【Preface】
After Professor Gérard Mourou, the inventor of chirped pulse amplification technology, returned to Europe from the University of Michigan in the United States,It is recommended that the EU build a 100PW ultra-powerful laser device.After discussions among EU countries, it was finally decided to establish ultra-intense lasers and user equipment with different scientific application focuses in the Czech Republic, Hungary and Romania, three countries with the second gradient of European economic development.Starting from this issue, this public account will invite laser scientists who have worked in the field of ultra-intense lasers for many years to give detailed introductions to the three sub-devices of ELI.We will introduce the parameters of ELI's laser device in three phases. Later, we will successively introduce the introduction of ELI laser physics experiments and the recruitment requirements of each sub-device, so stay tuned.
The ELI-BEAMLINE laser device introduced in this issue is located in the Czech Republic [1].The device's laser system is divided into four independent beams.The naming method is simple and crude.L1, L2, L3, and L4 respectively correspond to: high repetition frequency 15fs OPCPA system, 10Hz OPCPA petawatt laser system, 10Hz titanium sapphire petawatt laser system, and single-shot kilojoule petawatt laser system.These four systems will be introduced below.
L1 laser beam: optical parametric amplification system (100mJ/15fs)
The laser is based on short-pulse pumped OPCPA technology and adopts a homologous seed optical synchronization scheme. The design index is 100mJ/15fs/1kHz.The seed source of the system is an ultra-wide spectrum titanium sapphire oscillator.The special thing about this oscillator is that it can not only provide OPA’s broadband signal light,Moreover, the spectrum can be extended to 1030nm, providing a seed source for the OPA pump light.The natural optical synchronization scheme ensures the strict time synchronization required by the OPA process. With active synchronization feedback control, the synchronization accuracy can reach hundreds of attoseconds.OPA's pump laser uses Thin-disk technology, which is currently the first choice for high-repetition-frequency, high-energy lasers and has great advantages in thermal management of lasers.Germany's TRUMPF is the industry leader in this core technology. L1 Laser and TRUMPF's Scientific Laser Division have cooperated to develop a pump source with this performance advantage.In addition, one thing that needs to be highlighted is that the Czech Republic has invested heavily in the independent research and development of all-semiconductor-pumped Yb lasers and has reached the international leading level.For details, please refer to the HiLASE project website:http://www.hilase.cz/en/about-project/。
After the broadband signal light is amplified by 7-stage OPA, it is compressed in vacuum.Finally reached the design target: 100mJ/15fs/1kHz.Except for some technologies of the pump source, the laser system was independently developed by the Czech side.The project is currently progressing smoothly and can already reach an output of 10mJ/11fs/1kHz [2].
L2 laser beam: petawatt OPCA laser system (1PW/20J/10Hz)
The British Rutherford Laboratory is famous in the field of ultra-powerful lasers, especiallyIt is its unique high energy short pulse OPCPA technology that leads the way.ELI-BEAMLINE's L2 laser is cooperated with Rutherford Laboratory.As we all know, one of the biggest difficulties in OPA technology is how to obtain high-quality pump sources.Therefore, the L2 laser beam has made great efforts in the pump source [3].The technical solution adopts a low-temperature cooling all-semiconductor pumped Yb:YAG amplification method.The final fundamental frequency energy can reach 60J, and the repetition frequency can reach 50Hz.Showing the triple power of cryogenic cooling, all-semiconductor pumping and low Stokes loss Yb medium!After 4 levels of OPA amplification, the signal pulse energy can reach 26J. After compression, the energy is 18J, the pulse width is 15fs, and the pulse contrast reaches 1:1011.This is the ideal tool for generating high-quality laser-accelerated proton sources.
L3 laser beam: petawatt titanium sapphire laser system (1PW/10Hz/30J)
There are rumors that because the Lawrence Berkeley Laboratory in the United States purchased the PW laser system from Thales in France,The United States was dissatisfied and lobbied the European Union to purchase a high-repetition-frequency PW laser.This is the ELI-BEAMLINE L3 laser beam built by Livermore Laboratories.This may just be gossip,Because if Livermore Laboratory develops industrial lasers, it will definitely kill any commercial company in the world.With its strength, it is definitely a small case to build just one PW laser [4].The design index of this laser is 30J/1PW/10Hz.Its biggest highlight is the pump source: helium cooling and all-semiconductor pump technology are used, and neodymium glass is selected as the gain medium. The reason is probably based on the mature glass laser amplification technology of NIF.The front stage of this pump source uses the DPSS laser of the American CEO Company.The front stage of the PW laser system uses a former Femtolasers titanium sapphire kHz amplifier.Assists XPW technology for temporal purification and spectral broadening,Subsequent expansion, amplification and compression adopt mature commercial technologies and are highly reliable.
L4 laser beam: Nd:glass/OPCPA hybrid amplification (10PW/130fs/single shot)
Todd Ditmire of the University of Texas at Austin is a heavyweight in the laser field.It is also a pioneer in the industrialization of ultra-powerful lasers.The company he founded, National Energetics, successfully won a large order from ELI laser.Build a 10PW, kilojoule-level femtosecond laser device, which is Beamline’s L4 laser.National Energetics and Lithuanian company EKSPLA collaborated to build this laser system.SCHOTT Corporation and Livermore Laboratories in the United States are also involved.Integrating superior resources such as ultra-powerful laser design, flash lamp pumping, neodymium glass materials, and OPCPA,Ultimately providing users with a high-quality laser system.
The laser system has two working modes:
(1) 10PW/single shot mode:All the energy of the entire system is used to generate 10PW peak power,Nanosecond chirp pulses before compression can be individually derived to serve specific experiments.The seed laser in this mode is a broadband femtosecond oscillator.First, carry out picosecond OPCPA prevention,After broadening to the nanosecond level, continue to parametric amplification,Finally, the plate-shaped neodymium glass pumped by a super-large-diameter flash lamp was enlarged to the kJ level.The compressor uses dielectric film gratings.
(2) 2kJ/narrowband nanosecond output mode:The beamline is similar to NIF or China's Shenguang Facility.The front end of this model is an independent laser system.Flexible transformation of time and space modes can be achieved,Ensure the safe operation of the laser system,Serving different types of basic physics experiments.
[Afterword]
From the perspective of the ELI-BEAMLINE sub-device alone,It integrates the most cutting-edge laser technology in the world: optical parametric amplification, all-semiconductor pumping, cryogenic cooling, thin-chip amplifiers, etc.The use of these technologies will surely promote the rapid development of the entire ultrafast laser field.Based on the author’s many years of experience in the ultra-powerful laser industry,Routine maintenance and stable operation of these laser systems will pose great challenges,The demand for laser scientists and engineers will also continue to increase,This is a good opportunity for researchers who are interested in engaging in ultra-powerful laser careers.
One of the purposes of ELI placing three sub-devices in less developed countries in Europe may be to "technologically alleviate poverty."But to sum up, the core technologies of major laser systems come from Germany, the United States, France and the United Kingdom.This change actually stimulated the technological development of these developed countries.It has a limited role in promoting the scientific and technological development of the host country.This also has reference significance for China’s development of ultra-powerful laser technology.Self-sufficiency leads to long-term sustainability,What is gratifying is that the Shanghai Institute of Optics and Mechanics, the Institute of Physics of the Chinese Academy of Sciences, Tsinghua University and a group of outstanding returned personnel are making unremitting efforts to develop China's own ultra-powerful laser technology.Wish them success!
References
[1] ELI-BEAMLINEWebsite: https://www.eli-beams.eu
[2]František Batysta, Roman Antipenkov, Jakub Novák, Jonathan T. Green, Jack A. Naylon, Jakub Horáček, Martin Horáček, Zbyněk Hubka, Robert Boge, Tomáš Mazanec, Bedřich Himmel, Pavel Bakule, and Bedřich Rus, "Broadband OPCPA system with 11 mJ output at 1 kHz, compressible to 12 fs," Opt. Express 24, 17843-17848 (2016)
[3]Saumyabrata Banerjee, Paul D. Mason, Klaus Ertel, P. Jonathan Phillips, Mariastefania De Vido, Oleg Chekhlov, Martin Divoky, Jan Pilar, Jodie Smith, Thomas Butcher, Andrew Lintern, Steph Tomlinson, Waseem Shaikh, Chris Hooker, Antonio Lucianetti, Cristina Hernandez-Gomez, Tomas Mocek, Chris Edwards, and John L. Collier, "100 J-level nanosecond pulsed diode pumped solid state laser," Opt. Lett. 41, 2089-2092 (2016)
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