ABSTRACT
The nature of light is one of the most difficult concepts in modern physics. Due to its quantum nature, light has to be considered in some experiments as an electromagnetic wave, and in some others it has to be considered as a particle. However, in ordinary optical instruments we may just think of the light as an electromagnetic wave with an electric field and a magnetic field, mutually perpendicular, and both perpendicular to the path of propagation. If the light beam is plane (linearly) polarized, the electric and the magnetic fields have a constant fixed orientation, changing only in magnitude and sign as the wave propagates. The electric and magnetic fields are in phase with each other, as shown in Fig. 1.1. This is the simplest type of wave, but we may find more complicated light beams, where the electric and magnetic fields do not oscillate in a fixed plane. The different manners in which the fields change direction along the light trajectory are called polarization states. It is shown in any physical optics textbook that any polarization state may be considered as a superposition of two mutually perpendicular planepolarized light beams. The type of polarization depends on the phase difference between the two components and on their relative amplitudes as explained in any physical optics textbook. The frequency and the wavelength l of this wave are related by the speed of propagation v as follows
¼ v ð1:1Þ
Light waves with different frequencies have different colors, corresponding to certain wavelengths in the vacuum. In lens design the frequencies (or corresponding wavelengths in the vacuum) for the solar Fraunhofer lines are used to define the color of the light. These lines are shown in the Table 1.1.
