1 / 14

Technical aspects of a VMI experiment

Technical aspects of a VMI experiment. ICONIC kickoff meeting Berg en Dal 16-18 Oct 2009. Central idea. Start a technical discussion on the ICONIC website Collate ideas on a FAQ list Use these as input for Training Schools. Main questions. How to do a VMI experiment?

ash
Télécharger la présentation

Technical aspects of a VMI experiment

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Technical aspects of a VMI experiment ICONIC kickoff meeting Berg en Dal 16-18 Oct 2009

  2. Central idea • Start a technical discussion on the ICONIC website • Collate ideas on a FAQ list • Use these as input for Training Schools Berg en Dal, 16-18 October 2009

  3. Main questions • How to do a VMI experiment? • How to analyze the results? → What do you want to know? • Angular – β, γ parameters • Speed – branching b/w different channels Berg en Dal, 16-18 October 2009

  4. Molecular beam preparation • Pulsed valve / skimmers / chopper wheel • Cooling / heating nozzle • Hexapole state selector • IR excitation, Raman excitation • Ablation laser (MALDI) • Discharge AC/DC Berg en Dal, 16-18 October 2009

  5. Reactions / (in)elastic scattering • Crossed beams: on- / off-axis; fixed / differential angle • Single beam: co-expansion; single collision conditions (Theo) • Steric effects: oriented molecules • Ion-molecule / molecule-molecule / … Berg en Dal, 16-18 October 2009

  6. Photodissociation exps • Lasers for dissociation, REMPI detection • Single- / multiple colour • Laser polarization: linear ↔↕/ circular LR • Precursor preparations, e.g. OH from H2O Berg en Dal, 16-18 October 2009

  7. Detection • REMPI (1+1’)/(2+1’) • REMPI vs non-resonant MPI: all states the same sensitivity? • Electron recoil • Rydberg tagging + PFI • TOF: pulsed extraction? • Slice Imaging • Pulsing MCP’s, slow extraction • Laser sheet slicing • Cylindrical / spherical lens? Berg en Dal, 16-18 October 2009

  8. Data analysis • Without inversion method • Raw image analysis • Slice images analysis • Forward convolution (simulation) • With inversion method • Algorithms: BASEX, Iterative inversion, onion, Hankel, … • Programs: e.g. Jean-Paul Visticot (JPV) • Extraction angular & speed distributions: differences in programs. • From velocity to TKER distribution • Apparatus function: how to correct for image distortions, centroiding, sharpening / smoothing / deconvolution ideas. Berg en Dal, 16-18 October 2009

  9. How to set up: • Spectroscopy: laser wavelength scan • Doppler scanning (not for bound-free transitions) • Use broad / narrowband laser? • Autotracker; KDP, BBO X-tals • Zoom lens for VMI (to be developed, MarcV did it for electrons) • Electron imaging (avoid magnetic fields) • Coincidence exps: ion/electron; ion/ion • Oriented molecules / steric effects (MauriceJ) • Laser polarizations + data analysis ank, bnk (PeterR, ClaireV) • Proper calibration of TKER • Deconvolution 2-step dissociation • Flux-to-density transformation (George McBane) Berg en Dal, 16-18 October 2009

  10. How to deal with: • Laser instability? • Pulse-to-pulse fluctuations →multiphoton branching changes • Background subtraction • Detector inhomogeneities • Event counting / sequence summing? • error propagation in analysis • CCD Peltier cooling: dark counts reduction • Choice of CCD camera + MCP detector + PS/scintillator • Alternative: MediPix CCD for ions/electrons directly → pressures up to 1 torr. Berg en Dal, 16-18 October 2009

  11. What is the status of: • 3D imaging • 2 cameras; w/wo image intensifier (Zajfman) • Double exposure camera (WimvdZ, MarcV) • Delay line detectors (Gericke, RoentDek) • Other x,y,t cameras? (multi-anode, MediPix: NIKHEF) • FEL exps (THz region) Wim vdZ • Hi rep rate (FELIX) • μs macro pulse + pulsed extraction → space focusing (Joost Bakker) • Fs pump-probe exps (Soep, BenW, ValerieB, MarcV) • Study wavepacket evolution • Pulseshape optimization via genetic algorithms • CW exps • Spatial mode imaging • Multimass imaging (MarkB) • UV power measurement Berg en Dal, 16-18 October 2009

  12. Electrical discharge issues • AC/DC? • Electrode configuration? • Ground loops → camera failure • Current limitation • Background signals from plasma: ions, electrons, excited atoms, X-rays • Use deflection E-field? • Different plasma source? Microwave? • Beam stop for large center dot? Berg en Dal, 16-18 October 2009

  13. Electrode design • Flat plates, thick/thin • Rings • Shapes • Pulsed extraction pulsing a single electrode (Theo) • Simion, use version with time-varying extraction (Chris) • Status of automated design with genetic algorithms (M. Vrakking) Berg en Dal, 16-18 October 2009

  14. Example Photodissociation of CH3OH → CH3(v2) + OH(v=1,2,3,..) We’d like to know the OH(v) branching v=0:1:2:… • We can detect CH3(v=0) REMPI • Or CH3 non-resonant MPI • Or detect OH(v=0,1,2,…) REMPI • Or non-laser based ionzation? X-ray? e-impact? • VUV 1 photon ionization, synchrotron (Nahon,Orsay) Berg en Dal, 16-18 October 2009

More Related