Light trapping in solar cells at the extreme coupling limit

We calculate the maximal absorption enhancement obtainable by guided mode excitation in a weakly absorbing dielectric slab over wide wavelength ranges. The slab mimics thin film silicon solar cells in the low absorption regime. We consider simultaneously wavelength-scale periodicity of the texture, small thickness of the film, modal properties of the guided waves and their confinement to the film. Also we investigate the effect of the incident angle on the absorption enhancement. Our calculations provide tighter bounds for the absorption enhancement but still significant improvement is possible. Our explanation of the absorption enhancement can help better exploitation of the guided modes in thin film devices.Comment: accepted for publication in JOSA

High-contrast self-imaging with ordered optical elements

Creating arbitrary light patterns has applications in various domains, including lithography, beam shaping, metrology, sensing, and imaging. We study the formation of high-contrast light patterns obtained by transmission through an ordered optical element based on self-imaging. By applying the phase-space method, we explain phenomena such as the Talbot and the angular Talbot effects. We show that the image contrast is maximum when the source is either a plane wave or a point source, and it has a minimum for a source with finite spatial extent. We compare these regimes and address some of their fundamental differences. Specifically, we prove that increasing the source divergence reduces the contrast for the plane wave illumination but increases it for the point source. Also, we show that to achieve high contrast with a point source, tuning the source size and its distance to the element is crucial. We furthermore indicate and explore the possibility of realizing highly complex light patterns using a periodic transmission element. These patterns can have more spots in the far field than the number of diffraction orders of the periodic element. We predict that the ultimate image contrast is smaller for a point source compared to a plane wave. Our simulations confirm that the smallest achievable spot size in the image is imposed by diffraction regardless of the imaging regime. Our research can be applied to similar domains, e.g., quantum systems

Goldrausch in der Tiefsee

Als Forscher 1979 die ersten heißen Tiefseequellen im Pazifik entdeckten, war dies eine Sensation. Heute wissen wir mehr über die „Schwarzen Raucher”. Sie werden bis zu 400 Grad heiß und fördern wertvolle Elemente wie Gold, Kupfer und Zink aus dem Erdinneren. Professor Peter Herzig gibt Einblicke in die faszinierenden Oasen der Tiefsee