atomic and molecular physics ultrafast laser physics and laser spectroscopy instrumentation seminar...
TRANSCRIPT
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Atomic and Molecular PhysicsUltrafast Laser Physics and Laser Spectroscopy
Instrumentation seminar
Femtosecond spectroscopyUltrafast gas phase phenomenaFemtochemistry
Laser SpectroscopyLaser physics on surfacesPSP-investigations
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Personnell
Femtosecond spectroscopyUltrafast gas phase Femtochemistry
Laser SpectroscopyLaser physicsSonoluminiscence PSP-investigations
Lars-Erik BergÅsa LarssonRenée AnderssonNiklas GadorMing LiuPeter SalénBo Zhang
Marica SjödinNils Tillmark MTimmy Sigfrids MNathan Ross FOI
Mats Larsson SUTony Hansson Peter vd Meulen
Peder Royen Pia Johansson
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Fast Phenomena
Timescale
Bandwidth
10-15
10-14
10-13
10-12
10-11
100 nm 1 nm
Wavetrain
3 m 3 mmfs ps
s
Fast Phenomena
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Interested visitor at the fs-lab
Niklas
Bo
PiaGöran
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Femtosecond spectroscopy
The advent of the laser in 1960 and the development of thefemtosecond laser with t = 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
t = 0
t = T/2
t = T 0 T 2T t
Oscillation period T~ 100 fs
r
V
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Fragmentation of molecules
r
r
V
A + B
A* + B
1 Å in 50 fs
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Collisions atoms - atoms
r
Ar
Ar+ 10 eV - 10 keV
Timescale 100 fs - 1 fs
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Other Ultra-fast Phenomena
r
Electron - hole recombinationsTimescale 30 fs - 200 fs
Interaction times in liquidsTimescale 1ps - 100 ps
Fast relaxations in large moleculesTimescale 30 fs - 200 fs
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Femtosecond delay
1 fs 0.3 m
7 fs 2 m
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Wave packetsWave- packet splitting at a Curve- crossing
Diabatic states :
1 2
V Include V in H0
Adiabatic states :
VNAEne
rgy
r
TIME
Rb2, D system heat- pipe oven
Rb2, D;A system Effusive beam
TOF Crossed supersonic- effusive beamsHe: cooling of Rb2
Ar,Kr: Rb2 clusters
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Experimental
Mode-locked fiber laser
delay- mirror
/2 wave-plate
+ prism compressorsfor both beams
780 nm; 170 fs; 150 cm-1
Acetone inlet
Photon counter
computer
Pump: 427nm, 5 J per pulse,1kHzProbe: 927nm, 2 J per pulse,1kHz
PMtube Rb2
Topas 1, OPA
Topas 2, OPA
Fluorescence
Rb, Rb2
Laser
Thermo-couples T1
T2
coppershield
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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.
Delay stage
t
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Dynamics can be studied by
Femtosecond spectroscopy ..
Femtosecond laser:Pump laser, Er-doped fiber laser, kHz 2 YAG laser
Femtosecond laser:Pump laser, Er-doped fiber laser, kHz 2 YAG laserNon-linear setups
TOPAS: 270 nm ... 3 m
Non-linear setupsTOPAS: 270 nm ... 3 m
WLC generator: White light continuumWLC generator: White light continuum
Mirrors, mirrors, ....Mirrors, mirrors, ....
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"3D Nozzle": Compressible Flow with Shock,
Transition, Turbulence and Unsteadiness
Wind tunnel at KTH
p = ?
H Alfredsson, N Tillmark, T Sigfrids, L-E
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Pressure Sensitive Paint
Method:Laser excitation of pressure sensitive paintin order to measure the gas pressure over a surface.
1. Fluorescence measurements2. Life-time measurements
Laser light Pressure sensitive paint
Fluorescence
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Basic photophysics
Photon transitions in an energy diagram of the condensed phase
S0
S1
S2
SN
T1
Vibrationrelaxations
h
excitationexcitation
fluorescensfluorescens
inter system crossing ISC
fosforescensfosforescens
f p
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Ruthenium based paint
tris(2,2’-bipyridil) ruthenium Ru(bpy)
200 300 400 500 600 700 wavelength (nm)
Inte
nsit
yAbsorption and emnission spectrum
Binder: urethane, clear, is permeable to oxygen
Ar 488
2 YAG
3 YAG4 YAG
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Pressure measurementsDecay - ratesQuenching = kq [L*] [O2]
1/
[O2]
Stern-Vollmer plot
][1 2000 Ok
I
Iq
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Instrumentation
1. Pressure measurements on a surface with a jet nozzle2. Measurements in the wind tunnel
Frequency tripled YAG, Ar ion laser chopped, blue diod laserMechelle+ICCD or ICCD+filter
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ICCD-cameraANDOR iStarDigital delay generatorPropagation delay 40 nsOptical gate width <2nsCCD cooling -40oC
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Monochromator
Resoving power
1
7500
R
Wavelength coverage
190nm<< 1.1m3 m optical fibre
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MechelleMechelle
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Optical system
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Pressure Sensitive Paint
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PSP measurements
500 520 540 560 580 600 620 640 660
0
100
200
300
K60 transmission curve
532 nm
2000 shots averaged, filter K60, gain 700
Inte
nsity
nm
Frequency doubled YAG laser excitation t = 5ns, = 532 nm
PSP1 decay Stern-Vollmer plot
0.0005
0.001
0.0015
0.002
0.0025
0 200 400 600 800
Pressure /Torr)
Inve
sre
life
-tim
e (m
s)
Series1
= 4.0 (0.2) s= 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”PlanckRadiation”
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 = ?