Toward a Stark Decelerator for atoms and molecules exited into a Rydberg state Anne Cournol, Nicolas Saquet, Jérôme Beugnon, Nicolas Vanhaecke, Pierre Pillet 07/03/2008 Laboratoire Aime Cotton EGC 2008

Cold? For what? How to do? Cold atoms Into a gas: cold means weak velocity distribution around a mean velocity  Precision measurements  Quantum gases  …  Laser cooling  Evaporative cooling  …

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,ND 3,CO),Tiemann (SO 2 ), Hinds (YbF,CaF) Optical Stark decelerator: Barker (C 6 H 6 ) Zeeman decelerator: Merkt (H,D), Raizen (Ne*,O 2 ) Electric Stark decelerator (Rydberg state): Merkt (Ar,H), Softley (H 2 )

Stark deceleration Stark effect: - SO 2 :  =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 state Highly excited electronic state For hydrogen atoms, level energies for Rydberg electron states are: Particle in zero field Particle in electric field Stark effect Dipolar momentum ≈1000 Debye for n=18

Rydberg states into electric field m=2 18d 19d SO 2

Stark decelerator for Rydberg states Rydberg states: dipolar momentum ~1000 Debye Compact deceleratorVersatile decelerator Lower electric and shapeable field Continius deceleration  Constant force

Outline Supersonic beam Rydberg Excitation Deceleration: simulations 3D

The setup Production of pulsed supersonic beam Experiences P≈10 -8 mbar

A supersonic beam Effusive beam Supersonic beam Some properties of supersonic beam: Mean velocity Axis velocity distribution Perpendicular velocity distribution

Sodium pulsed beam Cw dye nm (Tekhnoscan on saturated absorption) Ablation laser 1.0 mJ/pulse Hz 10 cm 15 cm Detection by fluorescence induced by laser Detection areas Rotating sodium target Carrying gas ~1-10 bar

Time of flight Longitudinal velocity distribution (~10%v exp )

Parameter: ablation energy Carrying gas: Argon Pressure: 6 Bar

Parameter: ablation energy Carrying gas: Argon Pressure: 6 Bar

Parameter: pressure Neon with ablation energy of 0.6 mJ/pulse

Perpendicular temperature LL v Doppler measurement

Perpendicular temperature Perpendicular temperature about 1K Doppler profile 60 MHz 0

Beam characterization Heating effect when ablating Beam optimization Argon (v≈650 m/s) Axis temperature ≈ 5K Perpendicular temperature ≈ 1K Density ≈10 8 atoms/cm 3

Excitation toward a Rydberg state Laser excitation

Doubled pulsed dye Excitation process 3S 4P nd 330 nm 920 nm (18d m=2) Ionisation Ti:Sa

3S-4P Doubled pulsed dye 3S 4P 330 nm Ionisation First spectrum last week

3S-4P 170GHz 3S 4P 330 nm Ionisation

Simulations Deceleration: simulations 3D

Particle test: Na Initial state: 18d Field : 800 V/cm Number of electrodes: 20 pairs 3mm 1mm Beam axe Initial velocity: 370 m/s Final velocity: 0 m/s Laser excitation +V -V

Experienced force Time for deceleration ~10µs

Distribution of positions No deceleration 90% Deceleration 10% Initial cloud: atomes ∆x=2mm ∆v // /v // =10%, ∆v  /v // =3%

Conclusion 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

Conclusion HV: ±10kV L=1.8m 326 stages Efficiency: 1% Detection by fluorescence HV: ±40V L=3mm 20 ‘stages‘ Efficiency: 10% Ionic detection Stark decelerator (SO 2 ) Stark decelerator for atoms and molecules excited into a Rydberg states One laser to detect the molecules 4 lasers

Outlook Short time: ›Autumn: Rydberg excitation ›End of year: Proof of deceleration with 4 electrodes ›Spring: Na at standstill Long time: Production of cold Na 2, NaH, O, H 2 O, …

Merci