<s>
Resonance	B-Algorithm
ionization	I-Algorithm
is	O
a	O
process	O
in	O
optical	O
physics	O
used	O
to	O
excite	O
a	O
specific	O
atom	O
(	O
or	O
molecule	O
)	O
beyond	O
its	O
ionization	O
potential	O
to	O
form	O
an	O
ion	O
using	O
a	O
beam	O
of	O
photons	B-Application
irradiated	O
from	O
a	O
pulsed	O
laser	O
light	O
.	O
</s>
<s>
In	O
resonance	B-Algorithm
ionization	I-Algorithm
,	O
the	O
absorption	O
or	O
emission	O
properties	O
of	O
the	O
emitted	O
photons	B-Application
are	O
not	O
considered	O
,	O
rather	O
only	O
the	O
resulting	O
excited	O
ions	O
are	O
mass-selected	O
,	O
detected	O
and	O
measured	O
.	O
</s>
<s>
Depending	O
on	O
the	O
laser	O
light	O
source	O
used	O
,	O
one	O
electron	O
can	O
be	O
removed	O
from	O
each	O
atom	O
so	O
that	O
resonance	B-Algorithm
ionization	I-Algorithm
produces	O
an	O
efficient	O
selectivity	O
in	O
two	O
ways	O
:	O
elemental	O
selectivity	O
in	O
ionization	O
and	O
isotopic	O
selectivity	O
in	O
measurement	O
.	O
</s>
<s>
During	O
resonance	B-Algorithm
ionization	I-Algorithm
,	O
an	O
ion	O
gun	O
creates	O
a	O
cloud	O
of	O
atoms	O
and	O
molecules	O
from	O
a	O
gas-phase	O
sample	O
surface	O
and	O
a	O
tunable	O
laser	O
is	O
used	O
to	O
fire	O
a	O
beam	O
of	O
photons	B-Application
at	O
the	O
cloud	O
of	O
particles	O
emanating	O
from	O
the	O
sample	O
(	O
analyte	O
)	O
.	O
</s>
<s>
An	O
initial	O
photon	B-Application
from	O
this	O
beam	O
is	O
absorbed	O
by	O
one	O
of	O
the	O
sample	O
atoms	O
,	O
exciting	O
one	O
of	O
the	O
atom	O
's	O
electrons	O
to	O
an	O
intermediate	O
excited	O
state	O
.	O
</s>
<s>
A	O
second	O
photon	B-Application
then	O
ionizes	O
the	O
same	O
atom	O
from	O
the	O
intermediate	O
state	O
such	O
that	O
its	O
high	O
energy	O
level	O
causes	O
it	O
to	O
be	O
ejected	O
from	O
its	O
orbital	O
;	O
the	O
result	O
is	O
a	O
packet	O
of	O
positively	O
charged	O
ions	O
which	O
are	O
then	O
delivered	O
to	O
a	O
mass	O
analyzer	O
.	O
</s>
<s>
Resonance	B-Algorithm
ionization	I-Algorithm
contrasts	O
with	O
resonance-enhanced	O
multiphoton	O
ionization	O
(	O
REMPI	O
)	O
in	O
that	O
the	O
latter	O
is	O
neither	O
selective	O
nor	O
efficient	O
since	O
resonances	B-Application
are	O
seldom	O
used	O
to	O
prevent	O
interference	O
.	O
</s>
<s>
Also	O
,	O
resonance	B-Algorithm
ionization	I-Algorithm
is	O
used	O
for	O
an	O
atomic	O
(	O
elemental	O
)	O
analyte	O
,	O
whereas	O
REMPI	O
is	O
used	O
for	O
a	O
molecular	O
analyte	O
.	O
</s>
<s>
The	O
analytical	O
technique	O
on	O
which	O
the	O
process	O
of	O
resonance	B-Algorithm
ionization	I-Algorithm
is	O
based	O
is	O
termed	O
resonance	B-Algorithm
ionization	I-Algorithm
mass	I-Algorithm
spectrometry	I-Algorithm
(	O
RIMS	O
)	O
.	O
</s>
<s>
RIMS	O
is	O
derived	O
from	O
the	O
original	O
method	O
,	O
resonance	B-Algorithm
ionization	I-Algorithm
spectroscopy	O
(	O
RIS	O
)	O
,	O
which	O
was	O
initially	O
being	O
used	O
to	O
detect	O
single	O
atoms	O
with	O
better	O
time	O
resolution	O
.	O
</s>
<s>
Resonance	B-Algorithm
ionization	I-Algorithm
was	O
first	O
used	O
in	O
a	O
spectroscopy	O
experiment	O
in	O
1971	O
at	O
the	O
Institute	O
for	O
Spectroscopy	O
Russian	O
Academy	O
of	O
Sciences	O
;	O
in	O
that	O
experiment	O
,	O
ground	O
state	O
rubidium	O
atoms	O
were	O
ionized	O
using	O
ruby	O
lasers	O
.	O
</s>
<s>
 [ 4 ] 	O
In	O
1974	O
,	O
a	O
group	O
of	O
photophysical	O
researchers	O
at	O
the	O
Oak	O
Ridge	O
National	O
Laboratory	O
led	O
by	O
George	O
Samuel	O
Hurst	O
developed	O
,	O
for	O
the	O
first	O
time	O
,	O
the	O
resonance	B-Algorithm
ionization	I-Algorithm
process	O
on	O
helium	O
atoms	O
.	O
</s>
<s>
The	O
experiment	O
on	O
singlet	O
metastable	O
helium	O
atoms	O
was	O
seminal	O
in	O
the	O
journey	O
towards	O
using	O
resonance	B-Algorithm
ionization	I-Algorithm
spectroscopy	O
(	O
RIS	O
)	O
for	O
extensive	O
atomic	O
analysis	O
in	O
research	O
settings	O
.	O
</s>
<s>
Cesium	O
atoms	O
was	O
subsequently	O
used	O
to	O
show	O
that	O
single	O
atoms	O
of	O
an	O
element	O
could	O
be	O
counted	O
if	O
its	O
resonance	B-Algorithm
ionization	I-Algorithm
was	O
performed	O
in	O
a	O
counter	O
in	O
which	O
an	O
electron	O
could	O
be	O
detected	O
for	O
an	O
atom	O
in	O
its	O
ground	O
state	O
.	O
</s>
<s>
Subsequently	O
,	O
advanced	O
techniques	O
categorized	O
under	O
resonance	B-Algorithm
ionization	I-Algorithm
mass	I-Algorithm
spectrometry	I-Algorithm
(	O
RIMS	O
)	O
were	O
used	O
to	O
generate	O
the	O
relative	O
abundance	O
of	O
various	O
ion	O
types	O
by	O
coupling	O
the	O
RIS	O
lasers	O
to	O
magnetic	O
sector	O
,	O
quadrupole	O
,	O
or	O
time-of-flight	O
(	O
TOF	O
)	O
mass	O
spectrometers	O
.	O
</s>
<s>
The	O
field	O
of	O
resonance	B-Algorithm
ionization	I-Algorithm
spectroscopy	O
(	O
RIS	O
)	O
has	O
largely	O
been	O
shaped	O
by	O
the	O
formal	O
and	O
informal	O
communications	O
heralding	O
its	O
discovery	O
.	O
</s>
<s>
A	O
model	O
resonance	B-Algorithm
ionization	I-Algorithm
mass	I-Algorithm
spectrometry	I-Algorithm
(	O
RIMS	O
)	O
set-up	O
consists	O
of	O
a	O
laser	O
system	O
(	O
consisting	O
of	O
multiple	O
lasers	O
)	O
,	O
sample	O
from	O
which	O
the	O
atoms	O
are	O
derived	O
,	O
and	O
a	O
suitable	O
mass	O
spectrometer	O
which	O
mass-selectively	O
detects	O
the	O
photo	O
ions	O
created	O
from	O
resonance	B-Application
.	O
</s>
<s>
In	O
resonant	O
ionization	O
,	O
atoms	O
or	O
molecules	O
from	O
ground	O
state	O
are	O
excited	O
to	O
higher	O
energy	O
states	O
by	O
the	O
resonant	O
absorption	O
of	O
photons	B-Application
to	O
produce	O
ions	O
.	O
</s>
<s>
In	O
order	O
to	O
ensure	O
a	O
highly-efficient	O
sensitivity	O
and	O
process	O
saturation	O
,	O
the	O
atomic	O
or	O
molecular	O
beam	O
must	O
be	O
formed	O
from	O
the	O
ground	O
state	O
,	O
the	O
atoms	O
should	O
be	O
efficiently	O
excited	O
and	O
ionized	O
,	O
and	O
each	O
atom	O
should	O
be	O
converted	O
by	O
the	O
photon	B-Application
field	O
of	O
a	O
short-timed	O
pulsed	O
laser	O
to	O
produce	O
a	O
positive	O
ion	O
and	O
a	O
valence	O
electron	O
.	O
</s>
<s>
In	O
a	O
basic	O
RIS	O
process	O
,	O
a	O
pulsed	O
laser	O
beam	O
produces	O
photons	B-Application
of	O
the	O
right	O
energy	O
in	O
order	O
to	O
excite	O
an	O
atom	O
initially	O
in	O
its	O
ground	O
state	O
,	O
a	O
,	O
to	O
an	O
excited	O
level	O
,	O
b	O
.	O
</s>
<s>
This	O
high	O
laser	O
intensity	O
translates	O
into	O
a	O
photon	B-Application
fluence	O
(	O
photons	B-Application
per	O
unit	O
of	O
beam	O
area	O
)	O
large	O
enough	O
so	O
that	O
a	O
necessary	O
condition	O
for	O
the	O
saturation	O
of	O
the	O
RIS	O
process	O
has	O
been	O
met	O
.	O
</s>
<s>
If	O
,	O
in	O
addition	O
,	O
the	O
rate	O
of	O
photoionization	B-Algorithm
is	O
greater	O
than	O
the	O
rate	O
of	O
consumption	O
of	O
intermediates	O
,	O
then	O
each	O
selected	O
state	O
is	O
converted	O
to	O
one	O
electron	O
plus	O
one	O
positive	O
ion	O
,	O
so	O
that	O
the	O
RIS	O
process	O
is	O
saturated	O
.	O
</s>
<s>
Moderate	O
laser	O
powers	O
,	O
if	O
high	O
enough	O
to	O
affect	O
the	O
desired	O
transition	O
states	O
,	O
can	O
be	O
used	O
since	O
the	O
non-resonant	O
photoionization	B-Algorithm
cross	O
section	O
is	O
low	O
which	O
implies	O
a	O
negligible	O
ionization	O
efficiency	O
of	O
unwanted	O
atoms	O
.	O
</s>
<s>
This	O
is	O
due	O
to	O
the	O
low	O
cross-section	O
for	O
non-resonant	O
photo-ionization	B-Algorithm
produced	O
by	O
the	O
laser	O
.	O
</s>
<s>
A	O
pulsed	O
laser	O
system	O
facilitates	O
the	O
efficient	O
coupling	O
of	O
a	O
time-of-flight	O
mass	O
spectrometer	O
(	O
TOF-MS	O
)	O
to	O
the	O
resonance	B-Algorithm
ionization	I-Algorithm
set-up	O
due	O
to	O
the	O
instrument	O
's	O
abundance	O
sensitivity	O
.	O
</s>
<s>
The	O
total	O
selectivity	O
in	O
a	O
RIS	O
process	O
is	O
a	O
combination	O
of	O
the	O
sensitivities	O
in	O
the	O
various	O
resonance	B-Application
transitions	O
for	O
multiple	O
step-wise	O
excitations	O
.	O
</s>
<s>
The	O
probability	O
of	O
an	O
atom	O
to	O
come	O
in	O
contact	O
with	O
the	O
resonance	B-Application
of	O
another	O
atom	O
is	O
about	O
10−5	O
.	O
</s>
<s>
The	O
routes	O
were	O
formed	O
by	O
the	O
absorption	O
of	O
two	O
or	O
three	O
photons	B-Application
to	O
achieve	O
excitation	O
and	O
ionization	O
and	O
are	O
provided	O
on	O
the	O
basis	O
of	O
optically	O
possible	O
transitions	O
between	O
atomic	O
levels	O
in	O
a	O
process	O
called	O
the	O
bound-bound	O
transition	O
.	O
</s>
<s>
For	O
an	O
atom	O
of	O
the	O
element	O
to	O
be	O
promoted	O
to	O
a	O
bound-continuum	O
,	O
the	O
energies	O
emitted	O
from	O
the	O
photons	B-Application
must	O
be	O
within	O
the	O
energy	O
range	O
of	O
the	O
selected	O
tunable	O
lasers	O
.	O
</s>
<s>
Also	O
,	O
the	O
ionization	O
energy	O
of	O
the	O
last	O
emitted	O
photon	B-Application
must	O
exceed	O
that	O
of	O
the	O
atom	O
.	O
</s>
<s>
The	O
optical	O
ionization	O
schemes	O
are	O
denoted	O
by	O
the	O
amount	O
of	O
photons	B-Application
necessary	O
to	O
make	O
the	O
ion	O
pair	O
.	O
</s>
<s>
For	O
the	O
first	O
two	O
Schemes	O
1	O
and	O
2	O
,	O
two	O
photons	B-Application
(	O
and	O
processes	O
)	O
are	O
involved	O
.	O
</s>
<s>
One	O
photon	B-Application
excites	O
the	O
atom	O
from	O
the	O
ground	O
state	O
to	O
an	O
intermediate	O
state	O
while	O
the	O
second	O
photon	B-Application
ionizes	O
the	O
atom	O
.	O
</s>
<s>
In	O
Schemes	O
3	O
and	O
4	O
,	O
three	O
photons	B-Application
(	O
and	O
processes	O
)	O
are	O
involved	O
.	O
</s>
<s>
The	O
first	O
two	O
distinct	O
photons	B-Application
create	O
consecutive	O
bound-bound	O
transitions	O
within	O
the	O
selected	O
atom	O
while	O
the	O
third	O
photon	B-Application
is	O
absorbed	O
for	O
ionization	O
.	O
</s>
<s>
Scheme	O
5	O
is	O
a	O
three-photon	O
two-intermediate-level	O
photoionization	B-Algorithm
process	O
.	O
</s>
<s>
After	O
the	O
first	O
two	O
photons	B-Application
have	O
been	O
absorbed	O
by	O
the	O
optical	O
energy	O
,	O
the	O
third	O
photon	B-Application
achieves	O
ionization	O
.	O
</s>
<s>
A	O
major	O
advantage	O
of	O
using	O
resonance	B-Algorithm
ionization	I-Algorithm
is	O
that	O
it	O
is	O
a	O
highly	O
selective	O
ionization	O
mode	O
;	O
it	O
is	O
able	O
to	O
target	O
a	O
single	O
type	O
of	O
atom	O
among	O
a	O
background	O
of	O
many	O
types	O
of	O
atoms	O
,	O
even	O
when	O
said	O
background	O
atoms	O
are	O
much	O
more	O
abundant	O
than	O
the	O
target	O
atoms	O
.	O
</s>
<s>
In	O
addition	O
,	O
resonance	B-Algorithm
ionization	I-Algorithm
incorporates	O
the	O
high	O
selectivity	O
that	O
is	O
desired	O
in	O
spectroscopy	O
methods	O
with	O
ultrasensitivity	O
,	O
thus	O
making	O
resonance	B-Algorithm
ionization	I-Algorithm
useful	O
when	O
analyzing	O
complex	O
samples	O
with	O
several	O
atomic	O
components	O
.	O
</s>
<s>
Resonance	B-Algorithm
ionization	I-Algorithm
spectroscopy	O
(	O
RIS	O
)	O
thus	O
has	O
a	O
wide	O
range	O
of	O
research	O
and	O
industrial	O
applications	O
.	O
</s>
<s>
Other	O
uses	O
include	O
determining	O
high-precision	O
values	O
for	O
plutonium	O
and	O
uranium	O
isotopes	O
in	O
a	O
rapid	O
fashion	O
,	O
investigating	O
the	O
atomic	O
properties	O
of	O
technetium	B-Algorithm
at	O
the	O
ultra	O
trace	O
level	O
,	O
and	O
capturing	O
the	O
concurrent	O
excitation	O
of	O
stable	O
daughter	O
atoms	O
with	O
the	O
decay	O
of	O
their	O
parent	O
atoms	O
as	O
is	O
the	O
case	O
for	O
alpha	O
particles	O
,	O
beta	O
rays	O
,	O
and	O
positrons	O
.	O
</s>
<s>
Pulsed	O
laser	O
light	O
sources	O
provide	O
higher	O
photon	B-Application
fluxes	O
than	O
continuous-wave	O
lasers	O
do	O
,	O
however	O
the	O
use	O
of	O
pulsed	O
lasers	O
currently	O
limit	O
vast	O
applications	O
of	O
RIMS	O
in	O
two	O
ways	O
.	O
</s>
<s>
One	O
,	O
photo	O
ions	O
are	O
created	O
only	O
during	O
short	O
laser	O
pulses	O
,	O
thus	O
significantly	O
reducing	O
the	O
duty	O
cycle	O
of	O
pulsed	O
resonance	B-Algorithm
ionization	I-Algorithm
mass	O
spectrometers	O
relative	O
to	O
their	O
continuous-beam	O
counterparts	O
.	O
</s>
<s>
These	O
issues	O
affect	O
the	O
extent	O
to	O
which	O
resonance	B-Algorithm
ionization	I-Algorithm
can	O
be	O
used	O
to	O
solve	O
some	O
of	O
the	O
challenges	O
confronted	O
by	O
practical	O
analysts	O
today	O
;	O
even	O
so	O
,	O
applications	O
of	O
RIMS	O
are	O
replete	O
in	O
various	O
traditional	O
and	O
emerging	O
disciplines	O
such	O
as	O
cosmochemistry	O
,	O
medical	O
research	O
,	O
environmental	O
chemistry	O
,	O
geophysical	O
sciences	O
,	O
nuclear	O
physics	O
,	O
genome	O
sequencing	O
,	O
and	O
semiconductors	O
.	O
</s>
