Ultra-broadband mirrors for ultrafast and ultra-intense laser sciences

Ultra-broadband near-zero-dispersion mirrors (UbZdM) are the essential component for pulse reflection and beam transport in ultra-intense ultrafast lasers. By combining and optimizing the metal-dielectric hybrid structure, the TM-polarization UbZdM presented here has a high-reflection bandwidth of one octave (600-1200 nm) and, more importantly, a dispersion-free bandwidth of nearly 300 nm, which could also be increased to one octave with a commercial dispersion management device, much broader than those of current dielectric mirrors. The measured laser-induced damage threshold is around 0.40 J/cm2, which is similar to that of dielectric mirrors and twice that of metal mirrors. The damage results and mechanism are successfully explained with a proposed integral electric field intensity model, which could help improve the damage resistance for an even higher performance. The designed film structure of the UbZdM is quite robust to deposition errors, making it very suitable to meter-size coatings for high energy lasers. The UbZdM, introduced in this article, can be directly applied to current 100-Petawatt laser projects and future single-cycle Exawatt lasers. Our work is of great value for next steps in the development of both ultra-intense and ultrafast lasers, as well as related important applications such as physics in the exawatt and attosecond/zeptosecond regimes.