<s>
Coherent	B-Algorithm
anti-Stokes	I-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
,	O
also	O
called	O
Coherent	O
anti-Stokes	B-Algorithm
Raman	O
scattering	O
spectroscopy	O
(	O
CARS	O
)	O
,	O
is	O
a	O
form	O
of	O
spectroscopy	O
used	O
primarily	O
in	O
chemistry	O
,	O
physics	O
and	O
related	O
fields	O
.	O
</s>
<s>
It	O
is	O
sensitive	O
to	O
the	O
same	O
vibrational	O
signatures	O
of	O
molecules	O
as	O
seen	O
in	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
,	O
typically	O
the	O
nuclear	O
vibrations	O
of	O
chemical	O
bonds	O
.	O
</s>
<s>
Unlike	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
,	O
CARS	O
employs	O
multiple	O
photons	O
to	O
address	O
the	O
molecular	O
vibrations	O
,	O
and	O
produces	O
a	O
coherent	O
signal	O
.	O
</s>
<s>
These	O
beams	O
interact	O
with	O
the	O
sample	O
and	O
generate	O
a	O
coherent	O
optical	O
signal	O
at	O
the	O
anti-Stokes	B-Algorithm
frequency	O
( ωpr+	O
ωp-ωS	O
)	O
.	O
</s>
<s>
The	O
latter	O
is	O
resonantly	O
enhanced	O
when	O
the	O
frequency	O
difference	O
between	O
the	O
pump	O
and	O
the	O
Stokes	O
beams	O
(	O
ωp-ωS	O
)	O
coincides	O
with	O
the	O
frequency	O
of	O
a	O
Raman	B-Algorithm
resonance	I-Algorithm
,	O
which	O
is	O
the	O
basis	O
of	O
the	O
technique	O
's	O
intrinsic	O
vibrational	O
contrast	O
mechanism	O
.	O
</s>
<s>
Coherent	B-Algorithm
Stokes	I-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
(	O
CSRS	O
pronounced	O
as	O
"	O
scissors	O
"	O
)	O
is	O
closely	O
related	O
to	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
and	O
lasing	O
processes	O
.	O
</s>
<s>
It	O
is	O
very	O
similar	O
to	O
CARS	O
except	O
it	O
uses	O
an	O
anti-Stokes	B-Algorithm
frequency	O
stimulation	O
beam	O
and	O
a	O
Stokes	O
frequency	O
beam	O
is	O
observed	O
(	O
the	O
opposite	O
of	O
CARS	O
)	O
.	O
</s>
<s>
They	O
also	O
demonstrated	O
that	O
the	O
signal	O
increases	O
significantly	O
when	O
the	O
difference	O
frequency	O
ωv	O
between	O
the	O
incident	O
beams	O
matches	O
a	O
Raman	B-Algorithm
frequency	I-Algorithm
of	O
the	O
sample	O
.	O
</s>
<s>
The	O
name	O
coherent	B-Algorithm
anti-Stokes	I-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
was	O
assigned	O
almost	O
ten	O
years	O
later	O
,	O
by	O
Begley	O
et	O
al	O
.	O
</s>
<s>
Part	O
of	O
the	O
probe	O
,	O
originally	O
at	O
ωpr	O
will	O
now	O
get	O
modified	O
to	O
ωpr+	O
ωp-ωS	O
,	O
which	O
is	O
the	O
observed	O
anti-Stokes	B-Algorithm
emission	O
.	O
</s>
<s>
Under	O
certain	O
beam	O
geometries	O
,	O
the	O
anti-Stokes	B-Algorithm
emission	O
may	O
diffract	O
away	O
from	O
the	O
probe	O
beam	O
,	O
and	O
can	O
be	O
detected	O
in	O
a	O
separate	O
direction	O
.	O
</s>
<s>
Again	O
,	O
the	O
molecule	O
cannot	O
stay	O
in	O
the	O
virtual	O
state	O
and	O
will	O
fall	O
back	O
instantaneously	O
to	O
the	O
ground	O
state	O
under	O
the	O
emission	O
of	O
a	O
photon	O
at	O
the	O
anti-Stokes	B-Algorithm
frequency	O
.	O
</s>
<s>
CARS	O
is	O
often	O
compared	O
to	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
as	O
both	O
techniques	O
probe	O
the	O
same	O
Raman	O
active	O
modes	O
.	O
</s>
<s>
Theoretically	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
and	O
CARS	O
spectroscopy	O
are	O
equally	O
sensitive	O
as	O
they	O
use	O
the	O
same	O
molecular	O
transitions	O
.	O
</s>
<s>
Coherent	B-Algorithm
Stokes	I-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
(	O
CSRS	O
pronounced	O
as	O
"	O
scissors	O
"	O
)	O
is	O
a	O
form	O
of	O
spectroscopy	O
used	O
primarily	O
in	O
chemistry	O
,	O
physics	O
and	O
related	O
fields	O
.	O
</s>
<s>
It	O
is	O
closely	O
related	O
to	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
and	O
lasing	O
processes	O
.	O
</s>
<s>
It	O
is	O
very	O
similar	O
to	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
,	O
but	O
involves	O
a	O
lasing	O
process	O
that	O
dramatically	O
improves	O
the	O
signal	O
.	O
</s>
<s>
It	O
is	O
very	O
similar	O
to	O
the	O
more	O
common	O
CARS	O
except	O
it	O
uses	O
an	O
anti-Stokes	B-Algorithm
frequency	O
stimulation	O
beam	O
and	O
a	O
Stokes	O
frequency	O
beam	O
is	O
observed	O
(	O
the	O
opposite	O
of	O
CARS	O
)	O
.	O
</s>
<s>
This	O
is	O
disadvantageous	O
because	O
anti-stokes	B-Algorithm
processes	O
must	O
start	O
in	O
a	O
less	O
populated	O
excited	O
state	O
.	O
</s>
<s>
More	O
recently	O
,	O
CARS	B-Algorithm
microscopy	I-Algorithm
has	O
been	O
utilized	O
as	O
a	O
method	O
for	O
non-invasive	O
imaging	O
of	O
lipids	O
in	O
biological	O
samples	O
,	O
both	O
in	O
vivo	O
and	O
in	O
vitro	O
.	O
</s>
<s>
Moreover	O
,	O
RP-CARS	B-Algorithm
,	O
a	O
particular	O
implementation	O
of	O
the	O
Coherent	B-Algorithm
anti-Stokes	I-Algorithm
Raman	I-Algorithm
spectroscopy	I-Algorithm
microscopy	O
,	O
is	O
used	O
to	O
study	O
myelin	O
and	O
myelopathies	O
.	O
</s>
