Laser-microwave synchronisation for ultrafast electron diffraction

Ultrafast electron diffraction is a pump--probe technique that allows the visualisation of molecular dynamics with atomic scale resolution. However, the fastest electronic and atomic dynamics in light-driven matter transformations are, as yet, unmeasureable with this technique. This is because the temporal resolution in ultrafast electron diffraction is limited by difficulties in producing the shortest electron pulses, caused by the electron charge, via Coulomb repulsion (space charge), and rest mass, via vacuum dispersion of the electron wavefunction. Space charge effects and a finite energy bandwidth both lead to temporal broadening of electron pulses. Methods to compress such pulses in microwave fields have been developed, but these are fundamentally limited by the achievable temporal synchronisation of the employed microwave with the excitation laser pulses. This work is aimed at breaking this limitation and thereby advancing ultrafast electron diffraction towards the ultimate temporal resolution of any realistic light--matter interaction. Firstly, a high-resolution optical-microwave phase detector based on optical interferometry is designed for operation around the 800-nm wavelength of Ti:sapphire lasers best suited for sample excitation. The phase detector provides a resolution of 3 fs and the capability of functioning as an integral component in a phase-locked loop for synchronising a low-noise dielectric resonator oscillator with the Ti:sapphire laser. Furthermore, we demonstrate a separate, novel, passive synchronisation technique through direct microwave extraction of a harmonic of the laser repetition rate by photodetection. A record-low residual phase noise over nine frequency decades (mHz--MHz) is achieved through implementation of an optical-mode filter which circumvents thermal noise problems at low pulses energies to simultaneously reduce detrimental amplitude-to-phase noise conversion in the photodetection process. An amplification chain is designed to achieve a microwave power suitable for electron compression while preserving this excellent phase noise. Rigorous out-of-loop characterisation of the synchronisation with the optical-microwave phase detector shows a root-mean-square (rms) timing stability of 4.8 fs. This superior synchronisation has allowed the generation of 12 fs (rms) electron pulses, the shortest to our knowledge. Lastly, stability of the laser--electron synchronisation over many hours is also demonstrated on a sub-five-femtosecond scale through in-situ measurement and subsequent compensation for the entire range of possible long-term drifts. This shows that incorporating these techniques can allow ultrafast electron diffraction experiments to observe the fastest reversible atomic-scale light--matter interaction dynamics

Mach\u27s Principle: Why Are Some Reference Frames Inertial, And Others Not?

Mach\u27s principle is a conjecture that was popular among physicists in the early 1900s, and which still sees occasional interest today. The principle states that large accelerating masses induce a local inertial reference frame around them. This paper introduces the principle and its history, and discusses its influence on later theories, like Maxwellian theories of gravity and general relativity

First Woman Law Graduate at Notre Dame [Graciela Olivarez]

In the spring of 1970 the Notre Dame Law School will break with a century old tradition and confer the Juris Doctor degree on its first woman law student, Mrs. Grace Olivarez. In a three-part story, the Observer interviews Mrs. Olivarez about her life and work. In 1996, the Notre Dame Law School Hispanic Law Student Association awarded the first Graciela Olivarez Award to Judge Ricardo M. Urbina. Annually the association recognizes the outstanding Hispanic lawyer or judge that best exemplifies the principles and ideals of the pioneer for whom this award is named, including commitment to community service, demonstration of the highest ethical and moral standards, and dedication to justice

The status of the crown-of-thorns starfish (Acanthaster planci) in the Great Barrier Reef, Australia, assessed from the sediment record of John Brewer, Green Island and Heron Island reefs

[Extract from 1988 report] Over the last 30 years the crown-of-thorns starfish (Acanthaster planci) has caused extensive damage to many reefs in the Great Barrier Reef Province. John Brewer Reef and Green Island Reef are among those worst affected by A. planci predation during this period. Surface sediment from these two reefs was exhaustively picked for A. planci skeletal elements and found to be greatly enhanced in element abundance when compared to that of Heron Island Reef which has historically maintained very low-density starfish populations. Carbon-14 accelerator mass spectrometry (AMS) dating indicates that skeletal elements from the surface sediment of John Brewer and Green Island Reefs are of contemporary age. Core sampling shows that subsurface sediment at John Brewer and Green Island Reefs contains A. planci element densities comparable to those found in the surface sediment at these localities. Physical and biological reworking of elements within the sediment precludes the recognition of individual outbreaks in core stratigraphy. AMS element dates and bulk sediment dates, obtained by conventional Carbon-14 radiometry, show that subsurface elements are generally prehistoric and conform to an age structure preserved in the sediment pile. Assessed on a time-averaged basis, the density and distribution of subsurface elements suggest that A. planci outbreaks are not a recent phenomenon, but have been an integral part of the ecosystem for at least 7,000 years on John Brewer Reef and 3,000 years on Green Island Reef

Laser-microwave synchronisation for ultrafast electron diffraction

Ultrafast electron diffraction is a pump--probe technique that allows the visualisation of molecular dynamics with atomic scale resolution. However, the fastest electronic and atomic dynamics in light-driven matter transformations are, as yet, unmeasureable with this technique. This is because the temporal resolution in ultrafast electron diffraction is limited by difficulties in producing the shortest electron pulses, caused by the electron charge, via Coulomb repulsion (space charge), and rest mass, via vacuum dispersion of the electron wavefunction. Space charge effects and a finite energy bandwidth both lead to temporal broadening of electron pulses. Methods to compress such pulses in microwave fields have been developed, but these are fundamentally limited by the achievable temporal synchronisation of the employed microwave with the excitation laser pulses. This work is aimed at breaking this limitation and thereby advancing ultrafast electron diffraction towards the ultimate temporal resolution of any realistic light--matter interaction. Firstly, a high-resolution optical-microwave phase detector based on optical interferometry is designed for operation around the 800-nm wavelength of Ti:sapphire lasers best suited for sample excitation. The phase detector provides a resolution of 3 fs and the capability of functioning as an integral component in a phase-locked loop for synchronising a low-noise dielectric resonator oscillator with the Ti:sapphire laser. Furthermore, we demonstrate a separate, novel, passive synchronisation technique through direct microwave extraction of a harmonic of the laser repetition rate by photodetection. A record-low residual phase noise over nine frequency decades (mHz--MHz) is achieved through implementation of an optical-mode filter which circumvents thermal noise problems at low pulses energies to simultaneously reduce detrimental amplitude-to-phase noise conversion in the photodetection process. An amplification chain is designed to achieve a microwave power suitable for electron compression while preserving this excellent phase noise. Rigorous out-of-loop characterisation of the synchronisation with the optical-microwave phase detector shows a root-mean-square (rms) timing stability of 4.8 fs. This superior synchronisation has allowed the generation of 12 fs (rms) electron pulses, the shortest to our knowledge. Lastly, stability of the laser--electron synchronisation over many hours is also demonstrated on a sub-five-femtosecond scale through in-situ measurement and subsequent compensation for the entire range of possible long-term drifts. This shows that incorporating these techniques can allow ultrafast electron diffraction experiments to observe the fastest reversible atomic-scale light--matter interaction dynamics

The Interiority of Sleep & Power

This thesis explores interior immensity through the framework that targets the human being’s most inner self: the time human beings spend sleeping. The in-between state of sleep is left overlooked in architecture and leaves room for novel exploration. While spending time in a semi-conscious state, we can delve into the realms of the unknown. The primary goal is to challenge the conventional interior space of backpackers in New Zealand by inhabiting the beautiful ugliness of an industrial site. The boundary between the individual and mechanical piece of architecture is explored through a whimsical intimacy. A hydroelectric power station is the chosen apparatus. The power station allows a duality between operation and narration, between thematic qualities and program. The abnormalities hype the super-imagination of the client, somewhat like experiencing a dream state, the most active and often fantastic aspect within the threshold of consciousness.The thesis is grounded in three sections. I firstly explore the pragmatic site anomalies, the thematic qualities and their opportunities. I then move into conceptual exploration of the interior imagination while concluding with a fully functioning yet evocative design of sleep narration. The components of this thesis are largely visual

Structural and dynamical characteristics of mesoscopic H+^+[H2_2O]n_n clusters

Structural and dynamical characteristics pertaining to the solvation of an excess proton in liquid-like nanoclusters of the type [H$_2$O]$_n$ are investigated using Molecular Dynamics experiments. Three different aggregate sizes were analyzed: $n=10,$ 21 and 125. The simulation experiments were performed using a multistate empirical valence bond Hamiltonian model. While in the smallest aggregates the proton occupies a central position, the stable solvation environments for $n=21$ and 125 are located at the cluster boundaries. In all cases, the structure of the closest solvation shell of the excess charge remains practically unchanged and coincides with that observed in bulk water. Compared to results obtained in bulk, the computed rates for proton transfer in clusters are between one and two orders of magnitude slower, and tend to increase for larger cluster sizes.Comment: 16 pages, 6 figures, to be published in Journal of Molecular Liquids, EMLG2006 special issu