A plasma mirror is a dense plasma created at the surface of an initially solid target when this target is irradiated by an intense femtosecond laser pulse. Due to its high density (≈10 23 electrons/cm3), it efficiently reflects the incident laser field. In addition, given the brevity of the laser pulse, its interface remains optically-flat during the interaction: plasma mirrors thus specularly reflect the incident laser beam, and can be viewed as high-quality mirrors suitable for UHI beams [Kap91Dou04,Tha07] (Fig.1), with many potential applications (Applications of plasma mirrors). They are also ideal systems to investigate the fundamental physics of UHI interactions (Fundamental interest of plasma mirrors). The Physics at High Intensity group has made major contributions to the investigation of plasma mirrors in the last decade (Results of the PHI on this topic).
Fig. 1: Physics of plasma mirrors. When exposed to UHI laser fields, plasma mirrors specularly reflect the laser with a reflectivity higher than 70% (bottom left image). Their highly-nonlinear coupling with the field (upper left image, from PIC simulations) also leads to the emission of beams of high-order harmonics and relativistic electrons. Typical spatial patterns of these beams are shown in the central images, and their typical energy spectra in the rightmost images (from experiments with the UHI100 laser at I=3.1019 W/cm2).