Prospects and applications of an ultrafast nanometric electron source

Prospects and applications of an ultrafast nanometric electron source Peter Hommelhoff Catherine Kealhofer Mark Kasevich Physics and Applied Physics, Stanford University 1. Ultrashort pulse lasers Femtosecond frequency combs: master the laser electric field External pulse broadening and recompression 2. Tungsten field emission electron emitter Atomic level surface control Single atom tip 3. Femtosecond Laser induced frequency electron emission comb: comb: Field Field emission tip: tip: Extremely low low jitter jitter oscillator brightest electron source source Optical tunnel emission and photo-assisted field emission Very Very high high peak peak electric electric field field Sub-laser cycle emission duration (quasi-static process) 4. Prospects and applications SLAC Advanced Instrumentation Seminar, Jan. 24, 2007

Ultrafast electrons pulses Laser pulses emitted from a femtosecond frequency comb (synced to atomic clock): extremely low jitter Tungsten field emission tip: brightest DC electron source (point source) Electron source for various applications: Ultrafast X-ray sources Time-resolved electron microscopy Ultrafast A/D-converters Novel laser accelerators Gamma ray source Guided electron interferometers Miniaturized focusing and scanning setup (possibly laser dispersion control): mitigate electron pulse broadening

1. Ultrashort pulse lasers Femtosecond frequency combs: master the laser electric field External pulse broadening and recompression 2. Tungsten field emission electron emitter Atomic level surface control Single atom tip 3. Laser induced electron emission Optical tunnel emission and photo-assisted field emission Sub-laser cycle emission duration (quasi-static process) 4. Prospects and applications

Ti:Sapph crystal: Extremely broad gain medium Venteon picture Spectral broadening through optical Kerr effect Multilayer mirror dispersion control 8 fs (3 optical cycles) 150MHz 500mW ~1nJ P. Hommelhoff, Prospects and applications of an ultrafast Steinmeyer nanometric al., Science electron 1999 source, SLAC AIS, 01/24/2007

Frequency comb

Frequency comb Intensity Invented in 1998, 2005 Nobel Prize in Physics Frequency Fourier transformation State of the art: carrier envelope jitter as small as 60 as (1 as = 10-18 s)

Pulse broadening and recompression ~1mm Measured AC trace < 8 fs FWHM Calc. from Measured Calc. spectrum el. field AC assuming trace a flat phase Delay (fs) Laser output After photonic crystal fiber stub

Field emission and field ion microscope (FEM/FIM) FEM e - - + Ultra-high vacuum FIM ions + - Low pressure image gas (He or Ne) Vacuum vessel Microchannel plate detector with phosphor screen and CCD camera ~1 2004-02-25 @19-21-14 6UHZWSB.tif 2004-02-25 @19-16-10 56IW4J6A.tif

Atomic resolution surface control Hemispherical cut through W: Time series of images at a tip voltage slightly above field evaporation threshold Color coded: degree of protrusion 18 nm radius of of respective atom curvature tip Red: most protruding, green least W single crystal wire in <111> orientation

Single atom tip the ultimate source Stable up to ~10nA Inv. Brightness: ~10 10 A/(cm 2 sr) huge! FIM Evaporate Pd onto W(111) tip and anneal: grow pyramid FIM Electrons are emitted from a single atom brightest source We routinely make those tips in our lab

Light induced electron emission processes Photo-assisted field emission γ >> 1: multiphoton emission Optical field emission Energy Energy Φ μ hω hω Conduction band e - Conduction band e - distance distance Metal Vacuum Metal Vacuum Both processes are prompt Analogous to tunnel ionization in atoms

Setup camera Microchannel plate + phosphor screen 125 μm 100 nm Spot radius (1/e 2 ) ~ 4 μm Peak power ~12 kw Peak intensity 4 10 10 W/cm 2 Laser peak el. field 0.5 2 GV/m (field enhancement)

First results

Autocorrelator with tip as (non-linear) detector U tip = 330 220 652 V delay delay (a.u.) (a.u.)

Tunable non-linearity

Simulation Model: Electron emission from surface state ground state wavefunction with kinetic energy = Fermi energy. Laser modulates barrier Integrate time-dep. Schrödinger eq. Simulation result with no adjustable parameters. PH, C. Kealhofer, M. Kasevich, PRL 97, 247402 (2006)

Simulation: time-dependent flux Driving laser electric field: 8 fs pulse Electron current: A single 700 as pulse Electron current: Double pulse 700 attosecond emission duration Electric field driven Pulse shaping with CE dependence φ: carrier envelope phase (CE phase) PH, C. Kealhofer, M. Kasevich, PRL 97, 247402 (2006)

30nm radius tip without laser Field emission images Atomic size emission area with laser Up to 98(2)% photoelectrons (limited by dark count rate) Field ion microscope image 7 atoms emitting ~2nm diameter area PH, Y. Sortais, A. Aghajani-Talesh, M. Kasevich, PRL 96, 077401 (2006)

GLAST X-ray source needed for High-speed (secure) deep space and inter-satellite communication (DARPA interest) Satellite X-ray radar Remote sensing

Ultrafast x-ray source laser pulse electron lenses Maintain timing in electron emission: ok. Maintain timing during timeof-flight: to be demonstrated Maintain timing during x-ray emission: to be demonstrated DC acceleration to ~100kV ~0.6c dispersion management ~ 5mm? target Orders of magnitude advance in timing resolution over stateof-the-art.

Arbitrary optical waveform to arbitrary x-ray waveform Arbitrary X-ray waveform or sequence of X- ray pulses? Maintain electron waveform Prompt X-ray emission Arbitrary electron waveform Arbitrary optical waveform

100 GS/s Analog-to-Digital Converter Today: 2 GS/s, 8-10 bit available Architecture: Electron gun: fsec laser triggered electron source Deflector: MEMS microdeflector/focussing assembly (NovelX) Detector: CNT detector array (F. Pease, Stanford) Pease group, Stanford EE With 100fs electron pulse duration: 100 GS/s, up to 12 bit possible Control timing jitter with femtosecond frequency comb Also: Optical pulse sampling (deflector is optical pulse proof-ofconcept demonstration complete)

Miniaturized emitters and emitter arrays Itoh et al., JVST B, 2004 T. H. P. Chang et al., JVST B, 1996 Mini-SEM is at final stages of development at NovelX. We will get prototype structure within next months.

Time-resolved scanning electron microscopy Brightness: ~10 3 A/cm 2 sterad Field emission SEM (high resolution SEM) Brightness (20 kv): >10 8 A/cm 2 sterad Time resolution so far ~1 ps, we aim for <1 fs (~1000 fold improvement). M. Merano, EPFL (Nature 2005) Sub-nm spatial resolution (>10 times better)

Laser electron acceleration electron lenses dispersion management Integrated SEM: NovelX DC acceleration to 15 100kV 0.2 0.6c Together with T. Plettner, R. Byer (Stanford Applied Physics & SLAC) Taken from Cowan, PRST-AB 2003 see also T. Plettner et al. PRL 2005

Proposed SASE-FEL Table-top gamma ray source Self-amplified spontaneous emission free electron laser field emission tip low energy 2 m ½m laser accelerator high energy beam dump oscillator laser amplifiers undulator ~200 μm cylindrical lens vacuum channel cylindrical lens 1 pc, top view 2 GeV, λu = 200 μm, Lu = 40 cm z rb ~ 200 nm electron λ/2 B ~ 1 T beam y x P. Hommelhoff, Prospects and applications of an ultrafast nanometric electron λ source, SLAC AIS, 01/24/2007 laser beam ~50 μm ~ 40 cm parameters T. Plettner, B. Byer!

Near future Validate attosecond timing of electron emission Currently under way Demonstrate timing resolution and refocusing of electron beam Proof-of-concept for ultra-fast SEM Focus electron beam on x-ray target Demonstrate prompt x-ray generation with bremsstrahlung target Evaluate coherence properties and timing jitter properties

Conclusion Prompt Prompt electron emission from from atomic atomic scale scale source source demonstrated. Sub-1 Sub-1 fs fs electron source; source; emission area area diameter down down to to 2nm 2nm Orders Orders of of magnitude advance in in timing timing and and source source size size Applications: Ultrafast X-ray X-ray source source for for communication Ultrafast A/D A/D converter Table-top gamma gamma ray ray source source (MeV (MeVto to GeV) GeV)