<s>
Optical	B-Algorithm
conductivity	I-Algorithm
is	O
the	O
property	O
of	O
a	O
material	O
which	O
gives	O
the	O
relationship	O
between	O
the	O
induced	O
current	O
density	O
in	O
the	O
material	O
and	O
the	O
magnitude	O
of	O
the	O
inducing	O
electric	O
field	O
for	O
arbitrary	O
frequencies	O
.	O
</s>
<s>
While	O
the	O
static	O
electrical	O
conductivity	O
is	O
vanishingly	O
small	O
in	O
insulators	O
(	O
such	O
as	O
diamond	O
or	O
porcelain	O
)	O
,	O
the	O
optical	B-Algorithm
conductivity	I-Algorithm
always	O
remains	O
finite	O
in	O
some	O
frequency	O
intervals	O
(	O
above	O
the	O
optical	O
gap	O
in	O
the	O
case	O
of	O
insulators	O
)	O
.	O
</s>
<s>
The	O
optical	B-Algorithm
conductivity	I-Algorithm
is	O
closely	O
related	O
to	O
the	O
dielectric	O
function	O
,	O
the	O
generalization	O
of	O
the	O
dielectric	O
constant	O
to	O
arbitrary	O
frequencies	O
.	O
</s>
<s>
In	O
this	O
approximation	O
,	O
the	O
electric	O
current	O
density	O
(	O
a	O
three-dimensional	O
vector	O
)	O
,	O
the	O
scalar	O
optical	B-Algorithm
conductivity	I-Algorithm
and	O
the	O
electric	O
field	O
vector	O
are	O
linked	O
by	O
the	O
equation	O
:	O
</s>
<s>
The	O
optical	B-Algorithm
conductivity	I-Algorithm
is	O
most	O
often	O
measured	O
in	O
optical	O
frequency	O
ranges	O
via	O
the	O
reflectivity	O
of	O
polished	O
samples	O
under	O
normal	O
incidence	O
(	O
in	O
combination	O
with	O
a	O
Kramers	O
–	O
Kronig	O
analysis	O
)	O
or	O
using	O
variable	O
incidence	O
angles	O
.	O
</s>
