Project Tech Top study of lunar, planetary and solar topography Final report

Data acquisition techniques for information on lunar, planetary, and solar topograph

Terahertz Josephson plasma waves in layered superconductors: spectrum, generation, nonlinear, and quantum phenomena

The recent growing interest in terahertz (THz) and sub-THz science and technology is due to its many important applications in physics, astronomy, chemistry, biology, and medicine. We review the problem of linear and non-linear THz and sub-THz Josephson plasma waves in layered superconductors and their excitations produced by moving Josephson vortices. We start by discussing the coupled sine-Gordon equations for the gauge-invariant phase difference of the order parameter in the junctions, taking into account the effect of breaking the charge neutrality, and deriving the spectrum of Josephson plasma waves. We also review surface and waveguide Josephson plasma waves. We review the propagation of weakly nonlinear Josephson plasma waves below the plasma frequency, which is very unusual for plasma-like excitations. In close analogy to nonlinear optics, these waves exhibit numerous remarkable features, including a self-focusing effect, and the pumping of weaker waves by a stronger one. We also present quantum effects in layered superconductors, specifically, the problem of quantum tunnelling of fluxons through stacks of Josephson junctions. We discuss the Cherenkov and transition radiations of the Josephson plasma waves produced by moving Josephson vortices. We also discuss the problem of coherent radiation (superradiance) of the THz waves by exciting uniform Josephson oscillations. The effects reviewed here could be potentially useful for sub-THz and THz emitters, filters, and detectors

Miniature Broadband-NIRS System to Measure CNS Tissue Oxygenation and Metabolism in Preclinical Research

In-vivo measurement of CNS tissue oxygenation and metabolism is critical in health and disease. Broadband-near infrared spectroscopy is a non-invasive optical technique which measures tissue oxygenation, haemodynamics and metabolism through in-vivo quantification of concentration changes of oxy- and deoxy-haemoglobin (Δ[HbO2] and Δ[HHb]) and oxidised cytochrome-c-oxidase (Δ[oxCCO]). Current commercially available NIRS systems only use a few wavelengths to measure concentration change that fails to provide accurate Δ[oxCCO] measurement. Broadband-NIRS instruments however, use more than 100 wavelengths which enables quantification of change in [oxCCO], an important marker of cellular oxidative metabolism. These systems tend to be bulky, requiring extensive calibrations and trained staff to operate them; making them less versatile and difficult to be adapted in the clinical environment. Furthermore, existing broadband-NIRS systems quantify chromophore concentration changes assuming a fixed optical pathlength across all the subjects using a previously measured DPF (differential pathlength factor) with time or frequency domain systems. This thesis describes the development of a portable broadband-NIRS system called mini-CYRIL “CYtochrome Research Instrument and appLication”, based on easily sourced components. A miniature white light source (HL-2000-HP) and miniature spectrometers (QE65pro and Ventana VIS-NIR) by Ocean Optics were customised for measuring CNS tissue oxygenation and metabolism. While having the features of commercially available NIRS systems in terms of portability, ease of use and no need for wavelength calibration, in terms of performance mini-CYRIL is comparable to broadband-NIRS instruments providing reliable Δ[oxCCO] measurements that have been validated and assessed through in-vivo tissue studies in (a) preclinical model of: (i) neonatal hypoxic-ischaemic (HI) encephalopathy, (ii) multiple sclerosis (MS) and (iii) low-light level therapy in the aged retina; (b) infants during brain functional activation. Mini-CYRIL is furthermore novel in offering calculation of absolute change in the concentration of chromophores based on real-time measurement of the optical path of light traversing the tissue. None of the current NIRS systems offer this feature which is crucial in case of changing pathology following an injury

Atom Interferometers

Interference with atomic and molecular matter waves is a rich branch of atomic physics and quantum optics. It started with atom diffraction from crystal surfaces and the separated oscillatory fields technique used in atomic clocks. Atom interferometry is now reaching maturity as a powerful art with many applications in modern science. In this review we first describe the basic tools for coherent atom optics including diffraction by nanostructures and laser light, three-grating interferometers, and double wells on AtomChips. Then we review scientific advances in a broad range of fields that have resulted from the application of atom interferometers. These are grouped in three categories: (1) fundamental quantum science, (2) precision metrology and (3) atomic and molecular physics. Although some experiments with Bose Einstein condensates are included, the focus of the review is on linear matter wave optics, i.e. phenomena where each single atom interferes with itself.Comment: submitted to Reviews of Modern Physic

NIAC Phase II Orbiting Rainbows: Future Space Imaging with Granular Systems

Inspired by the light scattering and focusing properties of distributed optical assemblies in Nature, such as rainbows and aerosols, and by recent laboratory successes in optical trapping and manipulation, we propose a unique combination of space optics and autonomous robotic system technology, to enable a new vision of space system architecture with applications to ultra-lightweight space optics and, ultimately, in-situ space system fabrication. Typically, the cost of an optical system is driven by the size and mass of the primary aperture. The ideal system is a cloud of spatially disordered dust-like objects that can be optically manipulated: it is highly reconfigurable, fault-tolerant, and allows very large aperture sizes at low cost. This new concept is based on recent understandings in the physics of optical manipulation of small particles in the laboratory and the engineering of distributed ensembles of spacecraft swarms to shape an orbiting cloud of micron-sized objects. In the same way that optical tweezers have revolutionized micro- and nano-manipulation of objects, our breakthrough concept will enable new large scale NASA mission applications and develop new technology in the areas of Astrophysical Imaging Systems and Remote Sensing because the cloud can operate as an adaptive optical imaging sensor. While achieving the feasibility of constructing one single aperture out of the cloud is the main topic of this work, it is clear that multiple orbiting aerosol lenses could also combine their power to synthesize a much larger aperture in space to enable challenging goals such as exo-planet detection. Furthermore, this effort could establish feasibility of key issues related to material properties, remote manipulation, and autonomy characteristics of cloud in orbit. There are several types of endeavors (science missions) that could be enabled by this type of approach, i.e. it can enable new astrophysical imaging systems, exo-planet search, large apertures allow for unprecedented high resolution to discern continents and important features of other planets, hyperspectral imaging, adaptive systems, spectroscopy imaging through limb, and stable optical systems from Lagrange-points. Furthermore, future micro-miniaturization might hold promise of a further extension of our dust aperture concept to other more exciting smart dust concepts with other associated capabilities. Our objective in Phase II was to experimentally and numerically investigate how to optically manipulate and maintain the shape of an orbiting cloud of dust-like matter so that it can function as an adaptable ultra-lightweight surface. Our solution is based on the aperture being an engineered granular medium, instead of a conventional monolithic aperture. This allows building of apertures at a reduced cost, enables extremely fault-tolerant apertures that cannot otherwise be made, and directly enables classes of missions for exoplanet detection based on Fourier spectroscopy with tight angular resolution and innovative radar systems for remote sensing. In this task, we have examined the advanced feasibility of a crosscutting concept that contributes new technological approaches for space imaging systems, autonomous systems, and space applications of optical manipulation. The proposed investigation has matured the concept that we started in Phase I to TRL 3, identifying technology gaps and candidate system architectures for the space-borne cloud as an aperture

Tomographic Laser Absorption Imaging of Combustion Gases in the Mid-wave Infrared

This dissertation describes advancements in mid-infrared laser absorption tomography for spatio-temporal measurements of thermochemistry in reacting flows relevant to combustion systems. Tunable laser absorption spectroscopy is combined with tomographic reconstruction techniques to resolve small diameter ( < 1 cm) non-uniform flow fields with steep spatial gradients, leveraging emerging mid-wave infrared photonics. Multiple novel measurement methods, hardware configurations, and image processing techniques were investigated. Initially, a mid-infrared laser absorption tomography sensing method was developed for quantitative measurement of CO and CO2 concentrations and temperature distributions in turbulent premixed jet flames using a translation-stage-mounted optical system. This sensing approach was used to examine effects of varying fuel structure on carbon oxidation over a range of Reynolds number regimes. It was found that spatial and temporal resolution is limited in this method due to the finite laser beam size (~ 1 mm) and the slow mechanical translation of the optical system. To address these limitations, a novel laser absorption imaging (LAI) technique, that expands a single laser beam and replaces the detector with a high-speed infrared camera, was introduced to achieve enhanced spatial and temporal resolution for thermo-chemical imaging. As a demonstration of this new technique, distributions of combustion species were imaged in both axisymmetric and non-axisymmetric flow fields using linear tomography algorithms. For non-axisymetric flows, the limited view tomography problem often results in a blurring effect and artifacts in the reconstructed flow-field. In an effort to address these issues, state-of-the-art deep learning neural networks were developed and applied to solve the limited angle inversion. Initial results suggest that deep neural networks have potential to more accurately predict flame structures with fewer projection angles than linear tomography. This work provides a foundation for a new approach to quantitative time-resolved 3D thermo-chemical imaging in high-temperature reacting flows

Laser Systems for Applications

This book addresses topics related to various laser systems intended for the applications in science and various industries. Some of them are very recent achievements in laser physics (e.g. laser pulse cleaning), while others face their renaissance in industrial applications (e.g. CO2 lasers). This book has been divided into four different sections: (1) Laser and terahertz sources, (2) Laser beam manipulation, (3) Intense pulse propagation phenomena, and (4) Metrology. The book addresses such topics like: Q-switching, mode-locking, various laser systems, terahertz source driven by lasers, micro-lasers, fiber lasers, pulse and beam shaping techniques, pulse contrast metrology, and improvement techniques. This book is a great starting point for newcomers to laser physics

Advanced laser frequency stabilisation systems for mobile strontium optical lattice clocks

Strontium optical lattice clocks have undergone vast developments in the past decade with world leading frequency stability and uncertainty records. Now, a lot of scientists are moving from laboratory based clocks to transportable, and portable clocks for applications including space, fundamental science, finance, and communication. The research team at the University of Birmingham are working towards developing transportable apparatus for studying fundamental physics, global positioning system (GPS), and geodesy applications. This thesis reports on the progress towards two different transportable strontium optical lattice clocks, which we will call ‘miniclock’ and ‘Space Optical lattice Clock 2’ (SOC2). A diode-seeded tapered amplifier based narrow linewidth laser is developed and used to realise second stage cooling of strontium in miniclock apparatus. The laser has achieved a linewidth of 1 kHz after stabilising to a 3 cm long optical reference cavity. A multiple frequency stabilisation unit (FSU) for strontium lattice clocks is established. It is a robust, portable, and compact frequency stabilisation unit with a volume of 593 cm^3. Three different lasers are currently locked simultaneously to the FSU cavity, which could be extended to any number of lasers, enabling to use a single cavity for locking all the lasers required in a strontium lattice clock, except the clock laser. FSU is designed specifically for use in compact clocks. In the SOC2 system, realisation of clock transition and its characterisation are performed. A transition linewidth of 3 Hz is obtained for the SOC2 strontium clock. Further details and results are described in the thesis

Gold-silicide eutectic dynamics of mesotextured materials and their optical properties

Meso scaled pyramidal and inverse pyramidal structures, hereon referred to as Mesopyramids and Inverse Mesopyramids, are observed on Si[100] post annealing of a tri-layer of gold and silicon thin films. The structures are striated with a stochastic distribution of nano scaled plateaus and cavities. The cavities are on the order of tens of nano meters deep with a width up to a single micron. Growth of these pyramids is governed by the behavior of a eutectic under vacuo during annealing. The lattice structure of substrate plays an active role in the orientation of the array of mesopyramids on the silicon wafer. A native oxide promotes a wetting environment and acts as a barrier to diffusion of the eutectic into the silicon reservoir of the wafer. The quenching stage of pyramid fabrication initiates a final phase separation that results in the observed texturing. Dimensions of this texturing create optically active surfaces both in the far and near field. Diffraction patterns were generated with a beam of well collimated P-polarized light illuminating the concavity of the structures and the effect of the pyramid’s rounded edges. Calculating the radius of curvature allows for these structures to be modeled as spherical mirrors and explains the magnification or minimization of the Fraunhofer pattern produced. This square aperture effect also facilitated the creation of a mathematical model which is in good agreement with the physical results. Performing near field analysis allowed for the confirmation both visually and spectrally of the effective coupling of energy from photons to surface plasmon modes. This energy is observed to propagate as surface plasmon polaritons in the cavities of the mesopyramid and down an individual facet for the inverse mesopyramid. The spectral data obtained confirmed the presence of band transitions for gold from d-band to sp-band at 550nm and 650 nm wavelengths of light. Back scattered light from theses surface plasmon polaritons is analyzed as the average of the behavior at the gold-silicide dielectric interface. The opportunity to further develop these surfaces into optoelectronic devices as well as metalens materials provide impetus for this body of research