阿秒光脉冲:照亮通往物质内部电子世界的道路

Attosecond pulses of light:Shining the way to the world of electrons in matter

物理学始于对物质运动本质的哲学探索,而现代物理学则开端于对运动过程的定量实验测量.无论是速度还是加速度,这些最简单的物理量的定义都与时间密不可分.随着人类探索自然的脚步进入微观世界,就需要在更快的时间尺度上对微观粒子的运动过程进行观测,其根本原因在于越是处于基本层面的微观粒子,其特征运动时间越快.

Ferenc Krausz(from Max Planck Institute of Quantum Optics,Garching and Ludwig-Maximilians-Universität München,Germany)and Anne L’Huillier(from Lund University,Sweden),for their contributions to experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter.From the official website of the Nobel Prize,we can see the introduction“An attosecond(10–18 s)is so short that there are as many in one second as there have been seconds since the birth of the universe”.The attosecond pulses of light have given humanity new tools for exploring the world of electrons in matter and enabled the investigation of ultrafast processes that were previously impossible to follow.Back to 1887,Hertz discovered that under the irradiation of electromagnetic waves with a high enough frequency,electrons inside the material will be excited to form an electric current,which is the famous photoelectric effect.However,the photoelectric effect contradicted the electromagnetic wave theory founded by Maxwell and could not be understood for a long time.In 1905,Einstein explained the photoelectric effect for the first time by proposing the hypothesis of photons,which also promoted the establishment of quantum mechanics.However,Einstein’s theory of the photoelectric effect only holds true under the conditions of perturbative interactions caused by weak light intensity.Then,strong field physics emerges,with the introduction of multiphoton ionization,tunneling ionization,and above-threshold ionization,paving the way for the birth of attosecond pulses of light.In 1987,Anne L’Huillier achieved high harmonic generation in experiments when she transmitted infrared laser light through a noble gas.In 1993,the 3-step model of high harmonic generation was proposed by Kulander and Paul Corkum.In 2001,Pierre Agostini succeeded in producing attosecond pulse trains,in which each pulse lasted just 250 attoseconds.In the same year,Ferenc Krausz experimentally realized the first isolated attosecond pulse that lasted 650 attoseconds.After a long journey,humanity finally realized attosecond pulses of light and obtained the key to the electronic world.Nowadays,with the joint efforts of domestic and foreign researchers,attosecond pulses of light have already achieved the shortest pulse widths of 53 and 43 as,the highest photon energy of 1600 eV,the highest pulse energy of 240 nJ in the extreme ultraviolet band and pulse energies up to 10 nJ in the soft X-ray band.The attosecond pulses of light have been applied to various electronic dynamics studies,promoting the explanation of deep scientific problems in physics,chemistry,materials,biology,and other disciplines.To make breakthroughs and unleash the huge application potential of attosecond light sources,it has become an important development trend to build attosecond large-scale scientific facilities worldwide,for example,the European Extreme Light Infrastructure-Attosecond Light Pulse Source,and Advanced Attosecond Laser Infrastructure in China.The Nobel Prize in Physics 2023 has greatly inspired researchers in the field of attosecond science and technology.However,it is just the beginning for attosecond pulses,indicating that this field will have a more profound and extensive impact on mankind’s journey of exploring nature and innovating technology in the future.