13.2.The Optical Constants 249 and E2=2nk. (13.12) e is called polarization whereas e2 is known by the name ab- sorption.Values for n and k for some materials are given in Table 13.1.For insulators,k is nearly zero,which yields for dielectrics e1≈n2ande2→0. When electromagnetic radiation (e.g.,light)passes from vac- uum (or air)into an optically denser material,then the ampli- tude of the wave decreases exponentially with increasing damp- ing constant k and for increasing distance,z,from the surface, as shown in Figure 13.2.Specifically,the intensity,I,of the light (that is,the square of the electric field strength,)obeys the fol- lowing equation(which can be derived from the Maxwell equa- tions): 1=82=106 (13.13) TABLE 13.1.Optical constants for some materials (A 600 nm) 么 k R%ob Metals Copper 0.14 3.35 95.6 Silver 0.05 4.09 98.9 Gold 0.21 3.24 92.9 Aluminum 0.97 6.0 90.3 Ceramics Silica glass (Vycor) 1.46 3.50 Soda-lime glass 1.51 4.13 Dense flint glass 1.75 a 7.44 Quartz 1.55 4.65 Al203 1.76 7.58 Polymers Polyethylene 1.51 4.13 Polystyrene 1.60 5.32 Polytetrafluoroethylene 1.35 2.22 Semiconductors Silicon 3.94 0.025 35.42 GaAs 3.91 0.228 35.26 "The damping constant for dielectrics is about 10-7;see Table 13.2. bThe reflection is considered to have occurred on one reflecting surface only. See also Table 15.1.and 2
2nk. (13.12) 1 is called polarization whereas 2 is known by the name ab￾sorption. Values for n and k for some materials are given in Table 13.1. For insulators, k is nearly zero, which yields for dielectrics 1
n2 and 2
0. When electromagnetic radiation (e.g., light) passes from vac￾uum (or air) into an optically denser material, then the ampli￾tude of the wave decreases exponentially with increasing damp￾ing constant k and for increasing distance, z, from the surface, as shown in Figure 13.2. Specifically, the intensity, I, of the light (that is, the square of the electric field strength,
) obeys the fol￾lowing equation (which can be derived from the Maxwell equa￾tions): I

2
I0 exp  4 c k z  . (13.13) 13.2 • The Optical Constants 249 TABLE 13.1. Optical constants for some materials (
600 nm) n kR %b Metals Copper 0.14 3.35 95.6 Silver 0.05 4.09 98.9 Gold 0.21 3.24 92.9 Aluminum 0.97 6.0 90.3 Ceramicsc Silica glass (Vycor) 1.46 a 3.50 Soda-lime glass 1.51 a 4.13 Dense flint glass 1.75 a 7.44 Quartz 1.55 a 4.65 Al2O3 1.76 a 7.58 Polymers Polyethylene 1.51 a 4.13 Polystyrene 1.60 a 5.32 Polytetrafluoroethylene 1.35 a 2.22 Semiconductors Silicon 3.94 0.025 35.42 GaAs 3.91 0.228 35.26 aThe damping constant for dielectrics is about 107; see Table 13.2. bThe reflection is considered to have occurred on one reflecting surface only. cSee also Table 15.1.