<s>
Raman	B-Algorithm
spectroscopy	I-Algorithm
(	O
)	O
(	O
named	O
after	O
Indian	O
physicist	O
C	O
.	O
V	O
.	O
Raman	O
)	O
is	O
a	O
spectroscopic	O
technique	O
typically	O
used	O
to	O
determine	O
vibrational	O
modes	O
of	O
molecules	O
,	O
although	O
rotational	O
and	O
other	O
low-frequency	O
modes	O
of	O
systems	O
may	O
also	O
be	O
observed	O
.	O
</s>
<s>
Raman	B-Algorithm
spectroscopy	I-Algorithm
is	O
commonly	O
used	O
in	O
chemistry	O
to	O
provide	O
a	O
structural	O
fingerprint	O
by	O
which	O
molecules	O
can	O
be	O
identified	O
.	O
</s>
<s>
Raman	B-Algorithm
spectroscopy	I-Algorithm
relies	O
upon	O
inelastic	O
scattering	O
of	O
photons	B-Application
,	O
known	O
as	O
Raman	B-Architecture
scattering	I-Architecture
.	O
</s>
<s>
A	O
source	O
of	O
monochromatic	O
light	O
,	O
usually	O
from	O
a	O
laser	O
in	O
the	O
visible	O
,	O
near	O
infrared	O
,	O
or	O
near	B-Application
ultraviolet	I-Application
range	O
is	O
used	O
,	O
although	O
X-rays	O
can	O
also	O
be	O
used	O
.	O
</s>
<s>
The	O
laser	O
light	O
interacts	O
with	O
molecular	O
vibrations	O
,	O
phonons	B-Language
or	O
other	O
excitations	O
in	O
the	O
system	O
,	O
resulting	O
in	O
the	O
energy	O
of	O
the	O
laser	O
photons	B-Application
being	O
shifted	O
up	O
or	O
down	O
.	O
</s>
<s>
Spontaneous	O
Raman	B-Architecture
scattering	I-Architecture
is	O
typically	O
very	O
weak	O
;	O
as	O
a	O
result	O
,	O
for	O
many	O
years	O
the	O
main	O
difficulty	O
in	O
collecting	O
Raman	O
spectra	O
was	O
separating	O
the	O
weak	O
inelastically	O
scattered	O
light	O
from	O
the	O
intense	O
Rayleigh	O
scattered	O
laser	O
light	O
(	O
referred	O
to	O
as	O
"	O
laser	O
rejection	O
"	O
)	O
.	O
</s>
<s>
Historically	O
,	O
Raman	B-Algorithm
spectrometers	I-Algorithm
used	O
holographic	B-Algorithm
gratings	I-Algorithm
and	O
multiple	O
dispersion	O
stages	O
to	O
achieve	O
a	O
high	O
degree	O
of	O
laser	O
rejection	O
.	O
</s>
<s>
Dispersive	O
single-stage	O
spectrographs	O
(	O
axial	O
transmissive	O
(	O
AT	O
)	O
or	O
Czerny	O
–	O
Turner	O
(	O
CT	O
)	O
monochromators	O
)	O
paired	O
with	O
CCD	B-Algorithm
detectors	O
are	O
most	O
common	O
although	O
Fourier	O
transform	O
(	O
FT	O
)	O
spectrometers	O
are	O
also	O
common	O
for	O
use	O
with	O
NIR	O
lasers	O
.	O
</s>
<s>
The	O
name	O
"	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
"	O
typically	O
refers	O
to	O
vibrational	O
Raman	O
using	O
laser	O
wavelengths	O
which	O
are	O
not	O
absorbed	O
by	O
the	O
sample	O
.	O
</s>
<s>
There	O
are	O
many	O
other	O
variations	O
of	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
including	O
surface-enhanced	B-Algorithm
Raman	I-Algorithm
,	O
resonance	B-Algorithm
Raman	I-Algorithm
,	O
tip-enhanced	B-Algorithm
Raman	I-Algorithm
,	O
polarized	O
Raman	O
,	O
stimulated	O
Raman	O
,	O
transmission	B-Algorithm
Raman	I-Algorithm
,	O
spatially-offset	O
Raman	O
,	O
and	O
hyper	O
Raman	O
.	O
</s>
<s>
The	O
Raman	B-Architecture
effect	I-Architecture
was	O
named	O
after	O
one	O
of	O
its	O
discoverers	O
,	O
the	O
Indian	O
scientist	O
C	O
.	O
V	O
.	O
Raman	O
,	O
who	O
observed	O
the	O
effect	O
in	O
organic	O
liquids	O
in	O
1928	O
together	O
with	O
K	O
.	O
S	O
.	O
Krishnan	O
,	O
and	O
independently	O
by	O
Grigory	O
Landsberg	O
and	O
Leonid	O
Mandelstam	O
in	O
inorganic	O
crystals	O
.	O
</s>
<s>
Systematic	O
pioneering	O
theory	O
of	O
the	O
Raman	B-Architecture
effect	I-Architecture
was	O
developed	O
by	O
Czechoslovak	O
physicist	O
George	O
Placzek	O
between	O
1930	O
and	O
1934	O
.	O
</s>
<s>
In	O
the	O
years	O
following	O
its	O
discovery	O
,	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
was	O
used	O
to	O
provide	O
the	O
first	O
catalog	O
of	O
molecular	O
vibrational	O
frequencies	O
.	O
</s>
<s>
The	O
photons	B-Application
that	O
were	O
scattered	O
by	O
the	O
sample	O
were	O
collected	O
through	O
an	O
optical	O
flat	O
at	O
the	O
end	O
of	O
the	O
tube	O
.	O
</s>
<s>
The	O
magnitude	O
of	O
the	O
Raman	B-Architecture
effect	I-Architecture
correlates	O
with	O
polarizability	O
of	O
the	O
electrons	O
in	O
a	O
molecule	O
.	O
</s>
<s>
It	O
is	O
a	O
form	O
of	O
inelastic	B-Architecture
light	I-Architecture
scattering	I-Architecture
,	O
where	O
a	O
photon	B-Application
excites	O
the	O
sample	O
.	O
</s>
<s>
This	O
excitation	O
puts	O
the	O
molecule	O
into	O
a	O
virtual	O
energy	O
state	O
for	O
a	O
short	O
time	O
before	O
the	O
photon	B-Application
is	O
emitted	O
.	O
</s>
<s>
Inelastic	O
scattering	O
means	O
that	O
the	O
energy	O
of	O
the	O
emitted	O
photon	B-Application
is	O
of	O
either	O
lower	O
or	O
higher	O
energy	O
than	O
the	O
incident	O
photon	B-Application
.	O
</s>
<s>
For	O
the	O
total	O
energy	O
of	O
the	O
system	O
to	O
remain	O
constant	O
after	O
the	O
molecule	O
moves	O
to	O
a	O
new	O
rovibronic	O
(	O
rotational	O
–	O
vibrational	O
–	O
electronic	O
)	O
state	O
,	O
the	O
scattered	O
photon	B-Application
shifts	O
to	O
a	O
different	O
energy	O
,	O
and	O
therefore	O
a	O
different	O
frequency	O
.	O
</s>
<s>
If	O
the	O
final	O
state	O
is	O
higher	O
in	O
energy	O
than	O
the	O
initial	O
state	O
,	O
the	O
scattered	O
photon	B-Application
will	O
be	O
shifted	O
to	O
a	O
lower	O
frequency	O
(	O
lower	O
energy	O
)	O
so	O
that	O
the	O
total	O
energy	O
remains	O
the	O
same	O
.	O
</s>
<s>
This	O
shift	O
in	O
frequency	O
is	O
called	O
a	O
Stokes	B-Algorithm
shift	I-Algorithm
,	O
or	O
downshift	O
.	O
</s>
<s>
If	O
the	O
final	O
state	O
is	O
lower	O
in	O
energy	O
,	O
the	O
scattered	O
photon	B-Application
will	O
be	O
shifted	O
to	O
a	O
higher	O
frequency	O
,	O
which	O
is	O
called	O
an	O
anti-Stokes	O
shift	O
,	O
or	O
upshift	O
.	O
</s>
<s>
For	O
a	O
molecule	O
to	O
exhibit	O
a	O
Raman	B-Architecture
effect	I-Architecture
,	O
there	O
must	O
be	O
a	O
change	O
in	O
its	O
electric	O
dipole-electric	O
dipole	O
polarizability	O
with	O
respect	O
to	O
the	O
vibrational	O
coordinate	O
corresponding	O
to	O
the	O
rovibronic	O
state	O
.	O
</s>
<s>
The	O
intensity	O
of	O
the	O
Raman	B-Architecture
scattering	I-Architecture
is	O
proportional	O
to	O
this	O
polarizability	O
change	O
.	O
</s>
<s>
Therefore	O
,	O
the	O
Raman	B-Algorithm
spectrum	I-Algorithm
(	O
scattering	O
intensity	O
as	O
a	O
function	O
of	O
the	O
frequency	O
shifts	O
)	O
depends	O
on	O
the	O
rovibronic	O
states	O
of	O
the	O
molecule	O
.	O
</s>
<s>
The	O
Raman	B-Architecture
effect	I-Architecture
is	O
based	O
on	O
the	O
interaction	O
between	O
the	O
electron	O
cloud	O
of	O
a	O
sample	O
and	O
the	O
external	O
electric	O
field	O
of	O
the	O
monochromatic	O
light	O
,	O
which	O
can	O
create	O
an	O
induced	O
dipole	O
moment	O
within	O
the	O
molecule	O
based	O
on	O
its	O
polarizability	O
.	O
</s>
<s>
The	O
Raman	B-Architecture
effect	I-Architecture
should	O
not	O
be	O
confused	O
with	O
emission	O
(	O
fluorescence	O
or	O
phosphorescence	O
)	O
,	O
where	O
a	O
molecule	O
in	O
an	O
excited	O
electronic	O
state	O
emits	O
a	O
photon	B-Application
and	O
returns	O
to	O
the	O
ground	O
electronic	O
state	O
,	O
in	O
many	O
cases	O
to	O
a	O
vibrationally	O
excited	O
state	O
on	O
the	O
ground	O
electronic	O
state	O
potential	O
energy	O
surface	O
.	O
</s>
<s>
Raman	B-Architecture
scattering	I-Architecture
also	O
contrasts	O
with	O
infrared	O
(	O
IR	O
)	O
absorption	O
,	O
where	O
the	O
energy	O
of	O
the	O
absorbed	O
photon	B-Application
matches	O
the	O
difference	O
in	O
energy	O
between	O
the	O
initial	O
and	O
final	O
rovibronic	O
states	O
.	O
</s>
<s>
This	O
contrasting	O
feature	O
allows	O
rovibronic	O
transitions	O
that	O
might	O
not	O
be	O
active	O
in	O
IR	O
to	O
be	O
analyzed	O
using	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
,	O
as	O
exemplified	O
by	O
the	O
rule	O
of	O
mutual	O
exclusion	O
in	O
centrosymmetric	O
molecules	O
.	O
</s>
<s>
They	O
all	O
give	O
the	O
same	O
frequency	O
for	O
a	O
given	O
vibrational	O
transition	O
,	O
but	O
the	O
relative	O
intensities	O
provide	O
different	O
information	O
due	O
to	O
the	O
different	O
types	O
of	O
interaction	O
between	O
the	O
molecule	O
and	O
the	O
incoming	O
particles	O
,	O
photons	B-Application
for	O
IR	O
and	O
Raman	O
,	O
and	O
neutrons	O
for	O
IINS	O
.	O
</s>
<s>
In	O
order	O
to	O
convert	O
between	O
spectral	O
wavelength	O
and	O
wavenumbers	O
of	O
shift	O
in	O
the	O
Raman	B-Algorithm
spectrum	I-Algorithm
,	O
the	O
following	O
formula	O
can	O
be	O
used	O
:	O
</s>
<s>
where	O
is	O
the	O
Raman	O
shift	O
expressed	O
in	O
wavenumber	O
,	O
is	O
the	O
excitation	O
wavelength	O
,	O
and	O
is	O
the	O
Raman	B-Algorithm
spectrum	I-Algorithm
wavelength	O
.	O
</s>
<s>
Modern	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
nearly	O
always	O
involves	O
the	O
use	O
of	O
lasers	O
as	O
excitation	O
light	O
sources	O
.	O
</s>
<s>
Because	O
lasers	O
were	O
not	O
available	O
until	O
more	O
than	O
three	O
decades	O
after	O
the	O
discovery	O
of	O
the	O
effect	O
,	O
Raman	O
and	O
Krishnan	O
used	O
a	O
mercury	O
lamp	O
and	O
photographic	B-Algorithm
plates	I-Algorithm
to	O
record	O
spectra	O
.	O
</s>
<s>
Early	O
spectra	O
took	O
hours	O
or	O
even	O
days	O
to	O
acquire	O
due	O
to	O
weak	O
light	O
sources	O
,	O
poor	O
sensitivity	O
of	O
the	O
detectors	O
and	O
the	O
weak	O
Raman	B-Architecture
scattering	I-Architecture
cross-sections	O
of	O
most	O
materials	O
.	O
</s>
<s>
Technological	O
advances	O
have	O
made	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
much	O
more	O
sensitive	O
,	O
particularly	O
since	O
the	O
1980s	O
.	O
</s>
<s>
The	O
most	O
common	O
modern	O
detectors	O
are	O
now	O
charge-coupled	B-Algorithm
devices	I-Algorithm
(	O
CCDs	O
)	O
.	O
</s>
<s>
Photodiode	O
arrays	O
and	O
photomultiplier	B-Algorithm
tubes	I-Algorithm
were	O
common	O
prior	O
to	O
the	O
adoption	O
of	O
CCDs	O
.	O
</s>
<s>
Raman	B-Algorithm
spectroscopy	I-Algorithm
requires	O
a	O
light	O
source	O
such	O
as	O
a	O
laser	O
.	O
</s>
<s>
Generally	O
shorter	O
wavelength	O
lasers	O
give	O
stronger	O
Raman	B-Architecture
scattering	I-Architecture
due	O
to	O
the	O
4	O
increase	O
in	O
Raman	B-Architecture
scattering	I-Architecture
cross-sections	O
,	O
but	O
issues	O
with	O
sample	O
degradation	O
or	O
fluorescence	O
may	O
result	O
.	O
</s>
<s>
Continuous	O
wave	O
lasers	O
are	O
most	O
common	O
for	O
normal	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
,	O
but	O
pulsed	O
lasers	O
may	O
also	O
be	O
used	O
.	O
</s>
<s>
These	O
often	O
have	O
wider	O
bandwidths	O
than	O
their	O
CW	O
counterparts	O
but	O
are	O
very	O
useful	O
for	O
other	O
forms	O
of	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
such	O
as	O
transient	O
,	O
time-resolved	O
and	O
resonance	B-Algorithm
Raman	I-Algorithm
.	O
</s>
<s>
In	O
most	O
cases	O
,	O
modern	O
Raman	B-Algorithm
spectrometers	I-Algorithm
use	O
array	O
detectors	O
such	O
as	O
CCDs	O
.	O
</s>
<s>
Intensified	B-Algorithm
CCDs	I-Algorithm
can	O
be	O
used	O
for	O
very	O
weak	O
signals	O
and/or	O
pulsed	O
lasers	O
.	O
</s>
<s>
The	O
spectral	O
range	O
depends	O
on	O
the	O
size	O
of	O
the	O
CCD	B-Algorithm
and	O
the	O
focal	O
length	O
of	O
spectrograph	O
used	O
.	O
</s>
<s>
It	O
was	O
once	O
common	O
to	O
use	O
monochromators	O
coupled	O
to	O
photomultiplier	B-Algorithm
tubes	I-Algorithm
.	O
</s>
<s>
Germanium	B-Algorithm
or	O
Indium	O
gallium	O
arsenide	O
(	O
InGaAs	O
)	O
detectors	O
are	O
commonly	O
used	O
.	O
</s>
<s>
Notch	O
or	O
long-pass	B-Algorithm
optical	O
filters	O
are	O
typically	O
used	O
for	O
this	O
purpose	O
.	O
</s>
<s>
However	O
,	O
Volume	B-Algorithm
hologram	I-Algorithm
filters	O
are	O
becoming	O
more	O
common	O
which	O
allow	O
shifts	O
as	O
low	O
as	O
5cm−1	O
to	O
be	O
observed	O
.	O
</s>
<s>
Raman	B-Algorithm
spectroscopy	I-Algorithm
is	O
used	O
in	O
chemistry	O
to	O
identify	O
molecules	O
and	O
study	O
chemical	O
bonding	O
and	O
intramolecular	O
bonds	O
.	O
</s>
<s>
In	O
solid-state	O
physics	O
,	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
is	O
used	O
to	O
characterize	O
materials	O
,	O
measure	O
temperature	O
,	O
and	O
find	O
the	O
crystallographic	O
orientation	O
of	O
a	O
sample	O
.	O
</s>
<s>
As	O
with	O
single	O
molecules	O
,	O
a	O
solid	O
material	O
can	O
be	O
identified	O
by	O
characteristic	O
phonon	B-Language
modes	O
.	O
</s>
<s>
Information	O
on	O
the	O
population	O
of	O
a	O
phonon	B-Language
mode	O
is	O
given	O
by	O
the	O
ratio	O
of	O
the	O
Stokes	O
and	O
anti-Stokes	O
intensity	O
of	O
the	O
spontaneous	O
Raman	O
signal	O
.	O
</s>
<s>
Raman	B-Algorithm
spectroscopy	I-Algorithm
can	O
also	O
be	O
used	O
to	O
observe	O
other	O
low	O
frequency	O
excitations	O
of	O
a	O
solid	O
,	O
such	O
as	O
plasmons	O
,	O
magnons	O
,	O
and	O
superconducting	O
gap	O
excitations	O
.	O
</s>
<s>
Distributed	B-Algorithm
temperature	I-Algorithm
sensing	I-Algorithm
(	O
DTS	O
)	O
uses	O
the	O
Raman-shifted	O
backscatter	O
from	O
laser	O
pulses	O
to	O
determine	O
the	O
temperature	O
along	O
optical	O
fibers	O
.	O
</s>
<s>
Raman	O
active	O
fibers	O
,	O
such	O
as	O
aramid	O
and	O
carbon	O
,	O
have	O
vibrational	O
modes	O
that	O
show	O
a	O
shift	O
in	O
Raman	B-Algorithm
frequency	I-Algorithm
with	O
applied	O
stress	O
.	O
</s>
<s>
In	O
solid	O
state	O
chemistry	O
and	O
the	O
bio-pharmaceutical	O
industry	O
,	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
can	O
be	O
used	O
to	O
not	O
only	O
identify	O
active	O
pharmaceutical	O
ingredients	O
(	O
APIs	O
)	O
,	O
but	O
to	O
identify	O
their	O
polymorphic	O
forms	O
,	O
if	O
more	O
than	O
one	O
exist	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
drug	O
Cayston	O
(	O
aztreonam	O
)	O
,	O
marketed	O
by	O
Gilead	O
Sciences	O
for	O
cystic	O
fibrosis	O
,	O
can	O
be	O
identified	O
and	O
characterized	O
by	O
IR	O
and	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
.	O
</s>
<s>
Raman	B-Algorithm
spectroscopy	I-Algorithm
has	O
a	O
wide	O
variety	O
of	O
applications	O
in	O
biology	O
and	O
medicine	O
.	O
</s>
<s>
It	O
has	O
helped	O
confirm	O
the	O
existence	O
of	O
low-frequency	O
phonons	B-Language
in	O
proteins	O
and	O
DNA	O
,	O
promoting	O
studies	O
of	O
low-frequency	O
collective	O
motion	O
in	O
proteins	O
and	O
DNA	O
and	O
their	O
biological	O
functions	O
.	O
</s>
<s>
Raman	B-Algorithm
spectroscopy	I-Algorithm
has	O
also	O
been	O
used	O
as	O
a	O
noninvasive	O
technique	O
for	O
real-time	O
,	O
in	O
situ	O
biochemical	O
characterization	O
of	O
wounds	O
.	O
</s>
<s>
Spatially	B-Algorithm
offset	I-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
(	O
SORS	O
)	O
,	O
which	O
is	O
less	O
sensitive	O
to	O
surface	O
layers	O
than	O
conventional	O
Raman	O
,	O
can	O
be	O
used	O
to	O
discover	O
counterfeit	O
drugs	O
without	O
opening	O
their	O
packaging	O
,	O
and	O
to	O
non-invasively	O
study	O
biological	O
tissue	O
.	O
</s>
<s>
A	O
reason	O
why	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
is	O
useful	O
in	O
biological	O
applications	O
is	O
because	O
its	O
results	O
often	O
do	O
not	O
face	O
interference	O
from	O
water	O
molecules	O
,	O
due	O
to	O
the	O
fact	O
that	O
they	O
have	O
permanent	O
dipole	O
moments	O
,	O
and	O
as	O
a	O
result	O
,	O
the	O
Raman	B-Architecture
scattering	I-Architecture
cannot	O
be	O
picked	O
up	O
on	O
.	O
</s>
<s>
Raman	B-Algorithm
spectroscopy	I-Algorithm
also	O
has	O
a	O
wide	O
usage	O
for	O
studying	O
biominerals	O
.	O
</s>
<s>
Raman	B-Algorithm
spectroscopy	I-Algorithm
has	O
been	O
used	O
in	O
several	O
research	O
projects	O
as	O
a	O
means	O
to	O
detect	O
explosives	O
from	O
a	O
safe	O
distance	O
using	O
laser	O
beams	O
.	O
</s>
<s>
Raman	B-Algorithm
Spectroscopy	I-Algorithm
is	O
being	O
further	O
developed	O
so	O
it	O
could	O
be	O
used	O
in	O
the	O
clinical	O
setting	O
.	O
</s>
<s>
Raman4Clinic	O
is	O
a	O
European	O
organization	O
that	O
is	O
working	O
on	O
incorporating	O
Raman	B-Algorithm
Spectroscopy	I-Algorithm
techniques	O
in	O
the	O
medical	O
field	O
.	O
</s>
<s>
Raman	B-Algorithm
spectroscopy	I-Algorithm
is	O
an	O
efficient	O
and	O
non-destructive	O
way	O
to	O
investigate	O
works	O
of	O
art	O
and	O
cultural	O
heritage	O
artifacts	O
,	O
in	O
part	O
because	O
it	O
is	O
a	O
non-invasive	O
process	O
which	O
can	O
be	O
applied	O
in	O
situ	O
.	O
</s>
<s>
In	O
addition	O
to	O
paintings	O
and	O
artifacts	O
,	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
can	O
be	O
used	O
to	O
investigate	O
the	O
chemical	O
composition	O
of	O
historical	O
documents	O
(	O
such	O
as	O
the	O
Book	O
of	O
Kells	O
)	O
,	O
which	O
can	O
provide	O
insight	O
about	O
the	O
social	O
and	O
economic	O
conditions	O
when	O
they	O
were	O
created	O
.	O
</s>
<s>
Raman	B-Algorithm
spectroscopy	I-Algorithm
offers	O
several	O
advantages	O
for	O
microscopic	O
analysis	O
.	O
</s>
<s>
Thus	O
,	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
is	O
suitable	O
for	O
the	O
microscopic	O
examination	O
of	O
minerals	O
,	O
materials	O
such	O
as	O
polymers	O
and	O
ceramics	O
,	O
cells	O
,	O
proteins	O
and	O
forensic	O
trace	O
evidence	O
.	O
</s>
<s>
A	O
Raman	O
microscope	O
begins	O
with	O
a	O
standard	O
optical	O
microscope	O
,	O
and	O
adds	O
an	O
excitation	O
laser	O
,	O
a	O
monochromator	O
or	O
polychromator	O
,	O
and	O
a	O
sensitive	O
detector	O
(	O
such	O
as	O
a	O
charge-coupled	B-Algorithm
device	I-Algorithm
(	O
CCD	B-Algorithm
)	O
,	O
or	O
photomultiplier	B-Algorithm
tube	I-Algorithm
(	O
PMT	O
)	O
)	O
.	O
</s>
<s>
Ultraviolet	B-Application
microscopes	O
and	O
UV	O
enhanced	O
optics	O
must	O
be	O
used	O
when	O
a	O
UV	O
laser	O
source	O
is	O
used	O
for	O
Raman	O
microspectroscopy	O
.	O
</s>
<s>
The	O
most	O
common	O
approach	O
is	O
hyperspectral	B-Application
imaging	I-Application
or	O
chemical	O
imaging	O
,	O
in	O
which	O
thousands	O
of	O
Raman	O
spectra	O
are	O
acquired	O
from	O
all	O
over	O
the	O
field	O
of	O
view	O
by	O
,	O
for	O
example	O
,	O
raster	O
scanning	O
of	O
a	O
focused	O
laser	O
beam	O
through	O
a	O
sample	O
.	O
</s>
<s>
Furthermore	O
,	O
material	O
properties	O
such	O
as	O
stress	O
and	O
strain	O
,	O
crystal	O
orientation	O
,	O
crystallinity	O
and	O
incorporation	O
of	O
foreign	O
ions	O
into	O
crystal	O
lattices	O
(	O
e.g.	O
,	O
doping	B-Algorithm
,	O
solid	O
solution	O
series	O
)	O
can	O
be	O
determined	O
from	O
hyperspectral	B-Application
maps	O
.	O
</s>
<s>
Taking	O
the	O
cell	O
culture	O
example	O
,	O
a	O
hyperspectral	B-Application
image	I-Application
could	O
show	O
the	O
distribution	O
of	O
cholesterol	O
,	O
as	O
well	O
as	O
proteins	O
,	O
nucleic	O
acids	O
,	O
and	O
fatty	O
acids	O
.	O
</s>
<s>
However	O
,	O
the	O
intensity	O
of	O
Raman	B-Architecture
scattering	I-Architecture
at	O
long	O
wavelengths	O
is	O
low	O
(	O
owing	O
to	O
the	O
ω4	O
dependence	O
of	O
Raman	B-Architecture
scattering	I-Architecture
intensity	O
)	O
,	O
leading	O
to	O
long	O
acquisition	O
times	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
resonance	B-Algorithm
Raman	I-Algorithm
imaging	O
of	O
single-cell	O
algae	O
at	O
532nm	O
(	O
green	O
)	O
can	O
specifically	O
probe	O
the	O
carotenoid	O
distribution	O
within	O
a	O
cell	O
by	O
a	O
using	O
low	O
laser	O
power	O
of	O
~	O
5µW	O
and	O
only	O
100ms	O
acquisition	O
time	O
.	O
</s>
<s>
Raman	B-Architecture
scattering	I-Architecture
,	O
specifically	O
tip-enhanced	B-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
,	O
produces	O
high	O
resolution	O
hyperspectral	B-Application
images	I-Application
of	O
single	O
molecules	O
,	O
atoms	O
,	O
and	O
DNA	O
.	O
</s>
<s>
Raman	B-Architecture
scattering	I-Architecture
is	O
polarization	O
sensitive	O
and	O
can	O
provide	O
detailed	O
information	O
on	O
symmetry	O
of	O
Raman	O
active	O
modes	O
.	O
</s>
<s>
While	O
conventional	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
identifies	O
chemical	O
composition	O
,	O
polarization	O
effects	O
on	O
Raman	O
spectra	O
can	O
reveal	O
information	O
on	O
the	O
orientation	O
of	O
molecules	O
in	O
single	O
crystals	O
and	O
anisotropic	O
materials	O
,	O
e.g.	O
</s>
<s>
Polarization	O
–	O
dependent	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
uses	O
(	O
plane	O
)	O
polarized	O
laser	O
excitation	O
from	O
a	O
polarizer	O
.	O
</s>
<s>
It	O
is	O
convenient	O
in	O
polarized	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
to	O
describe	O
the	O
propagation	O
and	O
polarization	O
directions	O
using	O
Porto	O
's	O
notation	O
,	O
described	O
by	O
and	O
named	O
after	O
Brazilian	O
physicist	O
Sergio	O
Pereira	O
da	O
Silva	O
Porto	O
.	O
</s>
<s>
For	O
isotropic	O
solutions	O
,	O
the	O
Raman	B-Architecture
scattering	I-Architecture
from	O
each	O
mode	O
either	O
retains	O
the	O
polarization	O
of	O
the	O
laser	O
or	O
becomes	O
partly	O
or	O
fully	O
depolarized	O
.	O
</s>
<s>
If	O
the	O
vibrational	O
mode	O
involved	O
in	O
the	O
Raman	B-Architecture
scattering	I-Architecture
process	O
is	O
totally	O
symmetric	O
then	O
the	O
polarization	O
of	O
the	O
Raman	B-Architecture
scattering	I-Architecture
will	O
be	O
the	O
same	O
as	O
that	O
of	O
the	O
incoming	O
laser	O
beam	O
.	O
</s>
<s>
Hence	O
polarized	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
can	O
provide	O
detailed	O
information	O
as	O
to	O
the	O
symmetry	O
labels	O
of	O
vibrational	O
modes	O
.	O
</s>
<s>
In	O
the	O
solid	O
state	O
,	O
polarized	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
can	O
be	O
useful	O
in	O
the	O
study	O
of	O
oriented	O
samples	O
such	O
as	O
single	O
crystals	O
.	O
</s>
<s>
Therefore	O
the	O
intensity	O
of	O
the	O
Raman	B-Architecture
scattering	I-Architecture
will	O
be	O
different	O
when	O
the	O
laser	O
's	O
polarization	O
is	O
along	O
and	O
orthogonal	O
to	O
a	O
particular	O
bond	O
axis	O
.	O
</s>
<s>
The	O
spectral	O
information	O
arising	O
from	O
this	O
analysis	O
is	O
often	O
used	O
to	O
understand	O
macro-molecular	O
orientation	O
in	O
crystal	O
lattices	O
,	O
liquid	B-Device
crystals	I-Device
or	O
polymer	O
samples	O
.	O
</s>
<s>
The	O
symmetry	O
of	O
a	O
vibrational	O
mode	O
is	O
deduced	O
from	O
the	O
depolarization	O
ratio	O
ρ	O
,	O
which	O
is	O
the	O
ratio	O
of	O
the	O
Raman	B-Architecture
scattering	I-Architecture
with	O
polarization	O
orthogonal	O
to	O
the	O
incident	O
laser	O
and	O
the	O
Raman	B-Architecture
scattering	I-Architecture
with	O
the	O
same	O
polarization	O
as	O
the	O
incident	O
laser	O
:	O
Here	O
is	O
the	O
intensity	O
of	O
Raman	B-Architecture
scattering	I-Architecture
when	O
the	O
analyzer	O
is	O
rotated	O
90	O
degrees	O
with	O
respect	O
to	O
the	O
incident	O
light	O
's	O
polarization	O
axis	O
,	O
and	O
the	O
intensity	O
of	O
Raman	B-Architecture
scattering	I-Architecture
when	O
the	O
analyzer	O
is	O
aligned	O
with	O
the	O
polarization	O
of	O
the	O
incident	O
laser	O
.	O
</s>
<s>
At	O
least	O
25	O
variations	O
of	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
have	O
been	O
developed	O
.	O
</s>
<s>
The	O
usual	O
purpose	O
is	O
to	O
enhance	O
the	O
sensitivity	O
(	O
e.g.	O
,	O
surface-enhanced	B-Algorithm
Raman	I-Algorithm
)	O
,	O
to	O
improve	O
the	O
spatial	O
resolution	O
(	O
Raman	O
microscopy	O
)	O
,	O
or	O
to	O
acquire	O
very	O
specific	O
information	O
(	O
resonance	B-Algorithm
Raman	I-Algorithm
)	O
.	O
</s>
<s>
Terms	O
such	O
as	O
spontaneous	B-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
or	O
normal	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
summarize	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
techniques	O
based	O
on	O
Raman	B-Architecture
scattering	I-Architecture
by	O
using	O
normal	O
far-field	B-Algorithm
optics	O
as	O
described	O
above	O
.	O
</s>
<s>
Variants	O
of	O
normal	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
exist	O
with	O
respect	O
to	O
excitation-detection	O
geometries	O
,	O
combination	O
with	O
other	O
techniques	O
,	O
use	O
of	O
special	O
(	O
polarizing	O
)	O
optics	O
and	O
specific	O
choice	O
of	O
excitation	O
wavelengths	O
for	O
resonance	O
enhancement	O
.	O
</s>
<s>
Resonance	B-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
–	O
The	O
excitation	O
wavelength	O
is	O
matched	O
to	O
an	O
electronic	O
transition	O
of	O
the	O
molecule	O
or	O
crystal	O
,	O
so	O
that	O
vibrational	O
modes	O
associated	O
with	O
the	O
excited	O
electronic	O
state	O
are	O
greatly	O
enhanced	O
.	O
</s>
<s>
Angle-resolved	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
–	O
Not	O
only	O
are	O
standard	O
Raman	O
results	O
recorded	O
but	O
also	O
the	O
angle	O
with	O
respect	O
to	O
the	O
incident	O
laser	O
.	O
</s>
<s>
If	O
the	O
orientation	O
of	O
the	O
sample	O
is	O
known	O
then	O
detailed	O
information	O
about	O
the	O
phonon	B-Language
dispersion	O
relation	O
can	O
also	O
be	O
gleaned	O
from	O
a	O
single	O
test	O
.	O
</s>
<s>
Optical	O
tweezers	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
(	O
OTRS	O
)	O
–	O
Used	O
to	O
study	O
individual	O
particles	O
,	O
and	O
even	O
biochemical	O
processes	O
in	O
single	O
cells	O
trapped	O
by	O
optical	O
tweezers	O
.	O
</s>
<s>
Spatially	B-Algorithm
offset	I-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
(	O
SORS	O
)	O
–	O
The	O
Raman	B-Architecture
scattering	I-Architecture
beneath	O
an	O
obscuring	O
surface	O
is	O
retrieved	O
from	O
a	O
scaled	O
subtraction	O
of	O
two	O
spectra	O
taken	O
at	O
two	O
spatially	O
offset	O
points	O
.	O
</s>
<s>
Raman	B-Algorithm
optical	I-Algorithm
activity	I-Algorithm
(	O
ROA	O
)	O
–	O
Measures	O
vibrational	O
optical	O
activity	O
by	O
means	O
of	O
a	O
small	O
difference	O
in	O
the	O
intensity	O
of	O
Raman	B-Architecture
scattering	I-Architecture
from	O
chiral	O
molecules	O
in	O
right	O
-	O
and	O
left-circularly	O
polarized	O
incident	O
light	O
or	O
,	O
equivalently	O
,	O
a	O
small	O
circularly	O
polarized	O
component	O
in	O
the	O
scattered	O
light	O
.	O
</s>
<s>
Transmission	B-Algorithm
Raman	I-Algorithm
–	O
Allows	O
probing	O
of	O
a	O
significant	O
bulk	O
of	O
a	O
turbid	O
material	O
,	O
such	O
as	O
powders	O
,	O
capsules	O
,	O
living	O
tissue	O
,	O
etc	O
.	O
</s>
<s>
The	O
micro-cavity	O
has	O
a	O
radius	O
of	O
several	O
micrometers	O
and	O
enhances	O
the	O
entire	O
Raman	O
signal	O
by	O
providing	O
multiple	O
excitations	O
of	O
the	O
sample	O
and	O
couples	O
the	O
forward-scattered	O
Raman	O
photons	B-Application
toward	O
the	O
collection	O
optics	O
in	O
the	O
back-scattered	O
Raman	O
geometry	O
.	O
</s>
<s>
Stand-off	O
remote	O
Raman	O
–	O
In	O
standoff	O
Raman	O
,	O
the	O
sample	O
is	O
measured	O
at	O
a	O
distance	O
from	O
the	O
Raman	B-Algorithm
spectrometer	I-Algorithm
,	O
usually	O
by	O
using	O
a	O
telescope	O
for	O
light	O
collection	O
.	O
</s>
<s>
Remote	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
was	O
proposed	O
in	O
the	O
1960s	O
and	O
initially	O
developed	O
for	O
the	O
measurement	O
of	O
atmospheric	O
gases	O
.	O
</s>
<s>
X-ray	O
Raman	B-Architecture
scattering	I-Architecture
–	O
Measures	O
electronic	O
transitions	O
rather	O
than	O
vibrations	O
.	O
</s>
<s>
Enhancement	O
of	O
Raman	B-Architecture
scattering	I-Architecture
is	O
achieved	O
by	O
local	O
electric-field	O
enhancement	O
by	O
optical	O
near-field	B-Algorithm
effects	O
(	O
e.g.	O
</s>
<s>
Surface-enhanced	B-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
(	O
SERS	O
)	O
–	O
Normally	O
done	O
in	O
a	O
silver	O
or	O
gold	O
colloid	O
or	O
a	O
substrate	O
containing	O
silver	O
or	O
gold	O
.	O
</s>
<s>
Surface-enhanced	O
resonance	B-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
(	O
SERRS	O
)	O
–	O
A	O
combination	O
of	O
SERS	O
and	O
resonance	B-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
that	O
uses	O
proximity	O
to	O
a	O
surface	O
to	O
increase	O
Raman	O
intensity	O
,	O
and	O
excitation	O
wavelength	O
matched	O
to	O
the	O
maximum	O
absorbance	O
of	O
the	O
molecule	O
being	O
analysed	O
.	O
</s>
<s>
Tip-enhanced	B-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
(	O
TERS	O
)	O
–	O
TERS	O
combines	O
the	O
chemical	O
sensitivity	O
of	O
SERS	O
with	O
the	O
high	O
spatial	O
resolution	O
of	O
scanning	O
probe	O
microscopy	O
techniques	O
,	O
enabling	O
chemical	O
imaging	O
of	O
surfaces	O
at	O
the	O
nanometre	O
length-scale	O
with	O
high	O
detection	O
sensitivity	O
.	O
</s>
<s>
Surface	O
plasmon	O
polariton	O
enhanced	O
Raman	B-Architecture
scattering	I-Architecture
(	O
SPPERS	O
)	O
–	O
This	O
approach	O
exploits	O
apertureless	O
metallic	O
conical	O
tips	O
for	O
near	O
field	O
excitation	O
of	O
molecules	O
.	O
</s>
<s>
Stimulated	B-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
(	O
SRS	O
)	O
–	O
A	O
pump-probe	O
technique	O
,	O
where	O
a	O
spatially	O
coincident	O
,	O
two	O
color	O
pulse	O
(	O
with	O
polarization	O
either	O
parallel	O
or	O
perpendicular	O
)	O
transfers	O
the	O
population	O
from	O
ground	O
to	O
a	O
rovibrationally	O
excited	O
state	O
.	O
</s>
<s>
If	O
the	O
difference	O
in	O
energy	O
corresponds	O
to	O
an	O
allowed	O
Raman	B-Algorithm
transition	I-Algorithm
,	O
scattered	O
light	O
will	O
correspond	O
to	O
loss	O
or	O
gain	O
in	O
the	O
pump	O
beam	O
.	O
</s>
<s>
Inverse	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
–	O
A	O
synonym	O
for	O
stimulated	O
Raman	O
loss	O
spectroscopy	O
.	O
</s>
<s>
Coherent	B-Algorithm
anti-Stokes	I-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
(	O
CARS	O
)	O
–	O
Two	O
laser	O
beams	O
are	O
used	O
to	O
generate	O
a	O
coherent	O
anti-Stokes	O
frequency	O
beam	O
,	O
which	O
can	O
be	O
enhanced	O
by	O
resonance	O
.	O
</s>
<s>
Morphologically	O
Directed	O
Raman	B-Algorithm
Spectroscopy	I-Algorithm
(	O
MDRS	O
)	O
combines	O
automated	O
particle	O
imaging	O
and	O
Raman	O
microspectroscopy	O
into	O
a	O
singular	O
integrated	O
platform	O
in	O
order	O
to	O
provide	O
particle	O
size	O
,	O
shape	O
,	O
and	O
chemical	O
identification	O
.	O
</s>
