the next generation of laser induced molecular dissociation imaging Drew Rotunno Mentor Dr Itzik Ben Itzhak Bethany Joachim Motivations AMO Atomic and Molecular Collisions ID: 784967
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Slide1
Fast beams of neutral molecules – the next generation of laser induced molecular dissociation imaging
Drew
Rotunno
Mentor: Dr.
Itzik
Ben-
Itzhak
,
Bethany Joachim
Slide2MotivationsAMO – Atomic and Molecular Collisions
DETECTOR
Slide3MotivationsAMO – Femtosecond laser pulsesLaser-induced molecular dissociation imaging
DETECTOR
Slide4MotivationsLaser + Target NeutralsNot enough energy to detect
DETECTOR
DETECTOR
E
Slide5MotivationsLaser + Fast Neutrals
DETECTOR
Slide6MotivationsQ: How do we get fast neutrals?A: Neutralize fast ions
Slide7Remove an electron from a negatively charged ionAdd an electron to a positively charged ion
How do we neutralize?
e
Slide8Target Choice
Noble Gasses
Argon (jet, cell)
Ionization energy
~15eV / atom
v
s. Alkali ~5eV
Very cheap
a
nd available
and safe
Slide9The Theory
H
2
+
Ar
H
+
H
2
+
H
2
(H
2
*
)
Slide10Cross sectionsCollision probability, reinterpreted as areaDepends on species, both target and projectileDepends on Beam energy
Slide11Measurements of Cross sections
H2
+
+
Ar
, separated by product
Charge transfer from Cs, by projectile
A.V. Phelps (1992)
F.W. Meyer et al. (1977)
Slide12Conversion rates
Yield
(H2)
Number of incoming particles
(H2
+
)
Target particles per unit volume
Length
Cross Section
Slide13Conversion rates
Solving for target density shows we need about
At STP, this means we need 1
mTorr
= .001
mmHg of
pressure
~ 3
cm
for few
keV
H2
+
on
Ar
Want
10%
?
Slide14The Theory
H
2
+
Ar
H
+
H
2
+
H
2
(H
2
*
)
Slide15The Piece
d
iameter ~ 2 inches
Slide16The Cut-away
Argon gas in
MicroChannel
Plate
Slide17The Microchannel Plate
Slide18The Cut-away
Argon gas in
MicroChannel
Plate
“Gas Mask”
Slide19Fluid Flow Through TubesHigher length/radius ratio leads to more directed flowPreserves vacuum
Ours: L/R ~
8
0
W.
Steckelmacher et al. (1978)
Slide20Test Beamline
Slide21Next Step - TestingMeasuring conversion factor How much H2 do we get? ( H fragments too)MaximizeFast feedback to optimize pressureToo high – double collisions, more H fragmentsStates of moleculesPopulations of ground vs. excited states
Hard to determine, but interesting to study
Slide22EndThanks KSU, Dr. Itzik Ben-Itzhak, IBI Group,National Science Foundation