1. Superfluorescence in an Ultracold Thermal Vapor
FIP
Superfluorescence in an Ultracold Thermal Vapor
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 Cooperativity Ppeak tSFtsp/N tsp tD 1 SF Thresh time
Spontaneous Emission
Amplified Spontaneous Emission (ASE)
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)
Pump (F)
T=20 mK
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, ; 2) Yoshikawa PRL 94,
Inouye et al. Science 285, 571 (1999); Slama et al. PRL 98, (2007)

5. Results - SF Power (mW) t (ms) MOT beams F/B Pumps
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 tD 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?
Probe Spectroscopy
What is the mechanism responsible for SF?

8. What is the mechanism responsible for SF?
Probe Spectroscopy
What is the mechanism responsible for SF?
Pump (B)
Probe
Detector (B)
(wp =w+d)
Cold atoms
Detector (F)
Pump (F)
T=20 mK
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 Applications
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. Recoil-Induced Resonance (RIR)
Resonant Processes
Recoil-Induced Resonance (RIR)
Vibrational Raman
Initial state
atom
Final state
atom

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

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

17. Beatnote d (kHz) Df~450kHz fSF~-50kHz 1/Df
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 Pumps (w) Probe (wp=w+d) d (kHz) d (kHz) Backward Forward

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 tD Ppeak (mW) OD  N Power time
*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)