Coherent Field Research Articles

Scalable angular spectrum propagation

Coherent field propagation is an essential computational tool in optics with applications ranging from computational optics and optical design to iterative field reconstructions. An improvement in the computational speed of current propagation methods is therefore highly desired. We describe a scalable angular spectrum (SAS) algorithm with zoom capability for numerical propagation of scalar wave fields in homogeneous media. It allows for propagation models where the destination pixel pitch is larger than the source pixel pitch, requires a computational complexity proportional to the cost of three successive fast Fourier transform operations of the input field, and it is valid for high numerical aperture (NA) propagation geometries. We find that SAS propagation approaches the precision of the computationally far more expensive angular spectrum method in conjunction with zero-padding. This was computationally confirmed by propagation examples. Finally, we discuss the validity of the proposed SAS method, derive practical bandlimit criteria, and state a limit for the propagation distance. The scalability, efficiency, and accuracy at high NA of our proposed wave propagation algorithm yield benefits for a large variety of forward and inverse modeling problems with the ability to apply automatic differentiation.

Interference bunching and antibunching of coherent and atomic radiation fields

Interference bunching and antibunching of coherent and atomic radiation fields

Low-temperature magnetic ordering in Co core/CoO shell nanoparticles on the copper surface

Cobalt/cobalt oxide nanoparticles electrochemically deposited onto a copper surface revealed an unusual behavior of the coercivity and exchange bias at liquid helium temperature [V.G. Bayev et al., Appl. Surf. Sci. 440 (2018) 1252–1260], pointing out the necessity of careful consideration of magnetic properties at these temperatures. Here, it is shown that the approach based on the random anisotropy model and analysis of law of the approach to magnetic saturation adopted for the two-dimensional (2D) magnetic system allows obtaining the correlation function of the magnetic anisotropy axes in real space, as well as the exchange, random and coherent anisotropy magnetic fields. The long-range correlation in the magnetic anisotropy axes and the oscillating character of the correlation function is the characteristic feature, suggesting the important role of the interplay between the exchange bias and random anisotropy on the one hand and indirect exchange coupling via the conducting electrons of copper and magnetic dipole interaction, on the other.

Efficient two-dimensional Fraunhofer diffraction pattern via electron spin coherence

In this letter, we have discussed the two-dimensional diffraction pattern via electron spin coherence in a GaAs quantum dot. Impulsive stimulated Raman excitation utilizing coherent optical fields is employed for the purpose of regulating the electron spin coherence within a charged ensemble of GaAs quantum dots, by means of an intermediate charged exciton (trion) state. We show that for the coupling two-dimensional standing wave (SW) field in the x and y directions, the two-dimensional Fraunhofer pattern can be formed for a weak probe light. By using the experimental parameters and controlling the Rabi frequency of the SW field and relative phase between applied lights, the symmetry and asymmetry diffraction pattern are obtained for the weak probe light due to the four-wave mixing mechanism. Our proposed model may have potential applications in high-capacity optical communications and quantum information technologies.

Probing magnetic fields in the circumgalactic medium using polarization data from MIGHTEE

Context.The properties and evolution of magnetic fields surrounding galaxies are observationally largely unconstrained. The detection and study of these magnetic fields is important to understand galaxy evolution since magnetic fields are tracers for dynamical processes in the circumgalactic medium (CGM) and can have a significant impact on the evolution of the CGM.Aims.The Faraday rotation measure (RM) of the polarized light of background radio sources passing through the magnetized CGM of intervening galaxies can be used as a tracer for the strength and extent of magnetic fields around galaxies.Methods.We used rotation measures observed by the MIGHTEE-POL (MeerKAT International GHz Tiered Extragalactic Exploration polarization) survey by MeerKAT in the XMM-LSS and COSMOS fields to investigate the RM around foreground star-forming galaxies. We used spectroscopic catalogs of star-forming and blue cloud galaxies to measure the RM of MIGHTEE-POL sources as a function of the impact parameter from the intervening galaxy. In addition, we examined the dependence of the RM on redshift. We then repeated this procedure using a deeper galaxy catalog with photometric redshifts.Results.For the spectroscopic star-forming sample, we find a redshift-corrected |RM| excess of 5.6 ± 2.3 rad m−2which corresponds to a 2.5σsignificance around galaxies with a median redshift ofz = 0.46 for impact parameters below 130 kpc only selecting the intervenor with the smallest impact parameter. Making use of a photometric galaxy catalog and taking into account all intervenors withMg < −13.6 mag, the signal disappears. We find no indication for a correlation between redshift and RM, nor do we find a connection between the total number of intervenors to the total |RM|.Conclusions.We have presented tentative evidence that the CGM of star-forming galaxies is permeated by coherent magnetic fields within the virial radius. We conclude that mostly bright, star-forming galaxies with impact parameters less than 130 kpc significantly contribute to the RM of the background radio source.

Інтелектуальна система оцінювання ступеня локальної деполяризації полів лазерної автофлуоресценції двопроменезаломлюючих мереж протеїнових кристалів

The theoretical foundations of the description of scattered coherent radiation fields using a new correlation parameter - the degree of local depolarization (DLD) - are presented. The data of measuring the coordinate distributions of the DLD of laser images of healthy and pathologically altered rat skin are presented. The values and ranges of change of statistical (moments of the 1st - 4th orders), correlation (correlation area) and fractal (slopes and variance of extremes of logarithmic dependences of power spectra) parameters of the coordinate distributions of the DLD are investigated. The objective criteria for diagnosing oncological changes in the structure of the rat skin are determined.

Calculation of Dark Matter as a Feature of Space–Time

We derive the first analytical formula for the density of "Dark Matter" (DM) at all length scales, thus also for the rotation curves of stars in galaxies, for the baryonic Tully–Fisher relation and for planetary systems, from Einstein's equations (EE) and classical approximations, in agreement with observations. DM is defined in Part I as the energy of the coherent gravitational field of the universe, represented by the additional equivalent ordinary matter (OM), needed at all length scales, to explain classically, with inclusion of the OM, the observed coherent gravitational field. Our derivation uses both EE and the Newtonian approximation of EE in Part I, to describe semi-classically in Part II the advection of DM, created at the level of the universe, into galaxies and clusters thereof. This advection happens proportional with their own classically generated gravitational field g, due to self-interaction of the gravitational field. It is based on the universal formula ρD = λgg′2 for the density ρD of DM advected into medium and lower scale structures of the observable universe, where λ is a universal constant fixed by the Tully–Fisher relations. Here g′ is the gravitational field of the universe; g′ is in main part its own source, as implied in Part I from EE. We start from a simple electromagnetic analogy that helps to make the paper generally accessible. This paper allows for the first time the exact calculation of DM in galactic halos and at all levels in the universe, based on EE and Newtonian approximations, in agreement with observations.

Dynamics of phase space quasi-probability coherence of one of two moving atoms trapped in a cavity coherent field

This study explores the dynamics of atomic mixedness and phase space quasi-probability information of one of two moving atoms trapped in a cavity filled by a coherent field. The atom-photon interactions are considered with the resonance case through nonlinear intensity-dependent coupling. We investigate the impacts of the atom-photon and atomic motion couplings on the dynamics of the atomic Wehrl entropy's mixedness and phase space Husimi distribution information. By helping Wehrl entropy's mixedness dynamics, the dynamics of acceleration and enhancement of the generation of the atomic phase space quasi-probability coherence are examined, and the Husimi distributions of the generated atomic states of one of the two moving atoms are explored. The results are shown that the atomic Husimi distribution and Wehrl entropy's mixedness are susceptible to an increase in the atom-photon and the atomic motion couplings. Therefore, the atomic phase space Husimi distribution coherence can be improved by increasing the atomic motion and nonlinear atom-photon couplings.

Pump-Probe Optical Response and Four-Wave Mixing in a Zinc-Phthalocyanine-Metal Nanoparticle Hybrid System.

We investigate theoretically the optical response of a zinc-phthalocyanine molecular quantum system near a gold spherical nanoparticle with a radius of 80 nm. The quantum system is irradiated by a strong pump and a weak probe coherent electromagnetic field. Using the density matrix methodology, we obtain analytical expressions for the absorption, dispersion, and the four-wave-mixing coefficients. The influence of the nanoparticle on the spontaneous decay rate of the quantum system, as well as on the external fields, are obtained by an electromagnetic Green's tensor method. The spectroscopic parameters of the molecule are also obtained by ab initio methods. For the studied optical spectra, we find that, below a critical distance between the molecule and the plasmonic nanoparticle, determined by the minimal value of the effective Rabi frequency, single-peaked spectra are observed. Above this critical distance, the spectra exhibit the characteristic Mollow-shaped profiles. The enhancement of the pump field detuning induces the shift of the sideband resonances away from the origin. Lastly, and most importantly, regardless of the value of the detuning, the optical response of the system is maximized for an intermediate value of the interparticle distance.

Controlling optical bistability, multistability and all-optical switching through multi-photon excitation process

We present a theoretical study on optical bistability (OB), optical multistability (OM) and tunable all-optical switching in a four-level cascade type atomic system. The density matrix formalism is used to find out the response of the probe laser field. We explore OB and OM under unidirectional optical ring cavity configuration. A comparison between the effects of electromagnetically induced transparency and electromagnetically induced absorption windows on OB is presented. The threshold of OB and the hysteresis width can be tuned effectively by adjusting the applied coherent fields. A transition from OB to OM and vice-versa can be easily achieved by tuning the field parameters and the atomic cooperation parameter. Dynamic control of the probe laser propagating through the medium has been investigated. We also demonstrate conversion of a continuous wave input probe field into output switched pulse. The ON/OFF time of the switched probe pulse can also be controlled by tuning the field parameters.

The space-time structure of sound produced by stacked rotors in hover using Vold-Kalman filters and proper orthogonal decomposition

Proper orthogonal decomposition and the Vold-Kalman order tracking filter are combined to evaluate the most energetic components of the sound field produced by a coaxial, co-rotating rotor in hover. The study leverages the database generated by Tinney and Valdez (2020; AIAA J. vol. 58, no. 4) comprising an array of eight stationary microphones oriented to capture the acoustic near-field below the rotor disk plane where ground observers are expected to reside and where concerns over community annoyance are greatest. Changes to rotor conditions focus primarily on rotor speed and index angle (angular separation between the upper and lower rotors), as this has the greatest effect on the sound field produced by stacked rotors by way of the constructive and destructive interference of the sound generated, separately, by the upper and lower rotors. Proper orthogonal decomposition is performed using a kernel constructed from auto and cross-spectral densities of the spatially coherent sound field. The eigenvectors demonstrate the spatial extent of the sound field for discrete frequencies corresponding to the first few blade pass frequency harmonics. In order to improve the clarity and accuracy of the low-order reconstructions, a second generation, Vold-Kalman multi-order tracking filter is employed to isolate discrete frequencies. Relative to conventional spectral filtering methods, the Vold-Kalman filter is performed in the time-domain and is shown to accurately isolate discrete tones while preserving changes to the phase of the signal. Findings from this analysis reveal the effect of index angle on the spatial make-up of the coherent sound field produced by hovering stacked rotors.

Deterministic vortices evolving from partially coherent fields

Optical vortices—lines of zero intensity around which the field phase has a circulating or helical structure—have become important tools for many applications such as imaging, trapping, and communications. It has long been assumed, however, that there is an intrinsic conflict between optical vortices and partial coherence, in that a vortex is a deterministic phase structure, and a partially coherent field has a randomly fluctuating phase. In most cases, a vortex imposed on a partially coherent field evolves into a singularity of the two-point correlation function. We demonstrate, however, that it is possible to construct a beam that has no deterministic vortices in the source plane yet evolves such a deterministic vortex at a specified propagation distance.

A propagator approach to the dynamics of three-level laser with input coherent light

The squeezing and statistical features of the intracavity field produced by a three-level laser coupled to a vacuum reservoir with input coherent field are studied in this paper. Employing the propagator method, we determine the Q-function for the cavity field produced by a driven three-level laser. Using this Q-function, we have calculated the mean intensity, the quadrature variance, and the squeezing spectrum of the cavity field. It has been discovered that, despite the fact that the input coherent field improves the mean intensity of the cavity field, it has no effect on the quadrature squeezing of the cavity field. The degree of squeezing increases with the rate at which atoms are injected into a cavity and a substantial degree of squeezing is found close to the maximum initial injected atomic coherence.

Coherent memory for microwave photons based on long-lived mechanical excitations

Mechanical resonators, due to their capability to host ultralong-lived phonon modes, are particularly attractive for quantum state storage and as memory elements in conjunction with quantum computing and communication networks. Here we demonstrate absorptive-type coherent memory based on long-lived mechanical excitations. The itinerant coherent microwave field is captured, stored, and retrieved from a mechanical memory oscillator which is pre-cooled to the ground state. The phase space distribution allows us to distinguish between coherent and thermal components and study their evolution as a function of storage time. Our device exhibits attractive functions with an energy decay time of T1 = 15.9 s, a thermal decoherence rate of Γth = 2.85 Hz, and acquires less than one quantum noise during the τcoh = 55.7 ms storage period. We demonstrate that both the amplitude and phase information of microwave coherent states can be recovered, indicating the coherence of our memory device. These results suggest that high-Q mechanical resonators and long coherence time phonons could be ideal candidates for the construction of long-lived and on-demand microwave quantum memories.

Coherent Population Trapping Resonance Parameters and Field Shifts during the Detection of Signals from Different Cross-Sectional Areas of the Interaction of Laser Radiation with Atoms

Coherent Population Trapping Resonance Parameters and Field Shifts during the Detection of Signals from Different Cross-Sectional Areas of the Interaction of Laser Radiation with Atoms

Spatiotemporal dissipative soliton resonances in multimode fiber lasers

Spatiotemporal mode-locking in multimode fiber lasers is intriguing for the complex nonlinear dynamics and the increase of theoretical energy limit. In this paper, we enrich spatiotemporal mode-locking with dissipative soliton resonances, a kind of solitons which is characterized by large pulse energy in single mode fiber lasers, and demonstrate their emergence in multimode fiber lasers by employing the reverse saturable absorption effect from real saturable absorbers. The spatiotemporal dissipative soliton resonances are expected to raise the energy limit further by the locking of dissipative soliton resonances in different transverse modes, whose energy is about twice the maximum single-mode energy in our results. Moreover, properties of spatiotemporal dissipative soliton resonances are investigated by tailoring parameters of the multimode fiber laser, where evolution and transformation of the proposed pulses including shaping and broadening are disclosed. The spatiotemporal dissipative soliton resonances in multimode fiber lasers may open up new avenue for high-power and spatiotemporally engineered coherent light fields in laser dynamics and nonlinear optics.

Four-dimensional experimental characterization of partially coherent light using incoherent modal decomposition

Abstract The intensity distributions and statistics of partially coherent light fields with random fluctuations have proven to be more robust than for coherent light. However, its full potential in practical applications has not been realized due to the lack of four-dimensional optical field measurement. Here, a general incoherent modal decomposition method of partially coherent light field is proposed and demonstrated experimentally. The decomposed random modes can be used to, but not limited to, reconstruct average intensity, cross-spectral density, and orthogonal decomposition properties of the partially coherent light fields. The versatility and flexibility of this method allows it to reveal the invariance of light fields and to retrieve embedded information after propagation through complex media. The Gaussian-shell-model beam and partially coherent Gaussian array are used as examples to demonstrate the reconstruction and even prediction of second-order statistics. This method is expected to pave the way for applications of partially coherent light in optical imaging, optical encryption, and antiturbulence optical communication.

Transmission and Reflection properties of the incident Light via SW coherent laser field

The relative phase of the applied lights has been used to explore the position dependence of the transmitted and reflected light from a defective dielectric medium. The duplicated two-level atomic system that makes up the dielectric medium interacts with a position-dependent standing wave (SW) coupling light and a weak probe laser field. We found that identical behaviors can be produced for the transmitted and reflected light in various directions due to the relative phase of the applied light. Furthermore, we understood that the transmitted and reflected spectra of the incident light become asymmetric for the asymmetric profile of the coupling light, and that these circumstances will cause the probing field to be amplified. In this instance, we found that altering the relative phase of the applied lights can modify the position of the subluminal and superluminal light.

The effect of intrinsic decoherence on the dynamics of an Ξ-type qutrit system interacting with a coherent field

This paper solves milburn’s intrinsic noise (IN) model for a 3-level atom of an Ξ-type interacting with a coherent cavity field via multiphoton transitions. Therefore, the effects of the intrinsic noise and the multi-photon interactions are investigated for some quantum phenomena, such as total correlation, entanglement, and atomic inversion. In general, we found that the collapse-revival phenomenon occurs during the oscillatory behaviour of atomic population dynamics. In addition, the birth-death phenomenon is observed in the negativity dynamics. Entropy, negativity, and mutual information have various dynamics. It is found that, as the entropy increases, the negativity and mutual information diminish to stationary levels. When intrinsic noise is considered, all the phenomena of atomic inversion, entropies, negativity and mutual information exhibit high sensitivity to high intrinsic noise values, except the mutual information dynamics, which is more resistant than that of the other quantifiers.

Virtual sources for structured partially coherent light fields.

A virtual source (VS) is a hypothetical source instead of an actual physical entity, but provides a distinctive perspective to understand physical fields in a source-free area. In this work, we generalize the VS theory to structured partially coherent light fields (PCLFs) by establishing the partially coherent inhomogeneous Helmholtz equation, then demonstrate that PCLFs can be generated from the incoherent extended VS in imaginary space. Especially, we put forward an understanding of the Gaussian Schell-model beam, which consists of a group of partially coherent paraxial complex rays. The mutual coherence between these rays depends on the included angle between them. In previous studies, the analytical solution of the partially coherent Airy beam was obtained with difficulty by the Huygens-Fresnel integral; however, by applying the VS, we put forward, to our knowledge, an unprecedented analytical solution for a partially coherent Airy beam. We believe this example will qualify the VS as an important perspective to understand structured PCLFs.