Recent advances in solid-state organic lasers

Organic solid-state lasers are reviewed, with a special emphasis on works published during the last decade. Referring originally to dyes in solid-state polymeric matrices, organic lasers also include the rich family of organic semiconductors, paced by the rapid development of organic light emitting diodes. Organic lasers are broadly tunable coherent sources are potentially compact, convenient and manufactured at low-costs. In this review, we describe the basic photophysics of the materials used as gain media in organic lasers with a specific look at the distinctive feature of dyes and semiconductors. We also outline the laser architectures used in state-of-the-art organic lasers and the performances of these devices with regard to output power, lifetime, and beam quality. A survey of the recent trends in the field is given, highlighting the latest developments in terms of wavelength coverage, wavelength agility, efficiency and compactness, or towards integrated low-cost sources, with a special focus on the great challenges remaining for achieving direct electrical pumping. Finally, we discuss the very recent demonstration of new kinds of organic lasers based on polaritons or surface plasmons, which open new and very promising routes in the field of organic nanophotonics

Functional colloidal surface assemblies: Classical optics meets template-assisted self-assembly

Abstract: When noble metals particles are synthesized with progressively smaller dimensions, strikingly novel optical properties arise. For nanoscale particles, collective disturbances of the electron density known as localized surface plasmons resonances can arise, and these resonances are utilized in a variety of applications ranging from surface-enhanced molecular spectroscopy and sensing to photothermal cancer therapy to plasmon-driven photochemistry. Central to all of these studies is the plasmon’s remarkable ability to process light, capturing and converting it into intense near fields, heat, and even energetic carriers at the nanoscale. In the past decade, we have witnessed major advances in plasmonics which is directly linked with the much broader field of (colloidal) nanotechnology. These breakthroughs span from plasmon lasing and waveguides, plasmonic photochemistry and solar cells to active plasmonics, plasmonics nanocomposites and semiconductor plasmons. All the above-mentioned phenomena rely on precise spatial placement and distinct control over the dimensions and orientation of the individual plasmonic building blocks within complex one-, two- or three-dimensional complex arrangements. For the nanofabrication of metal nanostructures at surfaces, most often lithographic approaches, e.g. e-beam lithography or ion-beam milling are generally applied, due to their versatility and precision. However, these techniques come along with several drawbacks such as limited scalability, limited resolution, limited compatibility with silicon manufacturing techniques, damping effects due to the polycrystalline nature of the metal nanostructures and low sample throughput. Thus, there is a great demand for alternative approaches for the fabrication of metal nanostructures to overcome the above-mentioned limitations. But why colloids? True three-dimensionality, lower damping, high quality modes due to mono-dispersity, and the absence of grain boundaries make the colloidal assembly an especially competitive method for high quality large-scale fabrication. On top of that, colloids provide a versatile platform in terms of size, shape, composition and surface modification and dispersion media. 540The combination of directed self-assembly and laser interference lithography is a versatile admixture of bottom-up and top-down approaches that represents a compelling alternative to commonly used nanofabrication methods. The objective of this thesis is to focus on large area fabrication of emergent spectroscopic properties with high structural and optical quality via colloidal self-assembly. We focus on synergy between optical and plasmonic effects such as: (i) coupling between localized surface plasmon resonance and Bragg diffraction leading to surface lattice resonance; (ii) strong light matter interaction between guided mode resonance and collective plasmonic chain modes leading to hybrid guided plasmon modes, which can further be used to boost the hot-electron efficiency in a semiconducting material; (iii) similarly, bilayer nanoparticle chains leading to chiro-optical effects. Following this scope, this thesis introduces a real-time tuning of such exclusive plasmonic-photonic (hybrid) modes via flexible template fabrication. Mechanical stimuli such as tensile strain facilitate the dynamic tuning of surface lattice resonance and chiro-optical effects respectively. This expands the scope to curb the rigidity in optical systems and ease the integration of such systems with flexible electronics or circuits.:Contents Abstract Kurzfassung Abbreviations 1. Introduction and scope of the thesis 1.1. Introduction 1.1.1. Classical optics concepts 1.1.2. Top down fabrication methods and their challenges 1.1.3. Template-assisted self-assembly 1.1.4. Functional colloidal surface assemblies 1.2. Scope of the thesis 2. Results and Discussion 2.1. Mechanotunable Surface Lattice Resonances in the Visible Optical Range by Soft Lithography Templates and Directed Self-Assembly 2.1.1. Fabrication of flexible 2D plasmonic lattice 2.1.2. Investigation of the influence of particle size distribution on SLR quality 2.1.3. Band diagram analysis of 2D plasmonic lattice 2.1.4. Strain induced tuning of SLR 2.1.5. SEM and force transfer analysis in 2D plasmonic lattice under various strain 2.2. Hybridized Guided-Mode Resonances via Colloidal Plasmonic Self-Assembled Grating 2.2.1. Fabrication of hybrid opto-plasmonic structure via template assisted self-assembly 2.2.2. Comparison of optical band diagram of three (plasmonic, photonic and hybrid) different structures in TE and TM modes 2.2.3. Simulative comparison of optical properties of hybrid opto-plasmonic NP chains with a grating of metallic gold bars 2.2.4. Effect of cover index variation with water as a cover medium 2.3. Hot electron generation via guided hybrid modes 2.3.1. Fabrication of the hybrid GMR structure via LIL and lift-off process 2.3.2. Spectroscopic and simulative analysis of hybrid opto-plasmonic structures of different periodicities 2.3.3. Comparative study of photocurrent generation in different plasmonic structures 2.3.4. Polarization dependent response at higher wavelength 2.3.5. Directed self-assembly of gold nanoparticles within grating channels of a dielectric GMR structure supported by titanium dioxide film 2.4. Active Chiral Plasmonics Based on Geometrical Reconfiguration 2.4.1. Chiral 3D assemblies by macroscopic stacking of achiral chain substrates 3. Conclusion 4. Zusammenfassung 5. Bibliography 6. Appendix 6.1. laser interference lithography 6.2. Soft molding 6.3. Determine fill factor of plasmonic lattice 6.4. 2D plasmonic lattice of Au_BSA under strain 6.5. Characterizing order inside a 2D lattice 6.6. Template-assisted colloidal self-assembly 6.7. Out of plane lattice resonance in 1D and 2D lattices 6.8. E-Field distribution at out of plane SLR mode for 1D lattices of various periodicity with AOI 20° 6.9. Refractive index of PDMS and UV-PDMS 6.10. Refractive index measurement for sensing 6.11. Optical constants of TiO2, ma-N 405 photoresist and glass substrate measured from spectroscopic ellipsometry Acknowledgement/ Danksagung Erklärung & Versicherung List of Publication

Light and Single-molecule Coupling in Plasmonic Nanogaps

Plasmonic cavities confine optical fields at metal-dielectric interfaces via collective charge oscillations of free electrons within metals termed surface plasmon polaritons (SPPs). SPPs are confined in nanometre gaps formed between two metallic surfaces which creates an optical resonance. This optical resonance of the system is controlled by the geometry and the material of the nanogap. The focus of this work is to understand and utilize these confined optical modes to probe and manipulate the dynamics of single-molecules at room temperature. In this thesis, nanogap cavities are constructed by placing nanoparticles on top of a metal-film separated by molecular spacers. Such nanogaps act as cavities with confined optical fields in the gap. Precise position and orientation of single-molecules in the gap is obtained by supramolecular guest-host assembly and DNA origami breadboards. The interaction of light and single-molecules is studied in two different regimes of interaction strength. In the perturbative regime molecular light emission from electronic and vibrational states is strongly enhanced and therefore is used for the detection of single-molecules. In this regime the energy states remain unaltered, however profound effects emerge when the gap size is reduced to <1 nm. New hybridized energy states which are half-light and half-matter are then formed. Dispersion of these energies is studied by tuning the cavity resonance across the molecular resonance, revealing the anti-crossing signature of a strongly coupled system. This dressing of molecules with light results in the modification of photochemistry and photophysics of single-molecules, opening up the exploration of complex natural processes such as photosynthesis and the possibility to manipulate chemical bonds.I would like to acknowledge the financial support I received from the Dr. Manmohan Singh scholarship from St. John’s College, University of Cambridge

Optical properties of surface plasmon polaritons and semiconductor based quantum system

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Manipulating Light in Organic Thin-film Devices.

Optoelectronic devices based on organic semiconductors have been an active topic of research for more than two decades. While organic photovoltaic cells, organic semiconductor lasers, photodetectors and other organic electronics are still working to transition from the laboratory to commercialized products, organic light-emitting diodes (OLEDs) have found wide acceptance in small and medium, high-resolution displays, with signs of near-future adoption in TV panels and large-area lighting. The fundamentally different properties of the materials and principles of device operation offer great new possibilities in terms of energy-savings, color gamut, ease and cost of manufacturing, and novel form factors. In the first part of this thesis, we review the operation and optics of OLEDs, focusing on the problem of extracting light trapped in the high refractive index regions of the device. Since nearly 80% of generated light is lost before exiting in the forward viewing direction, detailed understanding of the underlying effects and methods to remedy the issue are necessary. We use 3D finite-element modeling to investigate techniques to outcouple light in a typical OLED. Furthermore, we demonstrate a method of fabricating an embedded dielectric grid with an ultra-low refractive index as an effective means of enhancing outcoupling. Lastly, we present progress in fabricating planarized scattering structures for light extraction. The second half of this thesis deals with the physics and applications of the strong-coupling regime in organic semiconductor microcavities, where a new quasiparticle (the polariton) emerges due to the strong interaction of light and matter. We review the progress of organic polaritonic lasers and present experimental evidence of Bose-Einstein statistics underlying their principle of operation. We show that the polariton lasing threshold in anthracene can be reduced by an order of magnitude as the temperature is decreased, in contrast to the behavior of conventional organic lasers. Additionally, we exploit the strong-coupling regime to engineer a hybrid organic-inorganic excited state at room temperature. Such photon-mediated hybridization of disparate Frenkel and Wannier-Mott excited states may allow new devices with tailored optical properties.PhDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/110410/1/mishas_1.pd

Light Trapping in Plasmonic Solar Cells

Subwavelength nanostructures enable the manipulation and molding of light in nanoscale dimensions. By controlling and designing the complex dielectric function and nanoscale geometry we can affect the coupling of light into specific active materials and tune macroscale properties such as reflection, transmission, and absorption. Most solar cell systems face a trade-off with decreasing semiconductor thickness: reducing the semiconductor volume increases open circuit voltages, but also decreases the absorp- tion and thus the photocurrent. Light trapping is particularly critical for thin-film amorphous Si (a-Si:H) solar cells, which must be made less than optically thick to enable complete carrier collection. By enhancing absorption in a given semiconductor volume, we can achieve high efficiency devices with less than 100 nm of active region. In this thesis we explore the use of designed plasmonic nanostructures to couple incident sunlight into localized resonant modes and propagating waveguide modes of an ultrathin semiconductor for enhanced solar-to-electricity conversion. We begin by developing computational tools to analyze incoupling from sunlight to guided modes across the solar spectrum and a range of incident angles. We then show the potential of this method to result in absorption enhancements beyond the limits for thick film solar cells. The second part of this thesis describes the integration of plasmonic nanos- tructures with a-Si:H solar cells, showing that designed nanostructures can lead to enhanced photocurrent over randomly textured light trapping surfaces, and develops a computational model to accurately simulate the absorption in these structures. The final chapter discusses the fabrication of a high-efficiency (9.5%) solar cell with a less than 100 nm absorber layer and broadband, angle isotropic photocurrent enhance- ment. Moreover, we discuss general design rules where light trapping nanopatterns are defined by their spatial coherence spectral density.</p