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Abstract: The focal switch of Hermite–Gaussian beams diffracted at an aperture and subsequently focused by a spherically aberrated lens is studied. Our main attention is focused on the effect of quartic-phase aberrations on the behavior of the focal switch. It is shown that quartic-phase aberrations affect the relative focal shift , turning position , and relative transition height . Apart from a critical maximum truncation parameter , there is a critical minimum truncation parameter . Within the region the focal switch can take place, but quartic-phase aberrations give rise to a decrease of in comparison with the aberration-free case. [Copyright &y& Elsevier]

Abstract: We demonstrate a multiwavelength fiber laser with ultradense wavelength spacing and ultrabroad bandwidth based on inhomogeneous loss mechanism with assistance of nonlinear polarization rotation. The inhomogeneous loss, implemented by incorporating a section of highly nonlinear fiber (HNLF) and a Sagnac filter in the laser cavity, can balance mode competition in erbium-doped fiber and result in ultradense multiwavelength generation. The bandwidth of the multiwavelength spectrum is greatly broadened owing to the intensity-dependent loss induced by nonlinear polarization rotation. Stable multiwavelength lasing with wavelength spacing of 0.08nm and wavelength number up to 254 is achieved at room temperature. Moreover, multiwavelength tuning is realized through modifying polarization-dependent cavity loss. [Copyright &y& Elsevier]

The crystal structure of Fe6Ge6Ho has been determined from single-crystal X-ray data. It crystallizes in the hexagonal, space group P6/mmm (no.191) with the Cu7Tb structure type and a=5.102(2) A˚, c=4.050(2) A˚, z=0.5, v=91.29(3) A˚3. [Copyright &y& Elsevier]