A Solitary Stalled 80S Ribosome Prevents mRNA Recruitment to Stress Granules.

In response to stress stimuli, eukaryotic cells typically suppress protein synthesis. This leads to the release of mRNAs from polysomes, their condensation with RNA-binding proteins, and the formation of non-membrane-bound cytoplasmic compartments called stress granules (SGs). SGs contain 40S but generally lack 60S ribosomal subunits. It is known that cycloheximide, emetine, and anisomycin, the ribosome inhibitors that block the progression of 80S ribosomes along mRNA and stabilize polysomes, prevent SG assembly. Conversely, puromycin, which induces premature termination, releases mRNA from polysomes and stimulates the formation of SGs. The same effect is caused by some translation initiation inhibitors, which lead to polysome disassembly and the accumulation of mRNAs in the form of stalled 48S preinitiation complexes. Based on these and other data, it is believed that the trigger for SG formation is the presence of mRNA with extended ribosome-free segments, which tend to form condensates in the cell. In this study, we evaluated the ability of various small-molecule translation inhibitors to block or stimulate the assembly of SGs under conditions of severe oxidative stress induced by sodium arsenite. Contrary to expectations, we found that ribosome-targeting elongation inhibitors of a specific type, which arrest solitary 80S ribosomes at the beginning of the mRNA coding regions but do not interfere with all subsequent ribosomes in completing translation and leaving the transcripts (such as harringtonine, lactimidomycin, or T-2 toxin), completely prevent the formation of arsenite-induced SGs. These observations suggest that the presence of even a single 80S ribosome on mRNA is sufficient to prevent its recruitment into SGs, and the presence of extended ribosome-free regions of mRNA is not sufficient for SG formation. We propose that mRNA entry into SGs may be mediated by specific contacts between RNA-binding proteins and those regions on 40S subunits that remain inaccessible when ribosomes are associated.

Tunable nanolaser based on quasi-BIC in a slanted resonant waveguide grating.

Nanolasers based on quasi-bound states in the continuum (quasi-BIC) have attracted much attention owing to their unique optical properties providing strong light-matter interaction. Although various quasi-BIC lasers have been designed, so far, few efforts have been devoted to their tunability in wavelength. Here we propose an approach to employ quasi-BIC and guided mode in a slanted resonant waveguide grating. The proposed structure supports a specially designed eigenmode localized both in the grating and in the 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) layer, which allows it to obtain lasing emission as well as the ability to tune the wavelength. Numerical simulation results show that the threshold is approximately 7.75 µJ/cm2 with the tuning range being 28 nm. In addition, we show that the distribution of the lasing intensity between the transmission and reflection directions can be controlled by changing the parameters of the structure. This work shows good potential of combining quasi-BIC with guided mode to design tunable nanolaser.

Optical computation of the Laplace operator at oblique incidence using a multilayer metal-dielectric structure.

We investigate the possibility of the optical computation of the Laplace operator in the oblique incidence geometry using a layered structure consisting of a set of homogeneous thin films. For this, we develop a general description of the diffraction of a three-dimensional linearly polarized optical beam by a layered structure at oblique incidence. Using this description, we derive the transfer function of a multilayer structure consisting of two three-layer metal-dielectric-metal structures and possessing a second-order reflection zero with respect to the tangential component of the wave vector of the incident wave. We show that under a certain condition, this transfer function can coincide up to a constant multiplier with the transfer function of a linear system performing the computation of the Laplace operator. Using rigorous numerical simulations based on the enhanced transmittance matrix approach, we demonstrate that the considered metal-dielectric structure can optically compute the Laplacian of the incident Gaussian beam with the normalized root-mean-square error of the order of 1%. We also show that this structure can be effectively utilized for optical edge detection of the incident signal.

Total absorption and coherent perfect absorption in metal-dielectric-metal resonators integrated into a slab waveguide.

We propose and investigate integrated metal-dielectric-metal (MDM) resonators operating with semi-guided waves (guided modes of dielectric slab waveguides). The MDM resonators are constituted by two metal strips "buried" in the waveguide core layer and separated by a dielectric waveguide segment. We theoretically prove and numerically demonstrate that by a proper choice of the mode incidence geometry, the widths of the metal strips, and the distance between them, it is possible to achieve either total absorption of the incident wave or coherent perfect absorption (in the case of symmetric incidence of two modes on the structure). The proposed planar MDM resonators may find application as absorbers or filters in integrated optical circuits.

Designing stigmatic lenses with minimal Fresnel losses: erratum.

This erratum includes a necessary additional reference for the article [J. Opt. Soc. Am. A38, 855 (2021)JOAOD60740-323210.1364/JOSAA.425379].

Supporting quadric method for designing refractive optical elements generating prescribed irradiance distributions and wavefronts.

We propose a method for designing a refractive optical element with two working surfaces transforming an incident beam with a plane wavefront into an output beam with prescribed irradiance distribution and a non-planar wavefront. The presented method generalizes the supporting quadric method [Opt. Express28, 22642 (2020)10.1364/OE.398990] proposed for collimated beam shaping to the case of a non-planar output wavefront. The method is simple to implement and is based on just a few main equations. We present several examples of designing optical elements (including elements with piecewise-smooth optical surfaces) generating light beams with prescribed irradiance distributions and wavefronts (spherical and aspherical). The examples demonstrate high performance of the method.

Hybrid design of diffractive optical elements for optical beam shaping.

Hybrid methods combining the geometrical-optics and diffraction-theory methods enable designing diffractive optical elements (DOEs) with high performance due to the suppression of stray light and speckles and, at the same time, with a regular and fabrication-friendly microrelief. Here, we propose a geometrical-optics method for calculating the eikonal function of the light field providing the generation of a required irradiance distribution. In the method, the problem of calculating the eikonal function is formulated in a semi-discrete form as a problem of maximizing a concave function. For solving the maximization problem, a gradient method is used, with analytical expressions obtained for the gradient. In contrast to geometrical-optics approaches based on solving the Monge-Ampére equation using finite difference methods, the proposed method enables generating irradiance distributions defined on disconnected regions with non-smooth boundaries. As an example, we calculate an eikonal function, which provides the generation of a "discontinuous" irradiance distribution in the form of a hexagram. It is shown that the utilization of the hybrid approach, in which the obtained geometrical-optics solution is used as a starting point in iterative Fourier transform algorithms, enables designing DOEs with a quasi-regular or piecewise-smooth microrelief structure. The calculation results are confirmed by the results of experimental investigations of a DOE generating a hexagram-shaped irradiance distribution.

Design of a stigmatic lens implementing a required ray mapping.

We consider a method for designing stigmatic lenses implementing required ray mappings. A ray mapping relates the angular coordinates of the rays at the image points with the angular coordinates of the rays coming from the object. The calculation of a stigmatic lens with a required ray mapping is reduced to solving an explicit ordinary differential equation. As examples, we design stigmatic lenses satisfying the Abbe sine condition, the Herschel's condition, and the constant angular magnification condition.

Designing stigmatic lenses with minimal Fresnel losses.

We present a method for designing lenses with two aspherical surfaces having minimal Fresnel losses among the class of stigmatic lenses. Minimization of Fresnel losses is achieved by ensuring equal ray deviation angles on the lens surfaces. Calculation of lenses with minimal Fresnel losses is reduced to solving an explicit ordinary differential equation. Simple analytical approximations are also obtained for the lens profiles.

Integrated Gires-Tournois interferometers based on evanescently coupled ridge resonators.

We propose integrated Gires-Tournois interferometers (GTIs) for guided modes of dielectric slab waveguides. The proposed GTIs consist of one or several dielectric ridge resonators separated by subwavelength-width grooves patterned into an abruptly terminated slab waveguide and operate at oblique incidence of the fundamental transverse-electric-polarized mode. The grooves act as partially reflective mirrors, whereas the end facet of the last ridge works in the total internal reflection regime and reflects all the incident radiation. We show that the single-ridge structure provides a nonlinear staircase-like phase response characteristic for GTIs. By using several properly arranged ridges, one can engineer group delay or group delay dispersion in a required spectral range. As an example, we design a three-ridge GTI providing an almost constant group delay dispersion in a 50-nm-wide wavelength range. The proposed planar GTIs may find application in integrated optical circuits for introducing or compensating for chromatic dispersion.

On the use of the supporting quadric method in the problem of designing double freeform surfaces for collimated beam shaping.

We propose a version of the supporting quadric method for calculating a refractive optical element with two working surfaces for collimated beam shaping. Using optimal mass transportation theory and generalized Voronoi cells, we show that the proposed method can be regarded as a gradient method of maximizing a concave function, which is a discrete analogue of the Lagrange functional in the corresponding mass transportation problem. It is demonstrated that any maximum of this function provides a solution to the problem of collimated beam shaping. Therefore, the proposed method does not suffer from "trapping" at a local extremum, which is typical for gradient methods. We present design examples of refractive optical elements illustrating high performance of the method.

Multiscale approach and linear assignment problem in designing mirrors generating far-field irradiance distributions.

We propose a multiscale approach for designing mirrors generating prescribed irradiance distributions in the far field. Our design method is based on calculating a ray mapping from a Monge-Kantorovich mass transportation problem and on reducing this problem to a linear assignment problem (LAP). The proposed multiscale formulation of the LAP allows one to efficiently calculate freeform mirror surfaces defined on meshes with a size of up to at least 1000×1000. As an example requiring a mesh of this size, we design a mirror generating a grayscale image of A. Einstein on a zero background. The proposed multiscale approach is general and can be applied to a wide range of inverse problems of nonimaging optics.

Design and fabrication of freeform mirrors generating prescribed far-field irradiance distributions.

We consider a method for designing freeform mirrors generating prescribed irradiance distributions in the far field. The method is based on the formulation of the problem of calculating a ray mapping as a Monge-Kantorovich mass transportation problem and on the reduction of the latter problem to a linear assignment problem. As examples, we design freeform mirrors generating a uniform irradiance distribution in a rectangular region and a complex chessboard-shaped distribution. The mirror generating a rectangular irradiance distribution is fabricated and experimentally investigated. The experimental results are in good agreement with the numerical simulations and confirm the manufacturability of the mirrors designed using the considered method.

Design of diffractive lenses operating at several wavelengths.

We propose a method for designing diffractive lenses having a fixed-position focus at several prescribed wavelengths, which we refer to as spectral diffractive lenses (SDLs). The method is based on minimizing an objective function describing the deviation of the complex transmission functions of the spectral lens at the operating wavelengths from the complex transmission functions of diffractive lenses calculated separately for each of these wavelengths. As examples, SDLs operating at three, five, and seven different wavelengths are designed. The simulation results of the calculated lenses confirm high efficiency of the proposed method. For experimental verification of the design method, we fabricate using direct laser writing and experimentally investigate an SDL operating at five wavelengths. The presented experimental results confirm the efficiency of the proposed method in practical problems of designing SDLs. The obtained results may find applications in the design and fabrication of novel flat diffractive lenses with reduced chromatic effects.

Optimal mass transportation problem in the design of freeform optical elements generating far-field irradiance distributions for plane incident beam.

We consider the problem of calculating a refracting surface generating a prescribed irradiance distribution in the far field in the case of a plane incident beam. We demonstrate that this problem can be formulated as a mass transportation problem (MTP) and obtain the cost function for the MTP. It is shown that with a special choice of coordinates, the cost function becomes quadratic. The obtained mass transportation problem also describes the problem of calculating a mirror, which can be considered as a special case of the problem of calculating a refracting surface. We propose a method of calculating a refracting surface based on the reduction of the MTP to a linear assignment problem. This method is applied to the design of several optical elements generating prescribed intensity distributions. The simulation results demonstrate high performance of the proposed approach.

Analytical design of flat-top transmission filters composed of several resonant structures.

Resonant properties of composite structures consisting of several identical resonant structures (e.g. multilayer thin-film structures or guided-mode resonance gratings) separated by phase-shift layers are investigated theoretically. Using the scattering matrix formalism, we analytically demonstrate that, at properly chosen thicknesses of the phase-shift layers, the composite structures comprising two or four resonant diffractive structures with a Lorentzian transmittance profile optically implement the Butterworth filters of the order two or three, respectively, and enable achieving flat-top transmission spectra with steep slopes and low sidebands. In addition, we show that the composite structures consisting of three or four second-order Butterworth filters can accurately approximate the fourth- or fifth-order Butterworth filters, respectively. The presented theoretical results are confirmed by rigorous numerical simulations of composite structures consisting of the so-called W-structures (simple three-layer resonant structures comprising a high-index core layer and two low-index cladding layers in a high-index dielectric environment). The simulation results confirm the formation of flat-top transmittance peaks, the shape of which fully agrees with the derived theoretical description. Moreover, we demonstrate an exceptionally simple mechanism of controlling the transmittance peak width, which consists in changing the thicknesses of the cladding layers of the initial W-structure and enables generating flat-top transmission peaks with a significantly subnanometer width.

Improving the sensitivity of guided-mode resonance sensors under oblique incidence condition.

We present an investigation on the use of oblique incidence condition to enhance the sensitivity of guided-mode resonance (GMR) sensors. By adjusting the incident angle, the enhancement of GMR sensitivity in non-subwavelength regime can be obtained. The measured results show that the bulk sensitivity of the GMR sensors with period of 809 nm climbs to 177% or 292% as the incident angle increases from 15° to 25° or 35°, respectively. The same trend is also obtained for the grating period of 994 nm. Simulations based on the rigorous coupled wave analysis (RCWA) method were performed, and we also built a new slab waveguide model to describe the relationship between bulk sensitivity and the incident angle. The present investigation demonstrates a new method for enhancing the bulk sensitivity of GMR sensor. Moreover, simple fabrication techniques can be utilized since a large grating period was used.

Resonant properties of composite structures consisting of several resonant diffraction gratings.

We theoretically and numerically investigate resonant optical properties of composite structures consisting of several subwavelength resonant diffraction gratings separated by homogeneous layers. Using the scattering matrix formalism, we demonstrate that the composite structure comprising N gratings has a multiple transmittance zero of the order N. We show that at the distance between the gratings satisfying the Fabry-Pérot resonance condition, an (N - 1)-degenerate bound state in the continuum (BIC) is formed. The results of rigorous numerical simulations fully confirm the theoretically predicted formation of multiple zeros and BICs in the composite structures. Near the BICs, an effect very similar to the electromagnetically induced transparency is observed. We show that by making the proper choice of the thicknesses of the layers separating the gratings, nearly rectangular reflectance or transmittance peaks with steep slopes and virtually no sidelobes can be obtained. In particular, one of the presented examples demonstrates the possibility of obtaining an approximately rectangular transmittance peak with a significantly subnanometer width. The presented results may find application in the design of optical filters, sensors and devices for optical differentiation and transformation of optical signals.

Optimal mass transportation and linear assignment problems in the design of freeform refractive optical elements generating far-field irradiance distributions.

We consider the problem of calculating a refractive surface generating a prescribed irradiance distribution in the far field in the case of a point light source. We show that this problem can be formulated as a mass transportation problem with a non-quadratic cost function. A method for calculating the refractive surface is proposed, which is based on reducing the problem of calculating an integrable ray mapping to finding a solution to a linear assignment problem. We discuss the application of the developed method for the design of optical elements with two "working" refractive surfaces. The method was applied to the calculation of refractive optical elements generating uniform irradiance distributions in a square and in a region in the form of the letters "AB" on a zero background. The results of the simulations of the designed optical elements demonstrate high performance of the proposed method.

Design of an axisymmetrical refractive optical element generating required illuminance distribution and wavefront.

The design of an axisymmetrical refractive optical element transforming a given incident beam into an output beam with prescribed illuminance distribution and wavefront is considered. The wavefront of the output beam is represented by the eikonal function defined in a certain plane behind the optical element. The design of the optical element is reduced to the solution of two explicit ordinary differential equations of the first order. These equations can be easily integrated using conventional numerical methods. As examples, we consider the design of two optical elements transforming a spherical beam from a point Lambertian light source into the uniform-illuminance beams with a plane wavefront and with a complex wavefront providing the subsequent focusing into a line segment on the optical axis.