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Amplified Spontaneous Emission (ASE). Spontaneous Emission (SE). Superfluorescence (SF). Collectivity. 1. SF Thresh. 3 cm. Vacuum. Trapping. MOT. y. Mirror. x. Cell. z. Cooling. Magnets. Probe. 3 cm. cold atoms. Scattering enhances grating. Grating enhances scattering. - PowerPoint PPT Presentation
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Duke University, Physics Department and the Fitzpatrick Institute for Photonics · Durham, NC
Collective Nonlinear Optical Effects in an Ultracold Thermal Vapor
Anisotropic MOT1
Joel A. Greenberg, Daniel J. Gauthier
Introduction
Citations
1) J.A. Greenberg, M. Oria, A.M.C. Dawes, D.J. Gauthier, Opt. Express 15, 17699 (2007)
2) M. Malcuit, Univ. of Rochester, PhD Dissertation (1987)
3) J.A. Greenberg and D.J. Gauthier, OSA Opt. Photonics Cong. Tech. Digest, ISBN 978-1-55752-873-5 (2009)
• Length: 3 cm, Radius: 150 m • Optical Depth ~55 (Iout/Iin = e-OD) • Density 7x1010 atoms/cm3
• Temperature ~30 μK • 87Rb trapped on F=2F’=3
Applications
Funding
NSF AMO Grant # PHY-0855399; DARPA Slow Light Contract PO #412785-G-2
Mirror
Cooling
Trapping
Probez
yx
MOT
Vacuum
CellMagnets
3 cm
Our magneto-optical trap (MOT) uses lasers and magnetic fields to trap and cool atoms
Collective Effects2
3 cm
cold atoms
MOT Characteristics:
MOT Setup:
Collective optical effects occur when the radiative properties of an atom are effected by the presence of additional atoms
Superfluorescence
• Few-photon NLO elements are critical for quantum information applications, but large atom-photon interaction strengths are needed• We obtain large nonlinear couplings in cold atoms by controlling the atoms’ internal and external states
Nonlinear Optics (NLO) with Cold Atoms
Goal: Single-photon NLO• Collective nonlinear effects allow for a drastic enhancement of the atom-photon coupling strength over single-atom effects, and may lower NLO thresholds to the single-photon limit
Trapping laser beam configuration Photo of MOT setup
CCD image of trapped atoms
1
Spontaneous Emission (SE)
Amplified Spontaneous Emission (ASE)
Superfluorescence (SF)
SF Thresh
Collectivity
The influence of the radiators on one another can take on a continuum of values (described by a collectivity parameter). On one end, atoms radiate independently (SE) – on the other, all atoms release their energy at the same time (SF)
Pow
er
SFSE/N
SE
D
Ppeak • Cooperative emission produces a short, intense pulse of light• Ppeak N2 (N times larger than SE!)
• Delay time (D) before pulse occurs• Threshold density/ pump power
The degree of atomic organization affects the radiation field, thus producing a nonlocal atom-atom coupling. The net result is a runaway process that gives rise to the collective emission of light
Scattering enhances grating
Grating enhances scattering
Ppe
ak (W
)
OD N
)(NExp2)( tNN
PF/B (mW)
D (s
)
2/1/
BFP
Ppe
ak (W
)
PF/B (mW)
BFP /
Self-organization
Collective Emission Characteristics
We observe SF light generated along the trap’s long axis in both the forward and backward directions3
t (s)
Pow
er (W
)
Forward
Backward
F/B Pump beams MOT beamson
off
• SF light is nearly degenerate with pump frequency • Light persists until atomic density falls below threshold • F/B SF temporal correlations• ~1 photon emitted/atom
SF Characteristics
Experimental Setup
10~
Pump (F)
Pump (B)
Cold atoms
Detector (B)
Detector (F)
SF light
SF light
• Counter-propagating pump beams• Detect emitted light in forward (F) and backward (B) directions
The forces exerted on atoms by multiple light beams give rise to a global spatial organization of the atoms
Atomic density grating
SF light
An atom recoils when it absorbs or a emits a photon
atom atomp
Example: Absorption
SF Light Observed on Detectors
SF Light Trends
before after
Laser timing scheme
We find good agreement with the predictions of superfluorescent collective atomic recoil lasing (CARL) theory
• New insight into free electron laser dynamics• Possible source of correlated photon pairs• Optical/Quantum memory
We may be seeing a nonlinear (N2) scaling of the peak SF power with atom number
SF Power vs N
time