Table 421 

 OPTICAL CONSTANTS OF METALS 



377 



Two constants are required to characterize a metal optically, the refractive index, n., and the 

 absorption index, k, the latter of which has the following significance: the amplitude of a wave 

 after travelling one wave-length, A 1 measured in the metal, is reduced in the ratio 1 i :e~ 2,rk or for 



27rdk , , , . ...... , 27rdnk 



any distance d, i : e — vv~. for the same wave-length measured in air this ratio becomes I : e \T~ . 



ttk is sometimes called the extinction coefficient. Plane polarized light reflected from a polished 

 metal surface is in general elliptically polarized because of the relative change in phase between 

 the two rectangular components vibrating in and perpendicular to the plane of incidence. For a 

 certain angle, $ (principal incidence) the change is 90 and if the plane polarized incident beam 

 has a certain azimuth ^ (Principal azimuth) circularly polarized light results. Approximately, 

 (Drude, Annalen der Physik, 36, p. 546, 18S9), 



n- > 1 sin di tan <j> , , „_, 



k = tan 24, ([ — cot 2 <j>) and 11= /t J_i,g\ i ( ! +2 cot 2 4,). 



(i + k 2 )i 



For rougher approximations the factor in parentheses may be omitted, 

 centage reflection. 



R = computed per- 



(The points have been so selected that a smooth curve drawn through them very closely indicates the characteristics 

 of the metal.) 



Drude, Annalen der Physik und Chemie, 39, p. 481, 1890; 42, p. 186, 1891 ; 64, p. 159, 1898. Minor, Annaleu 

 der Physik, 10, p. 581, 1903. Tool, Physical Review, 31, p. 1, 1910. Ingersoll, Astrophysical Journal, 32, p. 265, 

 1910; Forsterling and Fr^edericksz, Annalen der Physik, 40, p. 201, 1913. 



Smithsonian Tables. 



