Transient enhancement of the nonlinear atom-photon coupling via

recoil-induced resonances:

Joel A. Greenberg and Daniel. J. Gauthier

Duke University

5/22/2009

Cavity-less Rayleigh Superfluorescence in a Thermal Gas

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

0 100 200 3000

1

2

3

t (s)

Pow

er (W

)

Forward

Backward

F/B PumpsMOT beams

• Light persists until N falls below threshold

• F/B temporal correlations

• ~1 photon/atom large fraction of atoms participate

on

off

Wang et al. PRA 72, 043804 (2005)

0 1 2 3 401234

2 3 4255075

100

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 /

SF MechanismSF Mechanism

What is the mechanism responsible for SF?

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?

SF MechanismSF Mechanism

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

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

SFRayleigh scattering is critical

for observation of SF

• 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

ConclusionsConclusions

• Study dependence of Ppeak and D on N

• Look at competition between vibrational Raman and Rayleigh SF

Future WorkFuture Work

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

Forward: Rayleigh backscattering Backward: Recoil-mediated FWM

250 0 250

1

2

250 0 2500

1

2

(kHz) (kHz)

Probe (p=+)

Pumps ()

I ou

t/Iin

I ou

t/Iin

Forward

Backward

Rayleigh Rayleigh

Weak probeWeak probe

Probe (p=+)

Pumps ()

Forward

Backward

250 0 2500

2

4

6FWM Above Thresh

Below thresh

(kHz)

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

ConclusionsConclusionsRayleigh backscattering

Recoil-mediated FWM

250 0 250

1

2

250 0 2500

1

2

(kHz)

Superfluorescence (SF)Superfluorescence (SF)

L,N

Pump

Pow

er

SFsp/N

sp

D

Ppeak • Cooperative emission produces short, intense pulse of light

• Emission occurs along ‘endfire’ modes

• PpeakN2

Superfluorescence (SF)Superfluorescence (SF)

L,N

Pump

gL1

Spontaneous Emission

Amplified Spontaneous Emission (ASE)

Superfluorescence (SF)

SF Thresh

Weak probeWeak probe

Forward: Rayleigh backscattering Backward: Recoil-mediated FWM

250 0 250

1

2

250 0 2500

1

2

(kHz) (kHz)

Probe (p=+)

Pumps ()

I ou

t/Iin

I ou

t/Iin

Forward

Backward

Rayleigh Rayleigh

RNg 2

Probe SpectroscopyProbe Spectroscopy

0 100 200

Forward Detector Backward Detector (FWM)

250 0 250 250 0 250 (kHz) (kHz)

Rayleigh

SF signal

time (s)

Pro

be P

ower

Pro

be P

ower

Rayleigh pump beam alignment

Raman pump beam alignment

SF

Pow

erRaman

SF

Forward Detector Backward Detector (FWM)

Probe SpectroscopyProbe Spectroscopy

0 100 200

250 0 250 250 0 250 (kHz) (kHz)

Rayleigh

SF signal

time (s)

Pro

be P

ower

Pro

be P

ower

Rayleigh pump beam alignment

Raman pump beam alignment

SF

Pow

er

Rayleigh scattering is critical for observation of SF

Observation of Cavity-less Rayleigh Superfluorescence in a

Thermal Gas

Joel A. Greenberg and Daniel. J. Gauthier

Duke University

5/22/2009

Our SetupOur Setup

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

- No cavity- Thermal atoms- Counterprop. pumps

Inouye et al. Science 285, 571 (1999); Slama et al. PRL 98, 053603 (2007)

• Motivation

• Collective effects

• Self-organization

• Experimental results

• Conclusions/Future work

OutlineOutline