RESUMEN
Reaching light intensities above 1025 W/cm2 and up to the Schwinger limit of the order of 1029 W/cm2 would enable testing fundamental predictions of quantum electrodynamics. A promising - yet challenging - approach to achieve such extreme fields consists in reflecting a high-power femtosecond laser pulse off a curved relativistic mirror. This enhances the intensity of the reflected beam by simultaneously compressing it in time down to the attosecond range, and focusing it to sub-micrometre focal spots. Here we show that such curved relativistic mirrors can be produced when an ultra-intense laser pulse ionizes a solid target and creates a dense plasma that specularly reflects the incident light. This is evidenced by measuring the temporal and spatial effects induced on the reflected beam by this so-called 'plasma mirror'. The all-optical measurement technique demonstrated here will be instrumental for the use of relativistic plasma mirrors with the upcoming generation of Petawatt lasers that recently reached intensities of 5 × 1022 W/cm2, and therefore constitutes a viable experimental path to the Schwinger limit.
RESUMEN
Investigation of the iron phase diagram under high pressure and temperature is crucial for the determination of the composition of the cores of rocky planets and for better understanding the generation of planetary magnetic fields. Here we present X-ray diffraction results from laser-driven shock-compressed single-crystal and polycrystalline iron, indicating the presence of solid hexagonal close-packed iron up to pressure of at least 170 GPa along the principal Hugoniot, corresponding to a temperature of 4,150 K. This is confirmed by the agreement between the pressure obtained from the measurement of the iron volume in the sample and the inferred shock strength from velocimetry deductions. Results presented in this study are of the first importance regarding pure Fe phase diagram probed under dynamic compression and can be applied to study conditions that are relevant to Earth and super-Earth cores.
RESUMEN
We report on a nonlinear mirror (NLM) scheme that enables, for the first time to the best of our best knowledge, tunable mode locking of a Cr2+:ZnSe laser in the picosecond regime. The NLM-used as the output coupler of the laser cavity-consists of a periodically poled lithium niobate (PPLN) crystal with a fan-out grating coupled with a dichroic mirror and a wedged dispersive YAG plate. The Cr2+:ZnSe laser, pumped by a CW thulium-doped fiber laser, delivers 85 ps pulses at a repetition rate of 220 MHz with a 300 mW average power. Thanks to the use of a fan-out PPLN crystal, we benefit from the wide tunability of the Cr2+:ZnSe laser and achieve mode locking over the whole 2.44-2.55 µm range while maintaining a narrow-linewidth emission suitable for time-resolved nonlinear spectroscopy applications.
