laser spectroscopy group department of physics nui - university college cork cork, ireland
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Laser Spectroscopy GroupLaser Spectroscopy Group
Department of PhysicsNUI - University College
CorkCork, Ireland
Research ActivitiesResearch Activities
• Molecular Absorption Spectroscopy• Luminescence Excitation
Spectroscopy• Third-order Nonlinear Susceptibilities
(Z-scan)• Synthesis of Metal Nanoparticles by
Laser Ablation• Surface Enhanced (Resonance) Raman
Spectroscopy
Molecular Absorption Molecular Absorption SpectroscopySpectroscopy
• Cavity Ring-Down Spectroscopy (!)Dye laser based (vis): Static gas, supersonic jets.
• Cavity Enhanced Absorption Spectroscopy
Diode laser based (near IR): Static gas, flow chamber.
• Incoherent Broad-Band Cavity Enhanced Absorption SpectroscopyXenon Lamp based (UV / vis / near IR): Static gas.
[S.E. Fiedler, A. Hese, A.A. Ruth; Chem. Phys. Lett. 371 (2003) 284-294.]
Cavity Ring-Down Cavity Ring-Down SpectroscopySpectroscopy
Cavity-Ring Down (CRD): Highly sensitive direct absorption method for species in the gas-phase.
In CRD spectroscopy the rate rather than the absolute magnitude of a change of intensity is determined.Advantages: • intensity independent (in principle) • very long path-lengths
• high spectral resolution possible • applicable over a wide spectral
range
I0I1I2
mirror (R>0.999)
laser pulse of a dye laser
….. In1
no absorption
crd-1 /
s-1
/ nm
0 20 40 60 80 100
0,0
0,2
0,4
0,6
0,8
1,0
In
I2
I1
I0
rel.
inte
nsi
ty
time / s
1
c)1(
c)(1 R crd
fit I = A exp(-t/crd)
Principle of Cavity Ring-Down Principle of Cavity Ring-Down (CRD)(CRD)
c)1(
c)(1 R crd
fit I = A exp(-t/crd)
Principle of Cavity Ring-Down Principle of Cavity Ring-Down (CRD)(CRD)
I0I1I2
mirror (R>0.999)
laser pulse of a dye laser
….. In2
absorption
crd-1 /
s-1
/ nm
2
0 20 40 60 80 100
0,0
0,2
0,4
0,6
0,8
1,0 I2
I1
I0
rel.
inte
nsi
ty
time / s
Examples of investigations using Examples of investigations using Cavity Ring-Down SpectroscopyCavity Ring-Down Spectroscopy
• Spin forbidden transitions in aromatic thiocarbonyl compounds (in jet and static cell)
A.A. Ruth, W.G. Doherty, R.P. Brint; Chem. Phys. Lett. 352 (2002) 191-201. A.A. Ruth, T. Fernholz, R.P. Brint, M.W.D. Mansfield; J. Mol. Spectr. 214 (2002) 80-86.
• Fast decay dynamics in jet-cooled azulene
A.A. Ruth, E.-K. Kim, A. Hese; Phys. Chem. Chem. Phys. 22 (1999) 5121-5129.
• Nonlinear dynamics of UV multiphoton photolysis products of gaseous naphthalene
A.A. Ruth, E.W. Gash, M. Staak, S.E. Fiedler; Phys. Chem. Chem. Phys. 4 (2002) 5217-5220.
O
S
O
S
Experimental SetupExperimental Setup
Excimer Laser(XeCl, 308 nm)
Dye Laser
PMT
Pump
Probe
Computer
Filter
VacuumCell
HR Mirror
DigitalOscilloscope
GPIB
Lens
Iris
Shutter
CRD MirrorCRD Mirror
Dye LaserDye Laser
Excimer LaserExcimer Laser
CRD MirrorCRD Mirror
Shutter / LensShutter / Lens
PMTPMT
OscillationsOscillations
793 s
494 s483 s
561 sConditions:
Pnap = 0.10 mbarPHe = 77.5 mbar EPuls = 21.4 mJT = 24.1 oC
20 UV Pulses time / hrs.0 1 2 3 4 5
0
1
2
3
4
5
6
7
810
-7
/ cm
-1
Investigations using Cavity Investigations using Cavity Enhanced Absorption Enhanced Absorption
SpectroscopySpectroscopy
High spectral resolution (~60 MHz)
• Water vapour overtones in ambient air (vis)• Formaldehyde (~1.5 m) at 4 mbar
Investigations using Cavity Investigations using Cavity Enhanced Absorption Enhanced Absorption
SpectroscopySpectroscopy
5
10
15
20
~
rel.
abso
rban
ce
/ cm-1
6616.5 6617.0 6617.5 6618.0 6618.5
1511.4 nm 1510.8 nm
rotationally resolved
Z-scans of Pt-octaethylporphyrin Z-scans of Pt-octaethylporphyrin in toluenein toluene
Pt-OEP in toluene (8.6 x 10-5 M) Energy per pulse 8 J.
Closed aperture:’= 7.7 x 10-16 m2 W-1
0.0 0.5 1.0 1.5 2.0 2.5 3.00.8
0.9
1.0
1.1
1.2
1.3
norm
. tra
nsm
issi
on
z / mm
Open aperture:| | = (3.97±0.09) x 10-9 m W-1
0 10 20 30 40 50
1.0
1.1
1.2
1.3
1.4
norm
. tra
nsm
issi
on
z / mm
Synthesis of metal Synthesis of metal nanoparticles by laser nanoparticles by laser
ablationablation
lens
Nd:YAG532 nm
irises x
metal (target)
zy···· ·
······· ···················
·······
··
·
······ ······
cell
H2O
200 400 600 8000.00.20.40.60.81.01.21.4
optic
al d
ensi
ty
/ nm<d>~30 nm
Group MembersGroup Members Academic StaffProf. M. Mansfield (general supervision)
Post-Doctoral FellowsTo be appointed( CEAS and IBBCEAS – multi-component trace gas detection)
PhD StudentsE. Gash (CRD, nonlinear dynamics of naphthalene)M. Staak (CEA, formaldehyde, photolysis products - HO2)K. Lynch (Surface enhanced Raman scattering) One position vacant
Masters StudentsS. O’Brien (z-scan measurements of porphyrin solutions)A. Walsh (z-scan measurements of porphyrin thin films)[ R. Healy (Nanoparticle formation by laser ablation – alloys) ]
Research CollaborationsResearch Collaborations University College Cork – Physics DepartmentProf. D. Nikogosyan, Dr. A. Dragomir(nonlinear absorption measurements)
University College Cork – Chemistry DepartmentProf. P. Brint (LIF, LIP, forbidden transitions, supersonic jets)Prof. J. Sodeau, Dr. J. Wenger (atmospheric chemistry)Dr. J. Holmes, Dr. M. Morris, Prof. T. Spalding(nanoparticles and nanostructures, TEM)Prof. D. Burke (laser assisted electrocatalysis)
Technical University Berlin, GermanyProf. A. Hese, S. Fiedler (CRD spectroscopy, IBBCEAS)
Max-Planck-Inst. Biophys. Chemistry, Göttingen, GermanyProf. J. Troe (liquid phase spectroscopy and kinetics)
Univ. Paris-Sud (Dr. Orphal), Niels-Bohr-Inst. Copenhagen (Prof. Heimburg), Warsaw University (Dr. Borowicz) …. etc.
Future activitiesFuture activities
Multi-component gas analysis using Incoherent Broad-Band Cavity Enhanced Absorption Spectroscopy
Detection of NO2, NO3, O3 , H2O, HONO … (vis)
Alloy nanoparticle synthesisNew materials for SERS
Surface Enhanced (Resonance) Raman ScatteringPorphyrins and proteins on particle surfaces