In this communication, we report for the first time on a homemade 55 µm core VLMA “Yb-free” Er-doped aluminosilicate double-clad fiber manufactured by the REPUSIL powder sintering technology and its implementation within two different laser configurations emitting around 1560 nm, both pumped at 976 nm. First, a free-running free-space CW oscillator delivers up to 40 W of average power with optical-to-optical efficiency of 30 % and near-diffraction-limited beam, despite the large core size. In a second experiment, the fiber is used as the main amplifier of a MOPA system delivering up to 10 nJ pulses at GHz repetition rate.
We report on mid-infrared supercontinuum generation from 4 to 9 µm in orientation-patterned gallium-arsenide waveguides pumped by nanojoule-class ultrafast fiber lasers. The QPM waveguide and the laser source are optimized in tandem to pump the waveguides close to the degeneracy by means of sub-picosecond pulses at 2760 nm. The use of a waveguide geometry drastically reduces the required energy to the nanojoule level, thereby opening supercontinuum generation in GaAs platforms to fiber lasers.
High-harmonics generation (HHG) in solids require high-energy few-cycle laser drivers at near- to mid-infrared wavelengths with excellent beam quality to reach fluences of ~1 TW/cm2. Along this line, soliton sources based on large mode area silica-core singlemode fibers produce ultrashort (70 fs) pulses at remote wavelengths with hundreds of nJ, thus providing a new platform for driving HHG in solids. In this communication, we explore the potential of such soliton-based fiber driver for HHG in thin-films of zinc oxide. The laser delivers 41 nJ 70 fs solitonic pulses at 1764 nm and drives harmonics generation up to H7.
Many applications such as nonlinear microscopy and strong field optoelectonics require high-energy (> 100 nJ) ultrashort (< 100 fs) pulses above 1.55 µm out of a singlemode fiber. Here, we report on high-energy amplification in tapered Er-doped fiber fabricated by the powder technique. The system based on direct amplification is free from stretcher and compressor units. We generate 90 fs MW-class pulses at 1600 nm by amplification and management of nonlinear effects in the tapered fiber. Despite the output 100 µm core diameter, the emitted beam is near-diffraction limited.
All-optical poling was demonstrated for the first time in 1986 in single mode fibers: such nonlinear optical process enabled the introduction of a second-order susceptibility (χ(2)) in a doped silica fiber. By simply using an intense laser source, alloptical poling, later theoretically described by Stolen and coworkers, permitted the generation of a second harmonic (SH) signal in an otherwise centrosymmetric doped material. More recently, similar experiments have been carried out by exploiting complex beam propagation in multimode fibers. In this work we reveal, for the first time to our knowledge, the 3D spatial distribution of a χ(2) nonlinearity written in a graded-index (GRIN) multimode (MM) fiber. In particular, the presence of a doubly-periodic distribution of χ(2) is unveiled by means of multiphoton microscopy. The shortest period (tens of micrometers) is due to the beating between the fundamental and the SH beams, and it is responsible for their quasi-phase matching (QPM). Whereas the longest period (hundreds of micrometers) is associated with the periodic evolution, or self-imaging, of the power density of the MM beam along the GRIN MM fiber. The complex modal beating, leading to spatial self-cleaning of the fundamental beam, is thus printed inside the fiber core, and revealed by our measurements. We considered two fibers of similar composition and opto-geometric parameters, and we compared the evolution of the optical poling process with time. Despite the rather similar fiber characteristics, we observed a striking difference in the poling efficiency between the two fibers. Such observation led us to point out the importance of considering the complete fiber fabrication process (both the preform elaboration and the drawing steps) on the final structure and microstructure of optical fibers.
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