Femtosecond ultrabright electron sources with spatially structured emission are an enabling technology for free-electron lasers, compact coherent X-ray sources, electron diffractive imaging, and attosecond science. In this work, we report the design, modeling, fabrication, and experimental characterization of a novel ultrafast optical field emission cathode comprised of a large (>100,000 tips), dense (4.6 million tips·cm(-2)), and highly uniform (<1 nm tip radius deviation) array of nanosharp high-aspect-ratio silicon columns. Such field emitters offer an attractive alternative to UV photocathodes while providing a direct means of structuring the emitted electron beam. Detailed measurements and simulations show pC electron bunches can be generated in the multiphoton and tunneling regime within a single optical cycle, enabling significant advances in electron diffractive imaging and coherent X-ray sources on a subfemtosecond time scale, not possible before. At high charge emission yields, a slow rollover in charge is explained as a combination of the onset of tunneling emission and the formation of a virtual cathode.

We report on a multi-mJ 2.1 μm optical parametric chirped-pulse amplification (OPCPA) system operating at 1 kHz repetition rate, pumped by a picosecond cryogenic Yb:YAG laser, and the demonstration of soft x-ray high-harmonic generation (HHG) with a flux of ∼2×10(8)  photon/s/1% bandwidth at 160 eV in Ar. The 1 kHz cryogenic Yb:YAG pump laser amplifies pulses up to 56 mJ and delivers compressed 42 mJ, 17 ps pulses to the 2.1 μm OPCPA system. In the three-stage OPCPA chain, we have obtained up to 2.6 mJ of output energies at 2.1 μm and pulses compressed to 40 fs with good beam quality. Finally, we show cut-off extension of HHG driven by this 2.1 μm source in Ar and N2 gas cells to 190 eV with high photon flux. Our 3D propagation simulation confirms the generation of soft x-ray attosecond pulses from the experiment with Ar.

High-energy phase-stable sub-cycle mid-infrared pulses can provide unique opportunities to explore phase-sensitive strong-field light–matter interactions in atoms, molecules and solids. At the mid-infrared wavelength, the Keldysh parameter could be much smaller than unity even at relatively modest laser intensities, enabling the study of the strong-field sub-cycle electron dynamics in solids without damage. Here we report a high-energy sub-cycle pulse synthesiser based on a mid-infrared optical parametric amplifier and its application to high-harmonic generation in solids. The signal and idler combined spectrum spans from 2.5 to 9.0 µm. We coherently synthesise the passively carrier-envelope phase-stable signal and idler pulses to generate 33 μJ, 0.88-cycle, multi-gigawatt pulses centred at ~4.2 μm, which is further energy scalable. The mid-infrared sub-cycle pulse is used for driving high-harmonic generation in thin silicon samples, producing harmonics up to ~19th order with a continuous spectral coverage due to the isolated emission by the sub-cycle driver.

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Abstract. Asteroids and comets that cross Earth's orbit pose a credible risk of impact, with potentially severe disturbances to Earth and society. We propose an orbital planetary defense system capable of heating the surface of potentially hazardous objects to the vaporization point as a feasible approach to impact risk mitigation. We call the system DE-STAR, for Directed Energy System for Targeting of Asteroids and exploRation. The DE-STAR is a modular-phased array of kilowatt class lasers powered by photovoltaic's. Modular design allows for incremental development, minimizing risk, and allowing for technological codevelopment. An orbiting structure would be developed in stages. The main objective of the DE-STAR is to use focused directed energy to raise the surface spot temperature to ∼3000 K, sufficient to vaporize all known substances. Ejection of evaporated material creates a large reaction force that would alter an asteroid's orbit. The baseline system is a DE-STAR 3 or 4 (1-to 10-km array) depending on the degree of protection desired. A DE-STAR 4 allows initial engagement beyond 1 AU with a spot temperature sufficient to completely evaporate up to 500-m diameter asteroids in 1 year. Small objects can be diverted with a DE-STAR 2 (100 m) while space debris is vaporized with a DE-STAR 1 (10 m).