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Laser Spectroscopy Group

Laser Spectroscopy Group. Department of Physics NUI - University College Cork Cork, Ireland. Research Activities. Molecular Absorption Spectroscopy Luminescence Excitation Spectroscopy Third-order Nonlinear Susceptibilities (Z-scan) Synthesis of Metal Nanoparticles by Laser Ablation

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Laser Spectroscopy Group

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  1. Laser Spectroscopy Group Department of Physics NUI - University College Cork Cork, Ireland

  2. 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

  3. 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.]

  4. 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

  5. laser pulse of a dye laser mirror (R>0.999) I0 I1 1 I2 ….. In  no absorption fit I = A exp(-t/crd) Principle of Cavity Ring-Down (CRD) 1

  6. absorption fit I = A exp(-t/crd) Principle of Cavity Ring-Down (CRD) laser pulse of a dye laser 2 mirror (R>0.999) I0 I1 2 I2 ….. In 

  7. 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.

  8. Experimental Setup Excimer Laser (XeCl, 308 nm) Dye Laser Probe HR Mirror Iris Shutter Pump Vacuum Cell Lens Filter PMT Digital Oscilloscope GPIB Computer

  9. Excimer Laser Shutter / Lens Dye Laser PMT CRD Mirror CRD Mirror

  10. 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

  11. Investigations using Cavity Enhanced Absorption Spectroscopy

  12. 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

  13. Z-scans of Pt-octaethylporphyrin in toluene Open aperture: |  | = (3.97±0.09) x 10-9 m W-1 Closed aperture: ’= 7.7 x 10-16 m2 W-1 Pt-OEP in toluene (8.6 x 10-5 M) Energy per pulse 8 J.

  14. metal (target) irises x cell · · · Nd:YAG · · · · · · · · · · · · · · · · · · · · · · · · · z · · · · · · · · · · · · · y · H2O · · · · · · 532 nm · · · · · lens Synthesis of metal nanoparticles by laser ablation <d>~30 nm

  15. 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. 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) ]

  16. 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.

  17. 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

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