AMO Instrument Planning

1. AMO Instrument Planning Scientific Goals Experimental capabilities End-station layout Outstanding issues Schedule & status

2. AMO Scientific Goals • Capitalize on unique properties of the LCLS pulses to study interaction with simplest forms of matter – atoms, molecules & clusters, matter unencumbered with low-energy long-range collective phenomena • 826-2000 eV on soft x-ray branch – inner shell phenomena • Brightest x-ray source – multi-photon processes, high field studies • Short pulse ~200fs – time-resolved studies, time-evolving states

3. AMO Experimental Capabilities • High Field Physics end-station to study photo-ionization of atoms, molecules, clusters: • Optics to focus beam to ~1mm2– power density • Pulsed gas jet – easier to manipulate sample with pulsed laser if necessary • Electron spectrometers (qty 5) – measure electron KE, dipole and non-dipole asymmetries • Ion spectrometers (qty 3) – charge states, momenta • X-ray fluorescence spectrometers (qty2) – distinct de-excitation channels,charging problems At least initially LCLS will have • Chaotic pulses • Poor synchronization …so also need shot-by-shot diagnostics

4. AMO Pulse Diagnostics • AMO targets usually transparent – can measure pulse following experiment • What do we want to know ? • Photon energy, bandwidth – 0.2% from LCLS? • Pulse energy – 100% variation • Beam position & focal properties – to tune the refocus optics • Temporal relation to laser pump/probe – timing jitter, pulse duration

5. AMO end-station – refocus optics • Need adaptive optics to change spot size (control power), move focus ~1m between end-station and diagnostics • Ideally two sets of optics – for ~1μm focus and <100nm focus

6. AMO end-station – Field Strengths • LCLS Pulse: • 1.1×1013 ph @ 825 eV • 5 B4C mirrors with ~92% reflectivity = 7.2×1012 ph in 137fs (rms) pulse • Intensity will depend on focus size in end-station

7. AMO experiments – High Field Multiphoton ionization Tunneling ionization Above-threshold-ionization (ATI) Keldysh parameter:

8. AMO end-station – Sample source • Pulsed supersonic skimmed jet to match LCLS pulse • to reduce background signal need chamber pressure in low 10-10Torr range • Easier to produce large clusters (>104 atoms) from a pulsed source • Pulsed laser to desorb material from solid target and entrain in rare gas beam for cooling • Retain option of using CW jet, particularly for initial experiments

9. AMO end-station – Ion Spectrometers • Very first experiment – charge state distribution from atomic sample • Integrating TOF spectrometer initially • Velocity map imaging – no m/q resolution but obtain momentum images • ColTRIMS type detection with time and position sensitive detector – difficult if there is too much signal (4-10 events per shot)

10. AMO end-station – Electron Spectrometers • angle-resolved PES examines initial interaction - photoionization • time-of-flight energy dispersion ideally suited to LCLS • Multi-photon processes will be apparent in kinetic energy and angular distribution – many unknown processes

11. AMO end-station – Fluorescence Spectrometers • X-ray emission from highly excited/ionized sample interrogates different electronic states/de-excitation channels • In dense samples, intense LCLS pulse will create numerous electrons/ion • resulting charge density will smear out charged particle momenta – reducing electron and ion spectroscopies’ utility

12. AMO end-station – Laser systems • synchronized laser Ti:Sapphire laser & harmonics • For state preparation, temporal diagnostics, instrument commissioning, etc.

13. AMO Planning – need for diagnostics • Large pulse-to-pulse variations • Power – bolometer • Peak power – magnetic bottle electron spectrometer • Pulse length/arrival time – cross-correlation in magnetic bottle • Smaller variations, but diagnostics useful for • Photon energy/bandwidth – magnetic bottle • Beam position & focal properties – imaging screens or quadrant BPMs

14. AMO Diagnostics – magnetic bottle • High (2π) collection efficiency using asymmetric magnetic field to guide electrons into TOF –requires extensive modeling for high energy electrons • i.e. cross correlation of 12ps frequency doubled Nd:YLF laser pulse with 35.5eV FLASH pulse in photoionization of He M. Meyer et al, PRA, 74, 011401(R) 2006.

15. AMO Planning – high field physics

16. AMO Planning – imaging experiment • Desire within AMO community to use intense LCLS pulse to “image” size-selected clusters and time-evolving states • Considered diffraction of ionic (size-selected) clusters – i.e. what does a C6 cluster look like? • , or Mie scattering of larger clusters, both equilibrium states and temporally evolving states driven by external laser • Neither seems particularly well suited, but trying to describe a workable experiment

17. AMO Planning – hutch layout • Room for three experiments in the first two hutches • Space to install monochromator for future needs

18. AMO Planning – schedule highlights • Design process – through Oct 07 • Begin acquisitions – June 07 • Components arrive – March 08 • Install end-station – May 08 • First light – August 08 • Initial experiments – August 08 • Full capability end-station completed– January 09

19. AMO Planning - Status • Experimental requirements defined – completing Physics Requirement Document • System Concept Review imminent • Experimental apparatus ready for beneficial occupancy • Experimental capabilities ready for first light • Completed experimental apparatus in January 2009