Optics: principles and applications

Abstract

Visible light constitutes a small, albeit an important, segment of the broad spec- trum of electromagnetic waves encompassing -rays on one extreme and radio waves on the other. Between these two extremes, lie X-rays, ultraviolet radiation, visible light, infrared radiation and microwaves in decreasing order of frequency (Table 1.1). At the present stage of development of the field of optics, it is really not necessary to justify the wave nature of light. Having said that, it must also be mentioned that the original controversy between the two protagonists (Sir Issac Newton and Christian Huygens) representing two schools of thought – light being corpuscular and light having wave nature – took a new twist with the develop- ment of quantum mechanics. Light, like matter, is now understood to have a dual character – the wave-like behavior as well as the particle-like (photon) behavior. Both attributes may not be revealed in a single measurement. Broadly speaking, light propagation in free space and in other media can be described in classical terms whereas light–matter interaction (absorption and emission of light) can be understood only in the quantum mechanical description. In this book, we are primarily concerned with light propagation and hence the classical description in terms of Maxwell’s equations is quite adequate. Maxwell’s equations predict the velocity of propagation of electromagnetic waves in vacuum which is in close agreement with the measured velocity of light. This observation firmly establishes light in the realm of the electromagnetic waves.