Toward a Stark Toward a Stark Decelerator for Decelerator for

atoms and molecules atoms and molecules exited into a exited into a Rydberg stateRydberg state

Anne Cournol, Nicolas Saquet, Jérôme Beugnon,Nicolas Vanhaecke, Pierre Pillet

07/03/2008Laboratoire Aime CottonEGC 2008

• Cold?

• For what?

• How to do?

Cold atomsCold atoms

Into a gas: cold means weak velocity distribution around a mean velocity

Precision measurements Quantum gases …

Laser cooling Evaporative cooling …

Cold molecules?Cold molecules?• High resolution spectroscopy (very long

interaction time)• Cold chemistry • Polar molecules : dipole - dipole interaction• Variation of fundamental constants with time

(Ye OH)• Parity violation (DeMille BaF,HSiO)• EDM (DeMille PbO, Hinds YbF)

Why ?

How ? • From cold atoms (T<1mK)• Buffer gas cooling (T<1K)• Bolztmann filter (T < 1K)• Rotating nozzle (T~1K)• Beam collision (T~1K)• Deceleration of supersonic molecular beam (T<1K)

Electric Stark decelerator (polar species): Meijer (OH,NH,ND3,CO),Tiemann (SO2), Hinds (YbF,CaF)

Optical Stark decelerator: Barker (C6H6)

Zeeman decelerator: Merkt (H,D), Raizen (Ne*,O2)

Electric Stark decelerator (Rydberg state): Merkt (Ar,H), Softley (H2)

Stark decelerationStark decelerationStark effect: -

SO2: =1.6Debye, 326 stages, L=1.8 m, HV=10kV, =400ns ∆E=0.95cm-1/stage

5.5mm

2mm

+: Huge density in phase space (conserved by deceleration)

-: Dipolar momentum of polar molecules 1Debye

Rydberg stateRydberg state

Highly excited electronic state

€

E = −1

2n2

For hydrogen atoms, level energies for Rydberg electron states are:

€

E = −1

2n2+3

2nkF

Particle in zero field

Particle in electric field

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−(n −1− m ) < k < n −1− m

Stark effect

Dipolar momentum ≈1000 Debye for n=18

Rydberg states into Rydberg states into electric fieldelectric field

m=2

18d

19d

SO2

Stark decelerator for Stark decelerator for Rydberg statesRydberg states

Rydberg states: dipolar momentum ~1000 Debye

Compact decelerator Versatile decelerator

Lower electric and shapeable field

Continius deceleration

Constant force

OutlineOutline

Supersonic beam

Rydberg Excitation

Deceleration: simulations 3D

The setupThe setup

Production of pulsedsupersonic beamExperiences

P≈10-8mbar

A supersonic beamA supersonic beam

Effusive beam Supersonic beam

Some properties of supersonic beam:• Mean velocity• Axis velocity distribution• Perpendicular velocity distribution

Sodium pulsed beamSodium pulsed beam

Cw dye laser @589 nm (Tekhnoscan on saturated absorption)

Ablation laser Nd:YAG@532nm 1.0 mJ/pulse

10 - 50 Hz

10 cm 15 cm

Detection by fluorescence induced by laser

Detection areas

Rotating sodium target

Carrying gas~1-10 bar

Time of flightTime of flight

Longitudinal velocity distribution(~10%vexp)

Parameter: ablation Parameter: ablation energyenergy

Carrying gas: Argon Pressure: 6 Bar

Parameter: ablation Parameter: ablation energyenergy

Carrying gas: Argon Pressure: 6 Bar

Parameter: Parameter: pressurepressure

Neon with ablation energy of 0.6 mJ/pulse

Perpendicular Perpendicular temperaturetemperature

L

v

Doppler measurement

Perpendicular Perpendicular temperaturetemperature

Perpendicular temperature about 1K

Doppler profile

60 MHz

0

Beam characterizationBeam characterization

• Heating effect when ablating

• Beam optimization

• Argon (v≈650 m/s)• Axis temperature ≈ 5K• Perpendicular temperature ≈ 1K

•Density ≈108atoms/cm3

Excitation toward a Excitation toward a Rydberg stateRydberg state

Laser excitation

Doubledpulsed dye

Excitation processExcitation process

3S

4P

nd

330 nm

920 nm

(18d m=2)

Ionisation

Ti:Sa

3S-4P3S-4P

Doubledpulsed dye

3S

4P

330 nm

330 nm

Ionisation

First spectrum last week

3S-4P3S-4P

170GHz

3S

4P

330 nm

330 nm

Ionisation

SimulationsSimulations

Deceleration: simulations 3D

Particle test: NaParticle test: Na• Initial state: 18d• Field : 800 V/cm• Number of electrodes: 20 pairs

3mm1mm

Beam axe

• Initial velocity: 370 m/s

• Final velocity: 0 m/s

Laser excitation

+V

-V

Experienced Experienced forceforce

Time for deceleration ~10µs

Distribution of Distribution of positionspositions

No deceleration90%

Deceleration10%

Initial cloud: 500000 atomes ∆x=2mm∆v///v//=10%, ∆v/v//=3%

ConclusionConclusion

• Supersonic beam is characterized

• Excitation toward a Rydberg state is in process

• Simulations show we can stop a cloud of sodium atoms flying initially at 370m/s in 3mm

ConclusionConclusion

• HV: ±10kV• L=1.8m• 326 stages• Efficiency: 1%• Detection by fluorescence

• HV: ±40V• L=3mm• 20 ‘stages‘• Efficiency: 10%• Ionic detection

Stark decelerator (SO2)Stark decelerator for atoms and molecules excited into a Rydberg states

• One laser to detect the molecules

• 4 lasers

OutlookOutlook

Short time:

› Autumn: Rydberg excitation› End of year: Proof of deceleration

with 4 electrodes› Spring: Na at standstill

Long time:

Production of cold Na2, NaH, O, H2O, …

MerciMerci