Atomic and Molecular Physics Ultrafast Laser Physics and Laser Spectroscopy Instrumentation seminar

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Atomic and Molecular PhysicsUltrafast Laser
Physics and Laser SpectroscopyInstrumentation
seminar
Femtosecond spectroscopy Ultrafast gas phase
phenomena Femtochemistry
Laser Spectroscopy Laser physics on
surfaces PSP-investigations
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Personnell
Lars-Erik Berg Åsa Larsson Renée Andersson Niklas
Gador Ming Liu Peter Salén Bo Zhang Marica
Sjödin Nils Tillmark M Timmy Sigfrids M Nathan
Ross FOI
Femtosecond spectroscopy Ultrafast gas phase
Femtochemistry
Mats Larsson SU Tony Hansson Peter vd
Meulen Peder Royen Pia Johansson
Laser Spectroscopy Laser physics Sonoluminiscence
PSP-investigations
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Fast Phenomena
Fast Phenomena
-15
-14
-13
-12
-11
Time scale
10
10
10
10
10
s
fs
ps
3 mm
3 mm
Wave train
100 nm
1 nm
Band width
4
Interested visitor at the fs-lab
Bo
Göran
Pia
Niklas
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Femtosecond spectroscopy
The advent of the laser in 1960 and the
development of the femtosecond laser with Dt
100 fs in 1990 led to hope that the lasers
can steer chemical reactions hope that final
products can be selected the fs laser excites
molecules and probes the pot. surfaces the fs
laser exites molecules in studies of decay
channels the fs laser can excite quantum well
semiconductor surfaces giving information
about mesoscopic structures few experiments
done reveal real-time evolution
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Vibration of small molecules ..
r
Oscillation period T 100 fs
V
t 0
t T/2
t T
0
T
2T
t
r
7
Fragmentation of molecules
r
V
A B
A B
1 Å in 50 fs
r
8
Collisions atoms - atoms
r
Ar
10 eV - 10 keV

Ar
Timescale 100 fs - 1 fs
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Other Ultra-fast Phenomena
r
Electron - hole recombinations Timescale 30 fs
- 200 fs
Interaction times in liquids Timescale 1ps -
100 ps
Fast relaxations in large molecules Timescale
30 fs - 200 fs
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Femtosecond delay
1 fs
0.3 mm
Wave train
7 fs
2 mm
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Wave packets
Wave- packet splitting at a Curve- crossing
Diabatic states
Adiabatic states
?1
?2
V
Energy
Include V in H0
VNA
r
TIME
Rb2, D system heat- pipe oven
TOF
Crossed supersonic- effusive beams He cooling of
Rb2 Ar,Kr Rb2 clusters
Rb2, DA system Effusive beam
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Experimental
Photon counter
Mode-locked fiber laser
780 nm 170 fs 150 cm-1
computer
PM tube
Topas 2, OPA
Rb2
Topas 1, OPA
?/2 wave- plate
Acetone inlet
prism compressors for both beams
delay- mirror
Pump 427nm, 5 ?J per pulse,1kHz Probe 927nm, 2
?J per pulse,1kHz
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Molecular quantum dynamics (MQD), Wavepacket
(WP) and fs laser spectroscopy
1. MQD nuclear vibration, rotation
change of electronic configuration. 2.
WP nonstationary superposition of a set of
wavefunctions with fixed phase
relationship. 3. Pump-probe technique
pump process, probe process, delay time
and time zero.
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Dynamics can be studied by Femtosecond
spectroscopy ..
Femtosecond laser Pump laser, Er-doped fiber
laser, kHz 2w YAG laser
Non-linear setups TOPAS 270 nm ... 3 mm
WLC generator White light continuum
Mirrors, mirrors, ....
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"3D Nozzle" Compressible Flow with Shock,
Transition, Turbulence and Unsteadiness
H Alfredsson, N Tillmark, T Sigfrids, L-E
p ?
Wind tunnel at KTH
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Pressure Sensitive Paint

• Method
• Laser excitation of pressure sensitive paint
• in order to measure the gas pressure over
• a surface.
• Fluorescence measurements
• Life-time measurements

Laser light
Pressure sensitive paint
Fluorescence
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Basic photophysics
Vibration relaxations
SN
Photon transitions in an energy diagram of the
condensed phase
S2
inter system crossing ISC
S1
T1
tf
tp
h?
fosforescens
excitation
fluorescens
S0
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Ruthenium based paint
tris(2,2-bipyridil) ruthenium Ru(bpy)
Absorption and emnission spectrum
4w YAG
3w YAG
Ar 488
Intensity
2w YAG

• 300 400 500 600 700
• wavelength (nm)

Binder urethane, clear, is permeable to oxygen
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Pressure measurements
Decay - rates Quenching kq L
O2
1/t
Stern-Vollmer plot
O2
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Instrumentation

• Pressure measurements on a surface with a jet
  nozzle
• Measurements in the wind tunnel
• Frequency tripled YAG, Ar ion laser chopped, blue
  diod laser
• MechelleICCD or ICCDfilter

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ICCD-camera
ANDOR iStar Digital delay generator Propagation
delay 40 ns Optical gate width lt2ns CCD cooling
-40oC
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Monochromator
Resoving power
Wavelength coverage
190nmlt l lt 1.1mm
3 m optical fibre
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Mechelle
Mechelle
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Optical system
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Pressure Sensitive Paint
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PSP measurements
Frequency doubled YAG laser excitation Dt
5ns, l 532 nm
l
t0 4.0 (0.2) ms l 488 nm Ar ion
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Time-resolved spectrum
340 350
wavelength
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Time-resolved spectra cont.
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Sonoluminiscence Shocktubes
High pressure
Vacuum
Intense Planck Radiation
M Lesser, N Apazidis H Alfredsson, N Tillmark, H
Essén, Mechanics, L-E B
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Experimental setup
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Time-resolved spectra cont.
I
T ?
l