We demonstrated for the first time the production of highly polarized short-pulse positrons with a finite energy spread in accordance with a new scheme that consists of two-quantum processes, such as inverse Compton scattering and electron-positron pair creation. Using a circularly polarized laser beam of 532 nm scattered off a high-quality, 1.28 GeV electron beam, we obtained polarized positrons with an intensity of 2×10 4 e + /bunch. The magnitude of positron polarization was determined to be 73 ± 15(sta) ± 19(sys)% by means of a newly designed positron polarimeter.

X-ray generation based on laser-electron Compton scattering is one attractive method to achieve a compact laboratory-sized high-brightness x-ray source. We have designed, built, and tested such a source; it combines a 50 MeV multibunch electron linac with a mode-locked 1064 nm laser stored and amplified in a Fabry-Perot optical cavity. We directly observed trains of pulsed x rays using a microchannel plate detector; the resultant yield was found to be 1.2x10(5) Hz in good agreement with prediction. We believe that the result has demonstrated good feasibility of linac-based compact x-ray sources via laser-electron Compton scatterings.

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Interaction of a solid material with focused, intense pulses of high-energy photons or other particles (such as electrons and ions) creates a strong electronic excitation state within an ultra-short time and on ultra-small spatial scales. This offers the possibility to control the response of a material on a spatial scale less than a nanometer—crucial for the next generation of nano-devices. Here we create craters on the surface of a silicon substrate by focusing single femtosecond extreme ultraviolet pulse from the SACLA free-electron laser. We investigate the resulting surface modification in the vicinity of damage thresholds, establishing a connection to microscopic theoretical approaches, and, with their help, illustrating physical mechanisms for damage creation. The cooling during ablation by means of rapid electron and energy transport can suppress undesired hydrodynamical motions, allowing the silicon material to be directly processed with a precision reaching the observable limitation of an atomic force microscope.