Monochromatic ion and electron beams by ionization of cold atoms Daniel Comparat Laboratoire Aimé...
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Transcript of Monochromatic ion and electron beams by ionization of cold atoms Daniel Comparat Laboratoire Aimé...
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)
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+
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