Design and Construction of a Tunable Light Source with Light Emitting Diodes for Photosynthetic Organisms

This thesis describes and documents the design and construction of a light source which is tunable and has the ability to mimic the spectral output of the sun in the photosynthetic active radiation range (400 - 700 nm). To adjust the spectral output at different wavelengths different types of LEDs were chosen and combined. This thesis describes the design, construction, testing, and suggestions for further improvements to this light source. The light source is comprised of 900 LEDs with 26 different peak wavelengths within the photosynthetically active radiation range. The light source is made tunable through the use of a control system utilizing pulse width modulation. This unique light source will allow studies to be performed to understand spectral influences on microalgae and lipid production as well as other photosynthetic organisms

Optical tweezers combined with interference reflection microscopy for quantitative trapping and 3D imaging

Optical tweezers are an indispensable tool in biophysical single-molecule studies. They provide the ability to mechanically probe the characteristics of biological processes, such as active transport of cargo by molecular motors. To this end, functionalized (sub)micron- sized dielectric particles are held in a tightly focused laser trap while external forces lead to displacements of the particle from the trap center. The measurement and calibration of these displacements yield insights into the mechanical properties of the molecule of interest. The study of molecular motors, such as kinesins, is carried out in in vitro surface-based experimental assays. The experimental needs for such assays are challenging. The instrument must be stabilized, i.e. decoupled form external noise, and drift must be minimized, and it needs to be combined with state of the art microscopy techniques to visualize the sample. These are, on the one hand, single-molecule fluorescence detection and, on the other hand, robust label-free imaging of diffraction limited specimen. The latter is commonly realized by differential interference contrast (DIC) microscopy, which is an expensive and rather complicated technique that also restricts the design of the optical tweezers and, therefore, reduces the experimental possibilities. Optical tweezers experiments, moreover, rely on precise and reliable calibration. Despite its importance, calibration is, at times, carried out with obsolete methods or based on vague assumptions. Especially, in the vicinity of the sample surface, where hydrodynamic effects can have a significant influence, such assumptions fail largely. Here, height-dependent active power spectral density analysis of the Brownian motion of the trapped particle can ame- liorate these inaccuracies, but—compared to other methods—is rather cumbersome, time- consuming and easy-to-use solutions are lacking. In this work I designed and assembled an optical tweezers setup combined with total in- ternal reflection fluorescence (TIRF) microscopy. Furthermore, I succeeded to reduce design restrictions of the optical tweezers by combining it with interference reflection microscopy, which is a simple, cost-efficient and robust contrast technique that can visualize diffraction limited specimen in three dimensions, such as microtubules. Moreover, I was able to use this technique to determine the three-dimensional profile of an upward bent microtubule which I used to simultaneously calibrate the evanescent field depth of the TIRF microscope. In ad- dition, I programmed a free and open-source optical tweezers calibration software, PyOTC, that provides the means for height-dependent active power spectral density analysis. My work will possibly influence the design of optical tweezers instruments for surface-based experiments. LED-based IRM could further improve or complement label-free detection tech- niques such as interferometric scattering microscopy. The free and open-source calibration software package could help to precisely calibrate optical tweezers data. Moreover, because the source is available to anybody, calibration and therefore the analysis of optical tweezers data will be more transparent to the scientific community

Study of the reliability of power LEDs for color mixing applications

The aim of this thesis is the reliability analysis of high-power RGB and white LEDs\nprovided by six different manufacturers. In order to evaluate the characteristics of these devices in terms of lifetime and optical power maintenance combined thermal and current stress tests have been carried out, verifying the changes of the optical and electrical characteristics of the devices during\nthe stress. The results of this work have revealed several types of degradation of various\ndevices

Adaptive optics in high-contrast imaging

The development of adaptive optics (AO) played a major role in modern astronomy over the last three decades. By compensating for the atmospheric turbulence, these systems enable to reach the diffraction limit on large telescopes. In this review, we will focus on high contrast applications of adaptive optics, namely, imaging the close vicinity of bright stellar objects and revealing regions otherwise hidden within the turbulent halo of the atmosphere to look for objects with a contrast ratio lower than 10^-4 with respect to the central star. Such high-contrast AO-corrected observations have led to fundamental results in our current understanding of planetary formation and evolution as well as stellar evolution. AO systems equipped three generations of instruments, from the first pioneering experiments in the nineties, to the first wave of instruments on 8m-class telescopes in the years 2000, and finally to the extreme AO systems that have recently started operations. Along with high-contrast techniques, AO enables to reveal the circumstellar environment: massive protoplanetary disks featuring spiral arms, gaps or other asymmetries hinting at on-going planet formation, young giant planets shining in thermal emission, or tenuous debris disks and micron-sized dust leftover from collisions in massive asteroid-belt analogs. After introducing the science case and technical requirements, we will review the architecture of standard and extreme AO systems, before presenting a few selected science highlights obtained with recent AO instruments.Comment: 24 pages, 14 figure

Rosina - Rosetta Orbiter Spectrometer for Ion and Neutral Analysis

The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) will answer important questions posed by the mission's main objectives. After Giotto, this will be the first time the volatile part of a comet will be analyzed in situ. This is a very important investigation, as comets, in contrast to meteorites, have maintained most of the volatiles of the solar nebula. To accomplish the very demanding objectives through all the different phases of the comet's activity, ROSINA has unprecedented capabilities including very wide mass range (1 to >300 amu), very high mass resolution (m/Δ m > 3000, i.e. the ability to resolve CO from N2 and 13C from 12CH), very wide dynamic range and high sensitivity, as well as the ability to determine cometary gas velocities, and temperature. ROSINA consists of two mass spectrometers for neutrals and primary ions with complementary capabilities and a pressure sensor. To ensure that absolute gas densities can be determined, each mass spectrometer carries a reservoir of a calibrated gas mixture allowing in-flight calibration. Furthermore, identical flight-spares of all three sensors will serve for detailed analysis of all relevant parameters, in particular the sensitivities for complex organic molecules and their fragmentation patterns in our electron bombardment ion source

Thermal characterization and optical reliability investigation of high-power white leds

The LED technology has fatly been developed in the last decade, but there is the need to provide detailed investigations about the dynamics of the optical power and light quality after several hours of operation. Three different LED devices were studied, and a stress at high current injection were performed. The results highlight the efficacy increase in two cases, and the creation of nonradiative centers in the latte

Accurate efficiency measurements of organic light-emitting diodes via angle-resolved spectroscopy

Funding: EPSRC NSF-CBET lead agency agreement (EP/R010595/1, 1706207), the Leverhulme Trust (RPG-2017-231), the Volkswagen Foundation (No. 93404), and the Alexander von Humboldt Stiftung (Humboldt-Professorship to M.C.G.). C.K. acknowledges support from the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2017R1A6A3A03012331). Diese Arbeit wurde mitfinanziert durch Steuermittel auf der Grundlage des vom Sächsischen Landtag beschlossenen Haushaltes.The accurate characterization of thin-film LEDs – including organic light emitting diodes (OLEDs), perovskites and quantum dot LEDs – is crucial to our understanding of the factors that influence their efficiency and thus to the fabrication of LEDs with improved performance and stability. In addition, detailed information about the angular characteristics of LED emission is useful to assess the suitability of individual architectures, e.g. for display applications. Here, the implementation of a goniometer-based measurement system and corresponding protocol are described that allow to accurately determine the current-voltage-luminance characteristics, external quantum efficiency and luminous efficacy of OLEDs and other emerging thin-film LEDs. The system allows recording of angle-resolved electroluminescence spectra and accurate efficiency measurements for devices with both Lambertian and non-Lambertian emission characteristics. A detailed description of the setup and a protocol for assembling and aligning the required hardware are provided. Drawings of all custom parts and the open-source Python software required to perform the measurement and to analyze the data are included.Publisher PDFPeer reviewe