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Shaping and Sensing Light with Optical Fourier Surfaces
Item type: Doctoral Thesis
Glauser, Yannik Michael (2026)
Light lies at the core of modern science and technology. In the visible and near-infrared regime, diffractive structures on the nanoscale provide a powerful means to shape and sense its wavefronts. Such optical control depends critically on the fabrication accuracy. Despite significant progress, conventional grayscale methods still lack sufficient resolution. As a result, most current implementations rely on binary nanolithography with discretized designs. This discretization is intrinsically mismatched with the wave nature of light, ultimately limiting optical performance. Optical Fourier surfaces (OFSs)—continuous, grayscale relief profiles fabricated with nanometer accuracy using thermal scanning-probe lithography—open new possibilities for manipulating light with high precision.
In this thesis, we exploit OFSs in silver to explore both fundamental and applied aspects of Fourier engineering. First, we establish a foundational framework for diffraction from sinusoidal OFSs by comparing experimental data with analytical scalar diffraction models and full electrodynamic simulations. The high fidelity of the fabricated structures allowed us to perform these quantitative diffraction studies under well-defined, sinusoidally pure conditions that had not been accessible before. While the models show systematic deviations, simulations agree closely with experiments, confirming OFSs as reliable and precise diffractive elements.
Second, we build on this understanding to achieve holographic wavefront shaping with OFSs in free space. Specifically, we focus on computergenerated holography, where the diffractive structures are directly designed and physically realized. We demonstrate three complementary design approaches. While each has distinct strengths and limitations, all of them are fully compatible with OFSs, highlighting both the design flexibility and straightforward implementation enabled by our accurate grayscale nanofabrication.
Third, we introduce plasmonic Fourier pixels that extend OFSs to a plasmonic platform using surface plasmon polaritons. Fourier pixels act as multifunctional building blocks capable of generating and detecting arbitrary wavefronts in terms of amplitude, phase, and polarization. This bidirectional functionality provides a compact and modular architecture for wavefront engineering, with potential impact on the next generation of display and sensing technologies.
In summary, we present OFSs with increasing structural and functional complexity, from fundamental diffraction gratings to arbitrarily structured holograms, and eventually to integrated pixel architectures. This progression underscores the versatility of OFSs and their potential to open unexplored avenues in optics and photonics.
Agricultural labour and drug use. Insights from list experiments in Nigeria
Item type: Working Paper
Illien, Patrick; Aremu, Olayinka; Jann, Ben; et al. (2026)
-Background- The world is facing a severe drug crisis, posing serious public health and societal risks. Yet, little is known about drug use among farmers and farmworkers, key contributors to global food production. Poor mental health and precarious working conditions in agriculture are common. Farmers and workers may turn to drugs to cope with these conditions, however, evidence on drug use in agriculture is extremely limited. A challenge in collecting such data is social desirability bias stemming from the topic's sensitivity. We address this gap by using sensitive question techniques and offer novel evidence on drug use among farmers and farmworkers, highlighting links between working conditions, work-related health, and drug consumption. -Methods- We conducted item-count and item-sum double list experiments with 1,554 farmers and workers to measure the prevalence and frequency of drug use in Nigeria's labour-intensive tomato sector where the topic is highly relevant. List experiments avoid direct questioning and can estimate sensitive behaviours, while hiding respondents' answers from the interviewer. Using these estimates, we ran multivariate regressions to identify work-related risk factors of drug use, focusing on burnout, work-related pain and health problems, pesticide exposure, unusual working hours, and belief in work performance effects. -Results- The item-count experiment suggests that about 8% of farmers, 20% of seasonal workers, and 6% of casual workers used drugs in the previous 12 months. The item-sum experiment finds that drug-using farmers and seasonal workers have consumed drugs on about 8 days in the last month on average (farmers possibly more than that), and drug-using casual workers on 7 days. Multivariate regressions show that work-related pain and belief in performance-enhancing effects are the most important risk factors for frequent drug use. Our results also demonstrate that burnout levels are significantly higher among farmworkers than among farmers, but we do not find a significant association between work-related burnout and drug use. -Conclusions- Farmers and farmworkers suffer from important occupational health deficits. Drug use and mental health in rural areas in particular remain underappreciated on policy and research agendas. Implications for agricultural productivity and rural development should be further explored.
Tracing Social Differentiation: Debates and Fieldwork Practices
Item type: Other Publication
Illien, Patrick; Pérez Niño, Helena (2026)
On the Validity of Quasilinear Plasma Transport Equations
Item type: Journal Article
Schlickeiser, Reinhard; Kröger, Martin (2026)
Significant differences regarding their validity and applicability are found for the two variants of the quasilinear transport theory (QLT) for charged particles in partially turbulent electromagnetic fields. In homogeneous turbulence, the quasilinear theory, based on the Vlasov equation for the smoothly varying phase space density of particles (V-QLT), only holds for particle propagation times less than t − t0 < p/∣δK∣, where δK denotes the random Lorentz force and p the particle momentum. In magnetized plasmas, this requires propagation times shorter than τgyro/2πqL, where τgyroso denotes the gyroperiod, so that the condition can persist over many gyroperiods only when the relative fluctuation level qL = ∣δB∣/B0 is small. This condition does not apply to the quasilinear theory, based on the Klimontovich equation and phase space density, which accounts for the intrinsically discrete nature of matter (K-QLT). A much weaker K-QLT validity condition ∣δna∣ < na for the density fluctuations is found. The price to pay for the less severe validity condition and the much wider applicability for all propagation times is the additional presence of the drag terms, absent in V-QLT, besides the momentum diffusion terms.