Monochromatic ion and electron beams by ionization of cold atoms

Daniel ComparatLaboratoire Aimé Cotton, CNRS, UPR3321,

Bât. 505, Univ Paris-Sud, Orsay, 91405 FRANCE

Experiments in the « Cold atoms and molecules group »

Cesium Magneto-Optical Trap (P. Pillet, H. Lignier, D. Comparat)-Cold cesium molecules (formation, vibrational cooling, trapping, ..)

Cs,Ytterbium MOT: (D. Comparat, P. Cheinet, P.Pillet) Cold Rydberg atoms (dipole blockade, plasma ….)

Stark & Zeeman (mol.) decelerators (P. Pillet, J. Robert)

CERN: antigravity, antihydrogen, Ps spectroscopy: (L. Cabaret, D. Comparat)

Production of ion and electron sources from cold atoms (P. Pillet, D. Comparat)

-

+

Outline

Electron and ion sources

Laser cooled sources

Ion beam project

Electron beam project

Outlook

Outline

Electron and ion sources

Laser cooled sources

Ion beam project

Electron beam project

Outlook

Ion (focused) source applications

Sputtering

Array of holes Microlens

FIB pattern

FIB image of a Al sample Test surface with various sizes tin (Sn)

balls

Ion and Electron Beam induced deposition

Secondary particles:

M0,M+,M-,…

Imaging

Deposition

Electron source applications

• Particle accelerator, Televisions, …

• Electron spectrometers: • EELS (Electron Energy Loss Spectroscopy)

• Imaging + Scanning microscope

• Electron irradiation: • Mass spectrometry, • Sterilization, Desorption• Linking or breaking polymers

http://ehs.virginia.edu/ehs/ehs.rs/rs.images/sem.coutesy.iowa.state.jpg

Ion source

7nm

Limitations:• few element possible Ga, In, Cs, Bi, Au, Si, + Alloys…

• Gallium pollution

• Wide energy-spread ∆E=5eV

A single wide-spread technology (LMIS)Liquid Metal Ion Source

Electron sources

Limitations:

•Wide energy-spread ∆E=0.3eV

•Monochromators limits flux and brightness

•Complex Optics (chromatism) to focus

Several wide-spread technologies • Thermionic (LaB6)• Photocathode • Cold emission• Plasma

Outline

Electron and ion sources

Laser cooled sources

Ion beam project

Electron beam project

Outlook

Point source / colimated source

Want small A, small WI ~ 1 nA A ~ 100 nm2 E ~ 1-105 eV DE ~1eV

Needs: Mono-Energy (∆E < 0.1 eV) spectroscopy-chemistry-focus

Brightness Br = I/(AWE) : amount of current in a spot

New:

Small area A

Coulomb explosion

Large , ~1W DE eV

Ions +

Electrons -

Conventional sources

Large area A ~ 1 mm2

No Coulomb explosion

Small , W ~1 DE meV

- +LARGE SOURCE

G. Freinkman, A. V. Eletskii, and S. I. Zaitsev, Microelectron. Eng. 73, 139 (2004).

Ionization of COLD ATOMS !

A

A+

Laser

kB Te

1 K ~ 0.1 meV

OTHER ADVANTAGES: Low energy E for less damageLess aberrations (cheaper electrostactic optics)

Ultracold plasma evolution

Ultracold plasma production

0 ns1 ns 100 ns

1 µs5 µs

heating ofelectrons heating

of ionsexpansion

Tions ~ 1 K

Te- ~ 50 K

1 K ~ 0.1 meV

Partial Rydbergrecombination

Physics Reports 449 (2007) 77 – 130

A

A+

Laser

kB TeIn principle

1 K ~ 0.1 meV

not ultracold!

Tem

pera

ture

[K

]

103

10341028104103

Density [m]-3

102

105

104

109

106

107

108

Nebulises Solar Corona

FlamesAuroras

ITER

101

Inside Sun

1010 1022Neutral plasmas ultra - cold

Correlated Plasmas

Γ≥1

plasma screen

InterstellarSpace

Magnetosphere

KineticPlasmas Γ=Epot/Ecin<1

confined: magnetic, inertial, gravitationnalLaser Méga

Joule

Ultra-cold plasma-

-

+

-

Rydberg

atom

Neon

Laser

Browndwarfs

Trapped Ions

“dusty”

Disordered induced heatingThree body recombinaisonTions ~ 1 K Te- ~ 50 K

Proposal for ultracold electron sources from MOT

Pulsed extraction 1MV/cm in 1ns

B > 109 A.rad-2m-2 V-1

Claessens BJ, van der Geer SB, Taban G, Vredenbregt EJ, Luiten OJ.

PRL 95, 164801 (2005) e- diffraction, FEL or accelerator input

Rb MOT Values

Density 1018 m-3

Volume 1 mm3

Temperature 1 mK

Atom Number 10 9 (/s)

Several Elements (alkali, rare gaz, …)

B > 106 A.rad-2m-2 V-1

I ~ 1 nA

Focused <10nm at 1keV

cf. FIB 30keV

Emittance at quantum limit:

Cs

0.1nm sub-ps resolution

For 100eV beam

µeV dispersion

B ~ 1015 A.rad-2m-2 V-1

I ~ 0.5 pA

Cs+ e-n~800E~0.1V/cmR = n2 a0 ~ 1µm

Rydberg + ionization using chirped ns pulse

                  

MCP size of beam

Recent realizations Eindhoven (E. Vredenbregt) Rb MOT: electron pulse

PRL 105, 034802 (2010)

NIST (J. McClelland)

Crion

Liion

2011 New J. Phys. 13 103035

Melbourne (R. Scholten)

Nature Physics 7 785 (2011).

DU < 0.02 eV (ultimate Tion > 10 K)

Beam Energy as low as 1 eV

          

Eacc

All internal (average space charge) potential has been converted into kinetic energy

1nA

                                

differential voltage problem:

~30µm

Example on low energy dispersion

Limitations

Low flux well bellow 1nA

MOT ~ 107-109 atoms/s I < 1nA

Better to use atomic beams

2D-MOT ~ 109-1011 I < 10nA atomic beams ~ up to 1014 I < 1µA

Pulsed behaviour (advantage to play with time dependent

fields)

• Directly ionize atoms (need lots of laser power pulsed laser)

UltraCold Plasma formation NIST PRL 83, 4776 (1999)

• Better to use Rydberg atoms Our PRL 85 4466 (2000) Needs typically 10 000 lower laser power CW laser possiblePossibility to solve the differential voltage problem ?

Outline

Electron and ion sources

Laser cooled sources

Ion beam project

Electron beam project

Outlook

Ion source: Coldjet

V0 V0 0

1Recirculating oven

Beam Creation 2Optical Molasses:Beam Collimation

32D-Mot:

Beam Compression

4Laser excitation to Rydberg state

5Field

IonizationExtraction

6 To FIB ionic

optics

1 2 3 4-5

Longitudinale speed(m/s) 300 300 300 300

Divergence (mrad) 27 0.3 0.3 0.3

Flux (at/s) 1013 1013 1013 1012

Diameter (mm) 1 8 0.2-1 0.2-1

80°C

≤ 250°C

Silica wick

Copper Crucible

Stainless Steel Candelstick

1 mmAdjustable diameter (2 mm)

Pailloux, Review of Scientific Instruments, Volume 78, Issue 2, pp. 023102-023102-6 (2007).

1) Recirculating oven. Beam Creation

2-3 Beam Collimation + compression

4 m long!!

1 cm

2-3 Beam Collimation + compression

• Compression is not standard for a beam with speed v>100 m.s-1

• 1995: Pierre Pillet (Cs)transversal compression

for vz < 150 m.s-1

3 cm interaction zone100 mW laser power

Fluorescence of a cesium atomic beam compressed (a) without optical pumping and (b) with optical pumping

Stress and different thermal coefficients

New system with Viton ring

Screen and crucible Water cooling

Screen

Coldjet chamber

10 cm long compression zone

500 mW laser power we hope to collimate and compress all velocity v < 200 m/s

NEW IDEA: Sisyphus coolingNEW IDEA: Sisyphus cooling

Cool with only100 photon absorption

LASER COOLING FORMOLECULES

Blue detuned: dressed state

4. Ionization: excitation to Rydberg state

Previous experiments: Near threshold laser ionization

Our experiment: Field ionization of Rydberg atoms

Current 1 nA E > 1kV/cm

(waist >10µm) DV = E*waist > 1 Volt

TOO HIGH!!!

Rydberg atoms field ionized at a given electric field E = 1 /16n4 Ionization at a given position No differential voltage problem

Better excitation efficiency (sexc/sion = 104 for n=30)

Choice of the extraction field (n-dependent) with reduction of space charge effects

n~30

Ionization or Rydberg studies in cold atomic sample (Cs MOT)

6s1/2

6p3/2

7s1/2

np3/2

MOT lasers @852nm

Laser diode @1470nm

CW Ti:Sa laser

@750-830nm

Ions or

Rydberg atoms

Trapping Lasers

MCPs

Laser Diode

Ti:Sa Laser

Ions

np

0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6Time (µs)

For 300ns TiSa creating np states + field ionization

Cs+ e-

R = n2 a0 ~ 1µm

Study in electric field: C3/R3

M. Mudrich et al. PRL 95 233002 (2005)

Control of ion kinetic energy (Ice-Rydberg ) ?

Controled ionization: novel ultracold plasma production

Study in zero electric field: C6/R6

M. Viteau et al. PRA 78 040704 (2008)

Collisions Rydberg/Rydberg

Penning Ionization Formation of

an ultra-cold plasma

0 2500 5000 7500 100000

250

500

750

Nom

bre

d'io

ns a

près

10µ

s

nombre initial d'atomes de Rydberg

454443

Collisions

Rydberg/atomes

Black body ?

39

40

41

0 2500 5000 7500 100000

250

500

750

Nom

bre

d'io

ns a

près

10µ

s

nombre initial d'atomes de Rydberg

pp

ss '

E

R

n=39,40,41

np np

ns (n+1)s

ss’

pp

E

R

D

n=43,44,45ns (n+1)s

np np

N. Vanhaecke et al. PRA 71 013416 (2005)

T. Pohl et al. EPJD 40 45 (2006)

18.5 kV

-21.4 kV

Exctraction electrodes

Field ionization

area

Rydberg excitation lasers

Atomic Beam

5. Field Ionization. Electrodes design

0 50 100 150 200 250 300 350 400 4500

20

40

60

80

100

120

Electric field curve created by the 5 electrodes configuration designed with SIMION

Distance along beampath (0.1 mm)

Ele

ctric

fie

ld (

V.c

m-1

) Rydberg excitation in flat electric field No energy shift

Extraction to avoid aberrations

6 To FIB ionic optics• Evaluation of the performances

diameter, dispersion angle, energy spread, minimum spot size

• Optimizing Cc and Cs

Secondary Ion Mass Spectroscopy (chemical analysis)

• Smaller probe better lateral resolution• Low energy extraction (~100 eV) Better depth resolution

Expected performancies

He-tip

Cold atom source

Focused Ion Beam FIB @ 30keV

Plasma

Sp

ot D

iam

eter

(n

m)

0.1

1

10

100

1

000

10-4 0.01 1 100Beam Current (nA)

Outline

Physical ideas and goals of the project

Experience at LAC: cold atoms, cold Rydberg and cold plasma

Ion beam project

Electron beam project

Outlook

The electron source

Laser setup+

Control electronics

2D-MOT+

Electron opticsHost experimentUHV

- 2D cesium MOT- Flux ~ 1010 - 1011 atoms/s => up to 10nA current- Flexible setup, to be connected to existing experiments- Electron Energy Loss Spectroscopy + Microscope (LPS, A. Gloter)- Controlled breaking of molecular bonds (ISMO, A. Lafosse)

Optical fibers

The electron source: 2D MOT

Theoretical study: focusing

8 eV Beam DE < 10 meV Focused on ~ (10 nm)2

equivalent to 105 µA on (1mm)2

>103 times that of a standard gun

10pA e- current

General Particle Tracer®

High current: Limitation due to charge effects

1µm

10 cmEqually spacedGaussian randomUniform random

2 cm

Ex: I > 1 nA DE> 10meV

Stochastic space charge effect

B10

3

104

10

5

R

g

…R

g

R

g

Distance R

Rmin

laser

…R

g

BA

Blockade sphere radius: hDlaser ~Vdip-dip m 2 /Rmin3

A

B

How to create ordered particles: Dipole blockade

Dipole (n2)-Dipole(n2) interaction

dipole-dipole shiftRydbergLukin et al. PRL 87 037901 (2001)

Nearby atoms are not excited

Journal of the Optical Society of America B 27, A208 (2010)

Electric field: control (blockade) of Rydberg excitation

7s300ns Ti:Sa

Vdd m 2 /R3 ~ hDlaser nRyd D laser/m2

Vogt et al. PRL 99 073002 (2007)

Permanent dipole e-Cs+

F

e-Cs+

µ

µ

R

Journal of the Optical Society of America B 27, A208 (2010)

Expected performances

Gun : Tungsten LaB6 Schottky CFEG2-D MOT

Source

Brightness (A.m-2 sr-1 eV-1) 104 105 107 108 > 108

Cathode energy spread (eV) 1 0.5 0.4 0.3 < 0.01

T electrons (MOT / beam) < 10K 10 K ~ 1 meV

T electrons (Tungsten) ~ 2000 K

limited space charge effects: DE ~ 16 meV/nA

demonstrated with photoionization of effusive atomic beams (H. Hotop)

Review of Scientific Instruments, 72, 4098, (2001).

Laser cooling = collimation Rydberg = excitation + Field ionization

Improvefocus limit (10µm)x(∆E/E)

Huge domain of applications and improvement for: Spectrometers, irradiation, induced chemistry Imaging Sputtering, deposition

CONCLUSION: High flux of (ordered) ions/electronsBy field Rydberg ionization of cold atoms or molecules

Futur: Industrial product?Implantation of N atoms from Cooling of CN molecules

20162011

The TeamThe LAC team:Guyve Khalili, Yoann Bruneau, Joshua Gurian, Andréa Fioretti, Pierre Pillet, Daniel Comparat

The Orsay Physics Team:Leïla Kime, Bernard Rasser and Pierre Sudraud

+ the collaboration with the University of PisaNicolo’ Porfido, Francesco Fuso, Andréa Fioretti

Other collaborations: A. Gloter, C. Colliex (LPS, Orsay) A. Lafosse (ISMO, Orsay)

COLDBEAMS conference: Nîmes, France, Oct 1-3Marie Curie Industry-Academia Partnerships and Pathways: FP7-PEOPLE-2009-IAPPEuropean Reseach Council: ERC-StG- COLDNANO