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Periodic arrays of deep nanopores etched in silicon by deep reactive ion etching are desirable structures for photonic crystals and other nanostructures for silicon nanophotonics. Previous studies focused on realizing as deep as possible nanopores with as high as possible aspect ratios. The resulting nanopores suffered from structural imperfections of the nanopores, such as mask undercut, uneven and large scallops, depth dependent pore radii and tapering. Therefore, our present focus is to realize nanopores that have as cylindrical as possible shapes, in order to obtain a better comparison of nanophotonic observations with theory and simulations. To this end in our 2-step Bosch process we have improved the mask undercut, the uneven scallops, pore widening and positive tapering by optimizing a plethora of parameters such as the etch step time, capacitively coupled plasma (ion energy) and pressure. To add further degrees of control, we implemented a 3-step DREM (deposit, remove, etch, multistep) process. Optimization of the etching process results in cylindrical nanopores with a diameter in the range between 280 and 500 nm and a depth around 7 μm, corresponding to high depth-to-diameter aspect ratios between 14 and 25, that are very well suited for the realization of silicon nanophotonic structures.

In this PhD thesis, we study the propagation and behavior of waves in crystalline systems, with the emphasis on electromagnetic waves in photonic crystals and their confinement. In Chapter 1, we introduce the topic of wave manipulation by crystals and the basics of the mathematical description of electromagnetic waves in photonic crystals. Chapter 2 introduces a general scaling theory of identification and classification of wave confinement in crystal superlattices. Starting from the confinement energy and the mode volume, we use finite-size scaling to find that ratios of these quantities raised to certain powers yield the confinement dimensionality of each band. In Chapter 3, we investigate the possibility of improving the accuracy of our scaling method for classification of wave confinement in very small supercells by means of machine learning. We therefore slightly reformulate the scaling theory of Chapter 2 and use it to implement a physics- based clustering algorithm to classify wave confinement in photonic crystals. In Chapter 4, we employ the results of the previous chapters to analyze the light-confining properties of inverse woodpile photonic superlattices with respect to their structural parameters, namely the regular and defect pore radii. We create so-called confinement maps, depicting the dependence of the number and energy concentration of 3D confined bands on the crystal structural parameters. In Chapter 5 we investigate the problem of light propagation through realistically large photonic crystals - a notoriously computationally difficult task. To this end, we develop a size-robust discontinuous Galerkin finite element method, where we approximate the solution of a large but finite crystal by a set of Bloch modes, representing the solutions of an infinite crystal. We conclude in Chapter 6 by summarizing the results of this PhD thesis and providing suggestions for future research.

Controlling light scattering by nanoparticles is fundamentally important for the understanding and the control of light with photonic nanostructures, as well as for nanoparticle scattering itself, including Mie scattering. Here, we theoretically and numerically investigate the possibility to manipulate nanoparticle scattering by wavefront shaping that was initially developed to control light scattered by large numbers of nanoparticles in nanophotonic media. By employing a scattering matrix analysis, we find that even a single nanoparticle supports multiple strongly scattering eigenchannels, suggesting wavefront shaping as a promising tool to manipulate scattered light of a single nanoparticle. By sending in shaped wavefronts, we selectively excite eigenchannels, as is apparent from the distinct field distributions. These scattering eigenchannels are related to different resonant leaky modes of the scatterer, that reveal remarkable localized "hot spots" where the field is substantially enhanced. Moreover, we investigate the backscattered spectra; to this send in wavefronts relevant for a particular eigenchannel, and observe that the backscattered spectrum reveals not only the excited channel but also several others. This result points to the existence of short and long-range spectral correlations for an eigenchannel. Our work offers a flexible tool to manipulate light scattering of a single nanoparticle, and thus opens new possibilities to control field patterns and light-matter interactions in a nanoparticle, as well as to explore new features of nanoparticle scattering such as the spectral correlation and temporal response of light scattered by nano scatterers, including Mie spheres., 8 pages, 2 tables, 4 figures

Bose-Einstein condensation (BEC) is the massive occupation of a single quantum state in a gas of bosons at a finite temperature and is one of the few phenomena demonstrating quantum behaviour at the macroscopic scale. BEC of photons can be relised in quantum confined structures such as optical microcavities, where photons can thermalise to the temperature of the optical medium through repeated absorption and emission cycles. The critical particle number for such a system can be as low as 10 photons at room temperature, making photon BEC experimentally easily accessible. In an optical microcavity, photons behave like massive 2-dimensional particles confined in a potential defined by the mirror geometry and the optical medium refractive index. Controlling this potential is essential for exploring the physics of the condensation process. In this thesis, we develop, characterise and employ a number of flexible methods which rely on modified dielectric mirrors that have an additional optically absorptive silicon layer between the substrate and the dielectric stack. This layer allows us to locally heat the mirror using laser light. The first method is the permanent nanostructuring, resulting from pore formation inside the dielectric stack layers. The second method involves thermal expansion. Finally, introducing a thermoresponsive polymer into the optical medium allows us to control the refractive index. We experimentally investigate BEC under non-equilibrium conditions in potentials resembling a Mach-Zehnder interferometer. The switching behaviour of the interferometer in various configurations provides insight into the formation process of the condensate. We show that by adjusting their frequency, BECs naturally try to avoid particle loss and destructive interference in their environment. As a first step towards spin-glass simulators, an optical analogue of a 0,pi Josephson junction is implemented and characterised. Our experiments show a high degree of control over the junction state. Alternative types of condensate couplings and their possible implementations are investigated as well. In particular, we show that couplings can range from dispersive to dissipative, and show that the loss channel in dissipative couplings may be realised by drilling holes using focused ion beam milling.

Solar photovoltaic (PV) energy plays a pivotal role in the quest for achieving a sustainable and greener future. Increasing the yield of PV modules will not only help in meeting the everincreasing global electricity demands, but also make the PV more economically lucrative, as compared to other sources. Bifacial modules offer an effective way to increase the power generation by accepting the solar irradiance from both faces, i.e., front and rear. The yield of the module depends on the spectral [1] and angular [2] composition of the light incident on it. The spectro-angular composition of the irradiance in outdoor conditions depends on numerous factors, such as, the geographical location [1], time of the day [4] and year [5], climate [6], weather [7], cloud coverage [8], atmospheric conditions, and the reflectors [1] or surroundings. This leads to serious complications in irradiance modeling and, consequently, in PV yield modeling as the input irradiance influences the PV output. Measuring the spectro-angular irradiance helps in addressing this issue. A high-quality hour- or minute-resolved year-long spectro angular irradiance data will help in verifying and training existing and emerging models. Finally, to boost bifacial yield, understanding and optimizing the reflectors become vital. This thesis offers solutions for the above two challenges.

We discuss the design and fabrication of deterministic photonic scattering media using direct laser writing. Static measurements and light transport calculations validate that the light scattering parameters match the design model.

The synchronization of coherent states of light has long been an important subject of basic research and technology. Recently, a new concept for analog computers has emerged where this synchronization process can be exploited to solve computationally hard problems - potentially faster and more energy-efficient than what can be achieved with conventional computer technology today. The unit cell of such systems consists of two coherent centers that are coupled to one another in a controlled manner. Here, we experimentally characterize and analyze the synchronization process of two photon Bose-Einstein condensates, which are coupled to one another, either dispersively or dissipatively. We show that both types of coupling are robust against a detuning of the condensate frequencies and show similar time constants in establishing mutual coherence. Significant differences between these couplings arise in the behaviour of the condensate populations under imbalanced optical pumping. The combination of these two types of coupling extends the class of physical models that can be investigated using analog simulations.

We have uploaded all data to the Zenodo database, enabling everyone to reuse our data and to reproduce all the figures of our paper. The upload contains the file "README.txt" explaining the content of the upload., This work was supported by the NWO-TTW program P15-36 "Free-Form Scattering Optics" (FFSO) and the MESA+ Institute section Applied Nanophotonics (ANP).

Nanomesh is a Python library that allows users to quickly and easily create 2D and 3D meshes directly from images of the object they wish to mesh. The automated workflow can preprocess and segment the picture to extract different regions and create conforming meshes of the objects. Analysis tools allow evaluating the quality of the resuting mesh and the detection of problematic regions. The resulting meshes can be exported to a variety of popular formats so that they can be used in finite element simulations. Nanomesh can be used as python library for example in Jupyter notebooks, or through dedicated online dashboards.