Upload
preston-lester
View
229
Download
0
Tags:
Embed Size (px)
Citation preview
Atomic and Molecular PhysicsUltrafast Laser Physics and Laser Spectroscopy
Instrumentation seminar
Femtosecond spectroscopyUltrafast gas phase phenomenaFemtochemistry
Laser SpectroscopyLaser physics on surfacesPSP-investigations
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
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
Interested visitor at the fs-lab
Niklas
Bo
PiaGöran
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
Vibration of small molecules ..
r
t = 0
t = T/2
t = T 0 T 2T t
Oscillation period T~ 100 fs
r
V
Fragmentation of molecules
r
r
V
A + B
A* + B
1 Å in 50 fs
Collisions atoms - atoms
r
Ar
Ar+ 10 eV - 10 keV
Timescale 100 fs - 1 fs
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
Femtosecond delay
1 fs 0.3 m
7 fs 2 m
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
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
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
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, ....
"3D Nozzle": Compressible Flow with Shock,
Transition, Turbulence and Unsteadiness
Wind tunnel at KTH
p = ?
H Alfredsson, N Tillmark, T Sigfrids, L-E
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
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
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
Pressure measurementsDecay - ratesQuenching = kq [L*] [O2]
1/
[O2]
Stern-Vollmer plot
][1 2000 Ok
I
Iq
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
ICCD-cameraANDOR iStarDigital delay generatorPropagation delay 40 nsOptical gate width <2nsCCD cooling -40oC
Monochromator
Resoving power
1
7500
R
Wavelength coverage
190nm<< 1.1m3 m optical fibre
MechelleMechelle
Optical system
Pressure Sensitive Paint
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
Time-resolved spectrum
340 350 wavelength
Time-resolved spectra cont.
Sonoluminiscence – Shocktubes
High pressure
Vacuum
Intense”PlanckRadiation”
M Lesser, N Apazidis H Alfredsson, N Tillmark, H Essén, Mechanics, L-E B
Experimental setup
Time-resolved spectra cont.
I
T = ?