📰 Complex systems: draw me the optical response


While it is relatively simple to describe how an atom, molecule or solid absorbs, emits or scatters light, the exercise is much more delicate for hybrid or composite systems. This is why the scientists of theInstitute (An institution is a permanent organization created for a specific purpose. It is …) from physical chemistry (Physical chemistry is the study of the physical basis of chemical systems and … (CNRS / Université Paris-Saclay) and the GRASP-Biophotonics laboratory (University of Liège, Belgium) offer an original approach using the fundamental principles of physicist (Physics (from the Greek φυσις, nature) is etymologically the …) of the solid, which allows to describe thetogether (In set theory, a set intuitively designates a collection …) processes in place during theinteraction (An interaction is an exchange of information, affect or energy between two agents within …) light (Light is the set of electromagnetic waves visible to the eye …) – composite system, explicitly including the interactions between its different components, thus giving access to unique information on their composition and structure.

© Thomas Noblet

Be it molecules, nanostructures invisible to the naked eye or materials (A material is a material of natural or artificial origin that man shapes to …) Massive, the way these objects absorb, emit, deflect, scatter and reflect light provides information about their identity, composition and microscopic structure. Scientists describe these optical processes by means of so-called “response” functions that explain the link between the light sent on to object (In general, the word object (from the Latin objectum, 1361) designates an entity defined in …)than the experimenter check (The word control can have several meanings. It can be used as a synonym for examination, for …)and what escapes and what the experimenter measures.

For simple systems such as a atom (An atom (ancient Greek ἄτομος [atomos]” That…)a molecule (A molecule is an electrically neutral chemical set of at least two atoms, which …)a nanoparticle or solid, classical and quantum theories ofoptical (Optics is the branch of physics that deals with light, radiation …) allow to calculate the response functions associated with linear processes (the light at the exit of the Material (A material is a material of natural or artificial origin that man shapes …) keep the same frequency (In physics, frequency generally refers to the measurement of the number of times a …) than the input one) and non-linear (which generally induce a frequency variation). For hybrid or composite systems in which multiple objects (identical or of different nature) coexist, the more complex optical response functions are still difficult to rigorously evaluate.

To calculate them, let’s consider everything (The whole understood as the whole of what exists is often interpreted as the world or …) first the response of the “main” object is determined, then the changes implied by the presence of the other objects are determined. The execution of an “exact” calculation by integrating all the components of the system as a whole and their interactions remained for themoment (The instant designates the smallest constituent element of time. The instant is not …) inaccessible.

Scientists of the Institute of chemistry (Chemistry is a natural science divided into several specialties, a …) physics (CNRS / Université Paris-Saclay) and the GRASP-Biophotonics laboratory (University of Liège, Belgium) offer an original approach based on the principles used so far in solid state physics, which they have modified for optics. This new method, called “diagrammatic”, allows them to graphically describe all the processes taking place during the interaction between light and a composite system, this time explicitly including the interdependence of the different components.

Taking into account thepower (In common sense, energy means anything that allows you to do work, produce energy, etc.) exchange between these different components *, scientists have access to the response functions of all optical processes in composite systems, whatever the number (The notion of number in linguistics is dealt with in the article “Number …) and the nature of their constituents and their interactions, and thus provide a finer and more rigorous picture of the identity of these systems. Results to be found in the reviewPhys. Rev. B.

* The light-matter interactions between the different components are described by the exchange of virtual bosons.

T. Noblet, B. Busson and C. Humbert.
Schematic theory of linear and non-linear optics for composite systems
Phys.Rev. HAS, 104, 063504 (2021).
DOI: 10.1103 / PhysRevA.104.063504

T. Noblet and B. Busson.
Sum-frequency generation at molecule-nanostructure interfaces from the diagrammatic theory of nonlinear optics
Phys.Rev. B.105, 205420 (2022).
DOI: 10.1103 / PhysRevB.105.205420

-Bertrand Busson- Researcher (A researcher (female researcher) refers to a person whose job is to do research …) at the Institute of Physical Chemistry of Orsay – bertrand.busson at
– Stéphanie Younès – Manager Communication (Communication concerns both man (intrapsychic, interpersonal communication, etc.) – Institute of Chemistry of CNRS (The National Center for Scientific Research, better known by the acronym CNRS, is the largest …) – inc.communication on
– Anne-Valérie Ruzette – Manager scientific (A scientist is a person who devotes himself to the study of one or more sciences and who …) for communication – CNRS Institute of Chemistry – anne-valerie.ruzette on
– says Christophe Cartier mill (A mill is a machine for grinding cereal grains into flour and, by analogy, …) – Researcher at the Institute of Molecular Chemistry in Paris and Project Manager for scientific communication at the INC

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