400nm ultra-broadband gratings for near-single-cycle 100 Petawatt lasers.

Compressing high-energy laser pulses to a single-cycle and realizing the "λ laser concept", where λ is the wavelength of the laser, will break the current limitation of super-scale projects and contribute to the future 100-petawatt and even Exawatt lasers. Here, we have realized ultra-broadband gold gratings, core optics in the chirped pulse amplification, in the 750-1150 nm spectral range with a > 90% -1 order diffraction efficiency for near single-cycle pulse stretching and compression. The grating is also compatible with azimuthal angles from -15° to 15°, making it possible to design a three-dimensional compressor. In developing and manufacturing processes, a crucial grating profile with large base width and sharp ridge is carefully optimized and controlled to dramatically broaden the high diffraction efficiency bandwidth from the current 100-200 nm to over 400 nm. This work has removed a key obstacle to achieving the near single-cycle 100-PW lasers in the future.