Post-compression of powerful femtosecond pulses after second harmonic generation.

A proof-of-principle experiment of highly efficient (38%) second harmonic generation was implemented at a ∼1T W/c m 2 intensity of a 45 fs pulse in a composite nonlinear sample-a 1 mm KDP crystal glued onto a 1 mm fused silica substrate. The attenuated replica of the second harmonic pulse (455 nm) was compressed down to 28.6 fs by means of dispersive mirrors, with a significant reduction in both the wings and the far temporal contrast. The peak power of the second harmonic was ∼74% of the power of the fundamental harmonic, which ensured a three-fold increase in the focal intensity.

Upgrading the front end of the petawatt-class PEARL laser facility.

A new front-end laser system with optical synchronization of chirped femtosecond and pump pulses for the petawatt laser complex PEtawatt pARametric Laser (PEARL) has been developed. The new front-end system provides a broader femtosecond pulse spectrum, temporal shaping of the pump pulse, and a significant increase in the stability of the parametric amplification stages of the PEARL.

Crystal structure and migration paths of alkaline ions in NaVPO4F.

A sample with a nominal composition 'NaVPO4F' is prepared by mechanochemically assisted solid-state synthesis using quenching. A detailed study of its crystal and local structure is conducted by means of XRD and FTIR and solid-state 31P NMR spectroscopies in comparison with Na3V2(PO4)2F3. It is shown that the as-prepared 'NaVPO4F' has a multiphase composition, including NaVPO4F as the main phase and Na3V2(PO4)2F3 and Na2.57V4P4O17F as the side products. The crystal structure of NaVPO4F is described in the monoclinic C2/c space group. It is characterized by negligible V3+/V4+ oxidation with the corresponding F-/O2- substitution and the presence of structural disordering. Using the Voronoi-Dirichlet partition (VDP) method, the Na+ and Li+ migration pathways in Tavorite-like NaVPO4F and closely related LiVPO4F (with the triclinic structure, P1[combining macron] S.G.) are analyzed. While the Na+ migration is suppressed in both cases, the Na+/Li+ ion exchange in NaVPO4F with the formation of monoclinic LiVPO4F could occur, but is difficult due to the sodium immobility rather than the instability of the lithium derivatives as was concluded from the DFT calculations.

200 TW 45 fs laser based on optical parametric chirped pulse amplification.

200 TW peak power has been achieved experimentally using a Cr:forsterite master oscillator at 1250 nm, a stretcher, three optical parametrical amplifiers based on KD*P (DKDP) crystals providing 14.5 J energy in the chirped pulse at 910 nm central wavelength, and a vacuum compressor. The final parametrical amplifier and the compressor are described in detail. Scaling of such architecture to multipetawatt power is discussed.