lecture 2

Lecture 2
THE NATURE OF LIGHT
In this section we will try to understand the concept of light and how it gets from one place to another. The nature of light is a difficult concept to grasp because light sometimes behaves as if it were composed of waves, and other times it behaves as if it were composed of particles.
First we will consider some of the wave properties of light that are relevant to the understanding of lasers.
MAXWELL S EQUATIONS
Maxwell s wave equations, predicting the propagation - even in a vacuum (why is this important?) - of transversely oscillating electromagnetic waves (what does it mean?, were the first indication of the true nature of light. The wave equation, derived from Maxwell’s equations, predicted that the speed c of such a wave in vacuum is c=1/?(?_o ?_o ), where ?_ois the permeability of the vacuum and ?_o is the permittivity of the vacuum.
The fundamental electric and magnetic field vectors E (what is the electric field?) and B (what is the magnetic field?) (respectively) can produce forces on physical entities (what are these forces?). These vectors are measurable quantities that led to the experimentally derived laws of Gauss, Biot-Savart, Ampere, and Faraday. These laws in turn formed the foundation upon which Maxwell built to develop his equations predicting the existence and properties of electromagnetic radiation.
In terms of electromagnetic state of matter the properties below can define the matter in space:
A) The charge density ? (charge per unit volume);
B) The polarization P (electric dipole moment per unit volume (what does it mean?)) in particular for a dielectric material (what is dielectric?);
C) The magnetization M (magnetic dipole moment per unit volume (what does it mean?));
D) The current density J (current per unit area (what does it mean?)).