Transient enhancement of the nonlinear atom

Report
FIP
Transient enhancement of the
nonlinear atom-photon coupling via
recoil-induced resonances:
Cavity-less Rayleigh Superfluorescence in a Thermal Gas
Joel A. Greenberg and Daniel. J. Gauthier
Duke University
5/22/2009
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)
SF Threshold
Amplified Spontaneous
Emission (ASE)
Spontaneous
Emission
Superfluorescence (SF)
Cooperativity
1
SF Thresh
Ppeak
• Cooperative emission produces short,
intense pulse of light
tSFtsp/N
Power
• PpeakN2
• Delay time (tD) before pulse occurs
tsp
tD
• Threshold density/ pump power
time
Malcuit, M., PhD Dissertation (1987); Svelto, Principles of Lasers, Plenum (1982)
New Regime: Thermal Free-space SF
Detector (B)
* Counterpropagating,
collinear pump beams1
* Large gain path length2
Pump (B)
 ~ 10
Cold atoms
Pump (F)
- PF/B~4 mW
- DF2F’3=5G
NO CAVITY!
≠ Slama et al.
Detector (F)
- T=20 mK
- N~109 Rb atoms
- L=3 cm, R=150 mm F=R2/lL~1
NOT BEC!
≠ Inouye 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)
Power (mW)
Results - SF
Forward
Backward
3
• F/B temporal correlations
2
• ~1 photon/atom  large
fraction of atoms participate
1
0
0
• Light persists until N falls
below threshold
100
200
300
t (ms)
on
F/B Pumps
off
MOT
beams
Wang et al. PRA 72, 043804 (2005)
Results - SF
•Density/Pump power thresholds
Ppeak
Power
•PpeakPF/B
• tD (PF/B)-1/2
time
 PF / B
100
75
50
25
PF/1B/ 2
tD (ms)
Ppeak (mW)
tD
4
3
2
1
0
0
Consistent with CARL
superradiance*
1
2
PF/B (mW)
3
4
2
3
PF/B (mW)
*Piovella et al. Opt. Comm. 187, 165 (2001)
4
SF Mechanism
What is the mechanism
responsible for SF?
SF Mechanism
What is the mechanism
responsible for SF?
Probe
Pump (B)
Detector (B)
(wp =w+d)
 ~ 10
Cold atoms
Pump (F)
- PF/B~4 mW
- DF2F’3=5G
- T=20 mK
- L=3 cm, R=150 mm
- N~109 Rb atoms
Detector (F)
Probe Spectroscopy
Rayleigh pump
beam alignment
Raman pump
beam alignment
Rayleigh
Raman
250
SF signal
0
dSF
250
Probe Power
Backward Detector (FWM)
SF Power
Probe Power
Forward Detector
0
250
0
d (kHz)
250
100
time (ms)
200
Probe Spectroscopy
Rayleigh pump
beam alignment
Raman pump
beam alignment
Rayleigh
Raman
250
SF signal
0
dRayleigh
SF
250
scattering is critical
SF Power
Probe Power
Forward Detector
Probe Power
for(FWM)
observation
Backward Detector
of SF
0
250
0
d (kHz)
250
100
time (ms)
200
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
Future Work
• Study dependence of Ppeak and tD on N
• Look at competition between vibrational
Raman and Rayleigh SF
Beatnote
Power (F)
Look at beatnote between probe beam and SF light as
probe frequency is scanned
700
500
d (kHz)
300
Beatnote
Look at beatnote between probe beam and SF light as
probe frequency is scanned
Df~450kHz fSF~-50kHz
1/Df
170 172 174 176
time (ms)
700
500
d (kHz)
300
Weak probe
Backward
Pumps (w)
Probe (wp=w+d)
Forward
Forward: Rayleigh backscattering
Backward: Recoil-mediated FWM
Iout/Iin
Rayleigh
2
Wn
1
250
0
d (kHz)
250
Iout/Iin
2
Rayleigh
1 Wn
0
250
0
d (kHz)
250
Weak probe
Backward
Pumps (w)
Probe (wp=w+d)
Forward
FWM
Above Thresh
6
Below thresh
4
2
0
250
0
d (kHz)
250
Weak probe
Backward
Pumps (w)
Probe (wp=w+d)
Forward
Forward
400 200 0
d (kHz)
200 400
Backward
400 200 0
d (kHz)
200 400
Coherence Time
Power
1
PR
on
time
toff
F/B Pumps
PR
off
1.0
0.8
0.6
0.4
0.2
0.0
0 1 2 3 4 5 6
toff
Lin || Lin
Backward
Pumps (w)
Power
Forward
100 200 300
time (ms)
Results - SF
Power
Ppeak
Ppeak (mW)
tD
0.20
0.15
0.10
0.05
0.00
0
time
 Exp(N )
 ( N  Nt ) 2
5 10 15 20 25
OD  N
*Piovella et al. Opt. Comm. 187, 165 (2001)
CARL Regimes
Quantum:
wr>G
MIT
(1999)
Quantum
CARL
Tub (2006)
Semiclassical:
wr<G
Bad Cavity: k>wr
Tub (2006)
MIT
(2003)
Tub (2003)
In resonator
Free space
Slama Dissertation (2007)
Thermal Ultracold Atoms/BEC
Good Cavity: k<wr
Conclusions
Rayleigh backscattering
2
1
250
Recoil-mediated FWM
0
250
2
1
0
250
0
d (kHz)
250
Superfluorescence (SF)
Pump
L,N
Ppeak
Power
tSFtsp/N
• Cooperative emission produces short,
intense pulse of light
• Emission occurs along ‘endfire’ modes
tsp
tD
• PpeakN2
Superfluorescence (SF)
Pump
L,N
Amplified Spontaneous
Emission (ASE)
Spontaneous
Emission
Superfluorescence (SF)
gL
1
SF Thresh
Weak probe
Ng 2  kkR
Pumps (w)
Forward
Backward
Probe (wp=w+d)
Forward: Rayleigh backscattering
Backward: Recoil-mediated FWM
Iout/Iin
Rayleigh
2
Wn
1
250
0
d (kHz)
250
Iout/Iin
2
Rayleigh
1 Wn
0
250
0
d (kHz)
250
Probe Spectroscopy
Probe Power
Backward Detector (FWM)
Rayleigh
Raman
250
0
dSF
d (kHz)
250
250
0
d (kHz)
250
SF signal
Rayleigh pump
beam alignment
SF Power
Probe Power
Forward Detector
Raman pump
beam alignment
0
100
time (ms)
200
Probe Spectroscopy
Probe Power
Backward Detector (FWM)
Rayleigh
Wn
250
250
0
0
250
Rayleigh
scattering
is
critical
d (kHz)
d (kHz)
SF signal of SF
for observation
250
Rayleigh pump
beam alignment
SF Power
Probe Power
Forward Detector
Raman pump
beam alignment
0
100
time (ms)
200
Observation of Cavity-less
Rayleigh Superfluorescence in a
Thermal Gas
Joel A. Greenberg and Daniel. J. Gauthier
Duke University
5/22/2009
Our Setup
Detector (B)
Pump (B)
 ~ 10
Cold atoms
Pump (F)
- PF/B~4 mW
- DF2F’3=5G
T=20 mK
- No- cavity
- L=3 cm, R=150 mm
- Thermal
atoms
- N~109 Rb
atoms
- Counterprop. pumps
Detector (F)
Inouye et al. Science 285, 571 (1999); Slama et al. PRL 98, 053603 (2007)
Outline
• Motivation
• Collective effects
• Self-organization
• Experimental results
• Conclusions/Future work

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