[en] An aberration calculation method which was developed by Lu [1] can treat individual aberration term precisely. Spectral aberration is the linear sum of these aberration terms, and the aberrations of multi-element systems also can be calculated correctly when the stretching ratio, defined herein, is unity. Evaluation of focusing mirror-grating systems which are optimized according to Lu’s method, along with the Light Path Function (LPF) and the Spot Diagram method (SD) are discussed to confirm the advantage of Lu’s methodology. Lu’s aberration terms are derived from a precise wave-front treatment, whereas the terms of the power series expansion of the light path function do not yield an accurate sum of the aberrations. Moreover, Lu’s aberration terms can be individually optimized. This is not possible with the analytical spot diagram formulae.

[en] In this work, we theoretically investigate the local electric near-field distribution inside thin, nano-textured crystalline silicon (c-Si). We use rigorous wave-optical modeling to compare the impact of periodic nanostructures with different geometries on the electric near-field close to the surface. The ‘nano-muffins’ geometry is introduced as one example for an optical structure with promising light trapping features. By simulation, we show that this geometry features confined optical modes that create strong near-field enhancement. This enhancement is particularly beneficial for very thin c-Si solar cells and is investigated in detail. The nano-muffins structure can achieve an average of 29-fold near-field enhancement in the spectrum of interest for silicon photovoltaic applications, which is comparable to the enhancements achievable with plasmonic structures. Furthermore, we demonstrate that the near-field enhancement with nano-muffins can be achieved over a broad spectral range, which is a marked advantage of dielectric structures over plasmonic structures. The presented findings are of potential interest also for other optoelectronic devices, such as LEDs or sensors. (paper)

[en] X-ray in-line phase contrast tomography holds great promise for the quantitative analysis of soft materials. However, its applications have been limited, so far, by the fact that direct methods based on the transport-of-intensity equation and the contrast transfer function are sensitive to noise and applicable only to limited types of samples. Here, we propose an iterative method based on the Gerchberg-Saxton algorithm (R. W. Gerchberg and W. O. Saxton, Optik 35, 237 (1972)), but overcoming its slow convergence by an acceleration technique, named random signed feedback, which shows an excellent performance, both in numerical simulation and tomographic experiment, of discriminating various polymers even when using 53 keV synchrotron X-rays.