<s>
Brillouin	B-Algorithm
scattering	I-Algorithm
(	O
also	O
known	O
as	O
Brillouin	O
light	O
scattering	O
or	O
BLS	O
)	O
,	O
named	O
after	O
Léon	O
Brillouin	O
,	O
refers	O
to	O
the	O
interaction	O
of	O
light	O
with	O
the	O
material	O
waves	O
in	O
a	O
medium	O
(	O
e.g.	O
</s>
<s>
It	O
is	O
mediated	O
by	O
the	O
refractive	O
index	O
dependence	O
on	O
the	O
material	O
properties	O
of	O
the	O
medium	O
;	O
as	O
described	O
in	O
optics	B-Algorithm
,	O
the	O
index	O
of	O
refraction	O
of	O
a	O
transparent	O
material	O
changes	O
under	O
deformation	O
(	O
compression-distension	O
or	O
shear-skewing	O
)	O
.	O
</s>
<s>
mass	O
oscillation	O
(	O
acoustic	O
)	O
modes	O
(	O
called	O
phonons	B-Language
)	O
;	O
</s>
<s>
From	O
the	O
perspective	O
of	O
solid	O
state	O
physics	O
,	O
Brillouin	B-Algorithm
scattering	I-Algorithm
is	O
an	O
interaction	O
between	O
an	O
electromagnetic	O
wave	O
and	O
one	O
of	O
the	O
three	O
above-mentioned	O
crystalline	O
lattice	O
waves	O
(	O
e.g.	O
</s>
<s>
the	O
photon	B-Application
may	O
lose	O
energy	O
(	O
Stokes	B-Algorithm
process	O
)	O
and	O
in	O
the	O
process	O
create	O
one	O
of	O
the	O
three	O
quasiparticle	O
types	O
(	O
phonon	B-Language
,	O
polariton	O
,	O
magnon	O
)	O
or	O
it	O
may	O
gain	O
energy	O
(	O
anti-Stokes	O
process	O
)	O
by	O
absorbing	O
one	O
of	O
those	O
quasiparticle	O
types	O
.	O
</s>
<s>
Such	O
a	O
shift	O
in	O
photon	B-Application
energy	O
,	O
corresponding	O
to	O
a	O
Brillouin	B-Algorithm
shift	I-Algorithm
in	O
frequency	O
,	O
is	O
equal	O
to	O
the	O
energy	O
of	O
the	O
released	O
or	O
absorbed	O
quasiparticle	O
.	O
</s>
<s>
Thus	O
,	O
Brillouin	B-Algorithm
scattering	I-Algorithm
can	O
be	O
used	O
to	O
measure	O
the	O
energies	O
,	O
wavelengths	O
and	O
frequencies	O
of	O
various	O
atomic	O
chain	O
oscillation	O
types	O
( 	O
 '	O
quasiparticles	O
 '	O
)	O
.	O
</s>
<s>
To	O
measure	O
a	O
Brillouin	B-Algorithm
shift	I-Algorithm
a	O
commonly	O
employed	O
device	O
called	O
the	O
Brillouin	O
spectrometer	O
is	O
used	O
,	O
the	O
design	O
of	O
which	O
is	O
derived	O
from	O
a	O
Fabry	O
–	O
Pérot	O
interferometer	O
.	O
</s>
<s>
The	O
difference	O
is	O
that	O
Rayleigh	O
scattering	O
involves	O
only	O
the	O
random	O
and	O
incoherent	O
thermal	O
fluctuations	O
,	O
in	O
contrast	O
with	O
the	O
correlated	O
,	O
periodic	O
fluctuations	O
(	O
phonons	B-Language
)	O
that	O
cause	O
Brillouin	B-Algorithm
scattering	I-Algorithm
.	O
</s>
<s>
Raman	B-Architecture
scattering	I-Architecture
is	O
another	O
phenomenon	O
that	O
involves	O
inelastic	O
scattering	O
of	O
light	O
caused	O
by	O
the	O
vibrational	O
properties	O
of	O
matter	O
.	O
</s>
<s>
The	O
detected	O
range	O
of	O
frequency	O
shifts	O
and	O
other	O
effects	O
are	O
very	O
different	O
compared	O
to	O
Brillouin	B-Algorithm
scattering	I-Algorithm
.	O
</s>
<s>
In	O
Raman	B-Architecture
scattering	I-Architecture
,	O
photons	B-Application
are	O
scattered	O
by	O
the	O
effect	O
of	O
vibrational	O
and	O
rotational	O
transitions	O
in	O
the	O
bonds	O
between	O
first-order	O
neighboring	O
atoms	O
,	O
while	O
Brillouin	B-Algorithm
scattering	I-Algorithm
results	O
from	O
the	O
scattering	O
of	O
photons	B-Application
caused	O
by	O
large	O
scale	O
,	O
low-frequency	O
phonons	B-Language
.	O
</s>
<s>
The	O
effects	O
of	O
the	O
two	O
phenomena	O
provide	O
very	O
different	O
information	O
about	O
the	O
sample	O
:	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
can	O
be	O
used	O
to	O
determine	O
the	O
transmitting	O
medium	O
's	O
chemical	O
composition	O
and	O
molecular	O
structure	O
,	O
while	O
Brillouin	B-Algorithm
scattering	I-Algorithm
can	O
be	O
used	O
to	O
measure	O
the	O
material	O
's	O
properties	O
on	O
a	O
larger	O
scale	O
–	O
such	O
as	O
its	O
elastic	O
behavior	O
.	O
</s>
<s>
The	O
frequency	O
shifts	O
from	O
Brillouin	B-Algorithm
scattering	I-Algorithm
,	O
a	O
technique	O
known	O
as	O
Brillouin	O
spectroscopy	O
,	O
are	O
detected	O
with	O
an	O
interferometer	O
while	O
Raman	B-Architecture
scattering	I-Architecture
uses	O
either	O
an	O
interferometer	O
or	O
a	O
dispersive	O
(	O
grating	O
)	O
spectrometer	O
.	O
</s>
<s>
laser	O
)	O
traveling	O
in	O
a	O
medium	O
or	O
in	O
a	O
waveguide	O
,	O
such	O
as	O
an	O
optical	B-Architecture
fiber	I-Architecture
,	O
the	O
variations	O
in	O
the	O
electric	O
field	O
of	O
the	O
beam	O
itself	O
may	O
induce	O
acoustic	O
vibrations	O
in	O
the	O
medium	O
via	O
electrostriction	O
or	O
radiation	O
pressure	O
.	O
</s>
<s>
The	O
beam	O
may	O
display	O
Brillouin	B-Algorithm
scattering	I-Algorithm
as	O
a	O
result	O
of	O
those	O
vibrations	O
,	O
usually	O
in	O
the	O
direction	O
opposite	O
the	O
incoming	O
beam	O
,	O
a	O
phenomenon	O
known	O
as	O
stimulated	B-Algorithm
Brillouin	I-Algorithm
scattering	I-Algorithm
(	O
SBS	O
)	O
.	O
</s>
<s>
Stimulated	B-Algorithm
Brillouin	I-Algorithm
scattering	I-Algorithm
is	O
one	O
effect	O
by	O
which	O
optical	O
phase	O
conjugation	O
can	O
take	O
place	O
.	O
</s>
<s>
In	O
order	O
to	O
credit	O
Mandelstam	O
,	O
the	O
effect	O
is	O
also	O
called	O
Brillouin-Mandelstam	B-Algorithm
scattering	I-Algorithm
(	O
BMS	O
)	O
.	O
</s>
<s>
The	O
process	O
of	O
stimulated	B-Algorithm
Brillouin	I-Algorithm
scattering	I-Algorithm
(	O
SBS	O
)	O
was	O
first	O
observed	O
by	O
Chiao	O
et	O
al	O
.	O
</s>
<s>
Brillouin	B-Algorithm
scattering	I-Algorithm
can	O
also	O
be	O
employed	O
to	O
sense	O
mechanical	O
strain	O
and	O
temperature	O
in	O
optical	B-Architecture
fibers	I-Architecture
.	O
</s>
