Transparent Optical Media Research Articles

Double-step calculation of the intraocular lens power in lens opacities excluding the measurement of axial eye length by optical biometry. A clinical case

The main source of intraocular lens (IOL) power calculation errors in phacoemulsification (PE) is axial length (AL) measurement inaccuracy in cases if optical biometry cannot be used.bto describe an original double-step method of IOL power calculation in lens opacities which exclude AL measurement with optical biometry.Material and methods. Patient S. (male, 71) with a bilateral immature cataract underwent right eye phacoemulsification (PE) with no IOL implantation. After that, AL was measured in the aphakic state with transparent optical media and used in combination with preoperative anterior segment biometry data to calculate the IOL power. In the second stage, a selected lens with an extended focus range was implanted.Results. The patient was examined and discharged on the second day after surgery with visual acuity OD 0.3 sph +0.25 cyl -0.75 ax150 = 0.5 and signs of moderate postoperative keratopathy. After 2 weeks, uncorrected visual acuity was as high as 0.9 and could not be further corrected by spectacle lenses. The patient was admitted for surgical treatment of the left eye cataract and also operated in two stages. The AL measured by the optical method in the aphakic state, was 0.31 mm less than that measured before the operation. Six months after PE with IOL implantation, distance visual acuity in both eyes was 1.2, the patient could use binocular vision for reading and PC work with no difficulty.Conclusion. The double-step approach to IOL power calculation is justified in cases of strong decrease of crystalline lens transparency, especially in complicated cases, for example, in high myopia or “premium” lens implantation, in which patients are especially sensitive to correct target refraction, even though this approach requires a delayed IOL implantation, which should take place after a precise calculation of AL taken in the aphakic state.

Observation of nonlinear disclination states

Introduction of controllable deformations into periodic materials that lead to disclinations in their structure opens novel routes for construction of higher-order topological insulators hosting topological states at disclinations. Appearance of these topological states is consistent with the bulk-disclination correspondence principle, and is due to the filling anomaly that results in fractional charges to the boundary unit cells. So far, topological disclination states were observed only in the linear regime, while the interplay between nonlinearity and topology in the systems with disclinations has been never studied experimentally. We report here on the experimental observation of the nonlinear photonic disclination states in waveguide arrays with pentagonal or heptagonal disclination cores inscribed in transparent optical medium using the fs-laser writing technique. The transition between nontopological and topological phases in such structures is controlled by the Kekulé distortion coefficient r with topological phase hosting simultaneously disclination states at the inner disclination core and spatially separated from them corner-I, corner-II, and extended edge states at the outer edge of the structure. We show that the robust nonlinear disclination states bifurcate from their linear counterparts and that location of their propagation constants in the gap and, hence, their spatial localization can be controlled by their power. Nonlinear disclination states can be efficiently excited by Gaussian input beams, but only if they are focused into the waveguides belonging to the disclination core, where such topological states reside. Our results open new prospects for investigation of nonlinear effects in topological systems with disclinations and are relevant for different areas of science, including Bose-Einstein and polariton condensates, where potentials with the disclinations can be created.

Observation of [formula omitted] solitons in oscillating waveguide arrays

Floquet systems with periodically varying in time parameters enable realization of unconventional topological phases that do not exist in static systems with constant parameters and that are frequently accompanied by appearance of novel types of the topological states. Among such Floquet systems are the Su–Schrieffer–Heeger lattices with periodically-modulated couplings that can support at their edges anomalous π modes of topological origin despite the fact that the lattice spends only half of the evolution period in topologically nontrivial phase, while during other half-period it is topologically trivial. Here, using Su–Schrieffer–Heeger arrays composed from periodically oscillating waveguides inscribed in transparent nonlinear optical medium, we report experimental observation of photonic anomalous π modes residing at the edge or in the corner of the one- or two-dimensional arrays, respectively, and demonstrate a new class of topological π solitons bifurcating from such modes in the topological gap of the Floquet spectrum at high powers. π solitons reported here are strongly oscillating nonlinear Floquet states exactly reproducing their profiles after each longitudinal period of the structure. They can be dynamically stable in both one- and two-dimensional oscillating waveguide arrays, the latter ones representing the first realization of the Floquet photonic higher-order topological insulator, while localization properties of such π solitons are determined by their power.

Sensing with Femtosecond Laser Filamentation.

Femtosecond laser filamentation is a unique nonlinear optical phenomenon when high-power ultrafast laser propagation in all transparent optical media. During filamentation in the atmosphere, the ultrastrong field of 1013–1014 W/cm2 with a large distance ranging from meter to kilometers can effectively ionize, break, and excite the molecules and fragments, resulting in characteristic fingerprint emissions, which provide a great opportunity for investigating strong-field molecules interaction in complicated environments, especially remote sensing. Additionally, the ultrastrong intensity inside the filament can damage almost all the detectors and ignite various intricate higher order nonlinear optical effects. These extreme physical conditions and complicated phenomena make the sensing and controlling of filamentation challenging. This paper mainly focuses on recent research advances in sensing with femtosecond laser filamentation, including fundamental physics, sensing and manipulating methods, typical filament-based sensing techniques and application scenarios, opportunities, and challenges toward the filament-based remote sensing under different complicated conditions.

Time-resolved holographic study of laser-induced fatigue in bulk of sapphire and fused silica

In this work, the fatigue effect caused by multi-pulse laser irradiation in bulk of transparent optical medium for ultrashort pulses is investigated. Time-resolved digital holography is used as a sensitive tool for quantifying changes in material response below single-shot damage threshold. In case of two investigated fused quartz samples the survivable dose is limited by increase in the yield of free electrons and self-trapped exciton densities with number of expositions prior to damage formation. Meanwhile, no change was detected in free electron plasma for sapphire before multi-pulse damage which lead to nondeterministic damage. It was estimated that optical damage could form bellow critical plasma density for all samples. The data on low energy irradiation and damage morphology suggest a strong contribution from defects to the initiation of multi-pulse optical damage in bulk media.

Noise-robust phase retrieval by optics path modulation with adaptive feedback

We propose a compact computational imaging system with adaptive weighted feedback amplitude-phase retrieval (awfAPR) algorithm, in which the traditional axial linear scanning method is replaced by periodic optical path modulation (OPM) strategy. The introduced adaptive feedback scenario can significantly suppress noise contamination. Specifically, OPM is achieved by the rotation of gradient thicknesses of the transparent optical medium. Compared with multi-distance/height scanning (MDPR), all system components in the OPM system are fixed at discrete lateral positions. Besides, according to the auxiliary of corresponding auto-focusing criterion and sub-pixel registration algorithms, the OPM system is also self-calibration and independent of the accuracy of rotation and thickness parameter. Furthermore, experimental results show that the adaptive weighted feedback strategy remarkably improves the stability and robustness toward the noise. OPM has flexible adaptability to optical path modulation method. The proposed optical system configuration has minimal hardware requirements and is anticipated to expand dynamic real-time imaging.

Determination of Micropulse Modes with Targeted Damage to the Retinal Pigment Epithelium Using Computer Modeling for the Development of Selective Individual Micropulse Retinal Therapy

ABSTRACT Purpose When using a serial laser system for selective impact on the retinal pigment epithelium (RPE), there is a challenge to determine the optimal range of micropulse parameters which result in targeted damage to the RPE. This study proposes a computer model that has identified the optimal parameters to be applied. Methods This study was conducted on 18 patients who were diagnosed with acute central serous chorioretinopathy and transparent optical media, aged 35 to 46 years old, and type 2 and 3 on the Fitzpatrick scale. Testing of the micropulse mode was performed on the Navilas 577s laser system; 864 spots were analyzed in total. Considering the probability of damage visualization at different laser power, the computer simulation of tissue heating and protein denaturation was performed to determine the micropulse modes which resulted in selective damage to the RPE. Results The computer model parameter ΔE = 3.34 × 105 J/mol was determined from fitting the model predictions to the autofluorescence test results. The micropulse modes with a micropulse duration of 50–100 µs, duty cycle 2.4–4.8%, 10 ms-pulse envelope (5 micropulses), and spot diameter of 100 µm have efficiency and selectivity above 67% and correspond to the optimal therapeutic window for targeted RPE damage at a certain power. Increasing the micropulse duration, number of micropulses, and duty cycle leads to a decrease in the selective effect on the RPE and higher damage to adjacent tissues. Conclusion The concepts of efficiency and selectivity have been introduced to quantify the amount of damage caused. The optimal range of micropulse parameters which result in effective and selective damage on the RPE has been determined for the Navilas 577s laser system. The proposed method can be used for any other serial laser system. A comparison of the different micropulse modes, as well as the CW modes, has been performed.

The Essence and Application of the Optical Absorption Method for Quantitative and Qualitative Analysis of Radiation Defects in Optical Crystals

Today ionic crystals are widely used in devices for various purposes. In X-ray spectral optics they are widely used as crystal monochromators; ionic crystals are used in optical devices where lenses and transparent optical media (light filters) are made of optically pure materials - ionic crystals. In general, the main positive feature of these materials is transparency regarding the transmission of radiation in the visible region of the spectrum (transmittance of about 0.9) and neutrality - that is, approximately the same reaction of the medium to different spectral ranges of radiation. Ionic crystals are also widely used in detectors (scintillators, ionizing radiation dosimeters) and lasers. They are also widely used in acousto-optics and electrical engineering (lines of electrical signals delay, which gain efficiency due to the relatively small absorption of ultrasonic waves, and, therefore, it is possible to work with a wide sequence of signals probing the crystal). It is known that when ionizing radiation passes through ionic crystals, color centers appear in them, which can change the spectral composition of radiation both in the UV region and in the visible range. For example, the simplest configurations of color centers (F-centers) lead to the appearance in optical materials of additional absorption bands localized on the wavelength axis with a maximum at the wavelength lmax = 248 нм , but more complex configurations of radiation damage in solids already lead to the appearance of absorption bands at wavelengths in the visible range. This already presents some difficulties for developers and designers of relevant equipment, as changes in the spectral composition of radiation passing through the optical system of the device can lead, for example, to loss of efficiency of the selected radiation receiver, the main characteristic of which is primarily spectral sensitivity. Taking into account possible changes in the spectral composition of radiation is an important and urgent task of modern optical instrumentation. The purpose of this work is the analysis and justification of a method that takes into account structural changes in externally irradiated ionic crystals.

Laser recording of color voxels in lithium fluoride

The problem of creating three different types of spatially selective voxels by laser radiation in the volume of an transparent optical medium was solved. Each of the created voxels provides one base color: red, green, or blue. Red and green voxels are microvolumes inside a crystal in which femtosecond laser pulses create luminescence centers that emit, respectively, in the red and green regions of the spectrum when illuminated with blue radiation that excites luminescence. Voxels responsible for the blue glow are microvolumes in which light scattering centers are created by femtosecond pulses. These voxels do not contain any luminescence centers; they scatter blue radiation, which excites the luminescence of red and green voxels. To solve the problem of creating spatially separated voxels of all three types in the volume of an optical carrier, we studied the temperature dependences of the spectra, the output, and the decay time constants of the luminescence of quantum systems created by femtosecond laser radiation. These dependences were studied during heating and cooling. The change in the voxel size of the three basic colors from the energy and the number of femtosecond pulses of a titanium-sapphire laser was studied. Irradiation regimes were found in which only luminescence centers are formed in voxels and scattering centers are not formed. On the basis of the results, a three-stage technology of laser irradiation and heat treatment of optical media was proposed and experimentally tested. This technology allows for creation of three-dimensional, full-color images, visualized under blue light.

Effect of beam ellipticity on femtosecond laser multi-filamentation regulated by π-phase plate

The regulation of multiple filaments during an intense femtosecond laser propagation in a transparent optical medium is still challenging. In this study, by tracing the phase variation of the laser pulse during the propagation, the effect of the beam ellipticity on the generation of multiple filaments was investigated using the efficient π-phase plate. The spatial distribution of the generated multiple filaments did not follow the predesigned pattern of the phase plate when the laser beam was elliptic owing to the asymmetric change of the laser phase by the linear diffraction and nonlinear Kerr effect.

Physical nature and magnitude of optically induced forces derived from laws of mechanics

We derive the true magnitude of the optically induced force (OIF) in a linear transparent optical medium where ε≥1 and μ≥1 from unambiguous but contradictory results of two known thought experiments where no preliminary assumption about phenomena connected with electrical and magnetic fields are used. The analysis is based on laws of mechanics only. By means of comparing these forces with known types of forces we conclude that there are four kinds of force. First, this is the Coulomb force known in electrostatics. Second, this is the magnetic force known in magneto statics. Third, this is Ampere-like force arising at an interaction between the alternate polarization current and the alternate magnetic field of the light wave. Fourth, this is the force arising at an interaction between alternate magnetization current and the alternate electrical field of the light wave studied by Einstein and Laub in 1908. A sum of the third and fourth kinds of force in a field of an electromagnetic wave averaged over time is equal to zero at a steady state. We show that the existing formulas for third and fourth kinds need to be corrected for the medium where ε>1 and μ>1.

Kinds of optically induced force derived from laws of conservation of the momentum and energy

Optically induced forces (OIF) applied to a transparent optical medium are analyzed. We deliberately do not use any assumptions about a nature of optically induced force and analyze thought experiments where only notions and laws of conservation are used. Two unambiguous but contradictory thought experiments are used as a ground of an analysis. It is shown that only two kinds of well-known OIF is sufficient to match contradictory results of the experiments. This is the kind of density force known in electrostatics that is responsible for the density force arising in an inhomogeneous dielectric located in an electrical field. This is the Abraham density force arising at propagation of a light pulse in an optical medium. The force is located in the regions of the optical medium where leading and trailing edges of a light pulse are propagating. OIF in a homogeneous optical medium located in an inhomogeneous electrical field is equal to zero at a steady-state. This result contradicts to that obtained by means of the widely used approach based on the Lorentz density force.

Interrelation between various types of optically induced forces

Optically induced forces applied to a transparent optical medium are analyzed. It is shown on the basis of various approaches that the density of optically induced forces applied to a homogeneous optical medium located in an inhomogeneous electrical field is equal to zero at a steady-state. This result contradicts that obtained by means of an approach based on the Lorentz density force. An explanation is presented that the Lorentz density force is compensated at a steady-state by other kind of optically induced force. Thus, a calculation of optically induced force based on the approach using the Lorentz force is inconsistent.

Interrelation between striction forces in dielectrics and optically induced forces in transparent media

Optically induced forces applied to a transparent optical medium, which is inserted in a closed plane optical resonator, are calculated by means of an analysis of the changes in the eigenfrequency and energy stored in the resonator at various positions of the medium. These forces are compared with striction forces applied to the medium considered as a dielectric placed in an alternate electrical field within the resonator. It is shown that the optically induced forces are equal to the striction forces. The results of using the classical formula for striction forces in electrostatics are considered.

Comparison of various approaches to the calculation of optically induced forces

Various approaches used for the calculation of optically induced forces applied to a transparent optical medium imbedded in a close plane optical resonator are analyzed. The forces are calculated by means of analysis of a change in the eigen frequency and energy stored in the resonator at various positions of the medium. It is shown that results obtained are identical to those calculated by means of approaches based on the Maxwell stress tensor, based on an analysis of a change in the momentum of light. An exception is for results obtained on the base of last versions of the Lorentz density force.

New electrodynamic effects in transparent optical media

This paper presents a systematic theory of electrodynamic relativistic first-order effects in media with spatially inhomogeneous velocity. A geometrooptical approach is developed in terms of which the ray curvatures and changes of the polarization characteristics of the radiation as it passes through a continuous medium with inhomogeneous velocity are found. Nonreciprocal waveguides and lenses (that differ for opposite propagation directions) are demonstrated in a medium with transverse inhomogeneity of the velocity. Scattering (diffraction) of radiation at a localized velocity inhomogeneity is studied. The possibility of masking regions of space so that they become invisible is studied, and the influence of the motion of such a region is analyzed. The velocity inhomogeneity that appears when a region moves causes the radiation reflected from the boundary to appear and makes the inhomogeneity visible. A correct theory is constructed for the reflection of weak radiation from inhomogeneities induced by intense laser pulses in a fixed nonlinear medium and moving with the (group) velocity of light.

Method for analyzing the propagation dynamics of femtosecond pulses with a continuum spectrum in transparent optical media

Method for analyzing the propagation dynamics of femtosecond pulses with a continuum spectrum in transparent optical media

Three-dimensional optical memory in ferroelectric media

The physical principles underlying the development of three-dimensional nonvolatile optical memory in ferroelectric media are considered. Optical memory is realized in a transparent optical medium whose active components are ferroelectric microparticles. The optical medium is exposed to nondestructive laser radiation, which allows for bit-by-bit writing and reading of information. Writing of information is made inside the the laser caustic by changing the orientation of polarization of ferroelectric particles to the direction of the external electric field under the influence of the laser radiation. Written data can be read by detecting the laser-radiation second harmonic generated in the laser caustic.

FILAMENTATION AND SUPERCONTINUUM GENERATION DURING THE PROPAGATION OF POWERFUL ULTRASHORT LASER PULSES IN OPTICAL MEDIA (WHITE LIGHT LASER)

The fundamental physical mechanism responsible for the self-focussing, filamentation, supercontinuum generation and conical emission of a powerful ultrashort laser pulse in a transparent optical medium is reviewed. The propagation can be described by the model of moving focus modified by the defocussing effect of the self-induced plasma through multiphoton interaction with the medium. Spatial and temporal self-phase modulation in both the neutral Kerr medium and the plasma transform the pulse into a chirped (elongated) and strongly deformed pulse both temporally and spatially. The manifestation of the deformation is supercontinuum generation and conical emission. A new phenomenon of refocussing was observed. It is due to the diffraction of the trailing part of the pulse by the plasma that results in a ring structure of positive index changes surrounding the plasma column. This ring structure refocuses the pulse partially. The measured coherence lengths of the various frequencies components of the supercontinuum are independent of the optical media used and are essentially equal to that of the pump laser pulse when compared to an incoherent white light source. We thus justify that such a deformed pulse with a very broad spectrum could be called a chirped white light laser pulse.

MEASUREMENT OF THIRD-ORDER SUSCEPTIBILITY BY DEGENERATE FOUR-WAVE MIXING

In this paper, degenerate four-wave mixing was studied in various transparent optical media. Third-order susceptibility has been determined by the ratio of the input probing beam in tensity to the backward wave intensity in four-wave mixing. The results of some solvents and glass media are presented.