Konijnenberg A.P., Adam A.J.L., Urbach H.P. Bachelor Applied Physics

Second Edition. — TU Delft Open, 2024. — 288 p. — ISBN 978-94-6366-847-7; ISBN 978-94-6366-846-0.This book is about optics for advanced undergraduate and beginning graduate students of physics, electrical engineering and related fields. As a student of these subjects you are probably already familiar with many concepts of optics and the nature of light. You may remember Snell’s law of refraction, the lens formula, ray tracing and interference fringes as observed in the double-slit experiment. By now you have also learned that from Maxwell’s equations one can derive that light consists of electromagnetic waves, that its speed c was found to be constant, which resulted in the development of the theory of relativity, and that light exhibits a wave-particle duality that is explained by the De Broglie hypothesis in quantum mechanics. Although this is already a rather sizeable body of knowledge, there is still a lot to learn about optics. However, many of the important topics of optics do not require knowledge of quantum mechanics or even Maxwell’s equations. Instead, they concern approximate theories and models of the behaviour of light which are sufficiently advanced to explain the phenomena and sufficiently simple so that explicit computations of (approximate) solutions are possible. Using simplified models such a geometrical optics to study problems leads to approaches that differ quite substantially from applying more rigorous theories such as Maxwell’s equations. However, the simplified model give in many circumstances more insight in the physical phenomena and furthermore Maxwell’s equations are much too complicated to apply to macroscopic imaging systems in microscopy, lithography or astronomy. This will remain the case for a long time to come in spite of increasing computer resources. When studying different approximate models it is essential to understand their hierarchy and the limits of validity of the approximations made.
Maybe you wonder why you will learn to apply theories which are from the fundamental point of view not correct. But remember that in the end all of physics is merely a model that tries to describe reality. Some models, which tend to be more complex, are more accurate than others, but depending on the phenomena we want to predict, a simpler, less accurate model may suffice.
For example in many practical cases, such as the modelling of imaging formation in cameras, geometrical optics is already sufficiently accurate and a model based on Maxwell’s equations or even a model based on the scalar wave equation would be too computationally demanding. From a pedagogical point of view, it surely seems preferable to learn the simpler model prior to learning the more accurate model.