A brief history of attosecond optics—The story behind the Nobel Prize in Physics 2023
The Nobel Prize in Physics 2023 was awarded jointly to Pierre Agostini,Ferenc Krausz,and Anne L'Huillier"for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter".An attosecond is to one second as one second is to the age of the universe,as explained by the Nobel Prize website."L'Huillier discovered a new effect from laser light's interaction with atoms in a gas.Agostini and Krausz demonstrated that this effect can be used to create shorter pulses of light than were previously possible."stated by the Royal Swedish Academy of Sciences.In the advancement of ultrafast optics,to acquire details of ultrafast dynamics on the atomic scale requires a physical process as the tool which should take place on a similar time scale if not shorter.Attosecond is the time scale of electron motions in atoms and molecules,so attosecond pulses are the very tool to study electron dynamics.In the history of high-speed photography,which may be regarded as the predecessor of modern ultrafast optics,the stroboscopic photography by Harold Eugene Edgerton is a very nice example of studying fast-moving objects such as bullets.However,this technique only works for macroscopic objects.To study microscopic objects such as atoms or electrons,even shorter strobe light is necessary.Laser's invention in 1960 provided a new direction to generate shorter light flashes.After a series of technical breakthroughs,laser pulse duration reached the"femtosecond barrier"around the end of the twentieth century.However,even femtosecond pulses are not short enough to study electron dynamics.During the same time,ionization of atoms and molecules under the influence of laser fields,which carries certain similarity with the photoelectric effect explained by Einstein in 1905,has been studied intensively and it was found that the ionized electrons may gain significant energy in the laser field.The above-threshold ionization discovered by Agostini started a long series of studies toward even shorter flashes—Attosecond pulses.In 1988,L'Huillier found that a new radiation later termed as"high harmonics"when laser interacted with atoms.Then,theoretical work pointed out that the motion of the ionized electrons in the laser field produced such harmonics and it was possible to generate attosecond pulses with this radiation.Eventually,in 2001,Agostini studied the harmonics in the temporal domain and proved experimentally that the harmonics were actually a series of attosecond pulses.In the same year,Krausz successfully separated one pulse out of such a series,and produced the first isolated attosecond pulse ever in the lab.After that,several research groups around the globe observed shorter and shorter pulses in their labs and now the shortest coherent light pulse lasts only 43 attoseconds.By now,attosecond optical pulses have permitted researchers the capability to resolve electronic dynamics in real time,and different methods to produce high harmonics and attosecond pulses have been investigated.As the source and the foundation,the continual development of ultra-short light pulses is expected to open new avenues in ultrafast studies.In a future maybe not too far from now,even zeptosecond light pulses may become possible.
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