Optics

This paper outlines the design and fabrication of a portable optomechatronic system based on the theta-2theta configuration, which explores various optical characterization techniques for transparent materials and dielectric thin films. These techniques include Brewster angle and Abelès-Brewster angle measurements, critical angle measurements, and the surface plasmon resonance technique. The system consists of a mechanical assembly of rotating stages, a semiconductor laser, a photodiode connected to a data acquisition card, and a user interface for controlling the stepper motor rotation stages. Utilizing a BK7 substrate, the motorized stage achieved a resolution of 0.010. The Brewster angle measured was 56.550, with a refractive index (n) of 1.5137. The relative error obtained was Δn/n = 3.82 × 10⁻⁴, with a sensitivity of 164.27 RIU/degree and an accuracy of 0.37/degree. Furthermore, the discrepancies between theoretical and experimental refractive indices for different prisms at 639 nm ranged from ±7 × 10⁻⁴ to ±73 × 10⁻⁴. After testing various samples, the system demonstrated its capability to perform fast, precise, and non-invasive measurements. Its portability allows for use in diverse environments and applications. Full article

Airy beams showing curved paths have found extensive applications in fields such as optical trapping, biomedical analysis, and material processing. Despite their utility, dynamic control of Airy beams poses a significant challenge. This work investigates the experimental realization of dynamic steering of Airy beams by utilizing computer-generated holograms with phase-amplitude encoding on a phase-only spatial light modulator (SLM). We successfully generated and controlled Airy beams by imposing dynamic phase masks that manipulated both the phase and amplitude of the field, which sets our approach apart from conventional methods with only phase manipulation. By directly encoding in situ such a hologram and transferring it to an SLM, we are able to control the initial position and rotational orientation of Airy beams without relying on mechanical movement or traditional optical setups involving lenses and apertures. Generating Airy beams in any initial position and rotational direction is anticipated to significantly impact applications such as optical trapping, optical communication, and biomedical imaging by providing a flexible platform for dynamic Airy beam manipulation. Full article

Digital image correlation (DIC) is a non-contact measurement technique used to evaluate surface deformation of objects. Typically, pointwise moving least squares (PMLS) fitting is applied to process the noisy data from DIC to obtain an accurate strain field. In this study, a self-adaptive pointwise moving least squares (SPMLS) method was developed to optimize the process of window size selection, thereby attaining superior accuracy in measurements. The premise of this method is that the noise in the displacement field follows white Gaussian noise. Under this assumption, it analyses the random errors and systematic errors of the PMLS method under different calculation window sizes. The optimal size of the calculation window is determined by minimizing the errors. Subsequently, the strain field is computed based on the optimized calculation window. The results were compared with a typical PMLS method. Whether calculating low-gradient strain fields or high-gradient strain fields, the computational accuracy of SPMLS is close to the optimal accuracy of PMLS. This study effectively addresses the inherent challenge of manually selecting window size in the PMLS method. Full article

Phase holography is a critical optical imaging and information processing technique with applications ranging from microscopy to optical communications. However, optimizing phase hologram generation remains a significant challenge due to the non-convex nature of the optimization problem. This paper presents a novel multiplane optimization approach for phase hologram generation to minimize the reconstruction error across multiple focal planes. We significantly improve holographic reconstruction quality by integrating advanced machine learning algorithms like RMSprop and Adam with GPU acceleration. The proposed method utilizes TensorFlow to implement custom propagation layers, optimizing the phase hologram to reduce errors at strategically selected distances. Full article

In this paper, the magic wavelength of the ⁸⁷Sr optical lattice clock is determined by a method that bypasses the need for lattice trap depth modulation. Instead, it relies on an additional AC Stark shift generated by a dipole beam operating near the frequency of the lattice light and oriented perpendicular to the optical lattice. The magic wavelength is inferred by measuring the AC Stark shift induced by the dipole beam as a function of its power under various frequency detunings. The effect of the dipole beam on the external states of the cold ensemble is evaluated through comparative analysis of the radial and axial sideband spectra, both with and without the dipole beam. Variations in density shift resulting from changes in external states are evaluated using comprehensive numerical calculations. By avoiding trap depth modulation, this method effectively suppresses the influence of the density shift, thereby offering a promising avenue for accurately determining the magic wavelength. Full article

We investigate the dynamic excitation of surface plasmon polaritons (SPPs) using vector Laguerre–Gauss (LG) beams, which offer unique properties for manipulating the polarization and spatial distribution of light. Our study demonstrates the efficient coupling of SPPs with LG beams, characterized by their azimuthal and radial indices $(m,p)$, as well as polarization distribution type. Numerical simulations reveal that the vector nature of LG beams enables selective excitation of SPPs, depending on the polarization type of the beam. Experimental verification of our simulations is achieved using a gold circular Bragg grating and a spatial light modulator that generates vector LG beams. Leakage radiation imaging demonstrates the potential of vector LG beams for dynamic SPP excitation and manipulation. This study opens novel ways for the control of SPPs in plasmonic devices, such as modulators, and nanophotonic circuits. Full article

In the current study, we address the phase retrieval of one-dimensional phase objects from near-field diffraction patterns using the multiple-plane Gerchberg–Saxton algorithm, which is still widely used for phase retrieval. The algorithm was implemented in a low-cost digital signal processor capable of fast Fourier transform using Q15 arithmetic, which is used by the previously mentioned algorithm. We demonstrate similarity between one-dimensional phase objects, i.e., vectors cut out of a phase map of the tertiary spherical aberration retrieved by the multiple-plane Gerchberg–Saxton algorithm, and these vectors are measured with a non-contact profiler. The tertiary spherical aberration was induced by a phase plate fabricated using grayscale lithography. After subtracting the vectors retrieved by the algorithm from those measured with the profiler, the root mean square error decreased, while a corresponding increase in the Strehl ratio was observed. A single vector of size 64 pixels was retrieved in about 2 min. The results suggest that digital signal processors that are capable of one-dimensional FFT and fixed-point arithmetic in Q15 format can successfully retrieve the phase of one-dimensional objects, and they can be used for applications that do not require real-time operation, i.e., analyzing the quality of cylindrical micro-optics. Full article

This study focuses on creating micro-nano structures on the surface of 304 stainless steel using nanosecond lasers to achieve superhydrophobicity for fog water collection experiments in a fog chamber. By adjusting pattern parameters, an uneven wettability surface was processed, and six samples were placed at different positions in the chamber to study water collection efficiency from various surfaces. The experimental results indicate that the water collection efficiency of the patterned superhydrophobic surface is superior to that of the original surface, with the front sample collecting 0.4524 ± 0.005 g of water, representing a 90.38% improvement. As the kinetic energy of the fog flow gradually diminishes, a total of 1.1913 ± 0.005 g of water was collected, achieving a 60.25% improvement. The study also investigates the durability and optimal temperature conditions for fog water collection, ultimately achieving 1.4781 ± 0.005 g of water collection in a 5 °C fog environment, resulting in a 98.83% enhancement. Full article

Although effective, a portion of photorefractive keratectomy (PRK) patients will suffer residual myopia or relapse to myopic regression. This retrospective, non-randomized, comparative study, aimed to compare the efficacy of primary PRK versus PRK performed as retreatment after previous surgery for myopia. Data regarding the right eye of 220 consecutive myopic patients undergoing repeat or primary PRK in 2013–2017 were extracted. Groups were matched for demographics and preoperative spherical equivalent, sphere, astigmatism, uncorrected and corrected distance visual acuity (UDVA and CDVA). Primary outcomes were an efficacy index (ratio between the postoperative UDVA and the preoperative CDVA), a safety index (ratio between the postoperative and the preoperative CDVA), postoperative UDVA and CDVA, and deviation from target refraction. Primary PRK showed significant superiority in logMAR UDVA (0.01 ± 0.05 versus 0.05 ± 0.10, p = 0.001), logMAR CDVA (0.01 ± 0.05 versus 0.04 ± 0.08, p = 0.01), efficacy index (1.00 ± 0.05 versus 0.97 ± 0.09, p = 0.003) and safety index (1.00 ± 0.06 versus 0.98 ± 0.08, p = 0.04) compared to repeat PRK, but had a significantly higher share of patients with postoperative spherical equivalent (74.5% versus 67.3%) and cylinder (74.5% versus 68.2%) in the range of ±0.5 D. To conclude, enhancement PRK leads to inferior efficacy and safety with greater deviation from target refraction. Adjusted nomograms for repeat PRK may be warranted. Full article

This study explores electrochemical etching to form porous silicon (PS), which has diverse biomedical and energy applications. Our objective is to gain new insights and drive significant scientific and technological advancements. Specifically, we study the effect of electrochemical etching of P-type silicon using laser irradiation in a hydrofluoric acid (HF) solution. The formation of the nanoscale PS structure can be successfully controlled by incorporating laser irradiation into the electrochemical etching process. The wavelength and power of the laser influence the formation of nanoporous silicon (NPS) on the surface during the electrochemical etching process. The luminous flux is monitored with the help of a customized integrating sphere system and an LED-based excitation source to find the light flux values distributed across the P-type nanolayer PS wafers. Analysis of the NPS and luminescence characteristics shows that the laser bandwidth controls the band gap energy absorption (BEA) phenomenon during the electrothermal reaction. It is demonstrated that formation of the NPS layer can be controlled in this combined laser irradiation and electrochemical etching technique by adjusting the range of the laser wavelength. This also allows for further precise control of the numerical trend of the luminous flux. Full article

In this work, we present the exact equations for the back and effective focal lengths of a plano-concave thick lens. These equations are derived through a detailed ray-tracing approach, calculating the meridional ray’s path parallel to the optical axis while taking into account lens thickness, refractive index, and surface curvature. Our analysis bridges the gap between paraxial approximations and exact ray behavior, highlighting how traditional models (e.g., thin-lens equations) can be extended to thick lenses. Additionally, we review recent advancements in negative refraction and surface phase manipulation techniques to demonstrate how our equations compare to modern numerical methods and metacoating-enhanced designs. This work provides a comprehensive and exact framework for understanding the optical properties of plano-concave thick lenses, offering new insights into their application in precision optics. Full article

The position and linewidth of an emission spectrum reflect the physical properties of the luminophor. So, keeping the spectrum from distortion is very important in its measurement. However, we find that the spectrum linewidth will be broadened when the near-infrared radiation from a sodium lamp passes through a nonselective linear absorbing filter. This counterintuitive linewidth-broadening phenomenon is obvious when the residual light power after the filter is low enough, typically lower than $2.48\times {10}^{-4} \mathsf{\mu }\mathrm{W}$. This novel linewidth-broadening effect is different from the well-known Lorentzian, Doppler, and Voigt broadening, and is likely to be more independent evidence of the discrete wavelet structure of classical plane light waves. The effect is significant in high-sensitivity spectroscopy measurements, for example streak camera spectroscopy and Raman spectroscopy experiments. In addition, this effect may also be significant for cosmological research. Full article

In recent years, assistive technology usage among the visually impaired has risen significantly worldwide. While traditional aids like guide dogs and white canes have limitations, recent innovations like RFID-based indoor navigation systems and alternative sensory solutions show promise. Nevertheless, there is a need for a user-friendly, comprehensive system to address spatial orientation challenges for the visually impaired. This research addresses the significance of developing a deep learning-based walking assistance device for visually impaired individuals to enhance their safety during mobility. The proposed system utilizes real-time ultrasonic sensors attached to a cane to detect obstacles, thus reducing collision risks. It further offers real-time recognition and analysis of diverse obstacles, providing immediate feedback to the user. A camera distinguishes obstacle types and conveys relevant information through voice assistance. The system’s efficacy was confirmed with a 90–98% object recognition rate in tests involving various obstacles. This research holds importance in providing safe mobility, promoting independence, leveraging modern technology, and fostering social inclusion for visually impaired individuals. Full article

The World Health Organization (WHO) cancer agency predicts that more than 35 million cases of cancer will be experienced in 2050, a 77% increase over the 2022 estimate. Currently, the main cancers diagnosed are breast, lung, and colorectal. There is no standardized tool for cancer diagnoses; initially, clinical procedures are guided by the patient symptoms and usually involve biochemical blood tests, imaging, and biopsy. Label-free non-linear optical approaches are promising tools for tumor imaging, due to their inherent non-invasive biosafe contrast mechanisms and the ability to monitor collagen-related disorders, and biochemical and metabolic changes during cancer progression. In this review, the main non-linear microscopy techniques are discussed, according to three main contrast mechanisms: biochemical, metabolic, and structural imaging. Full article

In order to break the diffraction limit and improve the imaging resolution of optical microscope, in this article, we theoretically deduced the influence of phase difference on imaging resolution under coherent illumination. As the phase difference increased, the resolution improved gradually. Inspired by this conclusion, a super-resolution optical imaging system based on phase modulation was proposed and simulated. An optical mask was designed to generate additional phase difference for the adjacent area at the sample’s surface, and the influence of its structural parameters was analyzed numerically. The simulation results preliminarily confirm the feasibility of this scheme, laying the foundation for a more optimal and comprehensive super-resolution imaging scheme. Due to its advantages of high resolution, a wide field of view, and being compatible, this non-fluorescence super-resolution imaging scheme is worthy of further research and application. Full article

To address the challenge of image matching posed by significant modal differences in remote sensing images influenced by snow cover, this paper proposes an innovative image transformation-based matching method. Initially, the Pix2Pix-GAN conversion network is employed to transform remote sensing images with snow cover into images without snow cover, reducing the feature disparity between the images. This conversion facilitates the extraction of more discernible features for matching by transforming the problem from snow-covered to snow-free images. Subsequently, a multi-level feature extraction network is utilized to extract multi-level feature descriptors from the transformed images. Keypoints are derived from these descriptors, enabling effective feature matching. Finally, the matching results are mapped back onto the original snow-covered remote sensing images. The proposed method was compared to well-established techniques such as SIFT, RIFT2, R2D2, and ReDFeat and demonstrated outstanding performance. In terms of NCM, MP, Rep, Recall, and F1-measure, our method outperformed the state of the art by 177, 0.29, 0.22, 0.21, and 0.25, respectively. In addition, the algorithm shows robustness over a range of image rotation angles from −40° to 40°. This innovative approach offers a new perspective on the task of matching multi-temporal snow-covered remote sensing images. Full article

In order to test the performance of laser devices for attacking miniature UAVs, we studied the principle of laser devices on soft killing and hard killing. Then, the flight test conditions of miniature UAVs were constructed, and the laser devices were tested and evaluated with the two indexes of maximum jamming range and maximum intercepting range. The first step involves calculating the far-field beam power density corresponding to the unmanned aerial vehicle (UAV) detection equipment and laser device at different distances. Subsequently, the signal electron count received by the UAV detector from the incident laser source target within the integration time tint is computed and compared against the full well charge of the photodetector. This comparison analyzes the UAV detector’s potential for dazzle/blind effects. When the laser device is positioned 600 m from the UAV, the ratio of signal electrons received by the detector to the full well charge was 13.53, indicating that the detector receives signal electrons exceeding the full well charge by over 10 times, thus causing UAV detector blindness. At a distance of 1.2 km from the UAV, this ratio reduces to 2.92, where the detector receives signal electrons around three times the full well charge, causing UAV detector dazzle. Experimental testing determines that the maximum interception distance of this laser device for small, slow-moving UAV equipment is 500 m. Finally, it is proved that the method can effectively test the attacking performance of laser devices, and provides a basis for improving the function and performance of laser devices. Full article

Surface-enhanced Raman scattering (SERS) holds significant potential across environmental monitoring, materials science, and biomedical applications. However, challenges regarding ultra-sensitive detection and repeatability are bottlenecks for practical applications, especially in terms of detection uniformity. In this study, we utilized surface acoustic waves (SAW) in conjunction with Raman spectroscopy to actively enrich 5 μL of 50 nm gold nanoparticles (AuNPs), thereby achieving innovative SERS-active sensing. This dynamic enrichment process enables the dense and uniform aggregation of AuNPs in droplets, thereby facilitating reliable ultrasensitive detection. The SAW system was further optimized through hydrophobic surface treatment. Using 4-mercaptobenzoic acid as a probe analyte, our SAW-SERS method successfully detected concentrations as low as 10⁻⁸ mol/L. The surface acoustic waves had the capability to significantly amplify Raman signal intensity up to 100 compared to conventional drying methodologies. This SAW-induced AuNP clustering technology offers a rapid, label-free SERS sensing method characterized by exceptional sensitivity and uniformity. Full article

Recovery after visual loss is a key goal of neuroscience and treatments able to improve visual function are still largely lacking. Glaucoma, one of the leading causes of visual disability in the world, is usually associated with elevated intraocular pressure (IOP), but a subset of “normal tension glaucoma” patients develop damage without ever manifesting high IOP. Sometimes, even in patients with good control of IOP, retinal ganglion cell degeneration can progress to forward blindness. Moreover, usually the damage already caused by the disease remains. These considerations underline the need to find new, effective treatments and solutions to add to the standard ones. In this paper, we expose the most important data supporting the use of alternating current stimulation, including the theoretical bases of this approach, in glaucoma. Full article