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

Superfluorescence (SF) L Pump 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) W N ‘endfire’ modes W 2 /L 

SF Threshold time Power  SF  sp /N  sp Cooperative emission produces short, intense pulse of light P peak  N 2 Delay time (  D ) before pulse occurs Threshold density/ pump power DD P peak 1 Spontaneous Emission Amplified Spontaneous Emission (ASE) Superfluorescence (SF) SF Thresh Cooperativity Malcuit, M., PhD Dissertation (1987); Svelto, Principles of Lasers, Plenum (1982)

New Regime: Thermal Free-space SF Pump (F) Cold atoms Pump (B) Detector (B) Detector (F) - T=20  K - L=3 cm, R=150  m  - N~10 9 Rb atoms - P F/B ~4 mW -  F2  F’3 =5  F =R 2 / L~1 NO CAVITY! NOT BEC! ≠ Slama et al. ≠ Inouye et al. Inouye et al. Science 285, 571 (1999); Slama et al. PRL 98, (2007) * Counterpropagating, * Large gain path length 2 collinear pump beams 1 1) Wang et al. PRA 72, ; 2) Yoshikawa PRL 94,

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

DD time Power P peak P F/B (mW) P peak (  W)  D (  s) P F/B (mW) Density/Pump power thresholds P peak  P F/B  D  (P F/B ) -1/2 Results - SF Consistent with CARL superradiance * *Piovella et al. Opt. Comm. 187, 165 (2001)

SF Mechanism What is the mechanism responsible for SF?

Probe Pump (F) Cold atoms Pump (B) Detector (B) - T=20  K - L=3 cm, R=150  m - N~10 9 Rb atoms - P F/B ~4 mW -  F2  F’3 =5  Detector (F) (  p =  +  ) What is the mechanism responsible for SF? SF Mechanism

Probe Spectroscopy Forward Detector Backward Detector (FWM)  (kHz) Rayleigh SF signal time (  s) Probe Power Rayleigh pump beam alignment Raman pump beam alignment SF Power Raman  SF

Probe Spectroscopy Forward Detector Backward Detector (FWM)  (kHz) Rayleigh SF signal time (  s) Probe Power Rayleigh pump beam alignment Raman pump beam alignment SF Power Raman  SF Rayleigh scattering is critical for observation of SF

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 radiationConclusions

Study dependence of P peak and  D on N Look at competition between vibrational Raman and Rayleigh SF Future Work

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

Beatnote  (kHz) time (  s) 1/  f  f~450kHz  f SF ~-50kHz Look at beatnote between probe beam and SF light as probe frequency is scanned

Weak probe Forward: Rayleigh backscatteringBackward: Recoil-mediated FWM  (kHz) Probe (  p =  +  ) Pumps (  ) I out /I in Forward Backward   Rayleigh

Weak probe Probe (  p =  +  ) Pumps (  ) Forward Backward FWM Above Thresh Below thresh  (kHz)

Weak probe Probe (  p =  +  ) Pumps (  ) Forward Backward Forward  (kHz)

Coherence Time time Power F/B Pumps on off  off 1 PRPR PRPR

Lin || Lin Power time (  s) Pumps (  ) Forward Backward

DD time Power P peak P peak (  W) Results - SF *Piovella et al. Opt. Comm. 187, 165 (2001) OD  N

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

Conclusions Rayleigh backscattering Recoil-mediated FWM  (kHz)

Superfluorescence (SF) L,N Pump Power  SF  sp /N  sp DD P peak Cooperative emission produces short, intense pulse of light Emission occurs along ‘endfire’ modes P peak  N 2

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

Weak probe Forward: Rayleigh backscatteringBackward: Recoil-mediated FWM  (kHz) Probe (  p =  +  ) Pumps (  ) I out /I in Forward Backward   Rayleigh

Probe Spectroscopy Forward DetectorBackward Detector (FWM)  (kHz) Rayleigh SF signal time (  s) Probe Power Rayleigh pump beam alignment Raman pump beam alignment SF Power Raman  SF

Forward DetectorBackward Detector (FWM) Probe Spectroscopy  (kHz)  Rayleigh SF signal time (  s) Probe Power Rayleigh pump beam alignment Raman pump beam alignment SF Power Rayleigh scattering is critical for observation of SF

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

Our Setup Pump (F) Cold atoms Pump (B) Detector (B) Detector (F) - T=20  K - L=3 cm, R=150  m - N~10 9 Rb atoms - P F/B ~4 mW -  F2  F’3 =5  - No cavity - Thermal atoms - Counterprop. pumps Inouye et al. Science 285, 571 (1999); Slama et al. PRL 98, (2007)

Motivation Collective effects Self-organization Experimental results Conclusions/Future workOutline