Refractive Index Enhancement without Absorption N. A. Proite, J. P. Sheehan, J. T. Green, D. E. Sikes, B. E. Unks, and D. D. Yavuz University of Wisconsin, Madison Theory Proof-of-principle experiment and results Triple shielded  -metal 1mm cell, 130°C We report a proof-of-principle experiment where the refractive index of an atomic vapor is enhanced while maintaining vanishing absorption on a weak probe beam. We use strong control beams to induce Raman (2-photon) resonances in the vapor. One resonance amplifies the weak probe, while the other resonance absorbs the probe. All three beams are tuned far outside the excited D2 line of Rubidium-85. When the probe frequency is tuned to exactly between the amplifying and absorptive resonances, it travels through the vapor with perfect transmission. The steep dispersion curve produces an enhanced index of refraction. Enhanced Refractive Index (  ’ adds constructively) Zero absorption (  ’’ cancels to zero) Weak probe Control Beam 1 and Control Beam 2 Control Beam 1 and Control Beam 2 Weak probe is amplified Weak probe is absorbed p 100-fold improvement Susceptibility (  2-photon detuning Amplifying resonance 2-photon detuning Susceptibility (  Absorptive resonance 2-photon detuning Susceptibility (  How high of a refractive index is possible? The maximum achievable n is equal to the atom’s maximum two-level refractive index. We plot this curve below. A key advantage of our scheme is that the laser beams are tuned far from any excited state lines. This means that the scheme is relatively insensitive to excited-state dephasing mechanisms. We can use exceptionally high vapor densities, along with buffer gases for spatial confinement and radiation dampening. p Optical pumping high-density vapor cells |F=2 › |F=3 › D2 line of 85 Rb 10 GHz detuned We thank the Air Force Office of Scientific Research and Wisconsin Alumni Research Foundation for funding. The same probe is used in two different Raman resonances Control 1Control 2 In order to achieve a refractive index of  n=0.1 in a gas, we first need to efficiently optical pump vapor densities as high as cm -3. The plot demonstrates our optical pumping in a simple pump-probe experiment in 85 Rb. An amplifying and an absorbing Raman resonance are set up using strong (100 mW) control beams detuned 10 GHz from the excited rubidium D2 line. The experiment is conducted in magnetically shielded hot rubidium vapor. Amplifying resonance Absorptive resonance  n (10 -7 ) -2 0  n (10 -7 ) Enhanced Index 1 Suppressed Index 2 1 N. A. Proite, et. al., Phys. Rev. Lett., 101, (2008) In the time since the published results (above), we have made several changes that have resulted in a dramatic 100-fold improvement in our measured index of refraction. Improvements include: We showed 40% gain and 40% loss simultaneously in a 1mm vapor cell We demonstrated that two opposite Raman resonances can be constructed in a single isotope of rubidium Our next step is to perform this experiment in a magneto-optical trap, and to understand mechanisms that are limiting the magnitude of the achieved refractive index.  n = 3 × PBS P. Anisimov and O. Kocharovskaya, 38 th Winter Colloquium on Physics of Quantum Electronics, Snowbird, Utah, 2008 probe 2 Preliminary Results Probe Frequency (MHz)