* the Vulcan PW in the UK at 1 × 10^21 W/cm2 (2004);
* the Ti:sapphirebased HERCULES laser at the University of Michigan, USA at 1 × 10^22 W/cm2 (2004)
* J-KAREN-P in Japan at 1 × 10^22 W/cm2 (2018)
* record intensity of 5.5 × 10^22 W/cm2 was demonstrated at the CoReLS laser (2019)
Even the highest-peak-power laser systems (10 PW and beyond) proposed or already in commissioning make no exception to this trend and largely predict intensities of only up to 10^23 W/cm2
(notably L4-ELI, EP-OPAL , SULF and SEL).
A fundamental physics or engineering limit is not clear; however, material challenges such as imperfect diffraction gratings, optics and gain materials reduce the overall laser focusability in time and space.
The steady ascent of Ti:sapphire, OPCPA and Nd:glass technologies upward in peak power has, with the construction of several ten to multi-tens of petawatt systems, nearly reached the ∼100 PW limit of metre-scale gold diffraction gratings.