The latest large-scale diffraction grating developed abroad is expected to reali

A research cooperation coordinated by Lawrence Livermore National Laboratory (LLNL) has developed a new large-scale diffraction grating, which is believed to be able to provide ultrashort laser pulses with power up to 50 petawatts.

So far, the team has produced a high-energy pulse compression grating with a size of 85 x 70 cm, which will be installed in the L4-ATON laser system at the ELI Beamlines facility near Prague, Czech Republic. L4-ATON is expected to generate 1.5 kilojoules (kJ) of energy in 150 femtosecond (400 millionths of a second) pulses, equivalent to the unprecedented power of 10 petawatts, with a repetition rate of once per minute.

A technician checked one of the eight HELD gratings recently made, which will be installed on the 18 meter long, 55 ton compressor of the L4-ATON laser system.

Image source: LLNL

Based on the Nobel Prize winning chirped pulse amplification (CPA) technology, laser systems such as L4-ATON must stretch, amplify and compress high-energy pulses without damaging optical components. This means that the pulse compression grating used must be large, effective and solid enough to withstand the high photon flow of the laser pulse. Through cooperation with ELI Beamlines, Spectra Physics and National Energetics in Texas, LLNL's diffractive optics group has produced high energy, low dispersion (HELD) multilayer dielectric gratings.

Houng Nguyen, a senior laser scientist at LLNL, explained that it is said that the total energy they process is about three times more than the current most advanced technology. He said: "85 × The 70 cm HELD grating is configured at a 37 degree Littrow angle (the angle of maximum grating efficiency), allowing a larger beam width of - 62.5 cm. Increase the beam height to generate a square beam. Considering the difference of LIDT (laser induced damage threshold), compared with the grating design with high dispersion of ARC and 76.5 degree incidence angle, the total energy on the grating is about 3.4 times. "

Nguyen added: "The excellent uniformity of HELD grating is due to its high efficiency in a wide range of groove width and height, as well as its good control of the thickness of the dielectric layer. Working at the Littrow angle of the grating can obtain the maximum diffraction efficiency and bandwidth, but it needs to tilt the angle of the grating to make the beam slightly reflect upward or beyond the plane."

Multilayer dielectric (MLD) gratings are composed of a substrate, on which are stacked dielectric mirror layers with different refractive indexes, on which is a layer of ion etched photoresist, which is a light sensitive material and is finely tuned to the required diffraction specifications. MLD grating can greatly improve the diffraction efficiency of grating compressor in large bandwidth or frequency range. Unlike metals used in traditional gratings, dielectric materials are non-conductive and can absorb 500 times less energy than previous designs.

The L4-ATON laser, named after the Egyptian sun god, is a supporting product of the L3-HAPLS laser system designed, developed and built by NIF and the Photon Science Bureau. It was delivered to ELI Beamlines in 2017. L3-HAPLS (high repetition rate advanced Petawatt laser system) also benefits from the progress of LLNL grating technology.

L4 ATON was developed by a consortium led by National Energetics in cooperation with Lithuanian laser manufacturers Ekspla and ELI Beamlines. In addition, HELD grating is one of the three technologies that LLNL won the R&D 100 award in 2022. It can provide 3.4 times more total energy than the current most advanced technology, which is jointly developed by LLNL's diffractive optics group, ELI Beamlines, Spectra Physics Newport in California and National Energetics in Texas.

Source: OFweek