Circularly polarized light reduces damage to optical elements in inertial confinement fusion

Crossed-beam energy transfer (CBET), the process whereby lasers crossing in plasma can exchange energy with one another, is integral for inertial confinement fusion (ICF) experiments. Its efficiency depends strongly on laser polarization. High-power lasers have historically used linearly polarized light, but circular polarization should be less damaging to optical elements, allowing higher operating powers.

Michel et al. derived the first analytical expressions comparing two-beam CBET for linear and circular polarization. Using a wave mixing theory with arbitrary polarization and a new simulation tool, they investigated the interaction between 96 lasers in realistic ICF conditions.

For linearly polarized crossing lasers, CBET can be zero when the electric fields are orthogonal and maximal when they are parallel. Circular polarization leads to a smoothing effect where CBET never reaches zero or the maximum.

Simulations showed that linear polarization leads to significant beam-to-beam power variations due to CBET, while circular polarization significantly reduces these variations without changing the average CBET per cone of beams.

“This indicates that CBET should still work with the same efficacy to tune the implosion symmetry on future laser facilities using circular polarization, but it should also reduce beam-to-beam variations that can lead to high backscatter on some beams — all while helping mitigate optics damage of the laser,” said author Pierre Michel. “This paper should provide a strong incentive to consider using circularly polarized light on the next generation of high-power lasers used for inertial fusion energy or for high energy density sciences.”

Michel hopes to continue studying laser-plasma interactions in ICF experiments as well as plasma and gas optics for next-generation high-power lasers.

Source: “Laser polarization effects on crossed-beam energy transfer in inertial confinement fusion,” by P. Michel, A. Oudin, N. Lemos, E. Kur, A. Kritcher, and T. Chapman, Physics of Plasmas (2026). The article can be accessed at https://doi.org/10.1063/5.0335309 .