Plane mirror | EPFL Graph Search

A plane mirror is a mirror with a flat (planar) reflective surface. For light rays striking a plane mirror, the angle of reflection equals the angle of incidence. The angle of the incidence is the angle between the incident ray and the surface normal (an imaginary line perpendicular to the surface). Therefore, the angle of reflection is the angle between the reflected ray and the normal and a collimated beam of light does not spread out after reflection from a plane mirror, except for diffraction effects. A plane mirror makes an image of objects in front of the mirror; these images appear to be behind the plane in which the mirror lies. A straight line drawn from part of an object to the corresponding part of its image makes a right angle with, and is bisected by, the surface of the plane mirror. The image formed by a plane mirror is (meaning that the light rays do not actually come from the image) it is not (meaning that the light rays do actually come from the image). it is al

Extended Depth-of-Field for Color Images in Light Microscopy: Image Fusion and 3D Visualization

Niels Quack, Daniel Sage, Michaël Unser, Dimitri Nestor Alice Van De Ville

Bright-field microscopy suffers from a relatively small depth-of-field. Typically, the specimen’s profile covers a range larger than the depth-of-field, and parts of the specimen that lie outside the object plane appear blurred. The specimen can be ‘scanned’ by moving the object along the optical axis, and different images will contain different areas that are sharp. The purpose of image fusion is to combine those images into one single image with an extended depth-of-field. One promising method is based on the wavelet transform. We show how the wavelet-based image fusion technique can be successfully applied to obtain a sharp composite color image. The selection of the proper type of wavelets can improve the results. We also introduce a way to apply this technique for color images without introducing false colors. Finally, we show how height information on the specimen, which we obtain as a side product from our algorithm, can be used for 3D visualization.

2004

Volume refractometry of liquids using stable optofluidic Fabry-Perot resonator with curved surfaces

Maurine Malak Karam Awadallah

This work reports a simple, miniaturized optical sensing module for liquid refractometry. It is based on a stable Fabry-Perot resonator consisting of two silicon cylindrical mirrors with a cylindrical lens in the core. The lens is formed by a capillary tube through which the analyte to be analyzed passes. This setup enables volume refractometry, where light propagates through the sample realizing high interaction depth. The cylindrical surfaces achieve light confinement, reducing the light escaping loss encountered in classical cavities with straight mirrors; and hence high quality factor (Q) over 1,000 is attained. Exploiting this high Q, we adopt uncommon refraction index (RI) measurement criterion: we operate at a fixed wavelength and detect the power drop caused as a consequence to the spectral shift with RI change. Performing experimental testing using a tunable laser and a power-meter, the normalized spectra for different mixture ratios of acetone and deionized water are obtained. The wavelength corresponding to the maximal power transmission from pure acetone is taken as a reference. A vertical line at this wavelength cuts the successive transmission curves and enables measuring the power drop in the linear region, and from it the refractive index change Delta n above the refractive index of the reference solution can be determined for 0.0023

Spie-Int Soc Optical Engineering2015

Growth and characterisation of earth-abundant semiconductor nanostructures for solar energy harvesting

Simon Robert Escobar Steinvall

Zinc phosphide (Zn3P2) is a compound semiconductor based on earth-abundant elements with functional properties ideal for solar cell applications. Cheap, abundant, and renewable energy sources are increasingly imperative due to the imminent threat posed by climate change. So far, zinc phosphide has not been exploited due to limitations in the fabrication of a high-quality material as a consequence of challenges in growth, controllable doping, and heterostructure formation. The maximum conversion efficiency (~6%) was obtained 40 years ago. One route with potential to circumvent or minimise the impact of the limiting factors is the growth of zinc phosphide in the form of nanostructures. By growing the material into nanoscale objects one opens up new elastic strain relaxation mechanisms, minimise the interface area, and loosen the lattice-matching constraints for high-quality epitaxial growth. This thesis focuses on the growth and characterisation with electron microscopy of (i) zinc phosphide nanowires grown through a vapour-liquid-solid approach, and (ii) nanopyramids and thin films grown through selective area epitaxy and lateral epitaxial overgrowth. The first part of this thesis will introduce the reader to the motivation behind the research with regards to renewable energy and a review of zinc phosphide (Chapter 1), the growth of nanostructures (Chapter 2) with focus on molecular beam epitaxy and nan-owires, and then the use of electron microscopy for characterisation of these structures (Chapter 3). The second part of this thesis will focus on the scientific results from the investigations into the growth of zinc phosphide nanostructures. First, the epitaxial growth of zinc phosphide nanowires using an indium-catalysed vapour-liquid-solid approach was investigated (Chapter 4). The growth parameters and mechanism were explored, as well as their impact on the functional properties of the material. Four different nanowire morphologies were achieved, and a followup study focused on the structure and formation of the zigzag ones (Chapter 5). The structure of the zigzag nanowires was found to be analogous to the twin super-lattices found in e.g. III-V nanowires, with one exception. Instead of the standard twin, the zinc phosphide nanowires were found to contain a heterotwin based on a ~monolayer thick inclusion of indium at the mirror plane. It was shown that they did not influ-ence the optoelectronic properties. A more general model for the superlattice formation was also developed, taking into account the non-polar nature of zinc phosphide. The last study explored zinc phosphide growth by selective area epitaxy (Chapter 6). The growth was limited to nanoscale holes using a nano-patterned oxide mask, where it proceeds through a vapour-solid mechanism. Zinc phosphide then forms nanopyramids enclosed by (101) facets, its most energetically stable configuration. If allowed to grow for long enough, the pyramids would coalesce into a thin film, via so-called lateral epitaxial overgrowth. This approach constitutes a step forward in the quest of high-quality, reproducible, and tunable growth of zinc phosphide, and offers a new pathway for its use as an earth-abundant photovoltaic material. Finally, the work is summarised at the end alongside an outlook of future research building on the findings presented in this thesis (Chapter 7). The supplementary information to the different chapters can be found in appendices at the end of the thesis.

EPFL2020

Growth and characterisation of earth-abundant semiconductor nanostructures for solar energy harvesting

Simon Robert Escobar Steinvall

EPFL2020