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Superfluorescence in an Ultracold Thermal Vapor

Superfluorescence in an Ultracold Thermal Vapor. FIP. Joel A. Greenberg and Daniel. J. Gauthier Duke University 7/15/2009. Superfluorescence (SF). Pump. W. N. L. W 2 /L l~1. ‘endfire’ modes.

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Superfluorescence in an Ultracold Thermal Vapor

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  1. Superfluorescence in an Ultracold Thermal Vapor FIP Joel A. Greenberg and Daniel. J. Gauthier Duke University 7/15/2009

  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 • SF light nearly degenerate with pump frequency • Light persists until N falls below threshold • F/B temporal correlations • ~1 photon/atom  large fraction of atoms participate Forward Backward Power (mW) t (ms) on MOT beams F/B Pumps off

  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. Probe Spectroscopy What is the mechanism responsible for SF?

  8. What is the mechanism responsible for SF? Probe Spectroscopy 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. Recoil-Induced Resonance • Atom-photon interaction modifies the energy and momentum of an atom • Energy + momentum conservation result in resonance Absorption: atom atom Emission: atom atom

  10. Probe Spectroscopy Forward Detector Backward Detector (FWM) Pout/Pin RIR RIR PCR Raman Raman d (kHz) d (kHz) dSF dSF

  11. Probe Gain Typical SF gain threshold are Pout/Pin~exp(10)=104 PRIR/Pprobe SF Threshold F/B Pump Power (mW)

  12. Self-Organization RIR leads to spatial organization or atoms Backaction between atoms and photons leads to runaway process  Lower SF threshold Scattering enhances grating Grating enhances scattering

  13. Conclusions • Observe free-space superfluorescence in a cold, thermal gas • Temporal correlation between forward/backward radiation • Spectroscopy and beatnote imply RIR scattering as source of SF Applications • New insight into free electron laser dynamics • Possible source of correlated photon pairs • Optical/Quantum memory

  14. Resonant Processes Recoil-Induced Resonance (RIR) Vibrational Raman atom Initial state atom Final state

  15. 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)

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

  17. 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)

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

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

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

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

  22. 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)

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