High fidelity femtosecond pulses from an ultrafast fiber laser system via adaptive amplitude and phase pre-shaping

Abstract

Abstract:We report the generation of a 12.6W average power, 50MHz repetition rate pulse train, compressible to high fidelity 170fs pulses, from an ultrafast ytterbium-doped fiber laser system via adaptive amplitude and phase pre-shaping. IntroductionYtterbium-doped fibre laser systems, coupled with the chirped-pulse amplification (CPA) technique, have allowed the realization of compact ultrafast laser systems producing high average power at various repetition rates [1]. Power scaling in fibre CPA systems is non-trivial, because a number of factors can degrade the pulse fidelity at the output, such as uncompensated material dispersion, nonlinearity, and a non-uniform spectral gain profile with finite width. Due to the optical confinement and long interaction length of the fiber geometry, nonlinear effects, most notably self-phase modulation (SPM), are a critical consideration in constructing fiber CPA laser systems. However, conventional approaches in mitigating SPM have limitations; temporal stretching is physically limited by the finite size of the grating compressor, while the scaling of large-mode-area (LMA) fibers will eventually undermine the advantages of fiber geometry. Hence, novel approaches in mitigating SPM are necessary for further power scaling in fiber CPA laser systems while maintaining pulse fidelity.Adaptive pulse shaping allows for the generation of high-fidelity pulses by controlling the spectral phase profile [2]. However, due to damage limitations, pulse shaping often needs to be implemented prior to high power amplification in CPA systems [3]. In fiber CPA systems, amplitude-only shaping has recently been demonstrated to control the nonlinear-phase modulation induced by SPM at low energy [4], but it cannot compensate for higherorder spectral phase due to the material dispersion. Our group recently demonstrated a phase-only shaping to produce high-quality pulses in a high-energy fiber laser system [5].In this paper, we report our latest experimental result in generating high-fidelity femtosecond pulses in a fiber CPA system by adaptive amplitude and phase pre-shaping [6]. A pulse shaper based on a dual-layer liquid crystal spatial light modulator (LC-SLM) was implemented in the fiber CPA system for amplitude and phase shaping prior to amplification. The LC-SLM was controlled using a differential evolution (DE) algorithm, to maximize a two-photon absorption (TPA) detector signal produced by the compressed fiber CPA output pulses. We show that our approach compensates for both accumulated phase from higher-order material dispersion and nonlinear phase modulation. A train of pulses with an average power of 12.6 W at a 50 MHz repetition rate was produced from the fiber CPA system, compressible to high fidelity pulses with a full-width at half-maximum (FWHM) duration of 170 fs.

Simulations and experiments showing the origin of multiwavelength mode locking in femtosecond, Yb-fiber lasers

“…The pulse from port 1 has a FWHM duration of 70 fs (1.54 times transform limited, which is typical for this NPE rejected port of this type of fiber laser). Some residual third order dispersion remains, so the duration may be reduced further using an SLMbased pulse shaper [24,25]. The PICASO calculations for port 2 show a primary pulse compressed to 47 fs.…”

Adaptive Nonlinear Phase Compensation in a Femtosecond Hybrid Laser with Varying Pulse Repetition Rate

“…There have been many methods already demonstrated that allow for tunable compensation of the nonlinear phase such as the use of different pulse-shaping techniques in a feedback loop with a pulse characterization technique at the laser output [24][25][26][27][28][29]. It was recently shown that a tunable chirped fiber Bragg grating (TCFBG) can efficiently compensate nonlinear phase up to 4π [12].…”

A Programmable Mode-Locked Fiber Laser Using Phase-Only Pulse Shaping and the Genetic Algorithm

“…In [5], a programmable, mode-locked fiber laser was demonstrated through introducing a digital micromirror device (DMD)-based arbitrary spectrum amplitude shaper inside the cavity of the laser. Furthermore, the generation of high-fidelity femtosecond pulses has been experimentally demonstrated with a frequency domain pulse shaper [6]. Recently, a mode-locked fiber laser with an e-controlled cavity operating in the ultra wide range was demonstrated [7].…”