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 = ?