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