568 research outputs found

    Controlling nonlinear optics with dispersion in photonic crystal fibres

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    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

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    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 μ\muJ and efficiency up to 12 %, and experimentally characterize the generation dynamics in the time-frequency domain. A compact second stage generates multi-μ\muJ pulses from 210 nm to 700 nm using less than 200 μ\muJ 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

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    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 μ\mum) and pumping with 6.3 fs pulses at 800 nm. We generate pulses with energies of 4 to 6 μ\muJ across the deep ultraviolet in a 100 μ\mum capillary and up to 11 μ\muJ in a 150 μ\mum 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

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    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

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    Abstract not supplied. Keywords taken from contents page

    Computer teaching-aids for an undergraduate course in distillation

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    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

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    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