Download Atomic and Molecular Physics Ultrafast Laser Physics and

Atomic and Molecular Physics
Ultrafast Laser Physics and Laser Spectroscopy
Instrumentation seminar
Femtosecond spectroscopy
Ultrafast gas phase phenomena
Femtochemistry
Laser Spectroscopy
Laser physics on surfaces
PSP-investigations
Personnell
Lars-Erik Berg
Åsa Larsson
Femtosecond spectroscopy Renée Andersson
Ultrafast gas phase
Niklas Gador
Ming Liu
Femtochemistry
Peter Salén
Mats Larsson SU
Bo Zhang
Tony Hansson Peter vd Meulen
Peder Royen Pia Johansson
Laser Spectroscopy
Laser physics
Sonoluminiscence
PSP-investigations
Marica Sjödin
Nils Tillmark M
Timmy Sigfrids M
Nathan Ross FOI
Fast
FastPhenomena
Phenomena
-15
Time 10
scale fs
Wave
train
Band
width
-14
10
3 mm
100 nm
-13
10
-12
10
-11
10
ps
3 mm
1 nm
s
Interested visitor at the fs-lab
Göran
Pia
Bo
Niklas
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
Vibration of small molecules
..
Oscillation period T~ 100 fs
V
t=0
r
t = T/2
r
t=T
0
T
2T
t
Fragmentation of molecules
V
A* + B
A+B
r
r
1 Å in 50 fs
Collisions atoms - atoms
Ar
r
+
Ar
10 eV - 10 keV
Timescale 100 fs - 1 fs
Other Ultra-fast Phenomena
Electron - hole recombinations
Timescale 30 fs - 200 fs
Interaction times in liquids
r
Timescale 1ps - 100 ps
Fast relaxations in large molecules
Timescale 30 fs - 200 fs
Femtosecond delay
1 fs
7 fs
0.3 mm
2 mm
Wave packets
Wave- packet splitting at a Curve- crossing
Diabatic states :
Energy
1
Adiabatic states :
2
V
Include V in
H0
VNA
r
TIME
Rb2, D system
heat- pipe oven
TOF
Rb2, D;A system
Effusive beam
Crossed
supersonic- effusive
beams
He: cooling of Rb2
Ar,Kr: Rb2 clusters
Experimental
Photon counter
Mode-locked fiber laser
780 nm; 170 fs; 150 cm-1
Topas 2, OPA
PM
tube
Rb2
computer
Topas 1, OPA
/2 waveplate
Acetone inlet
+ prism compressors
for both beams
delaymirror
Rb, Rb2
Laser
copper
shield
Fluorescence
T2
Pump: 427nm, 5 mJ per pulse,1kHz
Probe: 927nm, 2 mJ per pulse,1kHz
Thermocouples
T1
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
Dt
laser: by
DynamicsFemtosecond
can be studied
Pump laser, Er-doped fiber
Femtosecond
Non-linear
setups
laser,
kHz spectroscopy
2w YAG
laser
TOPAS:
270
nm
...
3
mm
..
WLC generator:
White light continuum
Mirrors, mirrors, ....
"3D Nozzle": Compressible
Flow with Shock, Transition,
Turbulence and
Unsteadiness
H Alfredsson, N Tillmark, T Sigfrids, L-E
p=?
Wind tunnel at KTH
Pressure Sensitive Paint
Method:
Laser excitation of pressure sensitive paint
in order to measure the gas pressure over
a surface.
1. Fluorescence measurements
2. Life-time measurements
Laser light
Fluorescence
Pressure sensitive paint
Basic photophysics
SN
Vibration
relaxations
S2
inter system
crossing ISC
Photon transitions in
an energy diagram of
the condensed phase
S1
h
tf
tp
fosforescens
excitation
fluorescens
S0
T1
Ruthenium based paint
tris(2,2’-bipyridil) ruthenium
Ru(bpy)
Absorption and emnission spectrum
4w YAG
3w YAG
Ar 488
2w YAG
200
300
400 500 600
wavelength (nm)
700
Binder: urethane, clear, is permeable to oxygen
Pressure measurements
Decay - rates
Quenching = kq [L*] [O2]
I0 t 0
  1  kqt 0 [O2 ]
I t
1/t
Stern-Vollmer plot
[O2]
Instrumentation
1. Pressure measurements on a surface with a jet nozzle
2. Measurements in the wind tunnel
Frequency tripled YAG, Ar ion laser chopped, blue diod laser
Mechelle+ICCD or
ICCD+filter
ICCD-camera
ANDOR iStar
Digital delay generator
Propagation delay 40 ns
Optical gate width
<2ns
CCD cooling
-40oC
Monochromator
Resoving power
 7500
R

D
1
Wavelength coverage
3 m optical fibre
190nm<  < 1.1mm
Mechelle
Mechelle
Optical system
Pressure Sensitive Paint
PSP measurements
300
Frequency doubled YAG laser excitation Dt = 5ns,  = 532 nm
2000 shots averaged, filter K60, gain 700
532 nm
Intensity
200
100
K60 transmission curve
0
500
520
540
560
580
600
620
640
660

nm
PSP1 decay Stern-Vollmer plot
Invesre life-time (ms)
0.0025
0.002
0.0015
Series1
0.001
0.0005
0
200
400
Pressure /Torr)
600
800
t0 = 4.0 (0.2) ms
 = 488 nm Ar ion
Time-resolved spectrum
340
350
wavelength
Time-resolved spectra cont.
Sonoluminiscence – Shocktubes
High pressure
Vacuum
Intense
”Planck
Radiation”
M Lesser, N Apazidis H Alfredsson,
N Tillmark, H Essén, Mechanics, L-E B
Experimental setup
Time-resolved spectra cont.
I
T=?
