An output dielectric mirror is deposited on the central part (~15 μm diameter) at the end face of a 1-km graded-index fiber and tested as output mirror of multimode Raman laser with highly-multimode (M2~34) 940-nm LD pumping. In the cavity with highly-reflective input FBG, Raman lasing of Stokes wave at 976 nm starts at the threshold pump power of ~80 W. The output beam quality factor measured near the threshold (~1W at 976 nm) M2~2 confirms mode selective properties of such output mirror. The power scaling capabilities at increased pump power together with a more detailed characterization of the output beam (spatial profile, spectrum and its stability) are performed and the obtained characteristics are compared with those for output coupling based on Fresnel reflection from the mirror-free fiber end face.
We present the results of direct laser-induced periodic surface structuring of semiconductors thin films (a-Si, a-Ge) deposited on glass substrate at different ambient environments (air, vacuum, nitrogen) resulting in regular gratings with the period of 600 nm to 900 nm at the laser wavelength of 1026 nm oriented either along (a-Si) or transverse (a-Ge) to the linear laser polarization direction. The processing speed has a different effect on morphology of obtained structures: on a-Si film, an increase of scanning speed leads to the reorientation of gratings and reduction of their period, while on a-Ge, the uniformity degradation and increase of the period are observed. Changing the ambient atmosphere from air to nitrogen and vacuum, when writing structures on a-Ge, helps to minimize the uniformity degradation and obtain highly regular nanogratings.
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