These notes follow the lecture 'Quantum Electronics' taught by Prof. Gallmann in 2025, as well as the book Fundamentals of Photonics. This course is covered because I have to teach it. It can be seen as the introduction to Ultrafast Laser Physics. Many excellent gifs have been taken from Maxwell2D unless specified otherwise.

Table of Contents

Light is fundamental to life. It enables vision, drives photosynthesis, and governs countless natural processes. In this course, we will approach light not as a stream of particles but as a wave, a perspective that allows us to understand its behaviour in materials, its interaction with matter, and its technological applications.

Light originates from accelerating charges, primarily electrons, and manifests across a vast spectrum. As it propagates through different media, its optical properties—such as reflection, refraction, diffraction, and interference—emerge from its wave nature. These properties form the foundation of optics, which can be structured hierarchically: ray optics as an approximation of wave optics, which in turn is a subset of electromagnetic optics, all of which ultimately stem from quantum optics.

Quantum electronics focuses on the generation, manipulation, and application of coherent electromagnetic waves through quantum mechanical principles. The most notable example is the laser, a device that harnesses stimulated emission to produce highly directional, monochromatic, and coherent light. This course will explore the quantum mechanical basis of such devices and their applications.

We will primarily work with wavelengths in the visible and infrared range, spanning approximately $400\mathrm{nm}$ to $10\mu \mathrm{m}$, with photon energies ranging from about $0.1\mathrm{eV}$ to a few $\mathrm{eV}$. These scales are crucial for understanding optical and optoelectronic devices, including semiconductor lasers, modulators, and detectors.

The course progresses from field theory to devices. Maxwell's equations and material response define wave propagation; interfaces, diffraction, resonators, and guided modes define how fields are shaped; and the laser chapters connect those field concepts to gain, feedback, and coherent light generation.

Table of Contents

1 Electromagnetic Theory of Light
2 Propagation in Dispersive Media
3 Reflection and Transmission at Interfaces
4 Coherence and Interference
5 Fourier Optics
6 Beam Types
7 Optical Resonators
8 Laser Fundamentals
9 Polarisation Optics
10 Waveguides