"Xihe has not been raised, if Hua He is light?" Xihe, the mother of the sun, depicted in Tianwen, is embodied as a laser installation in Shanghai.
The device is named "Xihe" because it can achieve a peak laser output power of more than 10 petawatts. What kind of concept is this?
"If there is a huge lens outside the earth that can focus all the sunlight shining on the earth on a point the diameter of a human hair, the intensity of light produced is equivalent to the intensity of 1 petawatt, then 10 petawatts is equivalent to the intensity of 10 suns." Zhu Meiping, a researcher at the Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences (hereinafter referred to as the "Shanghai Institute of Optics and Mechanics"), said.
The operation of the ultra-strong and ultra-short laser experiment (Xihe) device is inseparable from key components large and small, and Zhu Meiping and her team are scientific research workers who "create blood vessels" for the Xihe device.
Zhu Meiping said in an interview with Yicai a few days ago that the laser film needs to resist the impact of the strong laser in the process of guiding the laser beam to be transmitted in the preset direction, and the laser can be accurately "escorted" to the target point, so the laser film is like the blood vessels of the entire laser device.
With the application of artificial intelligence (AI) technology, Zhu Meiping and her team are still imagining how to integrate AI technology into laser thin film technology, accelerate the development and screening of new materials, and promote the optimization of thin film design and process. "We're already in the first stages of exploring how machine learning can help with process optimization."
How difficult it is to have a "flawless" laser film
In addition to being used in large-scale devices such as Shenguang and ultra-strong ultra-short lasers, laser thin films are actually permeated in all aspects of the economy and society, from glasses, mobile phones, cameras, computers, automobiles, to lasers carried by space missions such as lunar exploration projects, and the application of laser thin film technology is indispensable.
In some high-intensity laser devices, the laser film even needs to withstand more than tens of thousands of joules of laser energy, which is very easy to be damaged by the laser, and it is extremely difficult to develop. Internationally, the optical switch composed of meter-sized laser polarization thin film elements and Pockel box is known as one of the seven wonders of the American national ignition device. The large-size laser thin film preparation technology in mainland China started late, and it was once a technical bottleneck in the construction and operation of large-scale high-intensity laser devices.
Zhu Meiping made an analogy, if you want to make a laser polarization film with a diagonal size of 1 meter, its control requirements for the thickness of the film layer are equivalent to the flight range of about 1,000 kilometers from Shanghai to Beijing, and the aircraft cannot be more than two millimeters up and down. "Defects are the main factor in the damage of thin films under laser irradiation, and the occurrence of defects is a probabilistic event, and it is basically impossible to achieve zero defects for components with a diagonal close to 1 meter in size."
In pursuit of "flawless" films, Zhu Meiping and her team members have been working hard to reveal the mechanism of laser-induced film damage and improve the damage threshold of laser films.
In 1964, the Shanghai Institute of Optics and Mechanics established the first team specializing in laser thin film research in mainland China (now known as the thin film optics laboratory), and Zhu Meiping, who stayed in the institute after graduating from graduate school, is already the fourth generation of "laser thin film people". The leaders of the first three generations of laser thin film teams, researcher Fan Zhengxiu, researcher Shao Jianda and senior engineer Yi Kuizheng, are her instructors.
Talking about the difficulties of making laser thin films, Zhu Meiping recalled that the most difficult thing was that there was a period of time when the coating repeatedly cracked. "Because the coating is done under vacuum, and the process also includes cooling, degassing, etc., in a vacuum, we don't know in which process the film splits. After two or three months of repeated experiments, one day when we opened the vacuum chamber door and shone a strong light on the film, we found that the film was a flawless, crack-free film, and we finally succeeded. ”
In the past 20 years, Zhu Meiping has continued to study and improve her technology, and has achieved the best results in several international competitions. She and her team members have achieved meter-sized high-performance laser-polarized thin films, and the related technology won the second prize of the 2018 National Technological Invention Award.
Zhu Meiping joked that getting along with laser films is a bit like "falling in love".
She explained that in raising the thin film laser damage threshold, it is actually a process of acquaintance, acquaintance, suppression, and then support with defects. "The first thing to do is to understand the defects, then to understand the defects and their causes, and then to suppress them as much as possible. In the end, it was found that it was basically impossible to completely eliminate these defects. So we thought of ways to help these defects better withstand lasers. ”
Applying AI to future research
The uniqueness of ultra-strong and ultra-short laser makes it one of the major frontiers of international scientific and technological competition, as it has great application value in the fields of laser acceleration, laser fusion, atomic and molecular physics, materials science, nuclear physics, plasma physics, high energy density physics, astrophysics, nuclear medicine, etc.
Late at night on October 24, 2017, the Shanghai "Xihe" laser installation achieved 10 petawatt laser amplification output for the first time. From January 4, 2016 to December 28, 2020, the project device has achieved a laser amplification output of 10.3 petawatts to a maximum peak power of 12.9 petawatts, breaking the world record. Since 2021, the device has been open to users, and a number of experimental results have been published in important international academic journals.
In the view of Zhu Meiping, who "makes blood vessels" for the strongest light, laser thin films and laser technology complement each other: the improvement of the performance of laser thin films can promote the performance of laser devices, and after the performance of laser devices is improved, higher requirements will be put forward for laser films.
"In the past two years, the development of laser technology in the world has also greatly promoted our research field, because there are new trends in the two relatively large application fields of laser thin films: fusion laser and ultra-strong and ultra-short laser."
In 2022, the Lawrence Livermore National Laboratory National Ignition Facility in the United States achieved a "net energy gain". This is a major breakthrough in the history of human energy, which verifies the feasibility of future nuclear fusion energy from scientific principles and engineering technology, and opens the door for mankind to enter the era of clean energy.
"The improvement of the performance of laser fusion devices also puts forward higher requirements for thin-film components." Zhu Meiping said that they are also considering how to integrate AI technology into laser thin film technology. "It's an inevitable phenomenon, and now we're already in the process of exploring how machine learning can optimize the process." In her opinion, it is not known how much time and what effect AI will help them achieve, but it will definitely shorten the time for process optimization, "because we can feed it some experimental data, and the predicted results can guide the next adjustment of process parameters."
As a scientist who has been engaged in laser thin film research for more than 20 years since graduation, Zhu Meiping also emphasized the need to increase support for young scientific research workers.
She said that in recent years, the state has introduced a number of measures to give long-term and stable support to the field of basic research, so that some scientific research workers do not have to consider funding to concentrate on research for a few years. However, because colleges and universities are expanding their enrollment and more and more young people are entering the field of scientific research, the number of people applying for financial support is also increasing year by year.
The above phenomenon mentioned by Zhu Meiping is also reflected in the actual data.
According to data from the Ministry of Education, a total of 1,301,700 graduate students will be enrolled nationwide in 2023, an increase of 4.76% over the previous year. Among them, 153,300 doctoral students were enrolled, an increase of 10.29% over the previous year. There were 3,882,900 graduate students, an increase of 6.28% over the previous year. Among them, there were 612,500 doctoral students, an increase of 10.14% over the previous year.
According to a report by the National Natural Science Foundation of China, with the continuous and rapid growth of the young scientific research team in mainland China, the funding rate of the Youth Science Fund is still showing a downward trend - from 25.2% in 2013 to 17.23% in 2022. It is expected that the number of PhD graduates will continue to grow each year in the next 10 years, peaking around 2030.
"I hope that more funding will be given at the national level. At the same time, create an atmosphere where failure can be tolerated. Because doing scientific research and taking the road that has not been taken, there will naturally be the possibility of failure. Zhu Meiping said.
(This article is from Yicai)