<p> A. La Rosa Lecture Notes APPLIED OPTICS ______2.1 Geometrical Optics: Optics in the regime where the wavelength  0 The electromagnetic spectrum </p><p>From: http://science.hq.nasa.gov/kids/imagers/ems/waves3.html </p><p> radiobroadcasts ( ~ 100 m) microwaves ( ~ mm) visible ( ~ 500 nm ) x-ray (( ~ 1 nm ) gamma-rays (( < 10-3 nm )</p><p>Coarse classification according to the detection systems 1. a) The wavelengths  involved are small compared with the dimensions d of the apparatus involved </p><p>(<<dappartaus). b) The photon energies h are small compared with the energy sensitivity E of the apparatus </p><p>(h <<E appartaus). Under these approximations we can make rough approximation by a method called geometrical optics, which practically omits the wave character of the electromagnetic radiation. That is  is considered practically equal to zero, d  0.</p><p>2. a) The wavelengths  ~ dappartaus (a bit hard to do it with visible light, but easier to implement with microwaves) b) The photon energies h are still small compared with the energy sensitivity E of the apparatus </p><p>(h <<E appartaus). In this case, a very useful approximation can be made considering wave theories, while still disregarding the quantum mechanics character. This is the realm of the classical theory of electromagnetic radiation.</p><p>3. a) For very short wavelengths (right side of the </p><p> spectrum shown above) <<dappartaus b) The photon energies h are large compared with the energy sensitivity E of the apparatus </p><p>(h>>Eapparatus ). This regime constitutes the realm of the photon picture of the light. Geometrical Optics Regime Within this approximation, Light travels out of its source along straight lines or rays Ray path along which light energy is transmitted from one point to another in an optical system.</p>