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

Controlled Excitation of Supermodes in a Multicore Fiber with a 5 × 5 Square Array of Strongly Coupled Cores

Coherent propagation of supermodes in a multicore fiber is promising for power scaling of fiber laser systems, eliminating the need for the active feedback system to maintain the phases between the channels. We studied the propagation of broadband pulsed radiation at a central wavelength of 1030 nm in a multicore fiber with coupled cores arranged in a square array. We designed and fabricated a silica multicore fiber with a 5 × 5 array of cores. For controllable excitation of a desired supermode, we developed a beam-forming system based on a spatial light modulator. We experimentally measured intensity and phase distributions of the supermodes, in particular, the in-phase and out-of-phase supermodes, which matched well the numerically calculated profiles. We obtained selective excitation and coherent propagation of broadband radiation with the content of the out-of-phase supermode of up to 90% maintained without active feedback. Using three-dimensional numerical modeling with allowance for a refractive index profile similar to those of the developed fiber, we demonstrated stable propagation of the out-of-phase supermode and collapse of the in-phase supermode at a high signal power.

Dual-band Tm3+-doped tellurite fiber amplifier and laser at 1.9 μm and 2.3 μm

Ultrabroadband amplification and two-color CW lasing simultaneously near 1.9 μm and 2.3 μm in a Tm³⁺-doped tellurite fiber were demonstrated experimentally, for the first time to the best of our knowledge. A low-loss Tm³⁺-doped core fiber from TeO₂–ZnO–La₂O₃–Na₂O glasses stable against crystallization was produced by a special technique, providing a low concentration of hydroxyl groups. Supercontinuum from a highly GeO₂ doped silica fiber pumped by an Er fiber laser system was used as a seed for an amplifier. A maximum gain of 30 dB and 7 dB was measured at 1.9 μm and 2.3 μm, respectively. We report detailed experimental and theoretical studies, which are in a very good agreement, of laser amplification and generation in the manufactured fiber with carefully measured and calculated parameters. A quantitatively verified numerical model was used to predict power scalability at 2.3 μm in schemes with optimized parameters at increased pump power. The presented results show that a high-quality tellurite fiber is a promising candidate for developing lasers in the 2.3 μm atmospheric window which are particularly relevant for applications in gas sensing, eye-safe laser radars, breath analysis, remote sensing and stand-off trace gas detection.

Computationally efficient method for Fourier transform of highly chirped pulses for laser and parametric amplifier modeling

We developed an improved approach to calculate the Fourier transform of signals with arbitrary large quadratic phase which can be efficiently implemented in numerical simulations utilizing Fast Fourier transform. The proposed algorithm significantly reduces the computational cost of Fourier transform of a highly chirped and stretched pulse by splitting it into two separate transforms of almost transform limited pulses, thereby reducing the required grid size roughly by a factor of the pulse stretching. The application of our improved Fourier transform algorithm in the split-step method for numerical modeling of CPA and OPCPA shows excellent agreement with standard algorithms.