1. Ultracold electron (& ion) source Edgar Vredenbregt with Merijn Reijnders, Gabriel Taban, Wouter Engelen, Nicola Debernardi, Bas van der Geer, Peter Mutsaers, Seth Brussaard and Jom Luiten Department of Applied Physics

2. 2011 Cockcroft Meeting Daresbury PAGE 2 27-9-2016 II MOT Magneto-Optical atom Trap (MOT) N = 10 8 rubidium atoms  = 0.9 mm, n = 10 10 cm -3 T < 0.001 K Laser cooling & trapping: (Nobel 1997) 6 laser resonant beams + quadrupole magnetic field

3. 2011 Cockcroft Meeting Daresbury PAGE 3 27-9-2016 TeTe Ultracold Plasma II Electron temperature Rolston, Killian, Bergeson,... & plasma effects

4. 2011 Cockcroft Meeting Daresbury PAGE 4 27-9-2016 Ultracold Rydberg gas II Gallagher, Pillet, Comparat,...

5. 2011 Cockcroft Meeting Daresbury PAGE 5 27-9-2016 Rb+Rb+ e-e- V II Ultracold ion and electron source - develop into practical source - investigate properties: cold! Ultrafast electron diffraction (Scholten) Low-energy microscopy (Comparat, Pillet) Focused ion beams & ion microscopy (McClelland) UCES UCIS Luiten group @ TU/e:

6. 2011 Cockcroft Meeting Daresbury PAGE 6 27-9-2016 Characterizing particle beams: brightness “conventional” approach: minimize source area - high current density - large space-charge effects - large divergence - large energy spread Liquid Metal Ion Source (LMIS): Ga Needles & Carbon NanoTubes (CNT) cold source: minimize   T keep source area large  minimize Coulombic effects high angular intensity low current density

7. 2011 Cockcroft Meeting Daresbury PAGE 7 27-9-2016 What is (ultimately) possible? simulations in Claessens et al, PRL 95 (2005) charge: up to 1 nC temporal length: fs range current: 20 A @ 100 pC emittance: 0.04  m @ 100 pC (normalized) brightness: 10 14 A/rad 2 m 2 (normalized) Other characteristics: ● “new source” for every shot (so far: 3 yrs) ● ionization volume = overlap of 2 laser beams → 3D shaping for control of space charge forces ● spin-polarized trapped atomic gas → polarized electron source

8. 2011 Cockcroft Meeting Daresbury PAGE 8 27-9-2016 Rb+Rb+ e-e- V II Ultracold ion and electron source investigate properties: low T Ultrafast electron diffraction (Scholten) Low-energy microscopy (Comparat, Pillet) Focused ion beams & ion microscopy (McClelland)

9. 2011 Cockcroft Meeting Daresbury PAGE 9 27-9-2016 ultracold i/e source setup ultracold particle accelerator

10. 2011 Cockcroft Meeting Daresbury PAGE 10 27-9-2016 2 cm Atom trap inside coaxial accelerator (cross section) cathode UHV laser beams (trapping, ionization) V 30 kV 300 ps e-e-

11. 2011 Cockcroft Meeting Daresbury PAGE 11 27-9-2016 Temperature from spot size 11 28-01-2010 measure extract linear beam transport diver- gence source size spot size known CCD Image Accelerator & trap transport coefs A,B known linear beam transport

12. 2011 Cockcroft Meeting Daresbury PAGE 12 27-9-2016 Electron spot size vs. lens strength: “waist scan” 12 σ xi = 30 μm U = 2.1 keV F = 1.13 kV/cm λ = 474 nm T = 405 ± 43 K Solenoid Current (A) Spot Size (  m) data vs GPT model T = 35 K

13. 2011 Cockcroft Meeting Daresbury PAGE 13 27-9-2016 Electron spot size vs. beam energy: “waist scan” data & GPT particle tracking simulations

14. 2011 Cockcroft Meeting Daresbury PAGE 14 27-9-2016 Temperature vs. excess energy 14 T ~ 15 K

15. 2011 Cockcroft Meeting Daresbury PAGE 15 27-9-2016 Temporal bunch length  = 2 ns rms @ 30 cm limited by pulse length laser (YAG-pumped dye) photo-ionization in a DC field working towards 1 ps (ultrafast OPA) electrons laser rms = 2 ns arrival time distribution @ MCP

16. 2011 Cockcroft Meeting Daresbury PAGE 16 27-9-2016 pulsed laser excitation Shorter bunches: “frozen” Rydberg gas n=35 n=29 n=26 pulsed field-ionization of excited Rydberg atoms principal quantum number n higher n → lower ionization field → smaller U wait

17. 2011 Cockcroft Meeting Daresbury PAGE 17 27-9-2016 Field ionization experiment: “waist scan” ● S states; T e = 10 K ● D states; T e = 35 K Measurement: 0.8 ns rms (electronics) Simulations:  = 50 ps (?) @ 30 cm from source ( limited by field homogeneity accelerator ) Atomic physics (Robicheaux, Auburn):  = 0.5 ns (zero- charge limit) n= bunch length

18. 2011 Cockcroft Meeting Daresbury PAGE 18 27-9-2016 Faster pulses: femtosecond OPA 100 fs & 10  J 5 nm BW → T = 200 K waist scan lens strength ● vary wavelength and field strength (excess energy) ● similar analysis → source temperature

19. 2011 Cockcroft Meeting Daresbury PAGE 19 27-9-2016 Femtosecond OPA results 100 fs & 10  J 5 nm BW → T = 200 K still achieve T ≈ 15 K near threshold ! (?) T ≈ 15 K Q ≈ 0.1 fC

20. 2011 Cockcroft Meeting Daresbury PAGE 20 27-9-2016 Excess energy Modeling: potential landscape Stark shift photon

21. 2011 Cockcroft Meeting Daresbury PAGE 21 27-9-2016 Electron trajectories U z r Classical electron trajectories Bordas et al., PRA 1998 3/2 kT < E exc dynamics from Coulomb and Stark potential not equipartitioned

22. 2011 Cockcroft Meeting Daresbury PAGE 22 27-9-2016 Femtosecond OPA results vs. Bordas model 100 fs & 10  J 5 nm BW → T = 200 K ● dynamics model (Bordas) explains fs data ! (?) ● where is the laser's bandwidth?

23. 2011 Cockcroft Meeting Daresbury PAGE 23 27-9-2016 UCES: Rb+Rb+ e-e- V II T e  15 K  < 1 ns (ps) 10 5 e per pulse T + = 1 mK UCIS T i  1 mK 1 eV ion beams 20 meV energy spread Ultracold electron AND ion source

24. 2011 Cockcroft Meeting Daresbury PAGE 24 27-9-2016 Conclusions Demonstrated application of the UCP: ultracold electron (and ion) source Alternate way to achieving high brightness; large coherence length; low energy spread Applications in UED, FIB and electron/ion microscopy Electron source T  15 K,  < 1 ns (ps), 10 5 e p.p. Normalized emittance 10 nm Claessens et al., PRL 95, 164801 (2005) Claessens et al., Phys. Plasmas 14, 093101 (2007) Van der Geer et al., JAP 102, 094312 (2007) Taban et al., PRST-AB 11, 050102 (2008) Reijnders et al., PRL 102, 034802 (2009) V.d. Geer et al., Microscopy and Microanalysis 15, 282 (2009) Reijnders et al., PRL 105, 034802 (2010) Taban et al., EPL 91, 46004 (2010) Reijnders et al., JAP 109, 104308 (2011)

25. 2011 Cockcroft Meeting Daresbury PAGE 25 27-9-2016 Outlook ultrafast & cold electron source for UED ultracold FIB with FEI Company quantum degenerate electron beams? n=10 18 /m 3, T=1 mK reduce disorder-induced heating effects (bring order into the system) order excited atoms: “Rydberg crystals” (Pohl et al) with Kokkelmans, Van Bijnen dipole-blockade mechanism: partial order optical lattice: order ground- state atoms J Phys B (2011) in press

26. 2011 Cockcroft Meeting Daresbury PAGE 26 27-9-2016 Bert Claessens (PhD 2007) Gabriel Taban (PhD 2009) Merijn Reijnders (PhD 2010) Thijs van Oudheusden (PhD 2010) Nicola Debernardi (PhD) Wouter Engelen (PhD) Marloes van der Heijden (MSc) Roland van Vliembergen (MSc) Bas van der Geer – Pulsar Physics (GPT) Several students – Msc and BSc Marieke de Loos – Pulsar Physics (GPT) Peter Mutsaers & Seth Brussaard - staff Jom Luiten – PI Robert Scholten (University of Melbourne) Bradley Siwick (McGill University) Fabrizio Carbone (EPFL Lausanne) Nico Sommerdijk (TU Eindhoven) Netherlands Technology Foundation NL Foundation for Fundamental Research on Matter FEI Company Technical support Louis van Moll Jolanda van de Ven Eddie Rietman Ad en Wim Kemper Harry van Doorn Iman Koole Acknowledgement NL Organization for Scientific Research Authors of the General Particle Tracer (GPT) code