Method for generating spatiotemporal coherency vortices and spatiotemporal dislocation curves.

A simple method for designing spatiotemporal coherency vortices (STCVs) and spatiotemporal dislocation curves (STDCs) is introduced by means of coherent-mode representation and Fourier transforms. A partially coherent pulsed beam is represented by an incoherent superposition of a Gaussian and a Hermite-Gaussian pulsed beam with different waist positions. It well demonstrates that there exist STCVs and STDCs in the space-time plane. The detailed numerical calculations are performed to address the dependence of waist distance of two modes, reference position, beam order, distribution of original spectrum, topological charge and mode weights ratio on the STCVs and STDCs. The physical interpretation behind numerical results is shown. A possible scheme for experimental synthesis of the STCVs is proposed. The obtained results may have potential applications in the fields of light-matter interaction, spatiotemporal spin-orbit angular momentum coupling and STCV-based optical trapping and optical manipulation.

Control of the total orbital angular momentum of light beams propagating through a turbulent medium.

The robustness of the orbital angular momentum (OAM) of light beams propagating in a turbulent medium, e.g., atmosphere, is critical for many applications such as OAM-based free-space optical communications and remote sensing. However, the total OAM of a beam interacting with the turbulent medium inevitably changes. Here, we demonstrate a practical algorithm to control the total OAM of a beam transmitted through a time-evolving, turbulent medium by dynamically modulating the weights of two coherently superimposed OAM modes, which served as the input beam. A cross-OAM matrix is introduced, and applied for checking whether the desired total OAM in the output plane can be achieved. Furthermore, analytical relations between the weights of two input modes and the output total OAM, as well as its modulation range, are established. As a numerical example, we study the behavior of total OAM of the two-mode beam after passing through a thermal convection occurring in an aqueous medium and suggest a possible application of our strategy.

Fast measurement of coherence-orbital angular momentum matrices of random light beams using off-axis holography and coordinate transformation.

We propose an effective protocol to measure the coherence-orbital angular momentum (COAM) matrix of an arbitrary partially coherent beam. The method is based on an off-axis holography scheme and the Cartesian-polar coordinate transformation, which enables to simultaneously deal with all the COAM matrix elements of interest. The working principle is presented and discussed in detail. A proof-of-principle experiment is carried out to reconstruct the COAM matrices of partially coherent beams with spatially uniform and non-uniform coherence states. We find an excellent agreement between the experimental results and the theoretical predictions. In addition, we show that the OAM spectrum of a partially coherent beam can also be directly acquired from the measured COAM matrix.

Welcoming 2024: editorial.

Editor-in-Chief Olga Korotkova summarizes the Journal's progress in 2023, outlines near-future plans, and introduces the editors who recently joined the board.

Propagation of coherence-OAM matrix of an optical beam in vacuum and turbulence.

Propagation of the coherence-orbital angular momentum (COAM) matrix of partially coherent beams in homogeneous and isotropic turbulence, e.g., atmosphere, is formulated using the extended Huygens-Fresnel principle. It is found that under the effect of turbulence the elements in the COAM matrix will generally be affected by other elements, resulting in certain OAM mode dispersion. We show that if turbulence is homogeneous and isotropic, there exists an analytic "selection rule" for governing such a dispersion mechanism, which states that only the elements having the same index difference, say l - m, may interact with each other, where l and m denote OAM mode indices. Further, we develop a wave-optics simulation method incorporating modal representation of random beams, multi-phase screen method and the coordinate transformation to simulate propagation of the COAM matrix of any partially coherent beam propagating in free space or in turbulent medium. The simulation method is thoroughly discussed. As examples, the propagation characteristics of the most representative COAM matrix elements of circular and elliptical Gaussian Schell-model beams in free space and in turbulent atmosphere are studied, and the selection rule is numerically demonstrated.

OAM-resolved source correlation-induced spectral changes in random light beams.

The phenomenon of the correlation-induced spectral changes (CISC) in the spectral density of a wide-stationary light beam is shown to occur for each component in its single-radius coherence-OAM (COAM) matrix, with the magnitude quantitatively depending on the OAM indices. As the diagonal elements of the COAM matrix are also radially resolved OAM spectrum components, the new effect may be viewed as the CISC in the OAM spectrum. Using the Gaussian Schell-model beam with the Gaussian spectral line, we then demonstrate the spectral shifts appearing on propagation in vacuum in its radially resolved OAM spectrum. We also prove the spectral invariance of the spatially integrated OAM spectrum.

OAM-resolved polarization in random light beams.

We establish the properties of the cross-spectral density orbital angular momentum (CSD-OAM) matrix of a stationary optical beam-like field and use them to introduce the OAM-resolved polarization properties. It is shown that sufficiently general random fields contain two types of polarization, one relating to a single OAM mode and the other to a pair of modes.

Matrices characterizing non-local OAM transformations of light beams.

Matrices characterizing the orbital angular momentum (OAM) transformations of deterministic and random light beams by commonly used OAM-modulating optical systems are revealed. Such matrices are the counterparts of the Jones and the Mueller matrices in polarization optics defined for the input and output OAM indices and the radial variables. In particular, matrices of systems leading to OAM mode shift, dispersion, and coupling are discussed.

Polarization resonance with sub-wavelength switching of random light self-interfering in open-end cavity.

Following recent work [Sci. China Phys. Mech. Astron.66, 274213 (2023)10.1007/s11433-023-2097-9] that revealed the sub-wavelength scale resonance phenomenon in scalar random beams counterpropagating in an open-end cavity, we extend the analysis to the vectorial domain and show a similar effect for the polarization properties. We found that, in contrast with the changes in the scalar properties, being of harmonic nature, changes in polarization involve alternating regions of constant values followed by sharp and complex changes.

Turning the page to 2023: editorial.

Editor-in-Chief Olga Korotkova sends winter holiday greetings to the optics community, celebrates journal achievements from 2022, and introduces the topical editors who recently joined the board.

Introducing JOSA A retrospectives: editorial.

JOSA A Editor-in-Chief Olga Korotkova and Deputy Editor Markus Testorf introduce a new paper type: "retrospective." They discuss the need for such articles and outline the acceptance criteria.

2022 JOSA A Emerging Researcher Best Paper Prize: editorial.

JOSA A Editor-in-Chief Olga Korotkova, Deputy Editor Markus Testorf, and the members of the 2022 Emerging Researcher Best Paper Prize Committee announce the recipient of the 2022 prize for the best paper published by an emerging researcher in the Journal.

Enhancement of activity and thermostability of Aspergillus niger ATCC 10864 phytase A through rational design.

Aspergillus niger ATCC 10864 phytase A was produced in Penicillium verruculosum. The enzyme was found to have two pH optima of 2.5 and 5.0, as well as a T-optimum of 50-55 °C. Two amino acid substitutions, A76M and S265P, were designed for improvement in thermostability, and two more, N300K and D363N, were designed for improvement in enzyme activity. The most thermostable variant, S265P, was characterized by a 3.8-fold increase in time of half-life at 55 °C and a 1.2-fold increase in residual activity at 90 °C compared to the wild-type. The most active variant, D363N, was 1.7-times more active at 40 °C and retained 1.3-times higher residual activity at 90 °C compared to the wild-type. The obtained results revealed the importance of substitutions with proline in α-helixes for the thermostability improvement of phytases. Also, the importance of sequence motif 361HDN363 was demonstrated with relevance to values of catalytic parameters.

Source coherence-induced control of spatiotemporal coherency vortices.

A novel method to achieve the coherence control of spatiotemporal coherency vortices of spatially and temporally partially coherent pulsed vortex (STPCPV) beams is proposed. The influence of spatial and temporal coherence of the source on the phase distributions and the positions of spatiotemporal coherency vortices of the STPCPV beams propagating through fused silica is investigated in detail, for the first time to our knowledge. It is found that the coherence width and the coherence time of the incident beam can be regarded as a perfect tool for controlling the phase distribution and position of a spatiotemporal coherency vortex. The results obtained in this paper will benefit a number of applications relating to light-matter interaction, quantum entanglement, quantum imaging, optical trapping and spatiotemporal spin-orbit angular momentum coupling.

Orbital angular momentum transformations by non-local linear systems.

A matrix description of orbital angular momentum (OAM) transformations in scalar optical beams by non-local, linear systems is introduced and the amplitude transfer function (ATF) is generalized to include information about mode-to-mode OAM coupling. In particular, the analysis of radially independent systems suggests the existence of unexplored types of OAM transforming systems. The results are extended to random beams and random non-local systems and the optical transfer function (OTF) is generalized to the OAM space.

Coherence-orbital angular momentum matrix of non-uniformly correlated sources.

The structure of the coherence-orbital angular momentum (OAM) matrix of a scalar, non-uniformly correlated source is revealed and its relation with the degree of coherence is established. It is shown that while this source class has a real-valued coherence state, it possesses a rich OAM correlation content and highly controllable OAM spectrum. In addition, the degree of OAM purity based on the information entropy measure is employed for, we believe, the first time, and is shown to be controlled by the choice of location and variance of the correlation center.

Tailoring the coherence-OAM matrices.

We establish a general framework for introducing novel, to the best of our knowledge, classes of beams possessing precisely tailored coherence-orbital angular momentum (COAM) matrices, with the help of Bochner's theorem. The theory is illustrated by several examples relating to COAM matrices having a finite and infinite number of elements.

Singular-value decomposition and electromagnetic coherence of optical beams.

We investigate the implications of the singular-value decomposition of the cross-spectral density (CSD) matrix to the description of electromagnetic spectral spatial coherence of stationary light beams. We show that in a transverse plane any CSD matrix can be expressed as a mixture of two CSD matrices corresponding to beams which are fully polarized but in general spatially partially coherent. The polarization and coherence structures of these constituent beams are specified, respectively, by the singular vectors and singular values of the full CSD matrix. It follows that vector-beam coherence, including the coherence Stokes parameters and the degree of coherence, can be formulated in terms of only two correlation functions. We further establish two-point analogs of the spectral and characteristic decompositions of the polarization matrix and show that in the case of a Hermitian CSD matrix their composition is specified by the so-called degree of cross-polarization.

Coherence-orbital angular momentum matrix of Schell-model sources.

The coherence-orbital angular momentum (COAM) matrix characterizes the second-order field correlations in stationary sources or fields, at a pair of spiral modes with the same or different topological charges, say l and m, and at a pair of radial positions. In this Letter, we reveal the general properties of the COAM matrix for the broad class of the Schell-model sources with circularly symmetric spectral densities. Our results imply that the structure of the COAM matrix is intimately related to the symmetries of the degree of coherence (DOC). In particular, the COAM matrix is diagonal if the DOC is real-valued and rotationally symmetric; otherwise, it may acquire non-zero off diagonal elements. In particular, if the real part of the DOC has Cartesian symmetry, the COAM matrix's elements with the even/odd index difference |l - m| contain information about the real/imaginary part of the DOC. A potential application of our results is envisioned for extracting the rotation angle of the DOC of light (or an object transparency) through measuring of the off-axis COAM matrix elements.

Measurement of the coherence-orbital angular momentum matrix of a partially coherent beam.

The recently introduced coherence-orbital angular momentum (COAM) matrix of a partially coherent beam [Phys. Rev. A103, 023529 (2021)10.1103/PhysRevA.103.023529] is experimentally measured for the first time, to the best of our knowledge. The new methodology based on Young's interference experiment with a pair of ring-shaped slits with embedded spiral phases is thoroughly described. By introducing the phase shift of 0 and π / 2 between two ring slits, the real and imaginary parts of the elements of the COAM matrix are obtained by measuring the on-axis spectral density in the far field of the double-ring slit. We validate our protocol through measuring the COAM matrix of an elliptical Gaussian Schell-model (GSM) beam which reveals the existence of non-trivial correlations between modes with different topological indices. The experimental results agree reasonably well with the theoretical predictions.