Table 353. 



OPTICAL CONSTANTS OF METALS. 



TABLE 363. 



295 



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

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

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



any distance d, i : e — rj-. for the same wave-length measured in air this ratio becomes i : e JS~ . 



nk 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, 1889), 



_ , o-v , sin ^ tan A , , , „_, 



k = tan 21/, (i — cot %) and n= t T. 1.2^ ^' "^" 2 cot^,;,). 



For rougher approximations the factor in parentheses may be omitted. R = computed per- 

 centage reflection. 



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

 of the metal.) 



I 



r 



Drude, Annalen der Physik und Chemie, 39, p. 481, 1890; 4a, p. 186, 1891 ; 64, p. 159, 189S. Minor, Annalen 

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

 1910; Forsterling and Freedericksz, Annalen der Physik, 40, p. aoi, 1913. 



Smithsonian Tables. 



