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Journal of the Optical Society of America B

Asymmetric manipulations on the coherent Raman sideband generation under molecular modulations

Penghong Yu, Xiaoxiong Wu, Zhaohui Dong, Juan Chen, Kai Wang, Luojia Wang, Xianfeng Chen, Luqi Yuan

Published Aug 10, 2023• 1 citation
Publisher

Abstract

We study the light evolution through a Raman-active medium, where a pair of fields pump molecules near-resonantly and excite the molecular coherence. A synthetic lattice including multiple frequency sidebands via the coherent Raman process is constructed. By varying the density of molecules in the light propagation direction, the system can present a lattice model undergoing dynamic modulations. Further considering the frequency-dependent couplings between synthetic lattice sites, we explore intriguing phenomena, including spectral Bloch oscillation and super Bloch oscillation with asymmetric patterns, which leads to interesting frequency-conversion phenomena with the Raman sideband generations. Our work could be useful for future experiments in coherent Raman sideband processes towards ultrashort pulse generations and higher-frequency conversion.

DOI
10.1364/josab.496489

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We study the light evolution through a Raman-active medium, where a pair of fields pump molecules near-resonantly and excite the molecular coherence. A synthetic lattice including multiple frequency sidebands via the coherent Raman process is constructed. By varying the density of molecules in the light propagation direction, the system can present a lattice model undergoing dynamic modulations. Further considering the frequency-dependent couplings between synthetic lattice sites, we explore intriguing phenomena, including spectral Bloch oscillation and super Bloch oscillation with asymmetric patterns, which leads to interesting frequency-conversion phenomena with the Raman sideband generations. Our work could be useful for future experiments in coherent Raman sideband processes towards ultrashort pulse generations and higher-frequency conversion.
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Recent experiments have shown that coherent molecular oscillations may generate a comb of coherent collinear sidebands with 50,000 cm/sup -1/ of spectral bandwidth. The essence of this technique is the use of a Raman transition with a sufficiently large coherence that the generation and phase slip length are of the same order. The coherence is established by driving the molecular transition with two single-mode laser fields slightly detuned from the Raman resonance, so as to excite a single molecular superposition state. This talk will summarize the characteristics of this light source and describe two recent experiments which show the mutual coherence of the generated sidebands.
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We demonstrate the efficient generation of Raman sidebands in a medium coherently prepared in a dark state by continuous-wave low-intensity laser radiation. Our experiment is performed in sodium vapor excited in $\ensuremath{\Lambda}$ configuration on the D1{D}_{1}D1​ line by two laser fields of resonant frequencies ${\ensuremath{\omega}}_{1}$ and ${\ensuremath{\omega}}_{2},$ and probed by a third field ${\ensuremath{\omega}}_{3}.$ First-order sidebands for frequencies ${\ensuremath{\omega}}_{1},$ ${\ensuremath{\omega}}_{2}$ and up to the third-order sidebands for frequency ${\ensuremath{\omega}}_{3}$ are observed. The generation starts at a power as low as 10 \ensuremath{\mu}W for each input field. Dependences of the intensities of both input and generated waves on the frequency difference $({\ensuremath{\omega}}_{1}\ensuremath{-}{\ensuremath{\omega}}_{2}),$ on the frequency ${\ensuremath{\omega}}_{3},$ and on the optical density are investigated.
We theoretically demonstrate nontrivial topological effects for a probe field in a Raman medium undergoing molecular modulation processes. The medium is driven by two noncollinear pump beams. We show that the angle between the pumps is related to an effective gauge potential and an effective magnetic field for the probe field in the synthetic space consisting of a synthetic frequency dimension and a spatial dimension. As a result of such an effective magnetic field, the probe field can exhibit a topologically protected one-way edge state in the synthetic space, as well as Landau levels which manifest as suppression of both diffraction and sideband generation. Our work identifies a previously unexplored route towards creating topological photonics effects and highlights an important connection between topological photonics and nonlinear optics.