Laser Spectroscopy Group

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Laser Spectroscopy Group

• Department of Physics
• NUI - University College Cork
• Cork, Ireland

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Research 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

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Molecular Absorption Spectroscopy

• 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
  Spectroscopy
• Xenon Lamp based (UV / vis / near IR) Static
  gas.
• S.E. Fiedler, A. Hese, A.A. Ruth Chem.
  Phys. Lett. 371 (2003) 284-294.

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Cavity Ring-Down Spectroscopy

• 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

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Principle of Cavity Ring-Down (CRD)
?1
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Principle of Cavity Ring-Down (CRD)
laser pulse of a dye laser
?2
mirror (Rgt0.999)
I0
I1
?2
I2
.. In
?
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Examples of investigations using Cavity
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.

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Experimental Setup
Excimer Laser (XeCl, 308 nm)
Dye Laser
Probe
HR Mirror
Iris
Shutter
Pump
Vacuum Cell
Lens
Filter
PMT
Digital Oscilloscope
GPIB
Computer
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Excimer Laser
Shutter / Lens
Dye Laser
PMT
CRD Mirror
CRD Mirror
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Oscillations
793 s
Conditions Pnap 0.10 mbar PHe 77.5 mbar
EPuls 21.4 mJ T 24.1 oC
561 s
494 s
483 s
time / hrs.
20 UV Pulses
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Investigations using Cavity Enhanced Absorption
Spectroscopy
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Investigations using Cavity Enhanced Absorption
Spectroscopy

• High spectral resolution (60 MHz)
• Water vapour overtones in ambient air (vis)
• Formaldehyde (1.5 ?m) at 4 mbar

1511.4 nm
1510.8 nm
rotationally resolved
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Z-scans of Pt-octaethylporphyrin in toluene
Closed aperture ? 7.7 x 10-16 m2 W-1
Open aperture ? (3.970.09) x 10-9 m W-1
Pt-OEP in toluene (8.6 x 10-5 M) Energy per
pulse 8 ?J.
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Synthesis of metal nanoparticles by laser ablation
ltdgt30 nm
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Group Members

• Academic Staff
• Prof. M. Mansfield (general supervision)
• Post-Doctoral Fellows
• To be appointed
• ( CEAS and IBBCEAS multi-component trace gas
  detection)
• PhD Students
• E. Gash (CRD, nonlinear dynamics of naphthalene)
• M. Staak (CEA, formaldehyde, photolysis products
  - HO2)
• K. Lynch (Surface enhanced Raman scattering)
• One position vacant
• Masters Students
• S. OBrien (z-scan measurements of porphyrin
  solutions)
• A. Walsh (z-scan measurements of porphyrin thin
  films)
• R. Healy (Nanoparticle formation by laser
  ablation alloys)

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Research Collaborations
? University College Cork Physics
Department Prof. D. Nikogosyan, Dr. A.
Dragomir (nonlinear absorption measurements) ?
University College Cork Chemistry
Department Prof. 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,
Germany Prof. A. Hese, S. Fiedler (CRD
spectroscopy, IBBCEAS) ? Max-Planck-Inst.
Biophys. Chemistry, Göttingen, Germany Prof. J.
Troe (liquid phase spectroscopy and
kinetics) Univ. Paris-Sud (Dr. Orphal),
Niels-Bohr-Inst. Copenhagen (Prof. Heimburg),
Warsaw University (Dr. Borowicz) . etc.
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Future activities

• Multi-component gas analysis using Incoherent
  Broad-Band Cavity Enhanced Absorption
  Spectroscopy
• Detection of NO2, NO3, O3 , H2O, HONO (vis)
• ? Alloy nanoparticle synthesis
• New materials for SERS
• ? Surface Enhanced (Resonance) Raman Scattering
• Porphyrins and proteins on particle surfaces