ELFT HÍRADÓ

[<vera.horvath AT eli-alps.hu>]

Előadó: Varró Sándor (Wigner RCP; ELI-ALPS)
Cím: Scattering of light by rough surfaces; „per aspera ad astra”

Időpont: 2020. október 16. 9 óra

Az előadás kivonata:

The scattering of electromagnetic waves on rough surfaces has been a very
extensively studied phenomenon, which is taking place permanently and
everywhere in our environment. Our knowledge on this phenomenon, and the
associated applications truly extend “from the rough roads to the stars”. The
accurate modelling of diffuse light scattering is, for example, not only the
subject of photometry, but it also serves as a mathematical-physical basis for
generating the appearance functions in computer graphics. The propagation of
radar signals along the rough surface of earth (terrain, sea surface), the
reflections of radiowaves from the fluctuating ionosphere or even from
celestial bodies all belong to this subject (see e.g. the famous experiment
performed by Zoltan Bay in Hungary on measuring the radar echo from the Moon).
The physical descriptions of these phenomena have several common features,
both in building up models and in performing the analysis. In the ‘everyday
practice of extreme light research’ the wave reflection on plasma mirrors is
an important phenomenon, which naturally belongs to the subject cathegory of
scattering by random rough surfaces.
Since, in general, the shapes of the various rough surfaces are very complex,
it has long been useful to model them by stochastic fields. In our recent
theoretical work, whose main results are to be presented in the talk, we have
applied the so-called ‘micro-facet-model’ (which is widely used in computer
graphics ). According to this model, the rough surface is an assembly of tiny
plane surfaces, whose orientations and slopes are subject to chance. We have
derived several new probability density functions of slopes, and some known
ones, which have earlier been introduced ad hoc. We have described the local
interaction of the plane electromagnetic waves with the random facets, their
scattering and propagation by the phenomenological Maxwell equations. The
measurable quantities have then been calculated by taking the ensemble
averages of the scattered field configurations.
In our talk, after an introductory section, we present new results on the
distribution of random slopes of the micro-facets, the amplitude correlation,
and the intensity distribution of the scattered radiation. On the basis of the
(mostly closed , analytic) formulae obtained one can keep track of how the
roughness (slope distribution) of the surface and its material constitution
(e.g. permittivity) are related with the properties of the scattered laser
radiation (e.g. with its increased divergence). Accordingly, our  analysis may
perhaps be applied in surface diagnostics and qualification.

A csatlakozáshoz szükséges link:
https://teams.microsoft.com/l/meetup-join/19%3ameeting_ZWZmMDZmZjEtMmJhNy00YTExLWJiZTktMmE1NmM2N2FjNzdj%40thread.v2/0?context=%7b%22Tid%22%3a%22b207389a-c5cb-4cb0-a1ad-227b94e96448%22%2c%22Oid%22%3a%22a12feac4-37de-4e24-89e9-c7833f7e5a28%22%2c%22IsBroadcastMeeting%22%3atrue%7d

A szeminárium angol nyelvű. Minden érdeklődőt szívesen látunk.
Horváth Vera