近日，英国贝尔法斯特女王大学Brendan Dromey团队报道了效率优化的极端场相对论等离子体谐波。2026年4月22日出版的《自然》杂志发表了这项成果。

来自相对论振荡激光等离子体的明亮谐波辐射为产生极端电磁场提供了一条直接途径。理论预测，在优化条件下，等离子体介质能够在相干谐波焦点（CHF）中支持激光能量的强时空压缩，从而提供比入射驱动激光脉冲高出多个数量级的强度增益。尽管衍射极限性能（空间压缩）和阿秒锁相（时间压缩）已在实验中得到证实，但迄今尚未实现将相对论强激光脉冲能量高效耦合到发射的谐波锥中。

研究组展示这种高度非线性相互作用可被调控，以实现模拟预测的最大转换效率。通过在亚皮秒（<10-12秒）时间尺度上精细调节驱动激光的时间波形，研究组在第12至第47次谐波之间观察到了超过9毫焦耳的能量。这些结果与理论上预期的效率对谐波阶次的依赖关系一致，验证了产生过程中已达到最优条件。

这是在实验中实现CHF预期强度增益所需的重要最终要素。尽管同时获得时空压缩和最优效率仍然具有挑战性，但通往接近量子电动力学临界场强（施温格极限，>1016 V/cm 或 >1029 W/cm2）的极端光场强度之路现已打开，为量子真空的全光学研究以及强场阿秒科学的新前沿提供了可能。

附：英文原文

Title: Efficiency-optimized relativistic plasma harmonics for extreme fields

Author: Timmis, Robin J. L., Fitzpatrick, Colm R. J., Kennedy, Jonathan P., Huddleston, Holly M., Denis, Elliott, James, Abigail, Baird, Chris, Symes, Dan, McGonegle, David, Atonga, Eduard, Martin, Heath, Rebenstock, Jeremy, Neely, John, Lee, Jordan, Redfern, Joshua, Bourgeois, Nicolas, Finlay, Oliver, Ruskov, Rusko, Astbury, Sam, Hawkes, Steve, Zhang, Zixin, Zepf, Matt, Krushelnick, Karl, Gumbrell, Edward, Rajeev, Paramel Pattathil, Yeung, Mark, Dromey, Brendan, Norreys, Peter

Issue&Volume: 2026-04-22

Abstract: Bright harmonic radiation from relativistically oscillating laser plasmas offers a direct route for generating extreme electromagnetic fields. Theory predicts that under optimized conditions, the plasma medium can support strong spatiotemporal compression of laser energy in a coherent harmonic focus (CHF), delivering intensity boosts many orders of magnitude greater than the incident driving laser pulse1,2,3,4. Although diffraction-limited performance5 (spatial compression) and attosecond phase locking6,7,8 (temporal compression) have been demonstrated experimentally, efficient coupling of relativistically intense laser pulse energy into the emitted harmonic cone has not been realized so far. Here we demonstrate that this highly nonlinear interaction can be tailored to deliver the maximum conversion efficiencies predicted from simulations. By fine-tuning the temporal profile of the driving laser on sub-picosecond (<1012s) timescales, energies >9mJ between the 12th and 47th harmonics are observed. These results are in agreement with the theoretically expected efficiency dependence on harmonic order, verifying that optimal conditions have been achieved in the generation process. This is the important final element required to achieve the expected intensity boosts from a CHF in experiments. Although obtaining spatiotemporal compression and optimal efficiency simultaneously remains challenging, the path to realizing extreme optical field strengths approaching the critical field of quantum electrodynamics (the Schwinger limit at >1016Vcm1 or >1029Wcm2) is now open, permitting all-optical studies of the quantum vacuum and new frontiers for intense attosecond science.

DOI: 10.1038/s41586-026-10400-2

Source: https://www.nature.com/articles/s41586-026-10400-2