AMO Instrumentation: Review, Status, and Design for Multiphoton X-ray Processes

1. AMO InstrumentationLehman Review Presentation, July 2007John Bozek, LCLS • Scientific goals of the instrument • Status before the CR • Effects of the CR & other descoping • Current designs • Looking forward AMO Team Leaders: Louis DiMauro (OSU) Nora Berrah (WMU)

2. Scientific Goals of the AMO instrumentation • Investigate multiphoton and high-field x-ray processes in atoms, molecules and clusters • Multi-photon ionization/excitation in atoms/molecules/clusters are well known in optical and recently EUV regime – little known about multi-photon inner-shell processes • Accessible intensity on verge of high-field regime where field of light interacts with electrons in the sample • Study time-resolved phenomena in atoms, molecules and clusters using ultrafast x-rays • Inner-shell side band experiments using LCLS and laser photons • Photoionization of aligned molecules • Temporal evolution of state-prepared systems

3. Scientific Goals – Multiphoton Ionization

4. Scientific Goals – Multiphoton Ionization

5. Scientific Goals – Field Ionization Multiphoton ionization Tunneling ionization Above-threshold-ionization (ATI) And subsequent high harmonic generation (HHG) Keldysh parameter:

6. Scientific Goals - Sidebands Two photons of different energy in interaction region at same time can result in multiphoton ionization (i.e. FLASH FEL & laser) Phenomenon provides a means to measure temporal overlap of two pulses – i.e. providing measure of temporal overlap between LCLS & laser • Measured relative jitter between two beams of 250fs using Xe 5p photoionization P. Radcliffe et al, APL, 90, 131108, 2007.

7. Scientific Goals – Temporal Evolution • Femtosecond time scale of LCLS pulse allows us to follow evolution of chemical reactions, but not fast enough for electron dynamics (requires <1fs).

8. Scientific Goals – Imaging Small System • Motivated by strong desire to image free clusters • Recent results from T. Moeller’s group at FLASH • Large RG clusters • Sometimes see twins • sometimes two in beam

9. Proposed AMO High Field Instrument Concept

10. Review of Concept…Dec 08, 2006 • Reviewers: Phil Heimann (ALS, LBNL), Gunther Haller (SLAC), Donghui Lu (SSRL, SLAC) • Review Findings: “The committee found the science & technical requirements well-undestood…recommend that the experimental team move forward to preparing a baseline design…” • 20 individual comments addressing different areas of the instrumentation which will be addressed in the PDR

11. Instrument Concept as presented: • Along with particle imaging, laser and controls

12. Conceptual Instrument designs • Gas jet (from below) • Five electron TOF spectro’s • 1of 3 ion spectrometers • X-ray emission spectrometers

13. Layout of instrument into hutch 2

14. Changes since SCR & previous Lehman review • Continuing resolution – reduction of funds available in FY07 & FY08 with bifurcation of project completion into 4a and 4b • Delayed focusing optics, x-ray emission spectrometers, ion imaging spectrometers • Descoped Particle Imaging end-station and high-power amplifier for laser system to cover cost of timing fibre • Advanced design towards a Preliminary Design Review

15. Schematic of Instrument at 4a • 4A instrument has capability of measuring ions and electrons from gaseous targets together with diagnostics

16. Schematic of Instrument at 4b • Add remaining capabilities for 4b

17. CR impacts on AMO Scientific Capabilities • Retained most of core capabilities in 4a instrument • Gas jet source for low density atomic – cluster targets • Electron & ion spectrometers to monitor photoionization processes • 2-3mJ laser to provide pulsed ionization capabilities for off-line testing/debugging etc • Diagnostics to monitor pulse wavelength, bandwidth, temporal overlap with laser, size and position • Primary limitation – lack of focusing optics will preclude high-field studies initially

18. AMO Instrument Design - Overview • Mechanical Design Team – Nadine Kurita (LUSI Lead Engineer), Jean Charles Castagna, Michael Kosovsky, Jim Defever

19. AMO Instrument Design – beam rate shutter • LCLS rate 120Hz • Some detectors/exp. Schemes may want lower rate or even single shot

20. AMO Instrument Design – focusing optics • Peak intensity depends on size of beam focus – accessible physics depends on intensity

21. AMO Instrument Design – electron spec’s • Based on a successful time-of-flight (TOF) design from D. Lindle’s (UNLV) group • Five spectrometers arrayed around interaction region to measure dipole & non-dipole angular distributions

22. AMO Instrument Design – diff. pumping • Isolate chamber from optics & diagnostics • Use of rare gases requires turbo pumps • Conflicting requirements of pumping & access

23. AMO Instrument Design – gas jet • 120Hz LCLS rate suggests pulsed valve • Good experience with Proch & Tickl piezo actuated valve • 3 axes motion, pulse duration & sync control

24. AMO Instrument Design – ion spectrometers • One of three spectrometers – simple ion TOF, velocity map imaging & ColTRIMS momentum imaging • Ion TOF will measure charge state & probe multiple ionization • Velocity map imaging maps ion velocity onto concentric rings on detector – provides quick look at ion momenta • ColTRIMS is the ultimate AMO detection (especially when combined with coincident electron detection • Suffers many limitations due to detector

25. AMO Instrument Design – magnetic shielding • Detection of charged particles requires nulling of magnetic field • Two schemes – high permeability shielding (mu-metal) – OR – Helmholtz coils • Shielding is passive but careful design required to ensure adequate attenuation, particularly junctions • Helmholtz coils are dynamically tunable but possible to set them wrong • Pursuing shielding option since high KE electron from inner-shell photoionization not very sensitive

26. AMO Diagnostics – magnetic bottle spectrometer • Primary diagnostic – provides wavelength, bandwidth, temporal overlap with laser • High collection efficiency – up to 2π angle P. Kruit & F.H. Read, J. Phys. E 16 313 (1983).

27. AMO Diagnostics – differential pumping • Transparent AMO sample allows diagnostics AFTER experiment • Want to decouple high-field end-station from diagnostics – may want to use each independently Differential pumping optically aligned to axis of diagnostics chamber, then whole chamber aligned to beam axis

28. AMO Diagnostics – beam screens • Simple diagnostic of beam position/size • Two YAG screens positioned ~1m apart monitored simultaneously • Requires 500nm YAG coating on 200nm SiN membrane for ~50% transmission

29. AMO Diagnostics – total energy monitor • Pulse power will vary dramatically shot-to-shot • XTOD is providing gas detector in FEE to measure pulse energy • Simultaneous measurement in diagnostics will highlight any significant losses in transport of pulse through 5 optics and multiple differential pumping stages

30. AMO Diagnostics - interconnectivity • High-field physics chamber and diagnostics chamber connected by bellows – make sure not to overextend • Significant difference in position depending on optics in/out – 30mrad deflection

31. AMO Instrument – looking forward • Complete Preliminary Design Review – Aug 07 • Finish detailing high field physics chamber, diagnostics • Advance design of Particle Imaging • Make decisions on emission spectrometers • Carry design to completion – Nov 07 • Build/buy and assemble – Jul 08 • Testing with laser – Nov 08 • Ready for first light – Jan 09