A Second Laser: For The Crazy Electronic Photography

Just as we use light to observe the macroscopic world around us, we can also use light to probe the subatomic world. But one principle must be observed: any measurement must be faster than the time required for the system under study to change significantly, otherwise only vague results can be obtained.
In a molecule, atoms move on the femtosecond (trillionth of a second, 10^-15 seconds) time scale, their positions and energies change in one to a few hundred attoseconds, and to measure their motion, femtosecond technology "can't help.
How short is an attosecond? 1 attosecond is 10^-18 seconds, which is one billionth of a billionth of a second. 1 attosecond is equivalent to 1 second of the age of the universe (13.8 billion years). A beam of light traveling from one side of the room to the opposite wall takes 10 billion arcseconds.
The "real life" of the attosecond pulse
How do you get a light pulse to the attosecond scale? Theoretically, shorter light pulses can be generated by combining short-wavelength laser pulses of multiple wavelengths.
Wei Zhiyi, a researcher at the Institute of Physics of the Chinese Academy of Sciences, explained to the Science and Technology Daily reporter: "To generate new wavelengths not only need a femtosecond laser drive, but also need to be focused on the gas, through the interaction of light and gas atoms to produce the so-called high harmonics, high harmonics is a cycle in the drive laser, the generation of two cycles of the wave."
In 1987, Lhuillier and colleagues focused an infrared laser beam onto an inert gas and found that the harmonics produced were more numerous and stronger than those previously produced with shorter-wavelength laser drives, and that many of the harmonics observed had similar light intensities.
Further studies found that, under the right circumstances, the harmonics overlapped to produce a series of laser pulses in the ultraviolet band, each of which was only a few hundred attoseconds long.
In 2001, Agostini and his colleagues in France succeeded in generating a series of pulse trains lasting only 250 arsec. Ferenc Krauss and his partners in Austria went the other way, isolating single isolated light pulses lasting 650 arcseconds and using them to track and study the process of "pulling" electrons out of atoms.
"It is the work of these three scientists, represented by the researchers for more than a decade, through ingenuity and unremitting efforts, so that ultrafast science into the era of attoseconds." Wei Zhiyi said.
Promising in a number of fields, "show your skills"
A small hummingbird can beat its wings 80 times per second, with the human eye is unable to see, but with a high-speed camera can be framed into a clear frame of action.
"A second light pulse is precisely the study of the microscopic material world of 'high-speed camera', can be 'raging' of the electron framed for observation." Wei Zhiyi said hopefully, "Studying and understanding electrons on such a short time scale (of attoseconds) is expected to facilitate the rapid development of ultrafast electronics, which may one day give rise to more powerful computer chips. It also allows us to distinguish molecules based on their electronic properties and to use them for rapid and accurate disease diagnosis."
According to Wei Zhiyi, at present, in addition to the above research teams internationally, a number of research teams in the United States, Canada, Italy, Switzerland, Japan, South Korea and other countries have also been carrying out research on the generation of attosecond pulses and their applications in many fields such as physics, chemistry and biology.
"For example, Prof. Chang Zenghu's team at the University of Central Florida in the United States set the world record for the shortest attosecond pulse twice, in 2012 and 2017, and the 43-attosecond pulse created by the Swiss Federal Institute of Technology in 2017 has so far held the current world record for the shortest. In particular, the EU has constructed the Extreme Light Facility (ELI-ALPS) in Hungary, with attosecond lasers as the main component, to provide scientists in different fields to carry out attosecond scientific research." Wei Zhiyi counts the results in the field of attosecond.
Research on attosecond light pulses has also been widely emphasized by Chinese scientists. The Institute of Physics of the Chinese Academy of Sciences, Shanghai Institute of Optical Mechanics, Xi'an Institute of Optical Mechanics, Peking University, East China Normal University, National University of Defense Technology, Huazhong University of Science and Technology and other units are carrying out research in the field of attosecond science. 2013, Wei Zhiyi's group for the first time in China to generate and measure the isolated attosecond pulse of 160 attoseconds, and is now further developing towards shorter pulse widths, higher energies, and higher repetition frequencies, which will provide the opportunity for the Chinese scientists to develop their own attosecond lasers. Combined with the terminal equipment, it provides an international leading platform and facilities for the research of attosecond laser in the fields of condensed matter physics, atomic and molecular physics, chemistry, biomedicine, information and energy.