Refractive Index Enhancement in Atomic Vapors Deniz Yavuz, Nick Proite, Brett Unks, Tyler Green, Dan Sikes Department of Physics, University of Wisconsin Madison, WI

Key Question  How much can we increase the refractive index, n, of an atomic medium while maintaining vanishing absorption?  When an electromagnetic wave is in a medium with refractive index n, the wavelength of the wave is /n. As a result the resolution is increased.

Two-level scheme  A laser beam tuned close to a two level resonance can experience a large refractive index.  In a gas with a pressure of 1 torr,  can get values as large as 100. However, this effect is not useful since,  is just as large.

Two two-level scheme +  +  The interference between an absorptive resonance and an amplifying resonance can result in a large refractive index with vanishing absorption. M. Fleischhauer et. al. Phys. Rev. A 46, 1468 (1992).

Numerical calculation in Rb susceptibility   p (MHz)   p (MHz) 87 Rb 85 Rb N=10 15 /cm 3 I c1  I c2  100 W/cm 2 Detuning=30 GHz

Maximum susceptibility I c1, I c2 (W/cm 2 ) real part of susceptibility  How much can one increase the real part of the susceptibility while maintaining vanishing imaginary part? D. D. Yavuz, Phys. Rev. Lett. 95, (2005)

First experiments F=0, 1, 2, 3 EpEp EcEc optical pumping laser F=1 F=2 87 Rb vapor cell EpEp EcEc optical pumping laser  85 GHz beam detection and diagnostics 87 Rb energy level diagram B. E. Unks, N. A. Proite, and D. D. Yavuz, Rev. Sci. Inst. 78, (2007). N=1.7  /cm 3

Raman self-focusing and self-defocusing normalized transmission  The refractive index increases and decreases on either side of the resonance causes self-focusing and self-defocusing.  >0, self-focusing  <0, self-defocusing

Self-focused and defocused profiles Intensity x (mm)  >0, self-focusing  <0, self-defocusing Intensity

Future work  Cold atomic clouds offer key advantages over vapor cells:  Narrow Raman linewidths  Tighter focusing  Orthogonal geometries  Spatial Raman Solitons  Combine an absorptive resonance with an amplifying resonance

All-optical devices EpEp atomic cloud E c1 E c2 Intensity pattern refractive index pattern I(x) n(x)  Since the refractive index enhancement is proportional to the intensity of the control lasers, an intensity pattern is transferred to a refractive index pattern.

Conclusions  Far-off resonant Raman systems offer a new approach for achieving large refractive index with vanishing absorption.  As a first step, we have observed Raman self-focusing and self-defocusing in an alkali vapor cell.

Adiabatic vs non-adiabatic evolution before the cell after the cell intensity (a. u.) time (  s) intensity (a. u.) time (  s) intensity (a. u.) adiabatic evolution non-adiabatic evolution