Focale | EPFL Graph Search

vignette|Le foyer image F' et la distance focale f,' (positive) d'une lentille convergente. vignette|Le foyer image F' et la distance focale f,' (négative) d'une lentille divergente. vignette|Le foyer image F' et la distance focale f,' (négative) d'un miroir concave. vignette|Le foyer image F' et la distance focale f,' (positive) d'un miroir convexe. La distance focale est une des caractéristiques principales d'un système optique. Elle est égale à la distance entre un des plans principaux et le foyer correspondant :

la distance focale objet, notée f = \overline{HF}, est la distance algébrique séparant le point principal objet H du foyer objet F ;
la distance focale image, notée f,' = \overline {H'F'}, est la distance algébrique séparant le point principal image H' du foyer image F'

Thermally reconfigurable metalens

Anna Archetti, Fateme Kiani Shahvandi, Ren-Jie Lin, Nathanaël Restori, Giulia Tagliabue, Theodoros Tsoulos

Reconfigurable metalenses are compact optical components composed by arrays of meta-atoms that offer unique opportunities for advanced optical systems, from microscopy to augmented reality platforms. Although poorly explored in the context of reconfigurable metalenses, thermo-optical effects in resonant silicon nanoresonators have recently emerged as a viable strategy to realize tunable meta-atoms. In this work, we report the proof-of-concept design of an ultrathin (300 nm thick) and thermo-optically reconfigurable silicon metalens operating at a fixed, visible wavelength (632 nm). Importantly, we demonstrate continuous, linear modulation of the focal-length up to 21% (from 165 mu m at 20 degrees C to 135 mu m at 260 degrees C). Operating under right-circularly polarized light, our metalens exhibits an average conversion efficiency of 26%, close to mechanically modulated devices, and has a diffraction-limited performance. Overall, we envision that, combined with machine-learning algorithms for further optimization of the meta-atoms, thermally reconfigurable metalenses with improved performance will be possible. Also, the generality of this approach could offer inspiration for the realization of active metasurfaces with other emerging materials within field of thermo-nanophotonics.

WALTER DE GRUYTER GMBH2022

Geometric calibration of Colour and Stereo Surface Imaging System of ESA's Trace Gas Orbiter

François Fleuret, Anton Ivanov, Nicolas Thomas, Stepan Tulyakov, Thomas Weigel

There are many geometric calibration methods for "standard" cameras. These methods, however, cannot be used for the calibration of telescopes with large focal lengths and complex off-axis optics. Moreover, specialized calibration methods for the telescopes are scarce in literature. We describe the calibration method that we developed for the Colour and Stereo Surface Imaging System (CaSSIS) telescope, on board of the ExoMars Trace Gas Orbiter (TGO). Although our method is described in the context of CaSSIS, with camera specific experiments, it is general and can be applied to other telescopes. We further encourage re-use of the proposed method by making our calibration code and data available on-line. (C) 2017 COSPAR. Published by Elsevier Ltd. All rights reserved.

Elsevier2018

Novel Concepts for Functional High Resolution Microscopy

Matthias Geissbühler

Functional imaging of biological cells and organs is one of the key techniques that drives new discoveries in life science research and medicine. In this thesis novel concepts for functional imaging at high spatial and temporal resolution are presented. In the first part, an imaging modality named Triplet Lifetime Imaging is developed. The technique allows oxygen consumption within single cells to be monitored at sub-cellular resolution. Measurement of tissue and cell oxygenation is important in order to understand cell metabolism. The method exploits oxygen induced triplet lifetime changes. The technique is applied to a biological cell system, employing as reporter a cytosolic fusion protein of -galactosidase SNAP-tag labeled with TMR. Oxygen consumption in single smooth muscle cells A7r5 during an [Arg8]-vasopressin (AVP) induced contraction is measured. The results indicate a consumption leading to an intracellular oxygen concentration that decays mono-exponentially with time. The proposed method has the potential to become a new tool for investigating oxygen metabolism at the single cell and sub-cellular level. The method is further applied to various other biological systems, demonstrating its versatility and the usefulness of this novel imaging modality. In the second part of this thesis, a concept for optical spectroscopy named nonlinear correlation spectroscopy (NLCS) is developed. The method allows monitoring of diffusing and flowing nanoparticles made of nonlinear optical material. NLCS is a method related to fluorescence correlation spectroscopy (FCS), but instead of fluorescence intensity fluctuations, NLCS analyses coherent field fluctuations of the second and third harmonic light. In bulk material, the third harmonic contribution vanishes due to the destructive interference of the third harmonic light generated in front of and behind of the focal field (Guoy phase shift). On the other hand, nanoparticles with dimensions comparable or smaller than the focal volume can generate strong higher harmonic signals. Particles based on non-centrosymmetric non-linear materials such as KNbO3 have been found to show a strong second and third harmonic signal. The method and the theory are introduced and NLCS results for diffusing polystyrene spheres (PS) as well as KNbO3 particles are presented. These spectroscopic results open the door for future extension into imaging concepts.

EPFL2011

Novel Concepts for Functional High Resolution Microscopy

Matthias Geissbühler

EPFL2011