Lawrence Livermore National Laboratory (LLNL) researchers have designed a compact multi-petawatt laser that uses plasma transmission arrays to overcome the power limitations of conventional solid-state optical arrays. The design could allow the construction of an ultrafast laser up to 1,000 times more powerful than existing lasers of the same size.
Petawatt (quadrillion-watt) lasers rely on diffraction gratings for chirped pulse amplification (CPA), a technique for stretching, amplifying and then compressing a high-energy laser pulse to avoid damaging optical components. The CPA, which won a Nobel Prize in Physics in 2018, is at the heart of the National Ignition Facility’s advanced radiographic capability as well as the NIF’s predecessor, the Nova Laser, the world’s first petawatt laser.
With a damage threshold several orders of magnitude higher than conventional reflection gratings, plasma gratings “allow us to deliver much more power for the same sized grating,” said the former LLNL postdoc. Matthew Edwards, co-author of a Applied physical examination article describing the new design published online on August 9. Edwards was joined on the paper by the leader of the Laser-Plasma Interactions group, Pierre Michel.
“Glass focusing optics for powerful lasers need to be large to avoid damage,” Edwards said. “Laser energy is distributed to maintain low local intensity. Because plasma is more resistant to optical damage than a piece of glass, for example, we can imagine building a laser that produces hundreds or thousands of times more more power than a current system without making that system bigger.”
LLNL, with 50 years of experience developing high-energy laser systems, is also a long-time leader in the design and manufacture of the world’s largest diffraction gratings, such as the gold gratings used to produce 500 joule petawatt pulses on the Nova laser. in the 1990s. However, even larger arrays would be needed for next-generation multi-petawatt and exawatt (1,000 petawatt) lasers to overcome the maximum fluence (energy density) limitations imposed by solid-state optics conventional (see “Holographic Plasma Lenses for Ultra-High-power Lasers”).
Edwards noted that optics consisting of plasma, a mixture of ions and free electrons, are “well suited to a relatively high repetition rate, high average power laser”. The new design could, for example, allow a laser system similar in size to the L3 HAPLS (High-Repetition-Rate Advanced Petawatt Laser System) to be deployed on ELI Beamlines in the Czech Republic, but with 100 times the peak power.
Designed and built by LLNL and delivered to ELI Beamlines in 2017, HAPLS was designed to produce 30 joules of energy in a pulse duration of 30 femtoseconds (quadrillionths of a second), equivalent to one petawatt, at 10 Hertz (10 pulses per second).
“If you imagine trying to build HAPLS with 100 times the peak power at the same repetition rate, that’s the kind of system where it would be most appropriate,” said Edwards, now an assistant professor of mechanical engineering at the University. from Stanford.
“The grating can be redone at a very high repetition rate, so we believe 10 Hertz operation is possible with this type of design. However, it would not be suitable for a high average power continuous wave laser.”
While plasma optics have been used successfully in plasma mirrors, the researchers said, their use for high-power pulse compression has been limited by the difficulty of creating a sufficiently uniform large plasma and the complexity dynamics of nonlinear plasma waves.
“It’s proven difficult to get plasmas to do what you want them to do,” Edwards said. “It is difficult to make them sufficiently homogeneous, to ensure that the variations in temperature and density are sufficiently small, etc.
“We’re aiming for a design where this kind of inhomogeneity is as minimal a problem as possible for the whole system. The design should be very tolerant of imperfections in the plasma you’re using.”
Based on simulations using the particle-in-cell (PIC) code EPOCH, the researchers said: “We expect this approach to be able to provide a degree of stability not accessible with other compression mechanisms at plasma base, and may prove more feasible to build in practice.” The new design “requires only gas as the initial medium, is robust to variations in plasma conditions, and minimizes plasma volume to make sufficient uniformity practical.”
“By using achievable plasma parameters and avoiding solid-density plasma and solid-state optics, this approach provides a feasible path to the next generation of high-power lasers.”
Researchers design plasma-based holographic lenses
Matthew R. Edwards et al, Plasma Transmission Arrays for High Intensity Laser Pulse Compression, Applied physical examination (2022). DOI: 10.1103/PhysRevApplied.18.024026
Provided by Lawrence Livermore National Laboratory
Quote: Researchers design compact high-power laser using plasma optics (August 19, 2022) Retrieved August 19, 2022 from https://phys.org/news/2022-08-compact-high-power-laser -plasma-optics.html
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