CN116131091A

CN116131091A - Isolated attosecond pulse generation method

Info

Publication number: CN116131091A
Application number: CN202310225078.2A
Authority: CN
Inventors: 吴朝辉; 左言磊; 曾小明; 李钊历; 王晓东; 王逍; 母杰; 胡必龙
Original assignee: Laser Fusion Research Center China Academy of Engineering Physics
Current assignee: Laser Fusion Research Center China Academy of Engineering Physics
Priority date: 2023-03-10
Filing date: 2023-03-10
Publication date: 2023-05-16

Abstract

The invention discloses an isolated attosecond pulse generation method, which belongs to the ultra-short pulse laser technology, and comprises the steps of introducing a beam of long pulse pump light on the basis of ionization gating, continuously injecting the energy of the pump light into ionization pulses, and generating attosecond pulses through the transfer from the pump energy to attosecond pulse energy; the invention provides a method for generating attosecond pulse by picosecond pulse for the first time, because the energy of picosecond pulse can reach thousands of joules, under the condition of about 0.1 percent conversion efficiency, the corresponding generated attosecond pulse energy can reach a plurality of joules, and compared with the existing microjoules, the energy is improved by 5-6 orders of magnitude.

Description

Isolated attosecond pulse generation method

Technical Field

The invention relates to an ultrashort pulse laser technology, in particular to an isolated attosecond pulse generation method.

Background

With the development of ultra-short pulse laser technology, the pulse width of the laser generated at present is already up to the magnitude of attosecond (10 ^-18 s). The isolated attosecond pulse has important application value in ultrafast diagnosis. Due to the extremely short duration of the pulse, the electronic transition processes in atoms, molecules, and solids can be directly diagnosed by isolated attosecond pulses.

The isolated attosecond pulse technique has evolved rapidly over the last 20 years. The generation of isolated attosecond pulses is currently mainly achieved in two ways:

the process of generating attosecond pulses for higher harmonics can be described by a three-step model: the first step, under the action of strong laser electric field, the coulomb barrier of atoms is depressed, electrons can tunnel through the barrier to generate tunneling ionization; secondly, accelerating free electrons after ionization in an external laser field and obtaining energy; and thirdly, after the electric field is reversed, part of electrons return to the vicinity of atoms to be combined with parent ions, photons are radiated, the photon energy is equal to the sum of ionization energy of the electrons and additional kinetic energy obtained by the electrons from a laser field, and due to the fact that the photon energy is high, the wavelength of light waves is generally in an extreme ultraviolet or soft X-ray wave band, and the light waves correspond to attosecond pulses in a time domain. However, since the laser pulse generally contains a plurality of periods, the attosecond pulse generated in this way is one pulse train. To obtain isolated attosecond pulses, various gating techniques, such as polarization gating, amplitude gating, and space gating, have been developed, the main principle of which is to limit the generation time of attosecond pulses to be within one laser period, so as to obtain isolated attosecond pulses. The conversion efficiency of the higher harmonic and the energy utilization rate of the gating technology are limited, and the efficiency of the higher harmonic for generating isolated attosecond pulse is 10 at present ^-5 The following is a nanofocus (10 ^-9 J) Magnitude. Among the many gating techniques, one effective technique is an ionization gating technique, whose main principle is to ionize the gas with a strong short pulse so that the pulse front completely ionizes the gas, and in the completely ionized region, higher harmonics cannot be generated due to phase mismatch. This produces higher harmonics only in the pulse front regionThereby producing isolated attosecond pulses.

In addition, germany maple developed a method of generating isolated attosecond pulses by means of a spectral coherent beam combination, which was mainly carried out by coherent beam combination using four small periodic pulses (5 fs-10 fs) from ultraviolet to infrared, by which a laser pulse of 380 as was generated with a pulse energy of up to 20 muj. The energy of the attosecond pulse is far higher than that of attosecond pulse generated by higher harmonic, however, the energy of the isolated attosecond pulse generated by the energy of the low-period laser pulse, particularly the energy of the ultraviolet low-period laser pulse is difficult to boost.

Disclosure of Invention

The present invention is directed to an isolated attosecond pulse generation method to solve the above-mentioned problems.

In order to achieve the above purpose, the technical scheme adopted by the invention is as follows: a method for generating isolated attosecond pulse includes introducing a beam of long pulse pumping light on the basis of ionization gating, continuously injecting the energy of said pumping light into ionization pulse, and generating attosecond pulse by transferring pumping energy to attosecond pulse energy.

The term "long pulse pump light" in the present invention means a laser light of 1ps to 100 ps.

As a preferable technical scheme, the method comprises the following specific steps: nanosecond-level long pulse laser (1 ns-20 ns) is divided into two beams in equal proportion through a spectroscope, then one of the two beams of laser sequentially passes through two light guide lenses and a focusing lens, and the other beam of laser sequentially passes through one light guide lens and one focusing lens and is focused into gas to generate high-frequency sound waves; finally, short pulse laser with the femtosecond magnitude is focused to a plasma grating with the ionized sound wave in the gas, the boundary of the plasma grating extends rapidly, the pumping pulse is dynamically reflected, a narrow intersection area is formed by the reflection area and the frequency up-conversion area, and isolated attosecond pulses are generated in the intersection area.

The invention relates to a 'nanosecond-level long pulse laser', which is 1ns-20ns laser; "short pulse laser of the femtosecond order" means a laser of 1fs to 100 fs.

First, two laser beams are interfered in the gas, and a gas grating structure is generated by the electrostriction effect in the gas. Subsequently, the gas grating is ionized by a short pulse laser to produce a plasma grating whose boundary extends as a beam. Finally, a beam of pumping light with the propagation direction opposite to the extending direction of the plasma grating is introduced, and when the pumping light and the plasma grating approach the Bragg condition, the pumping light can be dynamically reflected to continuously inject energy into the ionization pulse. Meanwhile, when the ionization pulse ionizes the gas, a frequency up-conversion effect is generated in the ionization region. There is a very short crossover region for reflection and frequency up-conversion of the laser light. In this region, the laser is continuously up-converted, while the pump light at the fundamental frequency is continuously injected, thereby generating an ultra-wideband attosecond pulse. The attosecond pulse energy is derived from 1ps-100ps long pulse pump light.

One of the cores of the ultrashort pulse compression method of the invention is to utilize the up-conversion effect of the laser ionized gas and the reflection of the pump light to inject energy into a crossing area where the ionized pulse is up-converted while the energy of the laser is replenished. The reflectivity of the pump light can be adjusted by the grating period, and the up-conversion effect of the ionization region can be adjusted by the pulse width of the ionization pulse. Finally, the width of the crossing area is controlled by adjusting the reflectivity of the pump light and the up-conversion effect area, so that the generation of isolated attosecond pulses is realized.

The fast-extending plasma gratings according to the present invention are produced by short pulse ionization of gas gratings. The gas grating is generated by Brillouin effect in gas, and the Brillouin effect exists in solid and liquid gas widely, wherein the gas grating (high-frequency sound wave) is a byproduct of Brillouin efficiency. The main principle is that laser generates stable intensity distribution area in gas by interference, and then periodic gas density intensity distribution is generated by utilizing electrostriction effect, thereby forming gas grating. When the included angle of the two laser beams is alpha, the period of the generated special sound wave is lambda/2 sin (alpha/2), wherein lambda is the wavelength of the laser. The period of the sound wave can be adjusted from lambda/2 to infinity by adjusting the included angle alpha of the two beams of light. When the gas grating is ionized by the short pulse, the gas grating is converted into a plasma grating, and the refractive index of the plasma grating with the same amplitude is changed into more than two orders of magnitude of the gas grating, so that the generated plasma grating can totally reflect pump light meeting Bragg regulation. Meanwhile, as the ionization pulse advances by the light beam, the generated plasma grating has a boundary extending from the grating, so that the pumping light can be dynamically reflected, and energy is continuously injected into the ionization pulse.

Compared with the prior art, the invention has the advantages that: the invention provides a method for generating attosecond pulse by picosecond pulse for the first time, because the energy of picosecond pulse can reach thousands of joules, under the condition of about 0.1 percent conversion efficiency, the corresponding generated attosecond pulse energy can reach a plurality of joules, and compared with the existing microjoules, the energy is improved by 5-6 orders of magnitude.

Drawings

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

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

FIG. 3 is a graph of simulation results according to an embodiment of the present invention.

In fig. 1: a. a gas grating; b. a plasma grating; c. ionizing laser pulses; d. a pump pulse; e. isolated attosecond pulses; 1. a long pulse laser; 2. a first spectroscope; 3. a first light guide mirror; 4. a second light guide mirror; 5. a third light guide mirror; 6. a first focusing lens; 7. a second focusing lens; 8. A short pulse laser focusing lens 9 and a second beam splitter.

Detailed Description

The invention will be further described with reference to the accompanying drawings.

Examples

An isolated attosecond pulse generation method is shown in figure 1:

firstly, when an ionization laser pulse c enters a gas grating a, the gas grating a is ionized into a plasma grating b, and the boundary of the generated plasma grating b extends with a light beam because the ionization laser pulse c propagates with the light beam; the boundary uses a plasma grating b extending from the light beam to dynamically reflect the pumping pulse d and inject the reflected energy into the ionization laser pulse c; meanwhile, when the gas grating a is ionized by the ionizing laser pulse c, up-converted light is generated, and an intersection area is formed by the up-converted light area and the reflecting area of the pumping pulse, and the intersection area generates an isolated attosecond pulse e.

Based on the above principle, the specific embodiment is shown in the light path diagram of fig. 2:

in fig. 2, a long pulse laser 1 with nanosecond level is split into two beams in equal proportion through a first spectroscope 2, one of the two beams of laser sequentially passes through a first light guide lens 3, a third light guide lens 5 and a first focusing lens 6, and the other beam sequentially passes through a second light guide lens 4 and a second focusing lens 7, so that high-frequency sound waves are generated in gas by focusing; finally, the ionization laser pulse c with the femtosecond magnitude is focused to a plasma grating b with the rapidly extending boundary of the ionization sound wave in the gas through a short pulse laser focusing lens 8, the pumping pulse d is dynamically reflected, up-converted light is generated by the reflection area and the frequency up-conversion area to form an isolated attosecond pulse e, and the isolated attosecond pulse e is finally led out through a second beam splitter 9.

The method is used for generating attosecond pulse, verification of particle model simulation is obtained, and the simulation is carried out by adopting an international open source particle simulation program Epoch. The simulation results obtained are shown in FIG. 3, which shows that the pump strength is 4X 10 ¹³ W/cm ² 、 1.6 ps (10 ^-12 s), pump light with a wavelength of 1 μm and a caliber of 100 μm (6 th order super Gaussian), and ionization pulse with a wavelength of 30 fs and a wavelength of 800nm and 100 μm (6 th order super Gaussian); the background gas was hydrogen gas having an average density of 0.1nc (about 5 atm) and a modulation degree of 50%; after 240 μm reaction, the obtained image of the 3D attosecond pulse is shown in fig. 3:

in fig. 3, the left plot is a 3D profile of an attosecond pulse, the upper right plot is a pulse width profile, and the lower right plot is a pulse focal spot center time waveform. The attosecond pulse intensity is 35 times of the pumping light intensity, the half-height pulse width is about 330 and as, the conversion efficiency is about 0.1%, and the attosecond pulse energy of the laser obtained in simulation is 1.45 mu J. However, the simulation only adopts a laser caliber of 100 mu m, and if the laser caliber is enlarged to the magnitude of 10cm, the attosecond pulse energy output of the magnitude of joule can be realized.

The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.

Claims

1. An isolated attosecond pulse generation method, which is characterized in that: and introducing a beam of long pulse pump light on the basis of ionization gating, continuously injecting the energy of the pump light into the ionization pulse, and generating an attosecond pulse through transferring the pump energy to the attosecond pulse energy.

2. The method for generating isolated attosecond pulses according to claim 1, comprising the specific steps of: the long pulse laser with nanosecond level is divided into two beams in equal proportion through a spectroscope, then one of the two beams of laser sequentially passes through two light guide lenses and a focusing lens, and the other beam of laser sequentially passes through one light guide lens and one focusing lens and is focused into gas to generate high-frequency sound waves; finally, short pulse laser with the femtosecond magnitude is focused to ionized sound waves in gas through a short pulse laser focusing lens to generate a plasma grating with a fast extending boundary, the plasma grating dynamically reflects pumping pulses, a narrow crossing area exists between a reflecting area and a frequency up-conversion area, and isolated attosecond pulses are formed in the crossing area.

3. The method of claim 2, wherein the reflectivity of the pump pulse is adjusted by the grating period, and the up-conversion effect of the ionization region is adjusted by the pulse width of the ionization pulse.