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Physical Review A

Rapidly reconfigurable slow-light system based on off-resonant Raman absorption

Praveen K. Vudyasetu, Ryan M. Camacho, John C. Howell

Published Nov 9, 2010• 3 citations
Publisher

Abstract

We present a slow-light system based on dual Raman absorption resonances in warm rubidium vapor. Each Raman absorption resonance is produced by a control beam in an off-resonant $\ensuremath{\Lambda}$ system. This system combines all optical control of the Raman absorption and the low-dispersion broadening properties of the double Lorentzian absorption slow light. The bandwidth, group delay, and central frequency of the slow-light system can all be tuned dynamically by changing the properties of the control beam. We demonstrate multiple pulse delays with low distortion and show that such a system has fast switching dynamics and thus fast reconfiguration rates.

DOI
10.1103/physreva.82.053807

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We present a slow-light system based on dual Raman absorption resonances in warm rubidium vapor. Each Raman absorption resonance is produced by a control beam in an off-resonant \ensuremathΛ\ensuremath{\Lambda}\ensuremathΛ system. This system combines all optical control of the Raman absorption and the low-dispersion broadening properties of the double Lorentzian absorption slow light. The bandwidth, group delay, and central frequency of the slow-light system can all be tuned dynamically by changing the properties of the control beam. We demonstrate multiple pulse delays with low distortion and show that such a system has fast switching dynamics and thus fast reconfiguration rates.
This thesis presents the applications of some of the coherent processes in a three-level atomic system, to control spatial and temporal properties of a signal pulse. We use two Raman absorption resonances in rubidium vapor separated by a few MHz to achieve a rapidly tunable slow-light system. We control the slow-light characteristics all-optically by tuning the frequency and power of a coupling beam. A dual absorption slow-light system is known to cause less pulse broadening than a single transmission resonance system, and thus, a tunable double absorption system is advantageous. We use a four-wave mixing process to demonstrate pulse storage in rubidium vapor for times much greater than the pulse width. We demonstrate storage of both the temporal and spatial profile of the pulse. We overcome the diffusion of spatial information during the storage in warm atomic vapor by storing the Fourier transform of the image instead of an image with a flat phase. The Raman absorption resonance is also used to control the transverse refractive index profile of the signal beam. The refractive index of the signal interacting with a coupling beam in a Raman process is dependent on the coupling beam intensity. We use a first order Laguerre-Gaussian (LG01) coupling beam to create a waveguide like transverse refractive index profile. We demonstrate propagation of a focused signal beam for lengths much greater than the Rayleigh length. Finally, we demonstrate a dual absorption atomic prism, which is capable
We consider group delay and broadening using two strongly absorbing and widely spaced resonances. We derive relations which show that very large pulse bandwidths coupled with large group delays and small broadening can be achieved. Unlike single resonance systems, the dispersive broadening dominates the absorptive broadening which leads to a dramatic increase in the possible group delay. We show that the double resonance systems are excellent candidates for realizing all-optical delay lines. We report on an experiment which achieved up to 50 pulse delays with 40% broadening.
We study ultrabroadband slow light in a warm rubidium vapor cell. By working between the D1 and D2 transitions, we find a several-nanometer window centered at 788.4 nm in which the group index is highly uniform and the absorption is small (<1%). We demonstrate that we can control the group delay by varying the temperature of the cell, and we observe a tunable fractional delay of 18 for pulses as short as 250 fs (6.9 nm bandwidth) with a fractional broadening of only 0.65 and a power leakage of 55%. We find that a simple theoretical model is in excellent agreement with the experimental results. Using this model, we discuss the impact of the pulse’s spectral characteristics on the distortion it incurs during propagation through the vapor.
We propose and experimentally demonstrate a scheme to generate optically controlled delays based on off-resonant Raman absorption. Dispersion in a transparency window between two neighboring, optically activated Raman absorption lines is used to reduce the group velocity of broadband 765 nm pulses. We implement this approach in a potassium titanyl phosphate (KTP) waveguide at room temperature, and demonstrate Raman-induced delays of up to 140 fs for a 650-fs duration, 1.8-THz bandwidth, pulse. Our approach should be applicable to single-photon signals, offers wavelength tunability, and is a step toward processing ultrafast photons.