E. A. Anashkina

Widely tunable mid-infrared fiber laser source based on soliton self-frequency shift in microstructured tellurite fiber.

A turnkey fiber laser source generating high-quality pulses with a spectral sech shape and Fourier transform-limited duration of order 100 fs widely tunable in the 1.6-2.65 μm range is presented. It is based on Raman soliton self-frequency shifting in the suspended-core microstructured TeO2-WO3-La2O3 glass fiber pumped by a hybrid Er/Tm fiber system. Detailed experimental and theoretical studies, which are in a very good agreement, of nonlinear pulse dynamics in the tellurite fiber with carefully measured and calculated parameters are reported. A quantitatively verified numerical model is used to show Raman soliton shift in the range well beyond 3 μm for increased pump energy.

All-fiber design of hybrid Er-doped laser/Yb-doped amplifier system for high-power ultrashort pulse generation

We propose a design of an all-fiber laser system that combines the most advanced Er:fiber laser in the telecommunication range and an efficient Yb-doped amplifier for generation of high-power ultrashort pulses. The system is based on nonlinear wavelength conversion of 1.56 μm ultrashort Er:fiber laser pulses to the 1 μm range in a short pigtail of dispersion-shifted silica fiber with subsequent amplification in the Yb-doped fiber amplifier. Pulses with a duration as short as 85 fs and averaged power of 200 mW are demonstrated.

Generating tunable optical pulses over the ultrabroad range of 1.6–2.5 μm in GeO 2 -doped silica fibers with an Er:fiber laser source

We report generation of femtosecond optical pulses tunable in the 1.6-2.5 μm range using GeO2-doped core silica-cladding fibers. Optical solitons with a duration of 80-160 fs have been measured by the FROG technique in the 2-2.3 μm range. To the best of our knowledge, these are the longest wavelength temporally characterized solitons generated in silica-based fibers. We have also demonstrated more than octave-spanning femtosecond supercontinuum generation in the 1.0-2.6 μm range.

Two-color optically synchronized ultrashort pulses from a Tm/Yb-co-doped fiber amplifier.

A method of producing high quality, optically synchronized two-color ultrashort pulses in an active thulium-doped fiber is proposed. We show that sech-shaped femtosecond pulses with essentially different wavelengths can be generated directly from a Tm/Yb-co-doped amplifier: one pulse at about 2 μm and the second pulse with a tunable wavelength up to 2.3 μm, which covers the pump and gain regions of Cr:ZnSe and Cr:ZnS amplifiers. The shortest pulses with durations of 145 fs at 2.25 μm and 125 fs at 2 μm were measured by the FROG (frequency-resolved optical gating) technique.

Towards Mid-Infrared Supercontinuum Generation With Germano-Silicate Fibers

A detailed study of supercontinuum (SC) generation in germano-silicate fibers with a femtosecond silica-based all-fiber laser system is performed. We report on more than octave spanning SC in the range 1-2.6 μm pumped at 1.6 μm as well as SC in the range 1.9-3 μm pumped at 2 μm. It is also shown theoretically that with optimal germano-silicate fiber parameters, SC extending beyond 3 μm can be produced effectively.

Toward a mid-infrared femtosecond laser system with suspended-core tungstate–tellurite glass fibers

A simple design of a fiber laser system for generating high-quality pulses with a duration of order 100 fs with ultrabroad wavelength tunability in the 2-5 μm range is discussed. This design incorporates conventional fs near-IR lasers and specially developed tungstate-tellurite fibers with two zero-dispersion wavelengths (ZDW) and relies on nonlinear wavelength conversion via either soliton self-frequency shift (SSFS) or red-shifted dispersive wave (DW) generation. The fiber parameters needed for such optical conversion have been scanned numerically and showed a possibility of SSFS beyond 4 μm and of DW generation beyond 5 μm. We have also studied and prepared tungstate-tellurite glasses and preforms that are highly stable against crystallization, exhibit extremely low level of hydroxyl groups absorption, and from which the suspended-core two-ZDW fibers can be manufactured.

All-fiber design of erbium-doped laser system for tunable two-cycle pulse generation

We report a simple all-fiber design of an Er-doped laser system that is capable of generating widely tunable two-cycle pulses. In particular, 13-fs pulses at a wavelength of 1.7 μm are produced. The mechanism of pulse shortening is identical to the higher-order soliton compression and is supported by modeling based on the slowly evolving wave approximation, which is well suited for down to single-cycle pulse propagation in nonlinear dispersion-shifted fibers.

Electronic (population) lensing versus thermal lensing in Yb:YAG and Nd:YAG laser rods and disks

A comparative study of electronic lenses (caused by population change of ground and excited states having different polarizabilities) and thermal lenses induced in Yb:YAG and Nd:YAG rods and disks under lasing and nonlasing conditions is carried out. The transient electronic lens can predominate over the thermal one in the pulsed-pump regime, whereas the stationary thermal lens may be predominant at CW broad pumping. The electronic lens effect is stronger in Yb:YAG than in Nd:YAG crystal.

Three-dimensional modeling of CPA to the multimillijoule level in tapered Yb-doped fibers for coherent combining systems

We developed a three-dimensional numerical model of Large-Mode-Area chirped pulse fiber amplifiers which includes nonlinear beam propagation in nonuniform multimode waveguides as well as gain spectrum dynamics in quasi-three-level active ions. We used our model in tapered Yb-doped fiber amplifiers and showed that single-mode propagation is maintained along the taper even in the presence of strong Kerr nonlinearity and saturated gain, allowing extraction of up to 3 mJ of output energy in 1 ns pulse. Energy scaling and its limitation as well as the influence of fiber taper bending and core irregularities on the amplifier performance were studied. We also investigated numerically the capabilities for compression and coherent combining of up to 36 perturbed amplifying channels and showed more than 70% combining efficiency, even with up to 11% of high-order modes in individual channels.

MW peak power diffraction limited monolithic Yb-doped tapered fiber amplifier

Chirped pulse monolithic fiber amplifier based on a newly developed tapered polarization maintaining Yb-doped fiber has been developed and optimized. A novel amplification regime in a relatively long (220 cm) tapered fiber of improved design, which has been theoretically predicted, allowed us to achieve an ultimate high peak power. In this regime, the signal propagates most of the fiber without amplification and growths very rapidly only in the last 80 cm of the tapered fiber, which has a mode field area of approximately 1000 μm2 near the output. We have demonstrated amplification of 20 ps chirped pulses centered at 1056-nm with spectral width of 20 nm to 0.7 MW peak power directly from the tapered fiber amplifier. The pulses had a diffraction limited quality (M2 ~ 1.124) and could be compressed down to 350 fs with 50% efficiency. In addition, amplification of narrow-band 9 ps pulses centered at 1064 nm to a peak power of 1.8 MW directly from the tapered fiber amplifier was demonstrated.