LIGHT-MATTER INTERACTION

The course is one of the core educational activities of the Bachelor’s Degree Programme in Engineering Physics. Its primary aim is to enable students to complete their knowledge and understanding of the main physical phenomena related to wave propagation in matter, with particular emphasis on the concepts needed to correctly frame the interaction between electromagnetic waves and condensed matter.
This perspective subsequently allows students to integrate their background in condensed matter physics with the theoretical and applied knowledge required for the study of material properties and the techniques used for their characterization, whenever radiation–matter interaction or wave propagation plays a central role.

The educational objectives of the course are:
1) to develop the ability to apply, to the study of materials, the physical theories describing radiation–matter interaction and wave propagation;
2) to develop the ability to correctly use different and complementary approaches in describing the physical and chemical properties of matter in relation to wave propagation;
3) to develop the ability to connect concepts and theoretical models with the experimental practice of material characterization and investigation, also in relation to other laboratory-based courses.

1. Knowledge and understanding
1.1. To know and understand the main theories underlying the propagation of electromagnetic radiation in matter and its interaction with matter, both from the wave and the particle perspective.
1.2. To know and understand the fields of application of the different descriptive approaches based on semiclassical theories, such as the description of the origin of the refractive index, and quantum theories, such as band structure.

2. Applying knowledge and understanding
2.1. To be able to use the laws and concepts learned in the design of experiments aimed at material characterization.

3. Making judgements
3.1. To be able to critically assess and choose the most appropriate experimental approaches for the study of the properties of individual materials, identifying when complementary techniques are required to ensure the logical consistency and reliability of the investigation.
3.2. To be able to integrate the study based on wave propagation with information obtained from different approaches or from other theoretical frameworks.
3.3. To be able to place the application potential of the materials under study within a broader perspective of integrated sustainability.

4. Communication skills
4.1. To be able to communicate both the knowledge acquired and the results of its application using appropriate scientific language.
4.2. To be able to interact constructively with the lecturer and with peers, especially during group experimental activities.

5. Learning skills
5.1. To be able to take thorough and rigorous notes, also through discussion and interaction with peers.
5.2. To be able to effectively identify and select appropriate reference sources for study, also through interaction with the lecturer, especially for those parts of the syllabus that cannot be easily traced back to a single textbook.

Students are expected to have achieved the learning objectives of the core Mathematics and Physics courses taught during the first and second year of the Degree Programme.

The course addresses the main classical and quantum aspects of radiation–matter interaction, with particular emphasis on wave propagation in matter, interference and diffraction phenomena, the interaction between electromagnetic waves and materials, and the main spectroscopic and material investigation techniques. More specifically, the course includes:

REVIEW OF WAVE PHYSICS
Mechanical waves: D’Alembert’s equation, longitudinal and transverse waves, wavefronts, plane and spherical waves.
Harmonic waves: amplitude, phase, (angular) frequency, period, velocity, intensity, wave number and wave vector. Sound waves. Standing waves on a stretched string.
Electromagnetic waves: Maxwell’s equations in vacuum and in matter, wave equation, plane (harmonic) waves, wave packets, energy, polarization states.

PROPAGATION OF ELECTRIC AND MAGNETIC FIELDS
Radiation from an oscillating electric dipole: intensity, Larmor’s law. Atomic radiation: classical model, light scattering. Electromagnetic spectrum.

INTERFERENCE AND DIFFRACTION
Interference: wave superposition, rotating vector method, interference from two distant sources (Young’s experiment), interferometer: chromatic effects and wavelength measurements, N-source interference.
Diffraction: phenomenology; Huygens-Fresnel-Kirchhoff principle; Fraunhofer diffraction: slit, circular aperture, grating; resolution limit; polychromatic light; dispersive and resolving power.
Applications: grating spectroscopy; emission and absorption spectra; Fraunhofer lines; intrinsic and instrumental line broadening; holography; X-rays: generation, Bragg’s law, crystal planes and Miller indices, diffraction patterns, peak intensity, lattice parameters.

ELECTROMAGNETIC WAVES IN DIELECTRIC MATERIALS
Optical anisotropy: birefringence (ordinary and extraordinary waves), dichroic crystals, polarizers, analyzers, waveplates, field-induced birefringence (Kerr cell), stress-induced birefringence.
Interaction and propagation: harmonic field (complex notation), damped driven oscillator model, electric dipole and polarizability, dielectric polarization, wave equation in dielectrics.
Absorption and dispersion: Lambert-Beer law, complex refractive index, k-oscillator model, light dispersion and absorption in transparent media, anomalous refractive index behavior, group velocity.

ELECTROMAGNETIC WAVES IN CONDUCTIVE MATERIALS
Propagation and absorption: wave equations in conductors; low- and high-frequency approximations; plasma frequency.

QUANTUM TREATMENT OF RADIATION-MATTER INTERACTION
Blackbody radiation: definition, energy density and emissive power, stationary EM modes, Rayleigh-Jeans law, ultraviolet catastrophe, Planck’s law, Wien’s law, Stefan-Boltzmann law.
Photoelectric effect: experiments (Hertz, Hallwachs, Lenard, Millikan), Einstein’s hypothesis and equation, quantum explanation, photon number and light intensity, EM spectrum, absorption constraints.
Toward the laser: photon energy and momentum, Bohr model, photon emission/absorption, stimulated emission (Einstein 1917), laser operation: population inversion, metastable states, three-level pumping, features and types of lasers.
Matter waves and electron behavior in solids: de Broglie relation, wave-particle duality, Bohr’s complementarity and Heisenberg’s uncertainty principles; Drude-Sommerfeld model of free electron gas and introduction to band theory.
Scattering: emission, absorption, and scattering spectroscopy; light scattering: Rayleigh, Mie, and Raman scattering.

TECHNIQUES FOR MATERIAL CHARACTERIZATION
Synchrotron-based techniques: EXAFS spectroscopy, X-ray photoelectron spectroscopy (XPS), and resonant inelastic X-ray scattering (RIXS).

For reviewing and strengthening the fundamentals of wave mechanics, any university-level General Physics textbook appropriate to the level of the course may in principle be used. If needed, the choice of textbook may be discussed with the lecturer. The following text is particularly recommended:
P. Mazzoldi, M. Nigro, C. Voci, Fisica, Vol. 2, Elettromagnetismo e Onde, Edizioni EdiSES.

The part of the course concerning radiation–matter interaction and radiation propagation in matter refers to a broad and articulated bibliography, in which the topics covered are not always collected in a single textbook. For this reason, the lecturer will indicate, topic by topic, the most appropriate references for the subjects addressed during the course. Among the recommended general reference texts is:
N. W. Ashcroft, N. D. Mermin, Solid State Physics, Cengage Learning, Fort Worth, 2003.

Additional material on topics that are more difficult to find in standard textbooks will be provided directly by the lecturer.

Assessment consists of a mandatory oral examination.

The oral examination is based on a series of questions covering the entire syllabus reported in the “Course contents” section. Students are expected to demonstrate both their knowledge of the topics discussed during the course and their ability to present them in a formally correct and rigorous way. They will also be required to show their ability to develop a coherent line of reasoning, using the knowledge acquired, when faced with simple problems involving the interpretation of experimental observations or the planning of an experimental activity.

The oral examination lasts approximately 30–45 minutes, must be taken during the officially scheduled exam sessions, and is graded on a scale from 18/30 to 30/30.

In addition, a mid-term written test will be held during the semester, approximately halfway through the course, mainly focusing on the classical part of radiation–matter interaction. Students who pass the mid-term test will have a lighter final oral examination, since they will be exempt from solving at the board a problem related to the topics covered by the written test.

oral

The instructor is responsible for ensuring the authenticity and originality of all examinations and coursework. In cases of suspected academic misconduct, an additional on-site assessment may be required during the exams, which may differ from the standard format.

A very good to excellent performance (27–30/30) will correspond to a solid and broad command of the concepts discussed during the course, together with a correct, rigorous, and well-organized presentation.

A fair to good performance (22–26/30) will reflect an overall adequate understanding of the main topics, although with limited ability to establish connections among them or with some uncertainty in presentation and application of the concepts.

A sufficient performance (18–21/30) will correspond to an essential knowledge of the course contents and a minimum understanding of the individual notions, sufficient to provide a simple but overall acceptable discussion.

The award of honours (lode) is reserved for outstanding performances, in which the student demonstrates a complete, broad, and critically aware mastery of the course contents, together with the ability to connect the different topics independently and rigorously, to apply the acquired knowledge to non-standard problems and situations, and to present the subject matter with particular clarity, precision, and appropriate scientific language.

The course is mainly organized through the use of PowerPoint presentations. Most lectures follow a teaching-oriented and pedagogical approach, while some are conceived as more advanced scientific seminars. The blackboard is used as a supporting tool whenever needed.

During the semester, group activities and home assignments will also be proposed, with the aim of fostering learning, encouraging active participation, and enabling students to keep up steadily with the topics covered in class. These activities will also help students become progressively more familiar with the types of questions and lines of reasoning that may be required in the final oral examination.

All materials presented during the course, including slides and lecture recordings, are made available on the university Moodle platform, together with specific handouts prepared by the lecturer for the in-depth study of selected topics.

This subject deals with topics related to the macro-area "Climate change and energy" and contributes to the achievement of one or more goals of U. N. Agenda for Sustainable Development