Superfluorescence in an Ultracold Thermal Vapor
Joel A. Greenberg and Daniel. J. Gauthier
Duke University
7/15/2009
FIP
Superfluorescence (SF)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)
WN
‘endfire’ modes
W2/L
SF ThresholdSF Threshold
time
Pow
er
SFsp/N
sp
• Cooperative emission produces short, intense pulse of light
• PpeakN2
• Delay time (D) before pulse occurs
• Threshold density/ pump power
D
Ppeak
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 SFNew Regime: Thermal Free-space SF
10~
Pump (F)Cold atoms
Pump (B)
Detector (B)
Detector (F)- T=20 K
- L=3 cm, R=150 m - N~109 Rb atoms
- PF/B~4 mW - F2F’3=-5
F=R2/L~1
NO CAVITY!NOT BEC!
≠ Slama et al. ≠ Inouye et al.
Inouye et al. Science 285, 571 (1999); Slama et al. PRL 98, 053603 (2007)
* Counterpropagating,
* Large gain path length2
collinear pump beams1
1) Wang et al. PRA 72, 043804; 2) Yoshikawa PRL 94, 083602
Results - SFResults - SF
t (s)
Pow
er (W
)
Forward
Backward
F/B PumpsMOT beams
• 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
on
off
Dtime
Pow
erPpeak
PF/B (mW)
Pp
eak
(W
)
D (s
)
PF/B (mW)
2/1/
BFP
•Density/Pump power thresholds
•PpeakPF/B
• D (PF/B)-1/2
Results - SFResults - SF
Consistent with CARL superradiance*
*Piovella et al. Opt. Comm. 187, 165 (2001)
BFP /
What is the mechanism responsible for SF?
Probe SpectroscopyProbe Spectroscopy
Probe
Pump (F)Cold atoms
Pump (B)Detector (B)
- T=20 K - L=3 cm, R=150 m- N~109 Rb atoms
- PF/B~4 mW - F2F’3=5
10~
Detector (F)
(p =+)
What is the mechanism responsible for SF?
Probe SpectroscopyProbe Spectroscopy
Recoil-Induced ResonanceRecoil-Induced Resonance
E
p
atom atomp
• Atom-photon interaction modifies the energy and momentum of an atom
• Energy + momentum conservation result in resonance
atom
p2
Absorption:
Emission:
p2
atomp
mp 2/2
Probe SpectroscopyProbe Spectroscopy
Forward Detector Backward Detector (FWM)
(kHz)
RIR
Po
ut/P
in
Raman
SF
RIR
Raman
(kHz) SF
PC
R
Probe Gain Probe Gain
F/B Pump Power (mW)
PR
IR/P
pro
be
SF Threshold
Typical SF gain threshold are Pout/Pin~exp(10)=104
Self-Organization 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
• 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
ConclusionsConclusions
• New insight into free electron laser dynamics• Possible source of correlated photon pairs• Optical/Quantum memory
ApplicationsApplications
Resonant ProcessesResonant Processes
E
p
E
Vibrational Raman Recoil-Induced Resonance (RIR)
atom
z
Initial state
Final state atom p
Probe SpectroscopyProbe Spectroscopy
0 100 200
Forward Detector
Backward Detector (FWM)
250 0 250
250 0 250 (kHz)
Rayleigh
SF signal
time (s)
Pro
be P
ower
P
robe
Pow
er
Rayleigh pump beam alignment
Raman pump beam alignment
SF
Pow
er
Raman
SF
700 500 300
BeatnoteBeatnote
(kHz)
Look at beatnote between probe beam and SF light as probe frequency is scanned
Pow
er (
F)
700 500 300
170 172 174 176
BeatnoteBeatnote
(kHz)
time (s)
1/f f~450kHz fSF~-50kHz
Look at beatnote between probe beam and SF light as probe frequency is scanned
Weak probeWeak probe
Probe (p=+)
Pumps ()
Forward
Backward
Backward
400 200 0 200 400 400 200 0 200 400
Forward
(kHz) (kHz)
Coherence TimeCoherence Time
0 1 2 3 4 5 60.00.20.40.60.81.0
time
Pow
er
F/B Pumpson
off
off
1
PR
PR
off
Lin || LinLin || Lin
100 200 300
Pow
er
time (s)
Pumps ()
Forward
Backward
Dtime
Pow
erPpeak
Pp
eak
(W
)Results - SFResults - SF
*Piovella et al. Opt. Comm. 187, 165 (2001)
0 5 10 15 20 250.000.050.100.150.20
OD N
)(NExp2)( tNN
CARL RegimesCARL Regimes
Slama Dissertation (2007)
Quantum CARL
Ultr
acol
d A
tom
s/B
EC
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)
The
rmal