The course gives the fundamental tools for the understanding
and the design of the electromagnetic response of optical dielectric materials
– specifically concerning the applications in photonics, fibre optics, and optoelectronics. At the end of the course, the student is able to relate the relevant physical properties of dielectrics to the structure, nanostructures, and short- and long-range order of the material. With these skills, the student is able to design possible strategies for obtaining optical dielectric materials with specific optical response, focusing on the role of disorder and local coordination of optically active species on the optical response of the system, with a focus on the strategies of substitution or reduction of critical materials in light-emitting optical devices.
The course starts from the description of
polarization effects in materials to achieve the consciousness of the physical
mechanisms responsible for the refractive index dispersion, optical absorption,
light emission yield and nonlinear response in homogeneous, composite, and
nanostructured systems as a function of materials features, structural order
and disorder, and working parameters as temperature, stress, and light
intensity. The lectures highlight the main properties making silica-based
oxides key dielectric materials in photosensitive systems for the fabrication of fibre
filters and fibre sensors, in optical amplifiers as doped active glasses, and in
even more complex systems via nonlinear response.
Topics include three main blocks:
1. Response of Dielectrics to electromagnetic waves
From Maxwell equations to the refractive index of optical materials. The reason why the propagation speed of light is reduced in dielectrics. Dissipation and dispersion in dielectrics: the Kramers Kronig relations between real and imaginary parts of the response functions. Relationship between refractive dispersion and optical absorption spectrum. Physical meaning of the Sellmeier parametrization. From Clausius-Mossotti and Lorenz-Lorents relations to the thermo-optic and elasto-optic coefficients and their technological importance in fibre-optics and fibre-sensors. Bragg gratings fundamentals and applications. Mechanisms of photosensitivity for functionalizing dielectric materials. Glass materials engineering and tools for the description of wave propagation in layered dielectrics: transfer matrix and scattering matrix.
2. Amorphous dielectrics: structure and effects on optical functions
Description of amorphous structures: ordering rules, deviations from order, topological disorder, defectiveness, bond angle and length distribution in amorphous structures. Raman spectrum of amorphous dielectric oxides and contributions from the statistics of coordination rings. Dependence of energy gap on the structural disorder: Tauc and Urbach spectral region. Effects of static and dynamic disorder in the Urbach spectral region of the absorption edge. Homogeneous and inhomogeneous contributions to the spectral broadening of transitions at localized states. Configurational coordinate diagram and cross-correlation effects on the spectral parameters. Electron-phonon coupling and relaxation energy. Huang Rhys factor and relationship with the Stokes shift and spectral band homogeneous broadening.
3. Structural effects on localized transitions
Crystal field effects. From the electrostatic potential of ligands to the Stevens operators in the description of the crystal field Hamiltonian. Introduction to the use of Tanabe-Sugano diagrams for the evaluation of the optical response of transition metal ions potentially substituting for rare earth ions in light emitters. Energy of the electronic configurations. Crystal field spectroscopic terms and relationships with free ion terms. Racah parameter. Spin allowed and spin forbidden transitions. Static and dynamic Crystal Field effects, spectral broadening of transitions between field dependent e field independent configurations. Judd-Ofelt theory and related parameters for the analysis of Crystal field effects on rare earth ions.
Nonlinear response in amorphous dielectrics. Anharmonic effects and asymmetry of the local potential on the polarization response: Second and third order effects and role of poling processes. Physical mechanisms responsible for the nonlinear refractive index. Experimental methods for the analysis of third order nonlinear refractive and dissipative response of amorphous dielectrics.
Basic knowledge of electromagnetism.
The course mainly comprises lectures, and includes sets of collective exercises of design and evaluation of
materials and material properties for technology. In the group exercises, students are
involved in the analysis of data, so as to apply knowledge in practical situations of investigation of dielectric
During Covid-19 emergency, class will be online. Online lectures will be available either in livestreaming or as recorded video files on the e-learning online system. Online collective exercises will be organized through forum sessions and online meeting. All lectures will be recorded and available on the e-learning page.
Textbook and teaching resource
Reference textbooks (available online as e-book at the University Library):
The physics of thin film optical spectra – O. Stenzel – Springer 2016
Optical Materials – J. H. Simmons, K. S. Potter – Academic press. 2000
An introduction to the optical spectroscopy of inorganic solids – J. García Solé, D. Jaque, L. E. Bausà – Wiley 2005
Specific scientific papers, tables, and diagrams, are available on the e-learning
Students must demonstrate in an interview to
know how the main principles for the description of the electromagnetic
response of dielectrics can be used as a tool for the analysis and the design
of optical functions of technological relevance. During the assessment, a specific
material system is analyzed or designed, so as to demonstrate the skills in applying the acquired
knowledge for solving a technological problem according to a sustainable strategy.
During Covid-19 emergency, exam sessions will be only online oral exams. Online exams will be taken via WebEx. An open link to the WebEx exam event will be available on the e-learning online system, also for virtual attendees.
9:00-13:00 Monday, Wednesday, Friday