Nonlinear holography is a powerful technique for shaping beams at new optical frequencies. Selectively reconstructing target wavefront information from multichannel nonlinear holography is challenging due to the critical phase-matching condition. Herein, we propose a scheme for all-optical controlled multichannel nonlinear holography using four-wave mixing (FWM) in Rb vapor. A dispersion-controlled wavevector was dynamically tuned to achieve a full phase-matching condition for efficient target wavefront reconstruction. We adjusted the frequency and intensity of the control beam to selectively reconstruct annular vortex arrays in the FWM signal. Four switchable holographic channels were established for beam shaping via experimental parameter optimization. Our study demonstrates that the atomic system is ideal for studying nonlinear control of structured light and aids in constructing all-optical multichannel devices for classical and quantum information processing.
Nonlinear holography is a powerful technique for shaping beams at new optical frequencies. Selectively reconstructing target wavefront information from multichannel nonlinear holography is challenging due to the critical phase-matching condition. Herein, we propose a scheme for all-optical controlled multichannel nonlinear holography using four-wave mixing (FWM) in Rb vapor. A dispersion-controlled wavevector was dynamically tuned to achieve a full phase-matching condition for efficient target wavefront reconstruction. We adjusted the frequency and intensity of the control beam to selectively reconstruct annular vortex arrays in the FWM signal. Four switchable holographic channels were established for beam shaping via experimental parameter optimization. Our study demonstrates that the atomic system is ideal for studying nonlinear control of structured light and aids in constructing all-optical multichannel devices for classical and quantum information processing.
Multichannel vortex beams serve as an essential physical source for enabling multi-spot laser processing and high-dimensional spatial multiplexing communications. We demonstrate a compact, flexibly tunable multichannel vortex beam generator using spatially structured bidirectional two-color pump vortex four-wave mixing in a single 133Cs vapor cell. To enhance spatial multiplexing, both sides of the cell are utilized. By engineering the propagation directions and frequencies of five input beams, we establish a nonlinear interaction region that supports 16 concurrent phase-matching conditions, thereby enabling the parallel generation of up to eight vortex channels. The orbital angular momentum of the output beams follows deterministic algebraic rules, allowing for programmable control via tailored input orbital angular momentum combinations. Moreover, the channel count can be linearly tuned by selectively deactivating pumps—each switched-off pump reduces the number of output channels by two. This flexible control over orbital angular momentum states, together with channel count and spatial arrangement, establishes a highly integrated platform for on-demand vortex generation. This work highlights the potential of spatially bidirectional structured pumping in atomic vapor to expand optical dimensionality and enhance multiplexing capacity, paving the way toward multidimensional communications, quantum networks, and integrated photonics.
Multi-photon nonlinear processes in atoms have served as important tools for quantum metrology, quantum communications, and quantum sensing. In this thesis, we experimentally address the interplay of various multi-photon Raman processes in hot Rb vapor, with the four-wave mixing (FWM) process being a central theme. FWM is the nonlinear response of a medium to a strong optical pump field inelastically scattering off atomic resonances and resulting in the generation of additional photons in different modes. FWM is a detrimental, but inherent part of electromagnetically induced transparency (EIT) and Raman based quantum memories. However, we were able to weaken the four-photon resonance by utilizing two-photon absorption to remove the additional photons without interfering with the signal beam. We also demonstrate the ability to tailor FWM to generate new photons in a controlled fashion for mode conversion. With this, we showed the conversion of 795 nm light to 420 nm light. While FWM is a source of noise in quantum memories, it can also be used for the generation squeezed twin-beams. Such beams have relative intensity noise reduced below the classical shot noise limit and share mode dependence based on the phase-matching conditions. Using this, we demonstrated that twin-beams can be generated with largely different spatial structure (optical angular momentum) and still share strong correlations, so long as the phase-matching conditions are satisfied. We then constructed and demonstrated the operation of a polarization-based quantum interferometer using squeezed twin-beams and showed that our beams were entangled under the inseparability condition. Using this interferometer, we were also able to achieve squeezing at low detection frequencies, which is necessary for things like quantum imaging and gravitational wave detection. We also demonstrated that squeezed twin-beams can be utilized to enhance the sensitivity of two-photon absorption spectroscopy. This research has touched on many different subjects related to quantum information science and improved upon some of the tools needed for the implementation of such technologies.
Spatial discrete control of the light field has long been regarded as a fascinating and prominent area in optics. Here, we propose two distinct approaches to spatially manipulate the four-wave mixing (FWM) signal by introducing a one-dimensional standing wave into its nonlinear generation and linear propagation dynamics. The FWM is generated by two pump fields and one reference field in an atomic vapor. First, we encode the standing-wave pattern into one pump field and successfully transfer its periodic distribution to the FWM signal. The spatially distributed pump field can modulate the third-order nonlinearity in a discrete manner and induce an equivalent nonlinear amplitude grating, which discretely diffracts the generated FWM signal within a rather wide frequency tuning range. In addition, we also established a linear refractive index grating with the assistance of electromagnetically induced transparency (EIT) by employing the same standing wave to modulate the Gaussian FWM signal in a cascaded atomic configuration. Owing to the instantaneously adjustable EIT condition, we have both theoretically and experimentally demonstrated the sensitive inversion on the bright and dark fringes of the discretized FWM signal by inverting the sign of the two-photon detuning. This work opens opportunities for engineering nonlinear optical effects through optically induced reconfigurable gratings.
We experimentally investigate the frequency conversion of vector beams with four-wave-mixing (FWM) in rubidium vapor. The conversion of vector beams from the probe beam to the conjugate beam is realized. In FWM experiments, the pump and the probe beam have orthogonal polarizations because of the polarization sensitivity of the FWM process and detection convenience. In order to satisfy the polarization sensitive phase matching condition and realize the nonlinear frequency conversion of vector beams, a Sagnac interferometer is used to form two FWM processes in the same rubidium cell, and two generated conjugate beams are combined with a polarizing beam splitter to form a conjugate vector beam. The experimental results agree well with our theoretical simulation. Compared with nonlinear optical crystals, the atomic vapor provides another platform to control and manipulate the vector beams nonlinearly.
Airy vortex beams, which integrate orbital angular momentum with diffraction-resistant and self-accelerating characteristics of Airy beams, offer unique capabilities for high-capacity optical communication and high-resolution imaging. Here, we experimentally demonstrate the generation and manipulation of frequency-converted Airy vortex beams through four-wave mixing in hot Rb vapor. A 780 nm vortex beam and a 776 nm two-dimensional Airy beam coherently participate in the four-wave mixing process, generating a 420 nm output beam that combines the orbital angular momentum of the vortex beam with the spatial structure of the Airy beam. The generated beam exhibits pronounced quasi-nondiffracting propagation and self-acceleration, with an intensity decay rate reduced by a factor of ∼1.88 relative to the input vortex beam and a transverse acceleration ∼1.84 times that of the input Airy beam. Moreover, both the intensity and the spatial profile of the generated beam are flexibly manipulated by varying the Rb vapor temperature and the pump beam power. This work provides a versatile approach for generating and controlling structured light at what we believe are new wavelengths, opening opportunities for short-wavelength optical manipulation and optical information processing.
We propose and experimentally demonstrate a controlled-not gate with light beams carrying orbital angular momentum (OAM) through a degenerate four-wave mixing process via a photonic band gap structure satisfying the phase-matching condition. By employing the different topological charges of a Laguerre-Gaussian beam as a qubit in this nonlinear process, the controlled-not gate with OAM can be realized. Moreover, we investigate the evolution of the controlled-not gate, which can be modulated by the frequency and the power of the incident beam, i.e. , under electromagnetically induced transparency conditions. The study results are useful for applications in quantum communication and information storage.