Raman Lasing and Transverse Mode Selection in a Multimode Graded-Index Fiber with a Thin-Film Mirror on Its End Face.

Multimode fibers are attractive for high-power lasers if transverse modes are efficiently controlled. Here, a dielectric thin-film mirror (R~20%) is micro-fabricated on the central area of the end face of a 1 km multimode 100/140 µm graded-index fiber and tested as the output mirror of a Raman laser with highly multimode (M~34) 940 nm diode pumping. In the cavity with highly reflective input FBG, Raman lasing of the Stokes wave at 976 nm starts at the threshold pump power of ~80 W.

Spectrum collapse in a 7-core Yb-doped fiber laser with an array of fs-inscribed fiber Bragg gratings.

Femtosecond inscription of fiber Bragg gratings (FBGs) in each core of a cladding-pumped seven-core Yb-doped fiber enables efficient (≈70%) 1064-nm lasing in a robust all-fiber scheme with ≈33 W power, nearly the same for uncoupled and coupled cores. However, the output spectrum is quite different: without coupling, seven individual lines corresponding to the in-core FBG reflection spectra sum up into a broad (0.22 nm) total spectrum, whereas the multiline spectrum collapses into a single narrow line at strong coupling.

Thermochemical Laser-Induced Periodic Surface Structures Formation by Femtosecond Laser on Hf Thin Films in Air and Vacuum.

Thermochemical laser-induced periodic surface structures (TLIPSS) are a relatively new type of periodic structures formed in the focal area of linear polarized laser radiation by the thermally stimulated reaction of oxidation. The high regularity of the structures and the possibility of forming high-ordered structures over a large area open up possibilities for the practical application for changing the optical and physical properties of materials surface. Since the mechanism of formation of these structures is based on a chemical oxidation reaction, an intriguing question involves the influence of air pressure on the quality of structure formation.

Advanced distributed feedback lasers based on composite fiber heavily doped with erbium ions.

Specially designed composite heavily Er-doped fiber in combination with unique point-by-point inscription technology by femtosecond pulses at 1,026 nm enables formation of distributed-feedback (DFB) laser with ultra-short cavity length of 5.3 mm whose parameters are comparable and even better than those for conventional Er-doped fiber DFB lasers having much longer cavity. The composite fiber was fabricated by melting rare-earth doped phosphate glass in silica tube.

Generating high-quality beam in a multimode LD-pumped all-fiber Raman laser.

We report on the first demonstration of an all-fiber CW Raman laser based on a multimode graded-index fiber directly pumped by multimode fiber-coupled laser diodes. A joint action of Raman clean-up effect and mode-selection properties of special fiber Bragg gratings inscribed in the central part of the graded-index fiber core, results in high-efficiency conversion of a multimode (M~26) pump at 915 nm into a high-quality (M~2.6) output beam at 954 nm.