Photonic Metasurfaces for Spatiotemporal and Ultrafast Light Control

The emergence of photonic metasurfaces - planar arrays of nano-antennas - has enabled a new paradigm of light control through wave-front engineering. Space-gradient metasurfaces induce spatially varying phase and/or polarization to propagating light. As a consequence, photons propagating through space-gradient metasurfaces can be engineered to undergo a change to their momentum, angular momentum and/or spin states

Particle trapping with functionalized hybrid optical fibers

Understanding processes on sub-micron scales that are obscured from the observer’s naked eye represents a long cherished desire of mankind. Unfortunately, single particle studies are time demanding and suffer from Brownian motion, which thus limits their practicability and range of applications. Optical and electrical trapping, however, both awarded with a Nobel prize, represent two sophisticated and widely applied solutions allowing for controlled access to individual particles via almost the entire room angle. Particle trapping via optical fibers in principle provides a flexible and low-cost photonic platform enabling remotely operable applications within difficult to reach environments, including in situ and in vivo scenarios. The microtechnologically functionalized tip of a hybrid optical fiber (HOF), in particular, which in contrast to conventional optical fibers incorporates additional materials, offers a unique platform for implementing electromagnetic, i.e., optical and electrical, fields that are essentially required for the trapping of particles and unavailable by standard fibers alone. Within the scope of this work, three unique implementations of HOF tip-based particle traps, which in detail rely on integrating a liquid channel, a pure silica section and metallic wires for functionalizing the fibers, are demonstrated, discussed, and compared to state-of-the-art concepts. First, the principles of optical phenomena, the motion of microscopic objects and influences of confinements including different particle trapping mechanisms, as well as required methods for analyzing and characterizing fiber-based particle traps are introduced. Subsequently, three unique concepts, which in detail consist of a dual fiber focus trap, a single meta-fiber trap and a fiber point Paul trap, and effectively represent two optical and one electrical trap, are discussed and compared with respect to current implementations. ..

Single molecule tracking with light sheet microscopy

The work presented here concentrates on light sheet based fluorescence microscopy (LSFM) and its application to single molecule tracking. In LSFM the sample is illuminated perpendicular to the detection axis with a thin light sheet. In this manner a simple optical sectioning microscope is created, because only the focal plane of the detection optics is illuminated and no out-of-focus fluorescence is generated. This results in an enhancement of the signal-to-noise-ratio and combined with the high acquisition speed of a video microscopy a powerful tool is created to study single molecule dynamics on a millisecond timescale, A completely new setup was designed and constructed, that combines light sheet illumination technique with single molecule detection ability. Theoretical calculations and quantitative measurements of the illumination light sheet thickness (2-3 µm thick) and the microscope point spread function were performed. A direct comparison of LSFM and epi-illumination of model samples with intrinsic background fluorescence illustrated the clear contrast improvement of LSFM for thick samples. Single molecule detection is limited by the number of photons emitted by a single fluorophore per observation time. So, the ability to track single molecules is dependent on molecule speed, background, detection sensitivity and frame rate. The imaging speed with the concomitant high signal-to-noise ratio that could be realized within the setup was unprecedented until then. It permitted the observation of single protein trajectories in aqueous solution with a diffusion coefficient greater than 100 µm²/s. The in vivo imaging of single molecules in thick biological samples was demonstrated in living salivary gland cell nuclei of Chironomus tentans larvae. These cell nuclei afford exceptional possibilities for the study of RNA mobility, but provide a microscopic challenge with a diameter of 50-75 µm and up 200 µm deep within the sample. To image the intranuclear mobility of individual messenger RNA particles, they were indirectly labeled via the fluorescently labeled RNA binding protein hrp36. Thus it was possible to identify at least three different diffusion modes of the mRNA particles and indirectly measure the nuclear viscosity. A high flexibility and easy adaptation of the optical sectioning thickness is required to visualize biological samples of various sizes. Often, however, the sheet geometry is fixed, whereas it would be advantageous to adjust the sheet geometry to specimens of different dimensions. Therefore, an afocal cylindrical zoom lens system comprising only 5 lenses and a total system length of less than 160 mm was developed. Two movable optical elements were directly coupled, so that the zoom factor could be adjusted from 1x to 6.3x by a single motor. Polytene chromosomes of salivary gland cell nuclei of C.tentans larvae were imaged in vivo to demonstrate the advantages in image contrast by imaging with different light sheet dimensions. The light sheet microscope introduced in this thesis proofed its suitability for in vivo single molecule imaging deep within a biological sample. It has the potential to reveal new dynamic single molecule interactions in vivo and enables new studies and experiments of intracellular processes

Deep tissue light-sheet microscopy

Light-sheet fluorescence microscopy, also recognised as selective plane illumination microscopy, or SPIM, has paved a new road towards imaging of entire specimens for long periods of time, in vivo. Nevertheless, as in any other microscopy technique, light-sheet fluorescence microscopy also heavily depends on the scattering and absorption properties of the imaged sample in order to generate 3D datasets with high signal to noise even at larger tissue depths. This thesis focuses on the development and implementation of new strategies and methods which target the minimization of scattering and absorption effects stemming from living specimens. Combined, the three methods provide the ability to perform gentle, high contrast deep tissue imaging and photomanipulation. Additionally, it allows easier handling and fusion of 3D multiview light-sheet images

Development of swept, confocally-aligned planar excitation (SCAPE) microscopy for high-speed, volumetric imaging of biological tissue

With the wide-spread adoption of exogenous fluorescent indicators – and more recently genetically encoded fluorescent proteins – over the past two decades, there exists a diverse chemical toolkit with which to probe biological systems. Individual cell types and sub-cellular compartments can be targeted in an increasingly wide range of model organisms. However, imaging these samples is often an exercise in balancing the needs of any given experiment against the constraints of the chosen imaging technology. For example, a volume of brain tissue is host to neurons, glia, vascular compartments and red blood cells that all occupy discrete locations in 3D space, but must work together to support healthy organ function. Single-cell activity on the order of milliseconds can trigger downstream processes that unfold over the course of multiple seconds or even minutes. The development of a technique capable of providing depth-resolved, volumetric imaging with scalable spatiotemporal resolution is crucial to developing a proper understanding of such biological systems. Bottlenecks in the throughput of existing technologies stem from a combination of inefficient illumination and volume acquisition strategies, and insufficient sensor read-out speeds. Light sheet microscopy is a promising solution, but individual designs tend to be highly specialized to specific types of samples and do not easily adapt to a wide range of experimental settings. In this thesis, I detail my work in developing swept, confocally-aligned planar excitation (SCAPE) microscopy from a first-generation prototype into a versatile, easy-to-reproduce, easy-to-use system for high-speed, 3D imaging. The first chapter introduces the challenges of designing optical systems capable of high-speed, volumetric imaging. An introduction to design choices faced in the construction of fluorescence microscopes, and current approaches to 3D imaging are discussed. The second chapter describes the progression from the 1st to 2nd generation SCAPE system. Improvements made through ray-tracing models and an enhanced optomechanical design are described, and results from this system in a number of model organisms are presented. The third chapter presents results from a range of biological applications to which SCAPE microscopy has been applied. Work in imaging the zebrafish heart to demonstrate the system’s improved imaging speed, the C. elegans to show the system’s resolution, and finally a number of examples of large field-of-view and high-resolution structural imaging are all described. Finally, the fourth chapter concludes with an overview of the work that lies ahead to both further develop of SCAPE microscopy, as well as to bring the existing system’s strengths to bear in a wider range of environments

Laser Pulses

This book discusses aspects of laser pulses generation, characterization, and practical applications. Some new achievements in theory, experiments, and design are demonstrated. The introductive chapter shortly overviews the physical principles of pulsed lasers operation with pulse durations from seconds to yoctoseconds. A theory of mode-locking, based on the optical noise concept, is discussed. With this approximation, all paradoxes of ultrashort laser pulse formation have been explained. The book includes examples of very delicate laser operation in biomedical areas and extremely high power systems used for material processing and water purification. We hope this book will be useful for engineers and managers, for professors and students, and for those who are interested in laser science and technologies

Roadmap on structured light

Structured light refers to the generation and application of custom light fields. As the tools and technology to create and detect structured light have evolved, steadily the applications have begun to emerge. This roadmap touches on the key fields within structured light from the perspective of experts in those areas, providing insight into the current state and the challenges their respective fields face. Collectively the roadmap outlines the venerable nature of structured light research and the exciting prospects for the future that are yet to be realized

Non-Hermitian and Space-Time Mode Management

In the last few years, optics has witnessed the emergence of two fields namely metasurfaces and parity-time (PT) symmetry. Optical metasurfaces are engineered structures that provide unique responses to electromagnetic waves, absent in natural materials. On the other hand, PT symmetry has emerged from quantum mechanics, when a new class of non-Hermitian Hamiltonian quantum systems was shown to have real eigenvalues. In this work, we demonstrate how PT-symmetric diffractive structures are capable of eliminating diffraction orders in specific directions, while maintaining/enhancing the remaining orders. In the second part of this work, we emphasize on supersymmetry (SUSY) and its applications in optics. Even though the full ramification of SUSY in high-energy physics is still a matter of debate that awaits experimental validation, supersymmetric techniques have already found their way into low-energy physics. In this work, we apply certain isospectral techniques in order to achieve single mode lasing in multi-element waveguide systems, where multimode chaotic emission is expected. In the third part of this dissertation, we emphasize on dynamically reconfigurable nanoparticle platforms. By exploiting the dielectrophoresis effect, we demonstrate how controllable lasing can be achieved in random photonic arrangements. Although this work focuses on the case of controlling random lasers, we expect that the proposed nanoparticle architecture can incorporate heterogeneous materials of a wide range of optical functionalities, including gain, scattering, plasmonic resonance, and nonlinearity. In the last part of the dissertation, we demonstrate the capability of synthesizing space-time (ST) wave packets, based on new propagation-invariant elementary solutions of the wave equation identified through a complexification of the spatial and temporal degrees of freedom. By establishing the connection between ST propagation-invariant pulses and tilted-pulse-front pulses, a path is opened to exploiting the unique attributes of such wave packets both in nonlinear and quantum optics

Geothermal Energy

Geothermal Energy Technology (GET) announces on a bimonthly basis the current worldwide information available on the technologies required for economic recovery of geothermal energy and its use as direct heat or for electric power production