
50-1
50.1 Introduction
Light is electromagnetic radiation of wavelength about 450–700 nm, in which region the human eye is
sen
sitive
an
d
re
fractive
in
dex
me
asurements
ar
e
co
mmonly
ma
de
.
e re
fractive
in
dex
or in
dices
of a
su
bstance
de
scribe
an im
portant
pa
rt
of it
s
in
teraction
wi
th
el
ectromagnetic
ra
diation
.
Re
fractive
in
dex
is a di
mensionless
qu
antity,
re
al
fo
r
tr
ansparent
ma
terials
an
d
co
mplex
if th
ere
is ab
sorption
.
It ge
ner-
ally
de
pends
on th
e
di
rection
of li
ght
re
lative
to ax
es
of th
e
ma
terial;
su
ch
su
bstances,
fo
r
ex
ample,
ma
ny
cr
ystals,
ar
e
an
isotropic
an
d
po
ssess
mo
re
th
an
on
e
re
fractive
in
dex
. In ge
neral,
th
e
in
dex
is a te
nsor
(3 × 3 ...