séminaire interne du groupe Atomes Froids Vendredi 08 octobre 2004

1. Determination of the s-wave scattering lengthin metastable helium : experimental results with single photon photoassociation séminaire interne du groupe Atomes Froids Vendredi 08 octobre 2004 Steven MOAL, Maximilien PORTIER, Jaewan KIM Michèle LEDUC, Claude COHEN-TANNOUDJI

2. 1st STEP : TWO PHOTONS EXPERIMENT

3. E 0u+ S + P0 v = 0 2 1 energy 5 g+ kBT S + S continuum r v=14 R interatomic distance PRINCIPLE OF EXPERIMENT

4. 0u+ (v = 0) 0u+ (v = 0) D 1 fixed 1 scanned 2 scanned 2 fixed S + S S + S 5 g+(v=14) 5g+ (v=14) Temperature (a.u.) Temperature (a.u.) -20 -10 0 10 20 Detuning with respect v=14 (MHz) -20 -10 0 10 20 Detuning with respect v=14 (MHz) FRUSTRATED PA vs. RAMAN TRANSITION

5. large width SOME DIFFICULTIES • a large range scan to explore • Orsay value : 11 4 nmrange of –15 MHz <  < -110 MHz • transition probabilities (FC factors) are not known precisely : • too many differents combinations of relative power. • large line width of the PA laser (3 MHz) : Temperature (a.u.) Temperature (a.u.) Temperature (a.u.) Temperature (a.u.) Detuning with respect v=14 (MHz) Detuning with respect v=14 (MHz)

6. 2nd STEP : ONE PHOTON EXPERIMENT 1- MEASURE OF LOSS SIGNAL

7. the loss of atoms depend of the Franck Condon factor one idea : we can measure the relative intensities of molecular lines v=4 measurement of the scattering length « a » BUT : v=3 v=2 v=1 v=0 relatives intensities of molecular lines • the loss measurement is too • noisy for a very precise value • of « a » • FC calculation is not enough • precise in our case scattering length a (a0) MESURE OF LOSS SIGNAL (1)

8. MESURE OF LOSS SIGNAL (2) • it’s NOT very precise • a very fast non-linear effect (some 60 ISAT) • not good agreement with this reference • John L. Bohn and P. S. Julienne, Phys. Rev. A 60, 414 (1999)

9. ONE PHOTON EXPERIMENT 2- MEASURE OF OSCILLATION OF THE CLOUD

10. the cloud moves… THE CLOUD MOVES ! when we put one photon at resonance with different Thermalization time : … with the frequency of the trap

11. THE CLOUD MOVES ! (2) it’s linear ! slope ratio : BUT : ? • the trap is harmonic. • for high intensities, the line is not at resonance • because of a shift with laser intensity.

12. ONE PHOTON EXPERIMENT 3- MEASURE OF THE SHIFT WITH LASER INTENSITY

13. DISCOVER OF A SHIFT WITH LASER INTENSITY line v=1 with 0.5 mW position = -667.7 MHz when we explore high power of PA beam : line v=1 with 4 mW position = -685.0 MHz • shift of 17.3 MHz ! • deformation of the line • at high intensities

14. INTERPRETATION one approach :A. Simoni, P. S. Julienne et al, Phys. Rev. A 66, 63406 (2002) shift due to the continuum shift due to a bound state v = 0 Veg Veg continuum v = 14 S - S

15. : energy of the continuum : energy of v=14 DIRECTION OF THE SHIFT • shift due to the bound state v=14 BLUE SHIFT • shift due to the continuum BLUE SHIFT contribution : if RED SHIFT RED SHIFT

16. EXPERIMENTAL SHIFT we have a RED SHIFT for v=0 always a RED SHIFT for v=1 BUT : slope ratio : • some uncertainty on the laser intensity • difficulty in deducing absolute values of FC factor

17. CONCLUSION for evaluation of Franck Codon factor : • the measurement of loss signal : too much uncertainty • the measurement of oscillation : ratio of 3.54  0.3 we need to understand the phenomenon of oscillations for precise value of the scattering length : • the measurement of the light shift of the molecular line BUT we need to finish the theory : to calculate accurately the shifts

18. J=0 29.6 GHz 23PJ 1 2.29 GHz 1083 nm 2 23S1 He* 11S0 AFTER… 1- spectroscopy of D2 to continue Raman 2 photons PA with a potentiel more adapted than 0u+ 2- optical Feshbach to change the scattering length « a » with light 3- BEC in linear lattice to study Mott transition