Particle physics research

LLNL diffraction gratings to activate the most powerful laser | Research & Technology | Sep 2022

LIVERMORE, Calif., September 27, 2022 – Researchers at Lawrence Livermore National Laboratory (LLNL) and their collaborators have developed high-energy pulse compression gratings that will be installed in what will be the world’s most powerful laser system. The laser system, called L4-ATON, which is currently under development, is designed to deliver up to 10 PW of peak power. One petawatt is about 1000 times the capacity of the entire US electrical grid.

The multilayer high-energy low-dispersion (HELD) dielectric networks will be installed in L4-ATON at the ELI-Beamlines facility in the Czech Republic. L4-ATON can generate 1.5 kJ of energy in 150 fs pulses, equal to 10 PW of power, at a repetition rate of one shot per minute.


Members of the LLNL diffractive optics group with four of the 85 × 70 cm HELD arrays to be installed in the ELI-Beamlines L4-ATON laser system. Meter-scale HELD arrays have the potential to facilitate future 20-50 PW class ultrafast laser systems. Courtesy of LLNL.


Multipetawatt laser technology opens the door to research in areas such as plasma and high-energy physics, astrophysics, laser particle acceleration, improved medical diagnostics, industrial processing techniques, and particle detection. nuclear materials.

LLNL’s HELD networks deliver 3.4 times more total energy than current state-of-the-art technology. They were developed through a collaboration between the Diffractive Optics group at LLNL, ELI-Beamlines, Spectra Physics-Newport and National Energetics.

Petawatt and multi-petawatt lasers rely on chirped pulse amplification to stretch, amplify, and then compress a high-energy laser pulse to prevent damage to optical components. Pulse compression arrays must be large, efficient, and robust enough to withstand the high fluence (energy density) of laser pulses generated by petawatt-class lasers such as the National Ignition Facility’s Advanced Radiographic Capability (ARC) (TIN).

According to LLNL senior scientist Hoang Nguyen, HELD arrays are advancements over NIF ARC-like arrays and allow significantly higher energy outputs. The 85 × 70 cm HELD gratings are configured at a Littrow angle (the grating’s maximum efficiency angle) of 37º and allow for a larger beamwidth – 62.5 cm. “Increasing the beam height to produce a square beam and accounting for the difference in LIDT (Laser Induced Damage Threshold) results in about 3.4 times more total energy on the array per compared to the high-dispersion ARC, 76.5º-angle-of-incidence array design,” Nguyen said.

Multilayer Dielectric (MLD) gratings are composed of a base substrate on which layers of dielectric mirrors with varying indices of refraction are stacked, topped with a layer of ion-etched photoresist, a light-sensitive material that is fine-tuned to the desired diffraction specifications.  MLD gratings can significantly improve the diffraction efficiency of grating compressors over a wide bandwidth or wide frequency range.  Unlike the metal used in traditional grids, the dielectric materials are non-conductive and can absorb 500 times less energy than previous designs.  Courtesy of LLNL.


Multilayer dielectric gratings (MLD) are composed of a base substrate on which are stacked layers of dielectric mirrors with variable refractive indices, surmounted by a layer of photoresist etched by ions. MLD gratings can significantly improve the diffraction efficiency of grating compressors over a wide bandwidth or wide frequency range. Unlike metal used in traditional grids, dielectric materials are non-conductive and can absorb 500× less power than previous designs. Courtesy of LLNL.


Additionally, the uniformity of HELD is due to high-efficiency design over a wide range of groove widths and heights and well-controlled dielectric layer thickness, according to Huang. Operating at the Littrow angle of the grating results in maximum diffraction efficiency and bandwidth, but requires tilting the angle of the gratings so that the beam reflects slightly up or out of plane.