Optics

Purpose: The aim of this in vitro study was to evaluate the influence of different models of commercially available portable dental radiometers on the measurement of light irradiance emitted by light-emitting diode (LED) photocuring units. Materials and Methods: Eight LED photocuring units, all emitting light in a single-wavelength spectrum, were tested. Light irradiance (mW/cm²) was measured using six portable dental radiometers: four digital models (D1–D4) and two analog models (A1, A2). Digital model D1 was used as the reference (control). All measurements were conducted under standardized conditions, and each LED–radiometer combination was tested in triplicate. Data were analyzed using Sigma Plot 12.0 (Palo Alto, CA, USA) to verify the assumptions of normality and homogeneity of variances. A one-way analysis of variance (ANOVA) was used to assess the effect of the radiometer model on irradiance values, followed by Tukey’s post hoc test for multiple comparisons. The significance level was set at α < 0.05. Results: No statistically significant difference in irradiance was found between D1 (control) and D2. However, significantly lower values were recorded with A2, while D3, D4, and A1 produced significantly higher irradiance values compared to the control (p < 0.05). Conclusion: Irradiance measurements can vary significantly depending on the radiometer model used. Clinicians should be aware of this variability and are encouraged to regularly check the irradiance of the light-curing units used in daily practice, ensure their proper maintenance, and implement periodic monitoring to maintain effective clinical performance. Full article

This study experimentally demonstrates transverse symmetry breaking—a mechanism governing laser planar trapping—and distinguishes its unique role from related phenomena such as the lateral Goos–Hänchen shift and angular deviations. While the latter effects describe positional or angular beam displacements at interfaces, transverse symmetry breaking fundamentally alters the beam’s spatial symmetry, enabling unprecedented control over its intensity and phase profiles. Empirical results exhibit exceptional agreement with a recently proposed theoretical model, validating its predictive capability. Crucially, our findings highlight transverse symmetry breaking as a critical tool for tailoring beam profiles, advancing applications in optical trapping, structured light systems, and photonic device engineering, where symmetry manipulation unlocks new degrees of freedom in light–matter interactions. Full article

When interferograms in space heterodyne spectrometers exhibit tilted or distorted fringes, significant errors may occur in the demodulated spectral information. To address this issue, we propose a method for interferogram correction based on automatic spectral analysis. Simulations on erroneous interferograms of monochromatic and polychromatic light demonstrate that this method effectively corrects fringe tilts and significantly improves spectral demodulation accuracy. The standard deviations between the corrected spectra and ideal spectra for monochromatic and polychromatic light are 0.016 and 0.019, respectively, compared to 0.104 and 0.127 for uncorrected spectra. Additionally, the method successfully corrects experimental interferograms of potassium and neon lamps, accurately demodulating characteristic peaks of potassium and neon emission lines. It also enables accurate displacement measurement in a Michelson interferometer experiment. This method, through automatic analysis and one-sided spectral correction, efficiently and accurately corrects erroneous interferograms and enhances spectral demodulation accuracy, showing broad application potential. Full article

This paper presents the results of theoretical and experimental investigations of a Hong–Ou–Mandel interferometer in which an optical beam splitter is replaced by an ultrasonic wave. The ultrasonic wave acts as an acousto-optical beam splitter for light, which is based on the phenomenon of Bragg diffraction on an ultrasonic wave. The Doppler effect was considered in the theoretical considerations and confirmed experimentally. It has been shown theoretically and experimentally that the Doppler effect changes the frequency of two-photon states at the outputs of an acousto-optical beam splitter. The frequency of the two-photon state in the positive diffraction order is increased by the frequency of the ultrasonic wave, whereas in the negative diffraction order, it is reduced by the frequency of the ultrasonic wave. It should be emphasized that there are no states $\left|{1⟩}_1\right|{1⟩}_2$ in the outputs (diffraction orders), which disappear as a result of Hong–Ou–Mandel interference; consequently, the probability of detecting coincidences of photons between the plus first and minus first diffraction orders is zero, as it occurs in the Hong–Ou–Mandel interferometer. The frequency difference between the two-photon states at the outputs of the acousto-optical beam splitter was confirmed by recording the two-photon beat phenomenon. The obtained results changed the current view that the Doppler effect caused by ultrasonic waves can be neglected in the interaction of correlated pairs of photons with ultrasonic waves. Full article

Higher-dimensional communications in optical fiber enables new possibilities, including increased transmission capacity and hyper-entangled state transfer. However, mode coupling between channels during transmission causes interference between channels and limits detection. In classical optical communications, MIMO (modes in modes out) is a means to deal with this issue; however, it is not possible to utilize this technology in quantum communications due to power limitations. Principal mode transmission is another means to deal with mode coupling and signal interference between channels. Conceptually, this can be used in quantum communications with some limitations. In this study, we numerically simulated this process using the time delay method and show how it can be implemented using two and four higher-dimensional quantum states, such as W or GHZ states. These numerical simulations are very illustrative of how the implementation proceeds. Full article

We present a theoretical framework for designing optical masks, which are useful for implementing nonconventional Schlieren techniques. We revisit the use of effective transfer functions, which emphasize the role of symmetries in the design of coded masks. The proposed technique implements an optical autocorrelation of a mask, which is coded with the Barker sequences. For the same purpose, one can also use masks coded with the pseudorandom sequences. For the sake of completeness, we link our deterministic theoretical framework with a simple statistical model. The proposed technique may be useful for the automatic sensing of phase gradients. Full article

In this study, TiO₂-Fe₂O₃/polyvinylpyrrolidone (PVP) hybrids were prepared using the sol–gel method. The iron content in the synthesized samples was 10 and 20 wt%. The influence of PVP on the phase transformation, morphology and optical properties of the as-prepared hybrids was characterized by various physicochemical methods—XRD analysis, UV–Vis spectroscopy, IR spectroscopy and SEM. The obtained sol–gel powders were tested for photocatalytic activity against tetracycline hydrochloride in distilled water under ultraviolet and simulated solar light illumination. The obtained results were compared to commercial TiO₂ P25 (Evonik). The investigated samples exhibited good photocatalytic efficiency for the degradation of tetracycline hydrochloride; however, better activity was demonstrated by the 90TiO₂-10Fe₂O₃/PVP sample. The latter one displayed weak antibacterial action against E. coli ATCC 25922 in the presence of UVA light. Full article

Changes in the refractive indices of a GaAs laser chip owing to bonding strain are investigated by two-dimensional (2D) and three-dimensional (3D) finite element method (FEM) simulations. The strain induced by die attach (i.e., the bonding strain) was estimated by fitting simulations to the measured degree of polarisation (DOP) of photoluminescence from the facet of the bonded chip. Changes in the refractive indices were estimated using the strains obtained from fits to DOP data. Differences between the 2D and 3D FEM estimations of the deformation and of the photo-elastic effect are noted. It is recommended that 2D FEM simulations be used as starting points for 3D FEM simulations. Elastic constants for GaAs in plane-of-the-facet coordinate systems for 2D (plane stress and plane strain) and 3D FEM simulations are given. Full article

The increasing demand for optical technologies with dynamic spectral control has driven interest in chromogenic materials, particularly for applications in tunable infrared metasurfaces. Phase-change materials such as vanadium dioxide and germanium–antimony–tellurium, for instance, have been widely used in the infrared regime. However, their reliance on thermal and electrical tuning introduces challenges such as high power consumption, limited emissivity tuning, and slow modulation speeds. Photochromic materials may offer an alternative approach to dynamic infrared metasurfaces, potentially overcoming these limitations through rapid, light-induced changes in their optical properties. This manuscript explores the potential of thiazolothiazole-embedded polymers, known for their reversible photochromic transitions and strong infrared absorption changes, for use in tunable infrared metasurfaces. The material exhibits low absorption and a strong photochromic contrast in the spectral range from 1500 ${\mathrm{cm}}^{-1}$ to 1700 ${\mathrm{cm}}^{-1}$, making it suitable for dynamic infrared light control. This manuscript reports on infrared imaging experiments demonstrating the photochromic contrast in thiazolothiazole-embedded polymer, and thereby provides compelling evidence for its potential applications in dynamic infrared metasurfaces. Full article

We designed lens systems for a smart-pixel-based optical convolutional neural network (SPOCNN) using optical software to analyze image spread and estimate alignment tolerance for various kernel sizes. The design, based on a three-element lens, was reoptimized to minimize spot size while meeting system constraints. Simulations included root mean square spot and encircled energy diagrams, showing that geometric aberration increases with the scale factor, while diffraction effect remains constant. Alignment tolerance was determined by combining geometric image size with image spread analysis. While the preliminary scaling analysis predicted a limit at a kernel array size of 66 × 66, simulations showed that a size of 61 × 61 maintains sufficient alignment tolerance, well above the critical threshold. The discrepancy is likely due to lower angular aberration in the simulated optical design. This study confirms that an array size of 61 × 61 is feasible for SPOCNN, validating the scaling analysis for predicting image spread trends caused by aberration and diffraction. Full article

The biomechanical and optical properties of the cornea are responsible for its functional response, structural integrity and refractive function. Corneal viscoelasticity is the cornea’s ability to absorb transient increases in intraocular pressure (IOP) and constitutes a biomarker of glaucoma. The use of silicone hydrogel soft contact lenses (SiH-SCLs) can affect both corneal viscoelasticity and IOP. However, the behavior of the pure elastic and viscous components remains hidden within viscoelastic properties, and their influence and relationship with IOP in the biomechanical changes observed with short-term SiH-SCL use remains unknown. This study investigates the effects of silicone hydrogel soft contact lenses (SiH-SCLs) on corneal elasticity and viscosity and their influence on IOP over different lens wear periods: 10 or 20 consecutive days. Ocular Response Analyzer (ORA) measurements were combined with a biomechanical Standard Linear Solid Model (SLSM) to differentiate and calculate the elastic and viscous components of the cornea. The results showed that after 10 days of lens wear, elasticity and viscosity increased, with a significant reduction in IOP. After 20 days, elasticity and viscosity decreased, with a further reduction in IOP, reflecting a time-dependent effect of SiH-SCLs on corneal biomechanics. The study indicates the potential protective role of corneal viscosity against changes in IOP, which may be used for glaucoma treatment. Full article

Automatic focusing is a crucial research issue for achieving high-quality reconstructed images in digital holographic microscopy. This paper proposes an automatic focusing method that combines the discrete cosine transform (DCT) sparse dictionary with edge preservation index (EPI) criteria for off-axis digital holographic microscopy. Specifically, within a predefined search range, Fresnel transform is utilized to reconstruct the off-axis digital hologram, yielding reconstruction images at various reconstruction distances. Synchronously, the DCT sparse dictionary is employed to reduce speckle noise, and the EPI is calculated between the denoised image and original image. The value of EPI is used as an indicator for assessing the focal position. A single-peak focusing curve is obtained within the search range 10 mm, with a step size of 0.1 mm. Once the optimal focus position is determined, a focused and noise-reduced reconstructed image can be simultaneously achieved. Full article

The mechanisms of material removal and structural transformation under laser radiation differ significantly between single-crystal diamond (SCD) and nanocrystalline diamond (NCD). This study employs atomic simulations to investigate the material removal mechanisms and structural transformation behaviors of SCD and NCD when subjected to laser irradiation. We analyze the effects of temperature and stress changes induced by laser radiation on structural transformations, revealing the driving mechanism behind graphitization transitions. Specifically, the thermal–mechanical coupling effect induced by lasers leads to graphitization in SCD, while in NCD, due to the stress concentration effects at the grain boundaries, graphitization preferentially occurs at these boundaries. The material removal processes for both SCD and NCD are attributed to thermal stress concentrations in the regions where the laser interacts with the diamond surface. This investigation provides a theoretical foundation for a more profound understanding of the behavior of diamond materials during laser irradiation. Full article

In this work, we explore an optimization idea for the complexity guidance of a phase retrieval solution for a single acquired hologram. This method associates free-space backpropagation with the fast iterative shrinkage-thresholding algorithm (FISTA), which incorporates an improvement in the total variation (TV) to guide the complexity of the phase retrieval solution from the complex diffracted field measurement. The developed procedure can provide excellent phase reconstruction using only a single acquired hologram. Full article

Yb_xEr_yZnO thin films with a low concentration (x = 5%, y = 0, 1, 3%) were made on glass substrates using the spray pyrolysis method. The films were characterized through the use of specific techniques to investigate their structural, optical, and electrical properties. The XRD structural analysis of the films revealed that they are polycrystalline with a hexagonal wurtzite structure and a preferential orientation in the (002) direction. The optical characterization of the co-doped layers in the range of 200 to 800 nm revealed that co-doping had a significant impact on the values of transmission. A well-defined peak in the infrared domain centered around 980 nm was observed in photoluminescence measurements. This peak signifies the transition between the electronic levels ²F_5/2 (ground state) and ²F_7/2 (excited state), proving that photons are efficiently transferred between the ZnO matrix and the Yb³⁺ ion. All layers exhibited n-type conduction and an electrical resistivity decrease to 6.0 × 10⁻² Ω cm according to Hall effect measurements at room temperature. Full article

Microlenses are essential optics widely used in many fields. The microfluidics-assisted fabrication method provides a rapid, convenient way to manufacture microlenses. However, there is no mathematical model to describe the profile of the liquid surface. This paper provides a theoretical explanation and mathematical model for the formation of the liquid surface of different curvatures in the microholes of different shapes. A numerical model based on the finite–difference time–domain method verifies the mathematical model. Furthermore, the optical properties of the microlenses in different shapes are analyzed through the demolded microlenses. The proposed theoretical model provides an analytical way to study the properties of microlenses. Full article

Light-emitting electronic devices are widely used at present, and this increases the risk of myopia. Thus, the early identification of myopia and the prevention of further exacerbation has become an essential issue in ophthalmology. Recently, choroidal imaging has been used to assist in the early identification and prevention of high myopia due to the fact that swept-source optical coherence tomography (SS-OCT) is an essential diagnostic tool in ophthalmology. This study presents a novel method to judge high myopia using the SS-OCT image dataset obtained from a university hospital. In order to relate the proposed method to the region of the SS-OCT image, the curvature analysis of an arbitrary segmented curve similar to the region of the SS-OCT is first illustrated by quadratic functions and matrix operations. Next, the curvature formula is derived and then applied to the choroidal curve obtained manually in each patient’s choroidal image. In particular, we applied the curvature analysis and its results to find the maximal curvature and average curvature of each patient’s choroidal curve. Finally, we used the maximal curvature and average curvature to evaluate high myopia. The accuracy of the proposed maximal curvature method and average curvature method in the experimental results to verify the proposed method. Full article

Wavefront sensing is an essential technique in optical imaging, adaptive optics, and atmospheric turbulence correction. Traditional wavefront reconstruction methods, including the Gerchberg–Saxton (GS) algorithm and phase diversity (PD) techniques, are often limited by issues such as low inversion accuracy, slow convergence, and the presence of multiple possible solutions. Recent developments in deep learning have led to new methods, although conventional CNN-based models still face challenges in effectively capturing global context. To overcome these limitations, we propose a Transformer-based single-shot wavefront sensing method, which directly reconstructs wavefront aberrations from focal plane intensity images. Our model integrates a Normalization-based Attention Module (NAM) into the CoAtNet architecture, which strengthens feature extraction and leads to more accurate wavefront characterization. Experimental results in both simulated and real-world conditions indicate that our method achieves a 4.5% reduction in normalized wavefront error (NWE) compared to ResNet34, suggesting improved performance over conventional deep learning models. Additionally, by leveraging Walsh function modulation, our approach resolves the multiple-solution problem inherent in phase retrieval techniques. The proposed model achieves high accuracy, fast convergence, and simplicity in implementation, making it a promising solution for wavefront sensing applications. Full article

Standard endoscopy of vocal folds is in general limited to two-dimensional imaging. Laser-based 3D imaging offers not only absolute measurements but also the possibility of assessing all three spatial directions. However, due to human inter-individuality, a fixed grid configuration (with fixed edge length and spot size) does not necessarily provide the best coverage and resolution. We present a liquid lens optical design for a diffractive spot array generator with dynamic adjustment capabilities for both array size and spot size. The tunable nature of the liquid lenses enables precise control over the spot array generated by a diffractive optical element (DOE). The first liquid lens controls the spot divergence in the observation plane, while the second liquid lens adjusts the zoom factor. The optical configuration provides a dynamic range of 1.8 with respect to array size, significantly enhancing adaptability in imaging across various applications. Full article