3,140 research outputs found
Infrared attosecond field transients and UV to IR few-femtosecond pulses generated by high-energy soliton self-compression
Infrared femtosecond laser pulses are important tools both in strong-field
physics, driving X-ray high-harmonic generation, and as the basis for widely
tuneable, if inefficient, ultrafast sources in the visible and ultraviolet.
Although anomalous material dispersion simplifies compression to few-cycle
pulses, attosecond pulses in the infrared have remained out of reach. We
demonstrate soliton self-compression of 1800 nm laser pulses in hollow
capillary fibers to sub-cycle envelope duration (2 fs) with 27 GW peak power,
corresponding to attosecond field transients. In the same system, we generate
wavelength-tuneable few-femtosecond pulses from the ultraviolet (300 nm) to the
infrared (740 nm) with energy up to 25 J and efficiency up to 12 %, and
experimentally characterize the generation dynamics in the time-frequency
domain. A compact second stage generates multi-J pulses from 210 nm to 700
nm using less than 200 J of input energy. Our results significantly expand
the toolkit available to ultrafast science.Comment: 8 pages, 5 figure
High-energy ultraviolet dispersive-wave emission in compact hollow capillary systems
We demonstrate high-energy resonant dispersive-wave emission in the deep
ultraviolet (218 to 375 nm) from optical solitons in short (15 to 34cm) hollow
capillary fibres. This down-scaling in length compared to previous results in
capillaries is achieved by using small core diameters (100 and 150 m) and
pumping with 6.3 fs pulses at 800 nm. We generate pulses with energies of 4 to
6 J across the deep ultraviolet in a 100 m capillary and up to 11
J in a 150 m capillary. From comparisons to simulations we estimate
the ultraviolet pulse to be 2 to 2.5 fs in duration. We also numerically study
the influence of pump duration on the bandwidth of the dispersive wave.Comment: 5 pages, 3 figure
Near-ionization-threshold emission in atomic gases driven by intense sub-cycle pulses
We study theoretically the dipole radiation of a hydrogen atom driven by an
intense sub-cycle pulse. The time-dependent Schr\"odinger equation for the
system is solved by ab initio calculation to obtain the dipole response.
Remarkably, a narrowband emission lasting longer than the driving pulse appears
at a frequency just above the ionization threshold. An additional calculation
using the strong field approximation also recovers this emission, which
suggests that it corresponds to the oscillation of nearly-bound electrons that
behave similarly to Rydberg electrons. The predicted phenomenon is unique to
ultrashort driving pulses but not specific to any particular atomic structure.Comment: 8 pages, 2 figure
Optical Solitons in Hollow-Core Fibres
I review the historical observation and subsequent research on optical
soliton dynamics in gas-filled hollow-core optical fibres. I include both
large-core hollow capillary fibres, and hollow-core photonic-crystal or
microstructured fibres with smaller cores, in particular photonic bandgap and
antiresonant guiding fibres. I discuss how the optical guidance properties of
these different fibre structures influence the soliton dynamics that can be
obtained. The dynamics I consider include: soliton propagation at peak power
levels ranging from the megawatt to terawatt level, and pulse energies from
sub-microjoule to millijoule range; pulse self-compression, leading to
sub-cycle and sub-femtosecond pulse duration; soliton self-frequency shifting
due to both the Raman effect, and the influence of photoionisation and plasma
formation; and resonant dispersive wave emission, leading to the generation of
tuneable few-femtosecond pulses across the vacuum and deep ultraviolet,
visible, and near-infrared spectral regions
Nonlinear optics in Xe-filled hollow-core PCF in high pressure and supercritical regimes
Supercritical Xe at 293 K offers a Kerr nonlinearity that can exceed that of
fused silica while being free of Raman scattering. It also has a much higher
optical damage threshold and a transparency window that extends from the UV to
the infrared. We report the observation of nonlinear phenomena, such as
self-phase modulation, in hollow-core photonic crystal fiber filled with
supercritical Xe. In the subcritical regime, intermodal four-wave-mixing
resulted in the generation of UV light in the HE12 mode. The normal dispersion
of the fiber at high pressures means that spectral broadening can clearly
obtained without influence from soliton effects or material damage
Continuously wavelength-tunable high harmonic generation via soliton dynamics
We report generation of high harmonics in a gas-jet pumped by pulses
self-compressed in a He-filled hollow-core photonic crystal fiber through the
soliton effect. The gas-jet is placed directly at the fiber output. As the
energy increases the ionization-induced soliton blue-shift is transferred to
the high harmonics, leading to a emission bands that are continuously tunable
from 17 to 45 eV
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