Researchers produce laser pulses with record-breaking intensity
High-intensity pulses allow astrophysical phenomena to be studied in the lab
IMAGE: RESEARCHERS CREATED HIGH-INTENSITY PULSES USING THE PETAWATT LASER (PICTURED) AT THE CENTER FOR RELATIVISTIC LASER SCIENCE (CORELS) IN THE REPUBLIC OF KOREA. THIS HIGH INTENSITY LASER WILL ALLOW SCIENTISTS TO... view more
CREDIT: CHANG HEE NAM, CORELS
WASHINGTON -- Researchers have demonstrated a record-high laser pulse intensity of over 1023 W/cm2 using the petawatt laser at the Center for Relativistic Laser Science (CoReLS), Institute for Basic Science in the Republic of Korea. It took more than a decade to reach this laser intensity, which is ten times that reported by a team at the University of Michigan in 2004. These ultrahigh intensity light pulses will enable exploration of complex interactions between light and matter in ways not possible before.
The powerful laser can be used to examine phenomena believed to be responsible for high-power cosmic rays, which have energies of more than a quadrillion (1015) electronvolts (eV). Although scientists know that these rays originate from somewhere outside our solar system, how they are made and what is forming them has been a longstanding mystery.
"This high intensity laser will allow us to examine astrophysical phenomena such as electron-photon and photon-photon scattering in the lab," said Chang Hee Nam, director of CoReLS and professor at Gwangju Institute of Science & Technology. "We can use it to experimentally test and access theoretical ideas, some of which were first proposed almost a century ago."
In Optica, The Optical Society's (OSA) journal for high impact research, the researchers report the results of years of work to increase the intensity of laser pulses from the CoReLS laser. Studying laser matter-interactions requires a tightly focused laser beam and the researchers were able to focus the laser pulses to a spot size of just over one micron, less than one fiftieth the diameter of a human hair. The new record-breaking laser intensity is comparable to focusing all the light reaching earth from the sun to a spot of 10 microns.
"This high intensity laser will let us tackle new and challenging science, especially strong field quantum electrodynamics, which has been mainly dealt with by theoreticians," said Nam. "In addition to helping us better understand astrophysical phenomena, it could also provide the information necessary to develop new sources for a type of radiation treatment that uses high-energy protons to treat cancer."
Making pulses more intense
The new accomplishment extends previous work in which the researchers demonstrated a femtosecond laser system, based on Ti:Sapphire, that produces 4 petawatt (PW) pulses with durations of less than 20 femtoseconds while focused to a 1 micrometer spot. This laser, which was reported in 2017, produced a power roughly 1,000 times larger than all the electrical power on Earth in a laser pulse that only lasts twenty quadrillionths of a second.
To produce high-intensity laser pulses on target, the generated optical pulses must be focused extremely tightly. In this new work, the researchers apply an adaptive optics system to precisely compensate optical distortions. This system involves deformable mirrors -- which have a controllable reflective surface shape -- to precisely correct distortions in the laser and generate a beam with a very well-controlled wavefront. They then used a large off-axis parabolic mirror to achieve an extremely tight focus. This process requires delicate handling of the focusing optical system.
"Our years of experience gained while developing ultrahigh power lasers allowed us to accomplish the formidable task of focusing the PW laser with the beam size of 28 cm to a micrometer spot to accomplish a laser intensity exceeding 1023 W/cm2," said Nam.
Studying high-energy processes
The researchers are using these high-intensity pulses to produce electrons with an energy over 1 GeV (109 eV) and to work in the nonlinear regime in which one electron collides with several hundred laser photons at once. This process is a type of strong field quantum electrodynamics called nonlinear Compton scattering, which is thought to contribute to the generation of extremely energetic cosmic rays.
They will also use the radiation pressure created by the ultrahigh intensity laser to accelerate protons. Understanding how this process occurs could help develop a new laser-based proton source for cancer treatments. Sources used in today's radiation treatments are generated using an accelerator that requires a huge radiation shield. A laser-driven proton source is expected to reduce the system cost, making the proton oncology machine less costly and thus more widely accessible to patients.
The researchers continue to develop new ideas for enhancing the laser intensity even more without significantly increasing the size of the laser system. One way to accomplish this would be to figure out a new way to reduce the laser pulse duration. As lasers with peaks power ranging from 1 to 10 PW are now in operation and several facilities reaching 100 PW are being planned, there is no doubt that high-intensity physics will progress tremendously in the near future.
CAPTION
A laser-matter interaction chamber for proton acceleration, in which the focal intensity over 1023 W/cm2 was demonstrated by tightly focusing a multi-petawatt laser beam with an F/1.1 off-axis parabolic mirror.
CREDIT
Chang Hee Nam
Paper: J. W. Yoon, Y. G. Kim, I. W. Choi, J. H. Sung, H. W. Lee, S. K. Lee, C. H. Nam, "Realization of laser intensity over 1023 W/cm2," Optica, 8, 5, 630-635 (2021).
DOI: https:/
About Optica
Optica is an open-access, journal dedicated to the rapid dissemination of high-impact peer-reviewed research across the entire spectrum of optics and photonics. Published monthly by The Optical Society (OSA), Optica provides a forum for pioneering research to be swiftly accessed by the international community, whether that research is theoretical or experimental, fundamental or applied. Optica maintains a distinguished editorial board of more than 60 associate editors from around the world and is overseen by Editor-in-Chief Prem Kumar, Northwestern University, USA. For more information, visit Optica.
About The Optical Society
Founded in 1916, The Optical Society (OSA) is the leading professional organization for scientists, engineers, students and business leaders who fuel discoveries, shape real-life applications and accelerate achievements in the science of light. Through world-renowned publications, meetings and membership initiatives, OSA provides quality research, inspired interactions and dedicated resources for its extensive global network of optics and photonics experts. For more information, visit osa.org.
Realization of the highest laser intensity
ever reached
The record-breaking laser intensity over 1023 W/cm2 enables us to explore novel physical phenomena occurring under extreme physical conditions
IMAGE: PANORAMIC VIEW OF THE CORELS PW LASER. view more
CREDIT: INSTITUTE FOR BASIC SCIENCE
Recently, laser scientists at the Center for Relativistic Laser Science (CoReLS) within the Institute for Basic Science (IBS) in South Korea realized the unprecedented laser intensity of 1023 W/cm2. This has been a milestone that has been pursued for almost two decades by many laser institutes around the world.
An ultrahigh intensity laser is an important research tool in several fields of science, including those which explore novel physical phenomena occurring under extreme physical conditions. Since the demonstration of the 1022 W/cm2 intensity laser by a team at the University of Michigan in 2004, the realization of laser intensity over 1023 W/cm2 has been pursued for nearly 20 years.
In general, achieving such a level of ultra-high laser intensity requires two things: laser with extremely high power output, and focusing that laser to the smallest spot as possible. While continuous-wave lasers are limited to megawatt-scale intensity, far higher peak power output (on the order of petawatt) is possible in pulsed laser systems by delivering the energy in the time scale as short as femtoseconds. In order to reach the goal of developing the world's most powerful laser, several ultrahigh power laser facilities with outputs of 10 PW and beyond, such as ELI (EU), Apollon (France), EP-OPAL (USA), and SEL (China), have been built or are being planned. A recent study from Osaka University even proposed a concept prototype for an exawatt class laser.
Meanwhile, the CoReLS laser team has been operating a 4-PW laser system since 2016. This year in April 2021, they have finally achieved the record-breaking milestone of 1023 W/cm2 by tightly focusing the multi-PW laser beam.
Several special techniques have been employed to achieve this feat. The power intensity was maximized by using a focusing optics called an off-axis parabolic mirror, which was used to focus a 28 cm laser beam down to a spot only 1.1 micrometers wide. Such a diffraction-limited tight focusing can be obtained only with a clean laser beam without wavefront distortion. The CoReLS laser team, thus, made its PW laser beam as clean as possible using a set of deformable mirrors to correct the wavefront distortion of the PW laser.
The CoReLS 4-PW laser is a femtosecond, ultrahigh power Ti:sapphire laser, based on the chirped pulse amplification (CPA) technique. The layout of the CoReLS 4-PW laser, including the experimental setup to control the wavefront and to measure the intensity, is given in Fig. 1. A low-energy femtosecond laser pulse from the front-end was stretched to a nanosecond pulse by the pulse stretcher. The initial laser pulse was then amplified to 4.5 J by the two power amplifiers and then up to 112 J by the two booster amplifiers. The size of the laser beam increased along the beam path by a series of beam expanders; 25 mm right after the power amplifiers, 65 mm at the entrance of the 1st booster amplifier, 85 mm at the entrance of the 2nd booster amplifier, and 280 mm at the entrance of the pulse compressor. In the pulse compressor, the laser pulse was recompressed to 20 fs (FWHM), which caused its peak power to become 4 PW after the compression.
In order to compensate for the wavefront distortion of the PW laser beam, two deformable mirrors were employed in the PW laser beamline. The first deformable mirror (DM1) with a diameter of 100 mm was installed after the final booster amplifier, with its role being to correct the wavefront distortion accumulated from the front end to the final beam expander. The second deformable mirror (DM2) with a diameter of 310 mm was installed after the pulse compressor, which corrects the additional aberrations induced from large aperture optics in the pulse compressor, the beam delivery line, and the target area. In the target chamber, the PW laser beam was tightly focused with an f /1.1 off-axis parabolic mirror, which possessed an effective focal length of 300 mm. For imaging and characterization of the focused spot, the focused beam was collimated by an objective lens. It was then divided into two beams with a beam splitter for the focal spot and wavefront characterization. A camera was used for the focal spot monitoring of the transmitted laser beam, and a wavefront sensor was used to measure the wavefront of the reflected laser beam. Figure 3 shows the 3-D focal spot image measured by the camera in the target chamber.
Prof. NAM Chang Hee, the Director of CoReLS, notes, "This work has shown that the CoReLS PW laser is the most powerful laser in the world. With the highest laser intensity achieved ever, we can tackle new challenging areas of experimental science, especially strong field quantum electrodynamics (QED) that has been dealt with mainly by theoreticians. We can explore new physical problems of electron-photon scattering (Compton scattering) and photon-photon scattering (Breit-Wheeler process) in the nonlinear regime. This kind of research is directly related to various astrophysical phenomena occurring in the universe and can help us to further expand our knowledge horizon."
CAPTION
Layout of the CoReLS petawatt laser and the experimental setup to achieve the laser intensity of over 1023W/cm2. BS, beam splitter; DM1-2, deformable mirrors; EM, energy meter; OAP, f /1.1 off-axis parabolic mirror; OL, objective lens; WFS1-2, wavefront sensors.
CREDIT
Institute for Basic Science
CAPTION
Measured 3-D focal spot image showing the laser intensity of 1.4x1023 W/cm2.
CREDIT
Institute for Basic Science
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