title: Chair-like pulses in an all-normal dispersion Ytterbium-doped mode-locked fiber laser.
abstract: We report, for what we believe is the first time, generation of stable chair-like pulses (a pulse shape with an initial long flat portion followed by a short high peak power portion resembling the shape of a chair) by mode locking of a Ytterbium (Yb)-doped fiber laser. Chair-like pulse shapes are achieved by implementing dual saturable absorbers, one based on a nonlinear optical loop mirror (NOLM) and the other based on nonlinear polarization rotation (NPR) inside the cavity. The transmission characteristics of the NOLM-NPR pair leading to the formation of chair-like pulses are numerically investigated. We also report the amplification characteristics of chair-like pulses in an external multistage Yb-doped fiber amplifier setup at different repetition rates of the pulse train. It was found that the chair-like pulses are suitable for amplification, and more than 10 W of average power at 460 kHz repetition rate have been obtained at total pump power of ∼20  W coupled to the power amplifier. At a lower repetition rate (115 kHz), ∼8  W of average power were obtained corresponding to ∼70  μJ of pulse energy with negligible contribution from amplified spontaneous emission or stimulated Raman scattering. We believe that such an oscillator-amplifier system could serve as an attractive tool for micromachining applications.
authors.forename: Pradeep K
authors.initials: PK
authors.lastname: Gupta
authors.forename: Chandra P
authors.initials: CP
authors.lastname: Singh
authors.forename: Amarjeet
authors.initials: A
authors.lastname: Singh
authors.forename: Sunil K
authors.initials: SK
authors.lastname: Sharma
authors.forename: Pranab K
authors.initials: PK
authors.lastname: Mukhopadhyay
authors.forename: Kushvinder S
authors.initials: KS
authors.lastname: Bindra