388 research outputs found
On type I cascaded quadratic soliton compression in lithium niobate: Compressing femtosecond pulses from high-power fiber lasers
The output pulses of a commercial high-power femtosecond fiber laser or
amplifier are typically around 300-500 fs with a wavelength around 1030 nm and
10s of J pulse energy. Here we present a numerical study of cascaded
quadratic soliton compression of such pulses in LiNbO using a type I phase
matching configuration. We find that because of competing cubic material
nonlinearities compression can only occur in the nonstationary regime, where
group-velocity mismatch induced Raman-like nonlocal effects prevent compression
to below 100 fs. However, the strong group velocity dispersion implies that the
pulses can achieve moderate compression to sub-130 fs duration in available
crystal lengths. Most of the pulse energy is conserved because the compression
is moderate. The effects of diffraction and spatial walk-off is addressed, and
in particular the latter could become an issue when compressing in such long
crystals (around 10 cm long). We finally show that the second harmonic contains
a short pulse locked to the pump and a long multi-ps red-shifted detrimental
component. The latter is caused by the nonlocal effects in the nonstationary
regime, but because it is strongly red-shifted to a position that can be
predicted, we show that it can be removed using a bandpass filter, leaving a
sub-100 fs visible component at nm with excellent pulse quality.Comment: 14 pages, 10 figures, 1 table, submitted to PR
Multimode Nonlinear Dynamics in Anomalous Dispersion Spatiotemporal Mode-locked Lasers
Spatiotemporal mode-locking in a laser with anomalous dispersion is
investigated. Mode-locked states with varying modal content can be observed,
but we find it difficult to observe highly multimode states. We describe the
properties of these mode-locked states and compare them to the results of
numerical simulations. Prospects for the generation of highly-multimode states
and lasers based on multimode soliton formation are discussed
Spatiotemporal mode-locking in multimode fiber lasers
A laser is based on the electromagnetic modes of its resonator, which
provides the feedback required for oscillation. Enormous progress has been made
in controlling the interactions of longitudinal modes in lasers with a single
transverse mode. For example, the field of ultrafast science has been built on
lasers that lock many longitudinal modes together to form ultrashort light
pulses. However, coherent superposition of many longitudinal and transverse
modes in a laser has received little attention. The multitude of disparate
frequency spacings, strong dispersions, and complex nonlinear interactions
among modes greatly favor decoherence over the emergence of order. Here we
report the locking of multiple transverse and longitudinal modes in fiber
lasers to generate ultrafast spatiotemporal pulses. We construct multimode
fiber cavities using graded-index multimode fiber (GRIN MMF). This causes
spatial and longitudinal mode dispersions to be comparable. These dispersions
are counteracted by strong intracavity spatial and spectral filtering. Under
these conditions, we achieve spatiotemporal, or multimode (MM), mode-locking. A
variety of other multimode nonlinear dynamical processes can also be observed.
Multimode fiber lasers thus open new directions in studies of three-dimensional
nonlinear wave propagation. Lasers that generate controllable spatiotemporal
fields, with orders-of-magnitude increases in peak power over existing designs,
should be possible. These should increase laser utility in many established
applications and facilitate new ones
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