1. Investigation of the Saturation Mechanism of Recoil-induced Resonances Joel A. Greenberg, Marcos Oria, and Daniel J. Gauthier Duke University 5/28/2008

2. Plasmonics Local field enhancement (Chang et al., 2007) Pattern-forming Instabilities Sensitivity to perturbations (Dawes, Kaiser)Motivation Nonlinear optical (NLO) effects typically require large intensities New techniques for realizing single-photon NLO effects are being developed Atom-filled Photonic Fibers Large intensities over long lengths (Bajcsy, Gaeta)

3. Our Approach 87 Rb F=2 F’=3 100:1 Aspect Ratio OD=55 (I/I 0 =e -OD ) Temperature= 30-50μK 3 cm Anisotropic Magneto-optical Trap (MOT) Use a ‘cold atom fiber’ Need to establish 1)Can the atoms guide and confine light? 2)What is the nonlinear optical response of the anisotropic MOT? See poster R1.00075 Greenberg et al. (2007), Vengalattore et al. (2002)

4. MOT Spectra detector MOT Pump beams Probe beam Mollow (MHz) Vengalattore et al. (2005)

5. MOT Pump beams Probe beam Recoil Induced Resonance (RIR) How does the RIR saturate? MOT Spectra (MHz) (kHz)

6. RIR Mechanism (Amplification) Weak Field Limit (Maxwell-Boltzmann) Courtois et al. PRL (1994)

7. Saturation Mechanism Two possibilities: 1) Saturate the narrow, “two level” transitions 2) Modify the momentum distribution I sat small I sat large (10 -2 mW/cm 2 ) … … ……

8. Experiment I out /I in detector MOT Pump beams Probe beam (kHz) Intensity

9. Gain Saturation data model I out /I in I probe (mW/cm 2 ) mW/cm 2 Large I sat indicates multiple scattering per atom

10. Resonance Broadening RIR HWHM (kHz) I probe (mW/cm 2 ) data model mW/cm 2 kHz Atom recycling dominant in saturation

11. Conclusions/Future Work The anisotropic MOT is a great NLO sample (i.e. large nonlinearity, difficult to saturate) “Atom recycling” is key to the process of RIR saturation The appearance of an effective two level atom may help direct a theoretical description of the high gain regime