Abstract
The performance of fiber mode-locked lasers is limited due to the high nonlinearity induced by the spatial confinement of the single-mode fiber core. To massively increase the pulse energy of the femtosecond pulses, amplification is obtained outside the oscillator. Recently, spatiotemporal mode-locking has been proposed as a new path to fiber lasers. However, the beam quality was either highly multimode and/or with low pulse energy. Here we present an approach to reach high energy per pulse directly in the mode-locked multimode fiber oscillator with a near single-mode output beam. Our approach relies on spatial self-beam cleaning via the nonlinear Kerr effect and we demonstrate a multimode fiber oscillator with M2<1.13 beam profile, up to 24 nJ energy and sub-100 fs compressed duration. The reported approach is further power scalable with larger core sized fibers and could benefit applications that require high power ultrashort lasers with commercially available optical fibers.
Highlights
Fiber laser dynamics have been studied extensively in the past decades to generate femtosecond pulses with high energies and peak powers.[1]
Spatiotemporal mode-locking has been demonstrated in commercially available multimode fiber (MMF) cavities with graded-index multimode fibers (GRIN MMFs) by harnessing their low modal dispersion and inherent periodic self-focusing to produce a coherent superposition of transverse and longitudinal modes in an all-normal dispersion regime.[9,10,11]
For the spatiotemporally mode-locked beam profile, the changes in the output beam quality are challenging to differentiate from the near-field beam profiles, but M2 measurements provide more significant information
Summary
Fiber laser dynamics have been studied extensively in the past decades to generate femtosecond pulses with high energies and peak powers.[1]. By tuning complex cavity dynamics in single-mode fiber cavities, self-organization of longitudinal cavity modes with various temporal profiles and central wavelengths has been realized, such as soliton,[2] similariton,[3,4] and dissipative soliton.[5,6] Due to the high spatial confinement in the small single-mode fiber core, nonlinear effects appear at moderate peak power in solid cores, and the accumulation of excessive nonlinear phase leads to pulse breakup, which limits the achievable pulse energies. The reported multimode fiber laser generates sub-100 fs pulses with high pulse energy (>20 nJ) and good beam quality if the M2 value is
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