Module 1-1 Continued Nature and Properties of Light

Basic Concepts Section 5 The nature of electromagnetic waves Light consists of electromagnetic waves moving through space. Figure 1-3 is a representation of connected electric and magnetic fields, moving from left to right, at one instant of time.

Basic Concepts Section 5 The wave consists of variations in two types of fields in space. In this case, the electric field (E) oscillates vertically to form an electric wave; the magnetic field (B) oscillates horizontally to form a magnetic wave. The two fields are perpendicular to each other, and both are perpendicular to the direction of propagation of the wave. All electromagnetic waves have this same basic composition. They differ only in frequency and wavelength.

Basic Concepts Section 5 Figure 1.3 Three-dimensional model of an electromagnetic wave

Basic Concepts Section 5 The wave consists of variations in two types of fields in space. In this case, the electric field (E) oscillates vertically to form an electric wave; the magnetic field (B) oscillates horizontally to form a magnetic wave. The two fields are perpendicular to each other, and both are perpendicular to the direction of propagation of the wave. All electromagnetic waves have this same basic composition. They differ only in frequency and wavelength.

Basic Concepts Section 5 The span of frequencies and wavelengths covered by electromagnetic radiation is indicated by Figure 1-4a. For example: ◦ radio AM and FM transmitters and receivers operate at frequencies in the 10 3 to 10 7 Hz ◦ X-ray tubes and films are designed for use in the to Hz frequency range.

Basic Concepts Section 5 Lasers generally produce laser light in the frequency and wavelength range indicated by Figure 1-4b. This range includes the spectral regions commonly identified as the infrared, visible, and ultraviolet regions. The human eye responds to the narrow visible region shown in Figure 1-4c, spanning a frequency from 4.3 × Hz to 7.5 × Hz or, correspondingly, from a wavelength of 0.7 × 10 − 6 m to 0.4 × 10 − 6 m

Basic Concepts Section 5

Index of refraction Recall, all electromagnetic (EM) waves travel through a vacuum at the constant speed of c = 3 × 10 8 m/s When these waves travel through a transmitting optical material, however, their speed is reduced.

Basic Concepts Section 5 The index of refraction of a material is the ratio of the speed of light in a vacuum to its speed in that material and is given by Equation 1-8. n = c/ V Equation (1-8) where: n = Index of refraction V = Speed of light inside material c = Speed of light in vacuum

Basic Concepts Section 5 The frequency of a light wave does not change when it enters a material, but its wavelength does change. ◦ Figure 1.5 Wavelength reduction of light passing through a material of refractive index n

Basic Concepts Section 5 The index of refraction is also given by the ratio of wavelength of light in vacuum to the wavelength of light in the material (Eq. 1-9). n = λ o / λ m Equation (1-9) where: λ o = Wavelength in vacuum λ m = Wavelength in material

Basic Concepts Section 5 When light leaves a material of index n and enters a vacuum of index n = 1.0, it returns to speed c and to wavelength λ 0. The index of refraction of air is about but is assumed to be 1.0 in most applications.

Basic Concepts Section 5 Examples 4 and 5 illustrate the application of Equations 1-8 and1-9. Page 18 in text