Stokes Field Research Articles

Phase Separation Study on the Storage of Technically Specification Natural Rubber Modified Bitumen

Overloading and climate change are often problems in pavement structures. For this reason, hard asphalt binders have high softening points, are elastic, and have good adhesion, which is needed to improve pavement performance. Asphalt binder performance can be enhanced by adding additives such as natural rubber or natural-rubber-modified asphalt. However, natural-rubber-modified asphalt shows poor storage stability problems. This is due to differences in density and viscosity between the constituent components of natural-rubber-modified asphalt. This study examines the phase separation mechanism in technically specified natural rubber (TSNR) modified asphalt. Prediction of the optimum storage length of modified asphalt before phase separation occurs, using a combined incompressible Navier–Stokes and phase field model and carried out with COMSOL Multiphysics software version 5.5. Experimental validation was conducted at TSNR levels of 8, 10, and 12% at 160 °C for 48 h, with and without sulfur. The simulation showed that the asphalt modified with TSNR experienced phase separation after 12 h of storage at 160 °C under conditions without stirring. This aligns with the experimental results, which showed phase separation at 160 °C after 48 h. Adding sulfur additives did not have much effect on improving storage stability. The combined incompressible Navier–Stokes and phase field model accurately describes the phase separation in TSNR-modified asphalt. The results of this research recommend that the industry store natural-rubber-modified asphalt in a constantly stirred condition to prevent phase separation of modified asphalt. In addition, the results of this research help the industry predict or increase the homogeneity of polymer-modified asphalt production and save time and costs.

Heralded Entanglement Distribution Between Two Spin‐Wave Memories Using Temporally Multiplexed Scheme

AbstractThe elementary link, which is formed by entanglement between two remote atomic ensembles, is a fundamental component of Duan–Lukin–Cirac–Zoller (DLCZ) quantum repeater. For practical realization of quantum repeaters, it is required that entanglement between two atomic‐ensemble‐based memories can be generated with high rates and retrieved with high efficiencies. However, so far, such quantum‐repeater links remain challenge in experiments. Here, heralded entanglement distribution between atomic‐ensemble‐based memories is demonstrated via temporally multiplexed scheme. A train of 12 write pulses in time is applied to a cloud of cold atoms along different directions, which generates temporally multiplexed pairs of Stokes photons and spin waves via DLCZ processes. The Stokes fields propagating in the two spatial modes, which are paired with two spin waves are combined to perform a single‐photon Bell‐state measurement. A successful detection projects the two spin waves into a single‐excitation entanglement, which represents entanglement distribution in an elementary link. Compared with single‐mode storage scheme, the temporally multiplexed scheme gives rise to a 11.8‐fold increase in entanglement generation rate. By using cavity‐enhanced scheme, spin waves stored in the atoms are retrieved on demand and the retrieval efficiencies are up to 70%, which is beneficial for the subsequent entanglement swapping between adjacent links.

Sudden change of the photon output field marks phase transitions in the quantum Rabi model

The experimental observation of quantum phase transitions predicted by the quantum Rabi model in quantum critical systems is usually challenging due to the lack of signature experimental observables associated with them. Here, we describe a method to identify the dynamical critical phenomenon in the quantum Rabi model consisting of a three-level atom and a cavity at the quantum phase transition. Such a critical phenomenon manifests itself as a sudden change of steady-state output photons in the system driven by two classical fields, when both the atom and the cavity are initially unexcited. The process occurs as the high-frequency pump field is converted into the low-frequency Stokes field and multiple cavity photons in the normal phase, while this conversion cannot occur in the superradiant phase. The sudden change of steady-state output photons is an experimentally accessible measure to probe quantum phase transitions, as it does not require preparing the equilibrium state.

Complete flow characterization from snapshot PIV, fast probes and physics-informed neural networks

Physics-informed neural networks (PINNs) are function approximators that can incorporate physics laws during training. In recent years, PINNs have been shown to be capable of reconstructing fluid behavior using constraints based on the Navier–Stokes equations and field data. On the downside, the lack of time resolution in a wide range of experimental applications severely limits the applicability of PINNs. We propose a novel methodology based on feeding PINNs with time-resolved fields estimated from non-time-resolved field measurements (e.g. particle image velocimetry) and time-resolved pointprobe measurements (e.g. hot-wires). First, the dimensionality of the problem is reduced by using as a target the temporal modes from a truncated proper orthogonal decomposition (POD) of the velocity fields. Then, using a multilayer perceptron (MLP), a correspondence is established between probe data and the POD time coefficients of the velocity fields. The estimated fields are then fed to the PINN to enhance the data and increase precision. As a further benefit, additional derived quantities not available in the raw data, such as the pressure distribution, can be extracted if suitable boundary conditions are provided. We validate the method on synthetic test cases based on the direct numerical simulation of the wake of a fluidic pinball. Furthermore, we test the algorithm in an experimental case of the wake of a stalled wing. The results show that the PINN is able to reduce the error in the estimated fields, provided that the reference data obtained from the estimation with the MLP are sufficiently accurate.

In‐Source High‐Resolution Spectroscopy Using an Integrated Tunable Raman Laser

AbstractTunable single‐frequency lasers are the most prominent tool for high‐resolution spectroscopy, allowing for the study and exploitation of the electronic structure of atoms. A significant milestone relies on the demonstration of integrated laser technology for performing such a task. The device presented here is composed of a compact Fabry–Perot monolithic resonator capable of producing tunable and Fourier‐limited nanosecond pulses with a MHz‐class frequency stability without active cavity stabilization elements. It also has the remarkable capability of exploiting the Raman effect to funnel efficiently the broad spectrum of an input laser to a spectrally‐bright Stokes pulse at hard‐to‐access wavelength ranges. The targeted atom for the demonstrations is 152Sm, released as an atomic vapor in a hot cavity environment. Here, the Stokes field is tuned to a wavelength of 433.9 nm, while a crossed‐beams spectroscopy setup is used to minimize the Doppler broadened spectral features of the atoms. With this work, the suitability of integrated diamond Raman lasers as a high‐resolution in‐source spectroscopy tool is demonstrated, enabling many applications in atomic and nuclear physics. The integrated form‐factor and inherent simplicity makes such a laser an interesting prospect for quantum‐technology based sensing systems and related applications.

An Axicon-Based Annular Pump Acousto-Optic Q-Switched Nd:GdVO4 Self-Raman Vortex Laser

We report, for the first time, the generation of a 1173 nm acousto-optic Q-switched self-Raman vortex laser with an axicon-based annular pump system. A 20 mm long Nd:GdVO4 crystal was used as the self-Raman crystal. Both the fundamental field and the first-Stokes field were investigated using the respective output couplers. In comparison with both vortex fields, a noticeable beam cleaning-up effect and pulse compression were observed from the 1063 nm fundamental field to the 1173 nm first-Stokes field. A Stokes field carrying a unitary topological charge was achieved. Finally, the average output power of the first-Stokes vortex emission reached 454 mW under an incident pump power of 19.5 W, corresponding to a pulse width of 45.7 ns. It was beneficial to apply a high peak power from the Q-switched laser and self-Raman conversion to expand the applications of the vortex laser beam.

Generalized stimulated Raman scattering with nonlocal effects

We present a generalized quantum theory of stimulated Raman scattering, which is based on coupled Heisenberg–Langevin equations. Analytical solutions in previous models neglect the effects of the frequency dispersion, assume far-off resonance and only consider slowly varying terms in the atomic operator. In obtaining the more general theory, we have derived partial integro-differential equation containing polarization kernels that include all the temporal nonlocal effects using systematic integral method over time. Analytical solutions of the Stokes field with greater generality for arbitrary spatial-temporal laser fields have been obtained using Laplace transform in the retarded space frame with minimal approximations made. The solutions are very general and potentially useful for studying systems in which highly accurate modeling is required such as quantum memories of a wide range of Raman systems.

Efficient Continuous-Wave Eye-Safe Nd:GdVO4/KGW Raman Laser and Sum Frequency Generation for Deep-Red Emission

A concise, efficient continuous-wave eye-safe Nd:GdVO4/KGW Raman laser at 1525 nm is here demonstrated. A Nd:GdVO4 crystal was used to produce the fundamental field at 1341 nm and a KGW crystal generated the intracavity Stokes field at 1525 nm via wavelength conversion of stimulated Raman scattering. The output power of the Stokes field at 1525 nm could achieve 2.1 W under the pump power of 30 W. Furthermore, two different lithium triborate (LBO) crystals with critical phase matching were exploited to obtain deep-red emission at 714 nm via the intracavity sum frequency generation of 1341 and 1525 nm waves. One cutting angle was in the XY plane and the other was in the XZ plane. The empirical thermo-optical coefficients for the LBO crystal were exploited to systematically analyze the critical phase matching conditions. Numerical results revealed that the type-I phase matching angle in the XY plane was near θ = 90° and ϕ = 3.3° at room temperature, whereas the type-I phase matching angle in the XZ plane was near θ = 86.3° and ϕ = 0° at a temperature around 47 °C. The numerical values for the optimal temperatures for the two different cutting angles were found to be in good agreement with experimental results. At the pump power of 30 W, the output power at 714 nm was approximately 2.9 W by using the LBO crystal with the cutting angle in the XY plane. On the other hand, the maximum output power at 714 nm could be up to 3.2 W under the pump power of 30 W by using the cutting angle in the XZ plane. Furthermore, the linewidth of the SFG emission was confirmed to be nearly the same for the two different cutting angles. The overall linewidth could be narrower than 0.2 nm. The developed laser at 714 nm can be useful in the exploration of ionic and atomic radium isotopes with laser spectroscopy.

Polarization singularities: Topological and dynamical aspects

The review describes general principles and characteristics of inhomogeneously polarized paraxial optical fields and, especially, the polarization singularities (PSs). Main parameters of the optical vector waves are discussed, with the emphasis on the physical relevance and topological distinctiveness of the PSs. Special features of the stochastic vector fields are considered in the context of the PSs’ genericity and structural stability. A detailed attention is paid to interrelations between the PSs and the phase singularities of scalar fields formed by the orthogonal polarization projections of the total field, and their derivatives (complex Stokes fields, phase-difference fields, etc.). On this base, the practical approaches are discussed for the experimental PS identification and characterization. A particular examination of the internal energy flows associated with the PSs, and accompanying distributions of the optical momentum and angular momentum, reveals meaningful dynamical features of PSs and supplies additional physically transparent and informative means for their studies and characterization.

Modeling and characterization of high-power single frequency free-space Brillouin lasers.

Free-space Brillouin lasers (BLs) are capable of generating high-power, narrow-linewidth laser outputs at specific wavelengths. Although there have been impressive experimental demonstrations of these lasers, there is an absence of a corresponding theory that describes the dynamic processes that occur within them. This paper presents a time-independent analytical model that describes the generation of the first-order Stokes field within free-space BLs. This model is based on the cavity resonance enhancement theory and coupled wave equations that govern the processes of stimulated Brillouin scattering (SBS). This model is validated using an experimental diamond BL to numerically simulate the influence of the cavity design parameters on the SBS threshold, pump enhancement characteristics, and power of the generated Stokes field. Specifically, the model is used to determine the SBS cavity coupler reflectance to yield the maximum Stokes field output power and efficiency, which is also a function of the pump power and other cavity design parameters. This analysis shows that the appropriate choice of Brillouin cavity coupler reflectance maximizes the Stokes field output power for a given pump power. Furthermore, the onset of higher-order Stokes fields that are undesirable in the context of single-frequency laser operation were inhibited. This study aids in understanding the relationship between the cavity parameters and resultant laser characteristics for the design and optimization of laser systems.

Efficient transfer of spatial intensity and phase information of arbitrary modes via four-wave mixing in an atomic vapor

We propose a scheme to transfer the spatial intensity as well as phase information encoded initially in the spatial profile of a weak probe field onto a newly generated Stokes field in a nonlinear process of four-wave mixing (FWM). The FWM process is explored in a gaseous medium consisting of atoms modeled as a three-level system in the $\mathrm{\ensuremath{\Lambda}}$ configuration. We found that different orders of Hermite-Gaussian and Laguerre-Gaussian modes carried by a probe beam are effectively transferred to a Stokes beam. Interestingly, the transferred intensity of the Stokes beam is a clone of the probe beam, whereas the phase profile is conjugate to the probe. The phase distribution of the transmitted modes at the exit of the medium is explored by superimposing them on a copropagating plane wave. Moreover, the parametric amplification due to the nonlinear process of FWM prevents any information loss due to linear absorption and permits us to work at high optical depths. We found a structural similarity between transferred images of about $99%$, which provides clear evidence for the successful transfer of information in the FWM process.

Quantum parametric double Raman oscillators with co- and counterpropagating fields: Relative intensity squeezing and spatial photon correlations

We present a comprehensive study of co- and counterpropagating Stokes and anti-Stokes quantum fields in double Raman four-wave mixing parametric oscillators using full quantum Heisenberg-Langevin framework with noise operators. General analytical solutions of the fields operators at any point in the Raman medium are obtained for four cases: two possible copropagating (forward) and two counterpropagating (backward) Stokes and anti-Stokes. We analyze the symmetrical properties of the complex linear and nonlinear susceptibilities spectra of the quantum fields, nonclassicality of two-photon correlation functions, spatial variations of the quantum fields, and the two-mode relative intensity squeezing. We compare the results of forward and backward cases for several limiting double Raman schemes. We find interesting resonant effects of medium length, laser detunings and laser field strengths (Rabi frequencies) for backward-propagating geometries. Analysis of the solutions provide insights on the resonant conditions while computation over multiple variables enables us to identify the values of laser detuning, field strength, and propagation length that give enhanced nonclassical intensity squeezing and persistent correlations. The present work sets the crucial foundations for optimization of the nonclassicality of photons in double Raman systems and would be useful for quantum information storage, quantum nonlinear optics, and quantum spectroscopy.

Robust stimulated Raman shortcuts to adiabatic passage with deep learning

One of the challenging tasks in quantum control is to manipulate quantum systems with high fidelity and as fast as possible. Simulated Raman shortcuts to adiabatic passage with invariant-based optimal control is an efficient technique accurately used to transfer population between two quantum states in three-level systems. This technique requires tuning parameters continuously which results in analog quantum control. However, a digital quantum controller design is of great importance in the era of digital quantum computing. Here, we use deep reinforcement learning to obtain digital Stokes and pump fields that can realize fast and accurate population transfer between states with the same parity in the three-level Λ configuration. We find that deep reinforcement learning follows exactly theshortcuts to adiabaticity (STA) based on dynamical invariant and leads to a robust population transfer against systematic errors and dephasing. This is a promising enhancement in digital quantum information processing.

Stokes Localized Structure in Kerr Resonators

We theoretically demonstrate generation of the Stokes temporal localized structure (TLS) by exploiting its Raman interaction in space and time within an optical potential well shared with another dark pulse. Excitation of the Stokes TLSs is feasible in both the normal and anomalous group-velocity dispersion regime, with a single modulated pump source. Stimulated Raman scattering constitutes influences on the stability and physical feature of the generated Stokes TLS (STLS). Particularly, breathing STLSs are also observed due to the periodic energy transfer between the primary and the Stokes fields. These findings could deepen the understanding of complex nonlinear dynamics in resonators and facilitate the excitation of different types of TLSs in potential platforms.

Generation of 1216 nm and 608 nm laser emission using cascaded Raman shifts in Nd:YVO4

We report the design and operation of two self-Raman lasers optimized for emission at 1216 nm and 608 nm, utilizing a combination of Raman shifts at 890 and 259 cm−1 in c-cut Nd:YVO4 crystal. Key to the efficient operation of these lasers was the use of a double-end diffusion-bonded Nd:YVO4 composite crystal. This enabled the generation of a maximum average output power of 2.6 W at 1216 nm (with a diode-Stokes conversion efficiency of 14.7%) from the Stokes-optimized cavity. With the incorporation of a non-critically phase matched LBO crystal and a slight cavity re-design, the Stokes field at 1216 nm was frequency doubled to the orange part of the visible spectrum (608 nm), where a maximum average output power of 1.71 W was achieved with a diode-orange conversion efficiency of 9.7%.

Power and energy scaling of an acousto-optically Q switched Raman deep-red laser.

An efficient high-power nanosecond pulsed deep-red laser at 745 nm is produced by intracavity frequency-doubling an acousto-optically Q switched Nd:YLF/KGW Raman laser using a lithium triborate (LBO) crystal. The critically phase-matched type-I LBO crystal with an optimized length of 25 mm is adopted to enable efficient second-harmonic generation and to suppress unwanted cascaded Stokes fields. Under a repetition rate of 4 kHz, the maximum average output power of 4.1 W is obtained with the launched pump power of 50 W, resulting in an overall optical power conversion efficiency of 8.2%. The average beam quality factor is determined to be M2 = 1.46. The pulse energy is scaled up to 3.3 mJ at the repetition rate of 1 kHz, corresponding to a pulse width of 4.2 ns and a peak power of up to 0.8 MW. Moreover, we theoretically investigate the dependence of the conversion efficiency on the walk-off angle as well as the fundamental and first-Stokes losses, which will guide further optimization of experimental devices.

Influence of phonon harmonicity on spectrally pure resonant Stokes fields

Due to their highly coherent emission, tunability, and compactness, integrated single-frequency diamond Raman lasers are interesting tools for applications in integrated quantum technology, high-resolution spectroscopy, or coherent optical communications. While the fundamental emission linewidth of these lasers can be Fourier limited, their thermo-optic characteristics lead to drifts in their carrier frequency, posing important challenges for applications requiring ultrastable emission. We propose here a method for measuring accurately the temperature-dependent index of refraction of diamond by employing standing Stokes waves produced in a monolithic Fabry-P\'erot diamond Raman resonator. Our approach takes into account the influence of temperature on the first-order phonon line and the average lattice phonon frequency under intense stimulated Raman scattering conditions. We further utilize this model to calculate the value of the average phonon frequency and then the temperature-dependent thermo-optic coefficient. The theory is accompanied by the demonstration of tunable Fourier-limited Stokes nanosecond pulses with a stabilized center frequency deviation of less than $4$ MHz.

Stimulated Raman adiabatic passage in a quantum system near a plasmonic nanoparticle

We investigate theoretically the population transfer process in a Λ-type three-level quantum system (QS) near a metallic nanosphere using the stimulated Raman adiabatic passage (STIRAP) technique. We combine density matrix quantum dynamical calculations with first-principle electromagnetic calculations, which quantify the influence of the plasmonic nanoparticle on the electric field of the pump and Stokes pulses in STIRAP as well as on the spontaneous emission rates within the Λ-type system. We study the population transfer process by varying the free-space spontaneous emission rate, the distance of the QS from the nanosphere, the polarization direction with respect to the nanoparticle surface and the relative strength of the pump and Stokes pulses used in STIRAP. We find that when the pump and Stokes fields have tangential and radial polarizations with respect to the nanosphere surface, the transfer efficiency is improved due to the increase of the decay rate of the excited state to the target state relatively to the decay to the initial state. The optimal population transfer is achieved for small interparticle distances, moderate free space spontaneous decay rate, large values of the pump Rabi frequency and small values of the Stokes Rabi frequency. When we exchange the polarization directions of the pump and Stokes fields we can still find a range of parameters where the population transfer remains efficient, but larger Stokes Rabi frequencies are necessary to overcome the increased decay rate from the excited state back to the initial state.

Enhanced stimulated Brillouin scattering utilizing Raman conversion in diamond

Cascaded Brillouin lasers based on guided-wave structures are applied across a range of important fields such as optical communications, microwave photonics, and sensing. However, restricted by the volume and available transmission range of the gain medium, the power output and wavelength diversity of guided-wave Brillouin devices are somewhat limited. In this work, we report the design and development of a cascaded Brillouin laser based utilizing a free-space optical layout with a diamond crystal as the Brillouin gain medium. A quasi-continuous-wave, 1 μm laser was used as the pump laser, and Raman wavelength conversion is used as an intermediate process to facilitate stimulated Brillouin scattering with a low threshold. When the output transmission of the diamond cavity is 0.37% and the incident pump power is 220 W, cascading of the Brillouin–Stokes field to the eighth Stokes and the seventh anti-Stokes orders was observed. By adjusting the cavity length, the order of the cascaded Brillouin laser output is controlled. A comprehensive analysis of the Brillouin generation process and the cascade of Stokes orders is undertaken for different incident pump powers and cavity lengths. This work is expected to enable practical applications of high-power Brillouin lasers and Brillouin frequency combs.

Phase-dependent controllable field generation in a ring cavity resonator

We investigate the control field phase-dependent output field transmission from a red detuned ring cavity optomechanical system. Our scheme displays a double transparency window in the presence of a strong control and weak probe field. Additionally, we invoke an external mechanical pump to one of the movable mirrors to modulate its vibration. Complete control over the output field transmission through one of the transparency windows can be achieved due to the combined effect of the amplitudes and the phases of the mechanical pump and the control field. Further, a tunable group delay of the probe pulse propagation can be obtained by the tailoring of the control field phase in the presence of a suitable mechanical drive. We further discuss the effect of control field phase on Stokes field generation via the four-wave mixing process. This scheme may find potential applications in weak signal sensing and all-optical communication purposes.