Transient enhancement of the nonlinear atom-photon coupling via recoil-induced resonances:

1
Transient enhancement of the nonlinear
atom-photon coupling via recoil-induced
resonances
FIP
Cavity-less Rayleigh Superfluorescence in a
Thermal Gas

• Joel A. Greenberg and Daniel. J. Gauthier
• Duke University
• 5/22/2009

2
Superfluorescence (SF)
Pump
W
N
L
W2/Ll1
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)
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SF Threshold
Amplified Spontaneous Emission (ASE)
Spontaneous Emission
Superfluorescence (SF)
Cooperativity
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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
time
tD
Malcuit, M., PhD Dissertation (1987) Svelto,
Principles of Lasers, Plenum (1982)
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New Regime Thermal Free-space SF
Counterpropagating,
collinear pump beams1
Large gain path length2
Detector (B)
Pump (B)
Cold atoms
Detector (F)
Pump (F)

• T20 mK

• N109 Rb atoms

• PF/B4 mW

• L3 cm, R150 mm ?

FR2/lL1

• DF2?F35G

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)
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Results - SF
Forward

• Light persists until N falls below threshold
• F/B temporal correlations
• 1 photon/atom ? large fraction of atoms
  participate

Backward
Power (mW)
t (ms)
on
MOT beams
F/B Pumps
off
Wang et al. PRA 72, 043804 (2005)
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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)
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SF Mechanism
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SF Mechanism
Pump (B)
Detector (B)
Probe
(wp wd)
Cold atoms
Detector (F)
Pump (F)

• T20 mK

• L3 cm, R150 mm

• PF/B4 mW

• N109 Rb atoms

• DF2?F35G

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

• 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
  radiation

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Future Work

• Study dependence of Ppeak and tD on N
• Look at competition between vibrational Raman and
  Rayleigh SF

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Beatnote
Look at beatnote between probe beam and SF light
as probe frequency is scanned
Power (F)
d (kHz)
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Beatnote
Look at beatnote between probe beam and SF light
as probe frequency is scanned
Df450kHz ?fSF-50kHz
1/Df
time (ms)
d (kHz)
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Weak probe
Pumps (w)
Backward
Probe (wpwd)
Forward
Forward Rayleigh backscattering
Backward Recoil-mediated FWM
Rayleigh
Rayleigh
Iout/Iin
Wn
Wn
Iout/Iin
d (kHz)
d (kHz)
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Weak probe
Pumps (w)
Backward
Probe (wpwd)
Forward
FWM
Above Thresh
Below thresh
d (kHz)
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Weak probe
Pumps (w)
Backward
Probe (wpwd)
Forward
Backward
Forward
d (kHz)
d (kHz)
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Coherence Time
1
Power
PR
time
on
toff
F/B Pumps
off
PR
toff
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Lin Lin
Pumps (w)
Backward
Forward
Power
time (ms)
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Results - SF
Ppeak
Power
tD
time
Ppeak (mW)
OD ? N
Piovella et al. Opt. Comm. 187, 165 (2001)
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CARL Regimes
Good Cavity kltwr
Bad Cavity kgtwr
Quantum wrgtG
MIT (1999)
Quantum CARL
Ultracold Atoms/BEC
MIT (2003)
Tub (2006)
Tub (2006)
Semiclassical wrltG
Tub (2003)
Thermal
In resonator
Free space
Slama Dissertation (2007)
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Conclusions
Rayleigh backscattering
Recoil-mediated FWM
d (kHz)
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Superfluorescence (SF)
Pump
L,N
Ppeak

• Cooperative emission produces short, intense
  pulse of light
• Emission occurs along endfire modes
• Ppeak?N2

tSF?tsp/N
Power
tsp
tD
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Superfluorescence (SF)
Pump
L,N
Amplified Spontaneous Emission (ASE)
Spontaneous Emission
Superfluorescence (SF)
gL
1
SF Thresh
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Weak probe
Pumps (w)
Forward
Backward
Probe (wpwd)
Forward Rayleigh backscattering
Backward Recoil-mediated FWM
Rayleigh
Rayleigh
Iout/Iin
Wn
Wn
Iout/Iin
d (kHz)
d (kHz)
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Probe Spectroscopy
Forward Detector
Backward Detector (FWM)
Probe Power
Probe Power
Rayleigh
Raman
d (kHz)
d (kHz)
dSF
SF signal
Rayleigh pump beam alignment
Raman pump beam alignment
SF Power
time (ms)
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Probe Spectroscopy
Forward Detector
Backward Detector (FWM)
Probe Power
Probe Power
Rayleigh
Wn
d (kHz)
d (kHz)
SF signal
Rayleigh pump beam alignment
SF Power
Raman pump beam alignment
time (ms)
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Observation of Cavity-less Rayleigh
Superfluorescence in a Thermal Gas

• Joel A. Greenberg and Daniel. J. Gauthier
• Duke University
• 5/22/2009

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Our Setup
Pump (B)
Detector (B)
Cold atoms
Detector (F)
Pump (F)

• T20 mK

- No cavity

• L3 cm, R150 mm

- Thermal atoms

• PF/B4 mW

• N109 Rb atoms

• DF2?F35G

- Counterprop. pumps
Inouye et al. Science 285, 571 (1999) Slama et
al. PRL 98, 053603 (2007)
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Outline

• Motivation
• Collective effects
• Self-organization
• Experimental results
• Conclusions/Future work