Synthetic radiation diagnostics as a pathway for studying plasma dynamics from advanced accelerators to astrophysical observations

In this thesis, two novel diagnostic techniques for the identi1cation of plasma dynamics and thequanti cation of essential parameters of the dynamics by means of electromagnetic plasmaradiation are presented. Based on particle-in-cell simulations, both the radiation signatures of micrometer-sized laser plasma accelerators and light-year-sized plasma jets are simulated with the same highly parallel radiation simulation framework, in-situ to the plasma simulation. The basics and limits of classical radiation calculation, as well as the theoretical and technical foundation of modern plasma simulation using the particle-in-cell method, are brie2y introduced. The combination of previously independent methods in an in-situ analysis code as well as its validation and extension with newly developed algorithms for the simultaneous quantitative prediction of both coherent and incoherent radiation and the prevention of numerical artifacts is outlined in the initial chapters. For laser wake1eld acceleration, a hitherto unknown off-axis beam signature is observed,which can be used to identify the so-called blowout regime during laser defocusing. Since signi cant radiation is emitted only after the minimum spot size is reached, this signature is ideally suited to determine the laser focus position itself in the plasma to below 100 _m and thus to quantify the in2uence of relativistic self-focusing. A simple semi-analytical scattering model was developed to explain the blowout radiation signature. The spectral signature predicted by the model is veri1ed using both a large-scale explorative simulation and a simulation parameter study, based on an experiment conducted at the HZDR. Identi1ed by the simulations, a temporal asymmetry in the scattered laser light, which cannot be described by state of the art quasi-static models of the blowout regime, makes it possible to determine the focus position precisely by using this radiation signature

Reduced volume and reflection for bright optical tweezers with radial Laguerre–Gauss beams

Spatially structured light has opened a wide range of opportunities for enhanced imaging as well as optical manipulation and particle confinement. Here, we show that phase-coherent illumination with superpositions of radial Laguerre–Gauss (LG) beams provides improved localization for bright optical tweezer traps, with narrowed radial and axial intensity distributions. Further, the Gouy phase shifts for sums of tightly focused radial LG fields can be exploited for phase-contrast strategies at the wavelength scale. One example developed here is the suppression of interference fringes from reflection near nanodielectric surfaces, with the promise of improved cold-atom delivery and manipulation

Topics in Three-Dimensional Imaging, Source Localization and Super-resolution

The realization that twisted light beams with helical phasefronts could carry orbital angular momentum (OAM) that is in excess of the photon\u27s spin angular momentum (SAM) has spawned various important applications. One example is the design of novel imaging systems that achieve three-dimensional (3D) imaging in a single snapshot via the rotation of point spread function (PSF). Based on a scalar-field analysis, a particular simple version of rotating PSF imagery, which was proposed by my advisor Dr. Prasad, furnishes a practical approach to perform 3D source localization using a spiral phase mask that generates a combination of Bessel vortex beams. For a special annular design of the mask, with the spiral-phase winding number in successive annuli changing by a fixed quantum number, this Bessel-beam combination can yield a shape and size invariant PSF that rotates as a function of the axial position of the source, and possesses a superior depth of field (DOF) when compared to other rotating PSFs. In the first part of this dissertation, we present a vector-field analysis of an improved rotating PSF design that encodes both the 3D location and polarization state of a monochromatic point dipole emitter for high numerical aperture (NA) microscopy, in which non-paraxial propagation of the imaging beam and the associated vector character of light fields are properly accounted for. By examining the angle of rotation and the spatial form of the PSF, one can simultaneously localize point sources and determine the polarization state of light emitted by them over a 3D field in a single snapshot. We also propose a more advanced approach for doing joint polarimetry and 3D localization using a SAM-OAM conversion device without the need for high NA is also proposed. A recent paradigm-shifting research proposal has focused on employing the toolbox of quantum parameter estimation for the problem of super-resolution of two incoherent point sources. Surprisingly, the quantum Fisher information (QFI) and associated quantum Cram\\u27er-Rao bound (QCRB) for estimating the one-dimensional transverse separation of the source pair are both finite constants that are achievable with purely classical measurements that utilize coherent projections of the optical wavefront. A second important contribution of this dissertation is the generalization of the previous quantum limited transverse super-resolution work to full 3D imaging with more general PSF. Under the assumption of known centroid, we first derive the general expression of $3\times 3$ QFI matrix with respect to (w.r.t.) the 3D pair separation vector, in terms of the correlation of the wavefront phase gradients in the imaging aperture. For a clear circular aperture, the QFI matrix turns out to be a separation-independent diagonal matrix. Coherent-projection bases that can attain the corresponding QCRB in special cases and small separation limits are also proposed with confirmation by numerical simulations. We next extend our 3D analysis to treat the more general 6-parameter problem of jointly estimating the 3D pair-centroid location and pair-separation vectors. We also present the results of computer simulation of an experimental protocol based on the use of Zernike-mode projections to attain these quantum estimation-limited bounds of performance

Measuring the Orbital Angular Momentum of Light for Astronomy

While the story of optical orbital angular momentum (OAM) dates back to the development of Maxwell's equations, the study of photon OAM by the physics community begins in earnest in the 1990s, led in part by a paper by Allen et al. describing the independent control of spin and orbital angular momentum in paraxial modes of light. The recognition of the orbital angular momentum of light in astronomy is a much more recent affair. This thesis explores the role of the OAM of light in astronomy and attempts to make the case for the measurement of photon OAM as a new tool in astronomy. Two contributions are made in order to prepare the groundwork for future endeavours: a laboratory assessment of the effectiveness of adaptive optics (AO) systems on atmospheric turbulence when measuring optical OAM, and an initial field test of an instrument measuring the optical OAM spectrum of the sun. Regarding the first study, the author finds that realistic atmospheric turbulence (1'' seeing) severely corrupts any incoming OAM signal at visible wavelengths, in spite of AO correction (<10% power recovered), however results suggest adequate correction at IR wavelengths. In the second study, an instrument to measure the OAM spectrum of a source is constructed and employed to measure the OAM spectrum of local regions of the sun. It represents the first measurement of its kind, distinguishing sunspots by analyzing their OAM spectrum and in addition, demonstrates the improvement of OAM measurements by implementing a lucky imaging routine. Finally, this thesis highlights a new avenue for further study into the measurement of OAM for observational astronomy. A new type of OAM measurement is proposed, capable of measuring rotations in the plane orthogonal to the line of sight. This measurement takes advantage of the rotational Doppler shift, an analogue of the translational Doppler shift, and an OAM interferometer designed to measure the associated phase shift is outlined. A future instrument is also proposed by combining the OAM interferometer with a high resolution spectrograph. This would allow for measurements of both the rotational and translational Doppler shifts, providing information about the three dimensional motion of an object

Vectorial light-matter interaction -- exploring spatially structured complex light fields

Research on spatially-structured light has seen an explosion in activity over the past decades, powered by technological advances for generating such light, and driven by questions of fundamental science as well as engineering applications. In this review we highlight work on the interaction of vector light fields with atoms, and matter in general. This vibrant research area explores the full potential of light, with clear benefits for classical as well as quantum applications

Engineering photonic entanglement and its practical applications

The quantum description of light offers a unique set of optical effects that has led to promising applications beyond those described by classical physics. Although well-defined quantum states of light do not persist in typical classical environments, phenomena such as entanglement often enhance optical approaches to communication, measurement, and sensing. With the emergence of new tasks in classical and quantum optical technology, new tools are required that must be specifically engineered including the generation of quantum states. This thesis is concerned with three principle tasks in engineering and implementing entangled photonic states. First, the use of frequency anti-correlated and polarization entangled two-photon states generated during spontaneous parametric down conversion (SPDC) to precisely evaluate optical delays with quantum interferometry is demonstrated in a realistic commercially available optical telecommunication device. Second, the study of correlated orbital angular momentum (OAM) states for efficient object identification is presented. Finally, experimental efforts towards the development of sources for entangled weak coherent states are discussed. The generation of broadband entangled states leading to well-defined second order interference patterns is a necessary step for the application of low coherence quantum interferometry as a metrological device. The flexibility of non-uniformly chirped periodically poled nonlinear crystals offers a rich set of tools for precise state engineering. The experimental evaluation of a broadband source of polarization entanglement is presented. In addition, design considerations for applications that require optimized quantum interference features are discussed along with a numerical investigation of the limits of quantum interferometry with even order dispersion cancellation. We present an experimental demonstration of correlated OAM sensing exploiting the two-dimensional and correlated nature of states produced during SPDC projected onto the OAM basis. Efficient object recognition through the identification of azimuthal symmetries of arbitrary objects is achieved by observing the full two-photon joint OAM spectrum and focusing on non-conserved OAM components not found in the natural OAM spectrum of SPDC. Finally, quantum key distribution (QKD) is currently the most successful quantum optical application; however, a limiting trade off between the achievable rates and distances confines the approach to niche applications. The generation of entangled coherent states has been proposed to transition QKD into a new regime that would set aside single photons and two-photon entangled states for higher intensity coherent pulses. The key technical limitation that has prohibited the demonstration of such states is a reliable source of single-photon cross phase modulation. The plausibility and experimental efforts towards creating such an environment in a solid state device is presented