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Atomic and Molecular Physics Ultrafast Laser Physics and Laser Spectroscopy Instrumentation seminar

Atomic and Molecular Physics Ultrafast Laser Physics and Laser Spectroscopy Instrumentation seminar

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Atomic and Molecular Physics Ultrafast Laser Physics and Laser Spectroscopy Instrumentation seminar

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  1. Atomic and Molecular PhysicsUltrafast Laser Physics and Laser SpectroscopyInstrumentation seminar Femtosecond spectroscopy Ultrafast gas phase phenomena Femtochemistry Laser Spectroscopy Laser physics on surfaces PSP-investigations

  2. Lars-Erik Berg Åsa Larsson Renée Andersson Niklas Gador Ming Liu Peter Salén Bo Zhang Marica Sjödin Nils Tillmark M Timmy Sigfrids M Nathan Ross FOI Personnell Femtosecond spectroscopy Ultrafast gas phase Femtochemistry Mats Larsson SU Tony Hansson Peter vd Meulen Peder Royen Pia Johansson Laser Spectroscopy Laser physics Sonoluminiscence PSP-investigations

  3. Fast Phenomena Fast Phenomena -15 -14 -13 -12 -11 Time scale 10 10 10 10 10 s fs ps 3 mm 3 mm Wave train 100 nm 1 nm Band width

  4. Interested visitor at the fs-lab Bo Göran Pia Niklas

  5. Femtosecond spectroscopy The advent of the laser in 1960 and the development of the femtosecond laser with Dt = 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

  6. Vibration of small molecules .. r Oscillation period T~ 100 fs V t = 0 t = T/2 t = T 0 T 2T t r

  7. Fragmentation of molecules r V A* + B A + B 1 Å in 50 fs r

  8. Collisions atoms - atoms r Ar 10 eV - 10 keV + Ar Timescale 100 fs - 1 fs

  9. Other Ultra-fast Phenomena r Electron - hole recombinations Timescale 30 fs - 200 fs Interaction times in liquids Timescale 1ps - 100 ps Fast relaxations in large molecules Timescale 30 fs - 200 fs

  10. Femtosecond delay 1 fs 0.3 mm Wave train 7 fs 2 mm

  11. Wave packets Wave- packet splitting at a Curve- crossing Diabatic states : Adiabatic states : 1 2 V Energy Include V in H0 VNA r TIME Rb2, D system heat- pipe oven TOF Crossed supersonic- effusive beams He: cooling of Rb2 Ar,Kr: Rb2 clusters Rb2, D;A system Effusive beam

  12. Rb, Rb2 Laser copper shield Fluorescence T2 Thermo- couples T1 Experimental Photon counter Mode-locked fiber laser 780 nm; 170 fs; 150 cm-1 computer PM tube Topas 2, OPA Rb2 Topas 1, OPA /2 wave- plate Acetone inlet + prism compressors for both beams delay- mirror Pump: 427nm, 5 J per pulse,1kHz Probe: 927nm, 2 J per pulse,1kHz

  13. Delaystage t 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.

  14. Femtosecond laser: Pump laser, Er-doped fiber laser, kHz 2w YAG laser Dynamics can be studied by Femtosecond spectroscopy .. Non-linear setups TOPAS: 270 nm ... 3 mm WLC generator: White light continuum Mirrors, mirrors, ....

  15. "3D Nozzle": Compressible Flow with Shock, Transition, Turbulence and Unsteadiness H Alfredsson, N Tillmark, T Sigfrids, L-E p = ? Wind tunnel at KTH

  16. Pressure Sensitive Paint • Method: • Laser excitation of pressure sensitive paint • in order to measure the gas pressure over • a surface. • Fluorescence measurements • Life-time measurements Laser light Pressure sensitive paint Fluorescence

  17. Basic photophysics Vibration relaxations SN Photon transitions in an energy diagram of the condensed phase S2 inter system crossing ISC S1 T1 tf tp h fosforescens excitation fluorescens S0

  18. Ruthenium based paint tris(2,2’-bipyridil) ruthenium Ru(bpy) Absorption and emnission spectrum 4w YAG 3w YAG Ar 488 Intensity 2w YAG • 300 400 500 600 700 • wavelength (nm) Binder: urethane, clear, is permeable to oxygen

  19. Pressure measurements Decay - rates Quenching = kq [L*] [O2] 1/t Stern-Vollmer plot [O2]

  20. Instrumentation • Pressure measurements on a surface with a jet nozzle • Measurements in the wind tunnel • Frequency tripled YAG, Ar ion laser chopped, blue diod laser • Mechelle+ICCD or ICCD+filter

  21. ICCD-camera ANDOR iStar Digital delay generator Propagation delay 40 ns Optical gate width <2ns CCD cooling -40oC

  22. Monochromator Resoving power Wavelength coverage 190nm< l < 1.1mm 3 m optical fibre

  23. Mechelle Mechelle

  24. Optical system

  25. Pressure Sensitive Paint

  26. Frequency doubled YAG laser excitation Dt = 5ns, l = 532 nm PSP measurements l t0 = 4.0 (0.2) ms l = 488 nm Ar ion

  27. Time-resolved spectrum 340 350 wavelength

  28. Time-resolved spectra cont.

  29. Sonoluminiscence – Shocktubes High pressure Vacuum Intense ”Planck Radiation” M Lesser, N Apazidis H Alfredsson, N Tillmark, H Essén, Mechanics, L-E B

  30. Experimental setup

  31. Time-resolved spectra cont. I T = ? l