superfluorescence in an ultracold thermal vapor
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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Superfluorescence in an Ultracold Thermal Vapor
Joel A. Greenberg and Daniel. J. Gauthier
Duke University
7/15/2009
FIP
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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
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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)
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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
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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
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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 /
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What is the mechanism responsible for SF?
Probe SpectroscopyProbe Spectroscopy
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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
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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
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Probe SpectroscopyProbe Spectroscopy
Forward Detector Backward Detector (FWM)
(kHz)
RIR
Po
ut/P
in
Raman
SF
RIR
Raman
(kHz) SF
PC
R
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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
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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
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• 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
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Resonant ProcessesResonant Processes
E
p
E
Vibrational Raman Recoil-Induced Resonance (RIR)
atom
z
Initial state
Final state atom p
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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
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700 500 300
BeatnoteBeatnote
(kHz)
Look at beatnote between probe beam and SF light as probe frequency is scanned
Pow
er (
F)
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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
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Weak probeWeak probe
Probe (p=+)
Pumps ()
Forward
Backward
Backward
400 200 0 200 400 400 200 0 200 400
Forward
(kHz) (kHz)
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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
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Lin || LinLin || Lin
100 200 300
Pow
er
time (s)
Pumps ()
Forward
Backward
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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
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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