573 research outputs found
Controlling nonlinear optics with dispersion in photonic crystal fibres
Nonlinear optics enables the manipulation of the spectral and temporal features of light.
We used the tailorable guidance properties of photonic crystal fibres to control and
enhance nonlinear processeswith the aim of improving nonlinearity based optical sources.
We utilised modern, high power, Ytterbium fibre lasers to pump either single photonic
crystal fibres or a cascade of fibres with differing properties. Further extension of our
control was realised with specifically tapered photonic crystal fibres which allowed for a
continuous change in the fibre characteristics along their length.
The majority of our work was concerned with supercontinuum generation. For continuous
wave pumping we developed a statistical model of the distribution of soliton
energies arising from modulational instability and used it to understand the optimum
dispersion for efficient continuum expansion. A two-fold increase in spectral width was
demonstrated, along with studies of the noise properties and pump bandwidth dependence
of the continuum. For picosecond pumping we found that the supercontinuum
bandwidth was limited by the four wave mixing phase-matching available in a single
fibre. A technique to overcome this by using a cascade of fibres with different dispersion
profiles was developed. Further improvement was achieved by using novel tapered PCFs
to continuously extend the phase-matching. Analysis of this case showed that a key role
was played by soliton trapping of dispersive waves and that our tapers strongly enhanced
this effect. We demonstrated supercontinua spanning 0.34-2.4 ¹mwith an unprecedented
spectral power; up to 5 mW/nm.
The use of long, dispersion decreasing photonic crystal fibres enabled us to demonstrate
adiabatic soliton compression at 1.06 ¹m. From a survey of fibre structures we found
that working around the second zero dispersion wavelength was optimal as this allows
for decreasing dispersion without decreasing the nonlinearity. We achieved compression
ratios of over 15
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
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
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
Australian perceptions of the Orient 1880-1910
Abstract not supplied. Keywords taken from contents page
Computer teaching-aids for an undergraduate course in distillation
Includes bibliographical references.[Not copying properly] Four computer programs dealing with the following aspects of distillation are developed as an integrated teaching package. (1) Binary batch distillation in tray columns. (2) Binary continuous distillation in tray columns. (3) Binary continuous distillation in packed columns. (4) Multicomponent distillation in tray columns. A plotting program utilizing CALCOMP plotting software and hardware is developed for graphical.representation of the results generated by .the above routines. The following diagrams are included: (1) McCabe-Thiele x,y diagrams for batch and continuous distillation. (2) Ponchon-Savarit diagram for continuous distillation. (3) Temperature, flowrate, and composition profiles for multicomponent distillation
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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