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

2. Berg en Dal, 16-18 October 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

3. 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

4. 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

5. 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 / …

6. 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 H 2 O

7. 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?

8. 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.

9. 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 a n k, b n k (PeterR, ClaireV) Proper calibration of TKER Deconvolution 2-step dissociation Flux-to-density transformation (George McBane)

10. 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.

11. 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

12. 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?

13. 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)

14. Berg en Dal, 16-18 October 2009 14 Example Photodissociation of CH 3 OH → CH 3 (v 2 ) + OH(v=1,2,3,..) We’d like to know the OH(v) branching v=0:1:2:… 1. We can detect CH 3 (v=0) REMPI 2. Or CH 3 non-resonant MPI 3. Or detect OH(v=0,1,2,…) REMPI 4. Or non-laser based ionzation? X-ray? e-impact? 5. VUV 1 photon ionization, synchrotron (Nahon,Orsay)