Attenuation in photonic bandgap guiding hollow-core photonic crystal fiber (HC-PCF) has not beaten the fundamental silica Rayleigh scattering limit (SRSL) of conventional step-index fibers due to strong core-cladding optical overlap, surface roughness at the silica cladding struts, and the presence of interface modes. Hope has been revived recently by the introduction of hypocycloid core contour (i.e., negative curvature) in inhibited-coupling guiding HCPCF. We report on several fibers with a hypocycloid core contour and a cladding structure made of a single ring from a tubular amorphous lattice, including one with a record transmission loss of 7.7 dB/km at ~750 nm (only a factor ~2 above the SRSL) and a second with an ultrabroad fundamental band with loss in the range of 10-20 dB/km, spanning from 600 to 1200 nm. The reduction in confinement loss makes these fibers serious contenders for light transmission below the SRSL in the UV-VIS-NIR spectral range and could find application in high-energy pulse laser beam delivery or gas-based coherent and nonlinear optics

Dissymmetric nano/microsized spheres are very appealing because controlled dissymmetry brings an additional degree of freedom for the synthesis of a new generation of materials with spatially separated chemical properties. We explore this aspect by extending to spherical surfaces the application field of lithographic techniques that was up to now essentially limited to planar and cylindrical substrates. The method proposed uses a strongly focused laser beam to generate dissymmetric coatings on microparticles by micro-photochemical deposition in a reactive solution. This is experimentally illustrated by considering the photochemical reduction of chromate ions induced by a continuous Ar + laser wave to "nucleate" and grow a dissymmetry on the surface of silica beads dispersed in a chromate solution. When properly rescaled, the coating growth laws measured at different laser excitations are reduced to a single master behavior that implies a simple strategy to control and predict the desired dissymmetry from its dynamics. The versatility of the technique is then demonstrated by scanning the beam (i) to tailor microscale patterning on one hemisphere and (ii) to assemble beads into ordered structures. Owing to its flexibility, the method can easily be extended to the coating of different types of particles and various photochemical reactions.

We present the experimental demonstration of a subaperture compression scheme achieved in the PETAL (PETawatt Aquitaine Laser) facility. We evidence that by dividing the beam into small subapertures fitting the available grating size, the sub-beam can be individually compressed below 1 ps, synchronized below 50 fs and then coherently added thanks to a segmented mirror.