Collapse of hybrid vector beam in Rb atomic vapor

Measuring the Optical Concurrence of Vector Beams with an Atomic-State Interferometer

We investigate the transmission of vector beams, correlated in their polarization and spatial degrees of freedom, through cold atoms in the presence of a transverse magnetic coupling field. The resulting phase-dependent dynamics allow us to imprint the spatially varying polarization of a vector beam onto atomic spin polarizations, thereby establishing a direct link between optical space-polarization correlations and atomic-state interference. We find that the resulting absorption profiles show interference fringes whose modulation strength is given by the squared concurrence of the vector beam, letting us identify optical concurrence from a single absorption image. We expect impact across a diverse range of applications, including spintronics, quantum memories, metrology, and clocks.

Pseudo-spin-orbit-coupling-based manipulation of vector beams using electromagnetically induced transparency

Based on the electromagnetically induced transparency (EIT) model and the higher-order Poincaré sphere (HOPS) framework, we establish a general paradigm to investigate the paraxial evolution of a vector beam in a tripod EIT system. By quantum-optical analogy, we introduce a formalism with a generalized Pauli-like equation under rotational invariance, in which the pseudo-spin-orbit coupling (PSOC) and the spin-orbit nonseparability of light can coexist. More importantly, we find that both the PSOC-based real and imaginary potentials play a key role in controlling and modulating the nonseparable state of the vector beam to traverse the entire HOPS, where the orientation and ellipticity of the transmitted polarization can be modified by varying the PSOC coefficients. Therefore, an all-optical scheme can be proposed to improve the flexibility for tailoring the space-variant polarization of light in coherent media, where the tunable spatial-polarization multiplexing may be useful in conventional and quantum information processing.

Identification of orbital angular momentum using atom-based spatial self-phase modulation

Optical vortex orbital angular momentum modes, namely the twists number of the light does in one wavelength, play a critical role in quantum-information coding, super-resolution imaging, and high-precision optical measurement. Here, we present the identification of the orbital angular momentum modes based on spatial self-phase modulation in rubidium atomic vapor. The refractive index of atomic medium is spatially modulated by the focused vortex laser beam, and the resulted nonlinear phase shift of beam directly related to the orbital angular momentum modes. The output diffraction pattern carries clearly distinguishable tails, whose number and rotation direction correspond to the magnitude and sign of the input beam orbital angular momentum, respectively. Furthermore, the visualization degree of orbital angular momentums identification is adjusted on-demand in the terms of incident power and frequency detuning. These results show that the spatial self-phase modulation of atomic vapor can provide a feasible and effective way to rapidly readout the orbital angular momentum modes of vortex beam.

All-optical information conversion in Rb vapor based on the spatial cross-phase modulation

All-optical information conversion, conveying optical signals without electro-optical transformation, plays a vital role in the all-optical devices and optical communication. We achieve the all-optical information conversion in Rb vapor by utilizing the spatial cross-phase modulation. The refractive index of atomic medium is spatially modulated by the strong switch laser beam, which makes it as a nonlinear focusing lens for the weak signal laser beam. As a result, the far-field diffraction ring patterns of the signal laser beam interacted with atoms can effectively carry the nonlinear phase shift information of the switch laser beam. The channel numbers, channel capacities and channel storage densities of information transmission from switch laser beam to signal laser beam are investigated in the terms of switch laser intensity and vapor temperature. Finally, a special "sxu" alphabetic string, encoded by ASCII code, is introduced to verify this all-optical information conversion scheme. This work paves the way for studying optical information processing and all-optical networking with atomic ensembles.

Suppression of Nonlinear Optical Rogue Wave Formation Using Polarization-Structured Beams

A nonlinear self-focusing material can amplify random small-amplitude phase modulations present in an optical beam, leading to the formation of amplitude singularities commonly referred to as optical caustics. By imposing polarization structuring on the beam, we demonstrate the suppression of amplitude singularities caused by nonlinear self-phase modulation. Our results are the first to indicate that polarization-structured beams can suppress nonlinear caustic formation in a saturable self-focusing medium and add to the growing understanding of catastrophic self-focusing effects in beams containing polarization structure.

Tunable high-order Bessel-like beam generation based on cross-phase modulation

Nonlinear atomic media are promising substitutes for spatial light modulators (SLMs) owing to the high tunability and fast response. We demonstrate the generation of high-order Bessel-like beam based on cross-phase modulation in ⁸⁵Rb atoms. The atomic medium, whose refractive index is spatially modulated by the focused Gaussian pump beam, acts as a nonlinear focusing lens for the Laguerre-Gaussian probe beam. As a result, the probe beam carries the nonlinear phase shift and is converted into a Bessel-like mode in far-field diffraction. The superior self-healing ability of the generated high-order Bessel-like beam is verified by inserting an obstruction in the beam path, and its high tunability is investigated in terms of the pump beam power and vapor temperature. Furthermore, this novel beam is used in an obstruction-immune rotation sensor to measure the angular velocity. Nonlinear atomic medium as a novel SLM promises considerable application prospects in modulating the light field structure.

Trans-spectral vector beam nonlinear conversion via parametric four-wave mixing in alkali vapor

Coherent frequency conversion of vector beams (VBs) without distorting their intensity profile or spatial polarization distribution is important for novel applications in quantum and classical regimes. Here, we experimentally and theoretically investigate VB transfer from near-infrared to blue light using a Sagnac interferometer, combining the parametric four-wave mixing process in atomic vapor. The vector probe beam is converted into a completely different wavelength, and the vector mode of the generated blue beam is highly similar to the incident probe beam. These results may provide a feasible solution for communication interfaces in classical and quantum science fields based on atomic ensembles.