compensation module 2 and the chirp amount D0 thereof satisfy the following formula:

[0033] D t =K·D0.

[0034] Where D t is the total dispersion amount that needs to be introduced by the dispersion compensation module 2.

[0035] Example:

[0036] The embodiment of the present invention is a 4PW Ti:Sapphire laser system, such as Figure 3 As shown, the system includes a high-contrast front end 6, a pulse stretcher 7, a regenerative amplifier 8, a preamplifier 9, a first power amplifier 10, a second power amplifier 11, a first terminal amplifier 12, a second terminal amplifier 13, a first pumping system 14, a second pumping system 15, a third pumping system 16, and a pulse compressor 17. The pulse compressor 17 outputs a laser beam with a diameter of 450 mm, a spectral range of 750 to 850 nm, a corresponding pulse width of 24 femtoseconds, and a peak power of 4 petawatts. According to the numerical simulation based on the Schrödinger equation, when this laser pulse passes through a quartz slice with a total thickness of 1.5 mm, the spectrum will be broadened to 650 to 930 nm, and then introduced into the -70 fs through a broadband chirped mirror. 2 The dispersion amount is 0.01, and the pulse will be compressed to ~7 femtoseconds.

[0037] To this end, the nonlinear spectrum broadening module 1 uses three coated mirrors 1-1, 1-2, and 1-3 with a diameter of 750 mm. The thickness of the nonlinear dielectric film 5 is 0.17 mm, and the corresponding laser incident angle of the high-reflection film 4 is 45 degrees. In addition, in order to suppress small-size self-focusing, the distance between two adjacent special coated mirrors is more than 2 m. The dispersion compensation module 2 uses a pair of broadband chirped mirrors 2-1 with a diameter of 700 mm, supporting a spectrum of 600 to 1050 nm, and a corresponding chirp amount of -70 fs. 2 After the system output laser passes through the nonlinear spectrum broadening module 1, the spectrum is broadened from 750-850nm to 620-1000nm; after the spectrum broadened pulse passes through the dispersion compensation module 2, the width is further compressed from 24fs to <7fs. The corresponding laser pulse spectrum and time domain shape evolution are as follows Figure 4 shown.

Claims

1. A reflective high peak power femtosecond laser post-compression device, comprising a nonlinear spectrum broadening module (1) and a dispersion compensation module (2), characterized in that: The nonlinear spectrum broadening module (1) is composed of N coated reflectors (1-1, 1-2, ..., 1-N) arranged in sequence along an optical path, wherein the coated reflectors are coated with a high reflection film (4) and a nonlinear dielectric film (5) in sequence on a glass substrate (3); laser light first passes through the nonlinear dielectric film (5), is then reflected by the high reflection film (4), and finally passes through the nonlinear dielectric film (5) again to be output; While the laser is guided and transmitted through the coated reflector, it interacts nonlinearly with the nonlinear dielectric film (5) to achieve nonlinear spectrum broadening. The distance between two adjacent coated reflectors can suppress small-size self-focusing during laser post-compression; The minimum distance L between two adjacent coated reflectors f Satisfies the following formula: In the formula, θ v is the transmission angle of the most unstable noise in the laser, and R is the radius of the laser beam.

Images