Coherence length

Résumé

In physics, coherence length is the propagation distance over which a coherent wave (e.g. an electromagnetic wave) maintains a specified degree of coherence. Wave interference is strong when the paths taken by all of the interfering waves differ by less than the coherence length. A wave with a longer coherence length is closer to a perfect sinusoidal wave. Coherence length is important in holography and telecommunications engineering. This article focuses on the coherence of classical electromagnetic fields. In quantum mechanics, there is a mathematically analogous concept of the quantum coherence length of a wave function. Formulas In radio-band systems, the coherence length is approximated by :L = \frac{ c }{, n, \mathrm{\Delta} f ,} \approx \frac{ \lambda^2 }{, n, \mathrm{\Delta} \lambda ,} ~, where , c , is the speed of light in vacuum, , n , is the refractive index of the medium, and , \mathrm{\Delta} f ,

Source officielle

https://en.wikipedia.org/wiki/Coherence_length

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Publications associées (38)

Publications associées

Chargement

Personnes associées (5)

Personnes associées

Chargement

Unités associées (2)

Unités associées

Chargement

Concepts associés (16)

Concepts associés

Chargement

Cours associés (30)

Cours associés

Chargement

Séances de cours associées (44)

Séances de cours associées

Chargement

UV-nanoimprint lithography and large area roll-to-roll texturization with hyperbranched polymer nanocomposites for light-trapping applications

Caroline Calderone, Philippe Couty, Diego Fischer, Marina Aymara González Lazo, Aïcha Hessler-Wyser, Yves Leterrier, Jan-Anders Månson, Rémy Teuscher

Light-trapping textures were produced in hyperbranched polymer (HBP) silica nanocomposites using a UV-nanoimprint lithography (UVNIL) replication method, either in batch or roll-to-roll processes. The hardness of the HBP was found to increase by a factor of 2.5 with the addition of 50 vol% of nanoparticles. A nickel master with random sub-micron pyramidal structures was used to imprint nanocomposites containing up to 20 vol% of silica on a polyethylene naphthalate (PEN) substrate. The influence of nanoparticle fraction and pressure on the texture morphology and light scattering properties of the replicas was studied using scanning electron microscopy and optical analysis. The roughness and coherence length of the textures were similar to those of the master for all investigated compositions and process pressures. Likewise, the light scattering performance of aluminum-coated texturized nanocomposites was identical to that of the metal template, with a haze of 90% over the 400–800 nm spectral range. Thin film amorphous silicon solar cells were deposited on the texturized substrates using a large-area roll-to-roll process. The photocurrent of these devices was found to be 23% higher than the reference value of a flat cell.

Elsevier2012

Chargement

, , ,

In digital holographic microscopy (DHM), the long coherence length of laser light causes parasitic interferences due to multiple reflections in and by optical components in the optical path of the microscope and thus degrades the image quality. The parasitic effects are greatly reduced by using a short coherence length light. The main drawback of using a short coherence light source in an off-axis digital holographic microscope, is the reduction of the interference fringe contrast occurring in the field of view. Previously, we introduced a volume diffractive optical element (VDOE) placed in the reference arm of a DHM to correct the coherence plane tilt so as to obtain a high interference contrast throughout the field of view. Here, we experimentally quantify the spatial and temporal phase noise in the extracted phase image caused by non-homogeneities and scattering of the VDOE element itself. The results over five VDOEs show that the temporal phase noise is unchanged and a slight increase (up to 20%) is observed in the spatial phase noise. These results show that even with a low coherence source, a full field of view can be obtained with an off-axis DHM thanks to the VDOE without introducing significant additional phase noise.

Spie-Int Soc Optical Engineering2013

Chargement

Single shot dual wavelength full field imaging in low coherence digital holographic microscopy

Christian Depeursinge, Zahra Monemhaghdoust, Frédéric Montfort, Christophe Moser

In off-axis digital holographic microscopy, short coherence length of the source results in an unwanted reduced field of view. A diffractive optical element (DOE) which combines two high efficiency transmission volume phase gratings holographically recorded into a thin photopolymer, is proposed to manipulate the coherence plane tilt of beam containing a plurality of wavelengths simultaneously. The DOE extends the interference pattern between object and reference beams in digital holographic microscope (DHM) over the whole physical beam overlap area. We experimentally demonstrate full field imaging in a commercial, two colors (685 nm and 794 nm) reflection digital holographic microscope (DHM). The synthetic wavelength created by the two colors extends the unambiguous depth range of the DHM from 0.39 mu m to 2.49 mu m.

Spie-Int Soc Optical Engineering, Po Box 10, Bellingham, Wa 98227-0010 Usa2012

Chargement