We created finite lasers

New record of laser intensity

Radiant milestone: researchers have constructed a laser system with previously unattainable strength. The intensity of the ultrashort laser pulses, which are concentrated to a diameter of just over a micrometer, reaches 1023 Watts per square centimeter - this corresponds to a focus of all the sunlight hitting the earth to just a hundredth of a millimeter. This record intensity now opens up completely new research opportunities.

Everyday applications, quantum technology or basic research: today hardly anything works without lasers. Depending on the energy and wavelength, the parallel light waves of the lasers oscillating at the same rate have innumerable applications. They can be used to cool and lock atoms, transmit data, but also carry out measurements from the microcosm to gravitational waves.

Immense light intensities in the smallest of spaces

However, in order to penetrate the deepest secrets of matter or the cosmos, lasers are required that focus extreme light energies on the smallest of spaces. In 2004 a team from the University of Michigan succeeded in generating the strongest laser pulses to date from 1022 To generate watts per square centimeter. Since then, laser researchers around the world have been working on increasing this intensity even further.

Now it has been successful: Researchers led by Jin Woo Yoon from the Institute for Basic Research (IBS) in South Korea have for the first time generated laser pulses with an intensity of more than 1023 Achieve watts per square centimeter - ten times more than its predecessor. "This laser will allow us to tackle new scientific challenges," explains Yuun's colleague Chang Hee Nam. "With it we can finally check some theoretical ideas, some of which were put forward 100 years ago."

Laser pulses are first amplified, then smoothed and compressed

In order to generate a laser pulse of this intensity, two things are necessary: ​​You need a laser with extremely high power and you have to focus the beam of this laser on as small a point as possible. The power is provided by a four petawatt titanium sapphire laser at the Center for Relativistic Laser Science (CoReLS) of the IBS. To further increase the energy of its femtosecond laser pulses, the team initially used several amplifiers, which, however, gradually widened the laser beam to a diameter of 28 centimeters.

Because the pulse length was also stretched to a nanometer, it was then compressed back to femtosecond length. However, in order to focus the laser beam again and bring it to high intensity, Yoon and his team first had to correct wavefront distortions that arose during the amplification. To do this, they use deformable mirrors that, like the adaptive optics of modern telescopes, compensate for the disruptive effects.

In the last step, the laser beam, which has now been smoothed and brought to short pulses, was focused by a parabolic mirror. This reduced the beam width from 28 centimeters to just 1.1 micrometers.

Usable from astrophysics to QED

Sensors and a special camera then confirmed that the resulting laser pulses had an intensity of 1023 Watts per square centimeter reached - world record. The laser bundles the equivalent of the total terrestrial solar radiation to just ten micrometers. “This makes the CoReLS petawatt laser the most powerful laser in the world,” says Nam. "With this intensity - the highest ever achieved - we can now open up completely new areas of experimental research."

Among other things, the physicists hope to use their super laser to explore the intricacies of quantum electrodynamics - the laws that shape the interaction of charged elementary particles. But astrophysical phenomena such as cosmic radiation or the processes in the vicinity of black holes could also be illuminated by experiments with this laser. “That could help us to broaden our knowledge horizons,” says Nam. (Optica, 2021; doi: 10.1364 / OPTICA.420520)

Source: Institute for Basic Science, The Optical Society

May 7, 2021

- Nadja Podbregar