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. I0I0 I1I1 I2I2 mirror (R>0.999) laser pulse of a dye laser ….. I n 1 no absorption 1 fit I = A exp(-t/  crd ) Principle of Cavity Ring-Down (CRD)

6. fit I = A exp(-t/  crd ) Principle of Cavity Ring-Down (CRD) I0I0 I1I1 I2I2 mirror (R>0.999) laser pulse of a dye laser ….. I n 2 absorption 2

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 PMT Pump Probe Computer Filter Vacuum Cell HR Mirror Digital Oscilloscope GPIB Lens Iris Shutter

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

10. Oscillations 793 s 494 s 483 s 561 s Conditions: P nap = 0.10 mbar P He = 77.5 mbar E Puls = 21.4 mJ T = 24.1 o C 20 UV Pulses time / hrs.

11. Investigations using Cavity Enhanced Absorption Spectroscopy

12. High spectral resolution (~60 MHz) Water vapour overtones in ambient air (vis) Formaldehyde (~1.5  m) at 4 mbar Investigations using Cavity Enhanced Absorption Spectroscopy 1511.4 nm1510.8 nm rotationally resolved

13. Z-scans of Pt-octaethylporphyrin in toluene Pt-OEP in toluene (8.6 x 10 -5 M) Energy per pulse 8  J. Closed aperture:  ’= 7.7 x 10 -16 m 2 W -1 Open aperture: |  | = (3.97±0.09) x 10 -9 m W -1

14. Synthesis of metal nanoparticles by laser ablation lens Nd:YAG 532 nm irises x metal (target) z y · ··· · · · · ··· · ··· · · · ··· · · · ··· · · · · · ··· · · · · · · · ·· · · · · ··· · · cell H2OH2O ~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 - HO 2 ) 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 NO 2, NO 3, O 3, H 2 O, HONO … (vis)  Alloy nanoparticle synthesis New materials for SERS  Surface Enhanced (Resonance) Raman Scattering Porphyrins and proteins on particle surfaces