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Transient enhancement of the nonlinear atom-photon coupling via recoil-induced resonances:

Transient enhancement of the nonlinear atom-photon coupling via recoil-induced resonances:. FIP. Joel A. Greenberg and Daniel. J. Gauthier Duke University 5/22/2009. Cavity-less Rayleigh Superfluorescence in a Thermal Gas. Superfluorescence (SF). Pump. W. N. L. W 2 /L l~1.

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Transient enhancement of the nonlinear atom-photon coupling via recoil-induced resonances:

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  1. Transient enhancement of the nonlinear atom-photon coupling via recoil-induced resonances: FIP Joel A. Greenberg and Daniel. J. Gauthier Duke University 5/22/2009 Cavity-less Rayleigh Superfluorescence in a Thermal Gas

  2. Superfluorescence (SF) Pump W N L W2/Ll~1 ‘endfire’ modes Dicke, Phys. Rev. 93, 99 (1954); Bonifacio & Lugiato, Phys. Rev. A 11, 1507 (1975), Polder et al., Phys. Rev. A 19, 1192 (1979), Rehler & Eberly, Phys. Rev A 3, 1735 (1971)

  3. SF Threshold Amplified Spontaneous Emission (ASE) Spontaneous Emission Superfluorescence (SF) Cooperativity 1 SF Thresh Ppeak • Cooperative emission produces short, intense pulse of light • PpeakN2 • Delay time (tD) before pulse occurs • Threshold density/ pump power tSFtsp/N Power tsp tD time Malcuit, M., PhD Dissertation (1987); Svelto, Principles of Lasers, Plenum (1982)

  4. New Regime: Thermal Free-space SF * Counterpropagating, collinear pump beams1 * Large gain path length2 Detector (B) Pump (B) Cold atoms Detector (F) • T=20 mK Pump (F) • N~109 Rb atoms • PF/B~4 mW • L=3 cm, R=150 mm  F=R2/lL~1 • DF2F’3=5G NOT BEC! NO CAVITY! ≠ Inouye et al. ≠ Slama et al. 1) Wang et al. PRA 72, 043804; 2) Yoshikawa PRL 94, 083602 Inouye et al. Science 285, 571 (1999); Slama et al. PRL 98, 053603 (2007)

  5. Results - SF Forward • Light persists until N falls below threshold • F/B temporal correlations • ~1 photon/atom  large fraction of atoms participate Backward Power (mW) t (ms) on MOT beams F/B Pumps off Wang et al. PRA 72, 043804 (2005)

  6. Results - SF Ppeak • Density/Pump power thresholds • PpeakPF/B • tD (PF/B)-1/2 Consistent with CARL superradiance* Power tD time tD (ms) Ppeak (mW) PF/B (mW) PF/B (mW) *Piovella et al. Opt. Comm. 187, 165 (2001)

  7. What is the mechanism responsible for SF? SF Mechanism

  8. SF Mechanism What is the mechanism responsible for SF? Pump (B) Detector (B) Probe (wp =w+d) Cold atoms Detector (F) • T=20 mK Pump (F) • L=3 cm, R=150 mm • PF/B~4 mW • N~109 Rb atoms • DF2F’3=5G

  9. Probe Spectroscopy Forward Detector Rayleigh pump beam alignment Raman pump beam alignment Probe Power Rayleigh Raman SF signal dSF SF Power Backward Detector (FWM) Probe Power time (ms) d (kHz)

  10. Rayleigh scattering is critical for observation of SF Probe Spectroscopy Forward Detector Rayleigh pump beam alignment Raman pump beam alignment Probe Power Rayleigh Raman SF signal dSF SF Power Backward Detector (FWM) Probe Power time (ms) d (kHz)

  11. Conclusions • Observe free-space superfluorescence in a cold, thermal gas • Large F/B gain path length + pair of pump beams • Spectroscopy and beatnote imply Rayleigh scattering as source of SF • Temporal correlation between forward/backward radiation

  12. Future Work • Study dependence of Ppeak and tD on N • Look at competition between vibrational Raman and Rayleigh SF

  13. Beatnote Look at beatnote between probe beam and SF light as probe frequency is scanned Power (F) d (kHz)

  14. Beatnote Look at beatnote between probe beam and SF light as probe frequency is scanned Df~450kHz fSF~-50kHz 1/Df time (ms) d (kHz)

  15. Weak probe Backward Pumps (w) Probe (wp=w+d) Forward Forward: Rayleigh backscattering Backward: Recoil-mediated FWM Rayleigh Rayleigh Iout/Iin Wn Wn Iout/Iin d (kHz) d (kHz)

  16. Weak probe Backward Pumps (w) Probe (wp=w+d) Forward FWM Above Thresh Below thresh d (kHz)

  17. Weak probe Backward Pumps (w) Probe (wp=w+d) Forward Forward Backward d (kHz) d (kHz)

  18. Coherence Time 1 Power PR time on toff F/B Pumps off PR toff

  19. Lin || Lin Backward Pumps (w) Forward Power time (ms)

  20. Results - SF Ppeak Power tD time Ppeak (mW) OD  N *Piovella et al. Opt. Comm. 187, 165 (2001)

  21. CARL Regimes Good Cavity: k<wr Bad Cavity: k>wr Quantum: wr>G MIT (1999) Quantum CARL Ultracold Atoms/BEC MIT (2003) Tub (2006) Tub (2006) Semiclassical: wr<G Tub (2003) Thermal In resonator Free space Slama Dissertation (2007)

  22. Conclusions Rayleigh backscattering Recoil-mediated FWM d (kHz)

  23. Superfluorescence (SF) Pump L,N Ppeak • Cooperative emission produces short, intense pulse of light • Emission occurs along ‘endfire’ modes • PpeakN2 tSFtsp/N Power tsp tD

  24. Superfluorescence (SF) Pump L,N Amplified Spontaneous Emission (ASE) Spontaneous Emission Superfluorescence (SF) gL 1 SF Thresh

  25. Weak probe Pumps (w) Forward Backward Probe (wp=w+d) Forward: Rayleigh backscattering Backward: Recoil-mediated FWM Rayleigh Rayleigh Iout/Iin Wn Wn Iout/Iin d (kHz) d (kHz)

  26. Probe Spectroscopy Forward Detector Backward Detector (FWM) Probe Power Probe Power Rayleigh Raman dSF d (kHz) d (kHz) SF signal Rayleigh pump beam alignment SF Power Raman pump beam alignment time (ms)

  27. Rayleigh scattering is critical for observation of SF Probe Spectroscopy Forward Detector Backward Detector (FWM) Probe Power Probe Power Rayleigh Wn d (kHz) d (kHz) SF signal Rayleigh pump beam alignment SF Power Raman pump beam alignment time (ms)

  28. Observation of Cavity-less Rayleigh Superfluorescence in a Thermal Gas Joel A. Greenberg and Daniel. J. Gauthier Duke University 5/22/2009

  29. Our Setup Pump (B) Detector (B) Cold atoms Detector (F) - No cavity • T=20 mK Pump (F) • L=3 cm, R=150 mm - Thermal atoms • PF/B~4 mW • N~109 Rb atoms • DF2F’3=5G - Counterprop. pumps Inouye et al. Science 285, 571 (1999); Slama et al. PRL 98, 053603 (2007)

  30. Outline • Motivation • Collective effects • Self-organization • Experimental results • Conclusions/Future work

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