This study explores sol-gel methods for fabricating erbium-doped silica microtoroid resonators, addressing the limitations of conventional doping techniques and enhancing device scalability. We develop a reproducible sol-gel process that yields defect-free films for photonic applications and detail common defects and troubleshooting strategies. Two fabrication methods are compared: traditional film deposition on substrates and the direct coating of prefabricated resonators. The latter enables the fabrication of larger resonator diameters (up to 450 µm) without buckling while achieving a high-Q factor and a low lasing threshold of 350 µW. These erbium-doped resonators exhibit multi-mode laser oscillations at 1550 nm, revealing the sol-gel method’s potential for realizing scalable, gain-doped photonic devices.

We investigated the moiré effect in combined objects with dissimilar curvatures (such as a flat surface combined with a cylinder) off the axis when the center of the cylinder is not on the camera axis. The theory is based on projections. The formula for the period of the moiré patterns in combined objects was obtained in a form similar to the on-axis case. An overall picture of the period was constructed. Specific specimens of the period behavior are described, including two primaries, five derived, and their progressions (transformations). Experiments confirm the theory. The region in the parameter space most suitable for measurements was found. The results can be used in minimization, nanoparticles, and measurements.

We study the light-atom interaction in a four-level atomic system in a ladder-vee type configuration employing the density matrix formalism with exact numerical solutions. By varying the third driving strength, we achieve continuous control over the quantum interference of the system, shifting it from destructive to constructive interference. Our analysis reveals a narrow existence window for the EIT signal when the driving field is active, suggesting effective control ability. Finally, we propose the required driving Rabi frequency as a function of the given coupling Rabi frequency to achieve a 90% reduction in EIT magnitude, effectively altering the quantum interference by a π/2 phase shift.

It has been demonstrated that nanoscale height variations on a bare silicon wafer can be reconstructed from a single image obtained in one shot using a color mapping imaging system of a reflectance direction field. This imaging system can acquire the direction of light rays reflected from the wafer's surface as color information by utilizing a filter with a multicolor stripe pattern. A prototype of the imaging system is capable of capturing an image of a 12 × 8 mm area of the silicon wafer with a resolution of 2.18 × 2.18 µm. The height error distribution in the reconstruction from the ideal surface varies between -18% and 6%.

Iterative phase retrieval is a computational imaging technique to recover the lost phase information from intensity-only images for lensless diffraction imaging. However, the conventional single-shot phase retrieval is always constrained by the precise selection of support region or sparse assumption. To address it, we propose a multi-rotation phase retrieval (MRPR) algorithm for lensless imaging. In our method, a support-based phase retrieval with total variation is first designed to calculate all illumination patterns, which removes the requirement of rotation angle estimation. Then, the illumination modulation and total variation regularization are combined to restrain the multi-rotation optimization function to iteratively reconstruct the complex-valued image of the sample. In comparison with support-based phase retrieval, our method does not rely on the selection of support region and shows high-fidelity image reconstruction. The simulation and experimental results are given to demonstrate the effectiveness of our method.

The optical response of a depolarizing element can be described by a statistical mixture of deterministic, non-depolarizing elements, and it is often expressed as a Mueller matrix acting on a Stokes vector. Here, we show that the statistical quantities involved in obtaining the Stokes states of the laser modes of a resonator containing depolarizing elements significantly differ from those entering a Mueller matrix. We apply our model to a resonator possessing an exceptional point, where polarization eigenstates coalesce at a specific value of a control parameter: a sharp drop in the degree of polarization is predicted and observed at the exceptional point, which cannot be explained with a simple Jones formalism.

Near-field direction control of terahertz metasurface provides a new paradigm in photonic devices for terahertz (THz) communications. The control of near-field patterns and polarization states is the major challenge for THz metasurface devices. In this work, the hybrid MXene (Ti3C2Tx)/ vanadium dioxide (VO2) metasurface structure is explored for the tuning of transmission amplitude modulation, polarization control, and near-field pattern switching. The hybrid metasurface device is comprised of Ti3C2Tx/VO2 hexagon resonators arranged in a periodic array having silicon (Si) as a substrate with a thin silicon dioxide (SiO2) layer. The response of Ti3C2Tx/VO2 hybrid structure has been investigated under the influence of gate biasing and different optical pump intensities. The enhanced bandwidth tuning has been realized under the polarization and phase control. The rise of MXene conductivity with increasing gate bias is also investigated for transmission tuning. The transition of VO2 from an insulator to a conductor is specifically induced by an increase in optical pump intensity, with 95% of the transmission achieved at the 1-4 THz range. Furthermore, π/2 rotation of near-field is realized with a change in near-field pattern symmetry at various planes. VO2 phase shifting, switch the near-field dipolar pattern from the z-axis to the x-axis into a twisted Gaussian pattern, when TMyx (p-polarized) incidence source is used. The low-cost MXene material can serve as a promising material for terahertz devices.

Coronary artery disease (CAD) remains one of the most widespread cardiovascular conditions and a leading cause of mortality globally. Computed tomography angiography (CTA) imaging is widely accepted as the gold standard for diagnosing CAD, enabling more accurate assessments through vessel segmentation and stenosis detection. Despite over 2 million coronary angiography procedures being performed annually, there are still limited methods available for the rapid and precise automated measurement of disease and localization of coronary anatomy. In this paper, we present what we believe to be a novel approach to vessel segmentation by categorizing the dataset based on object shape characteristics, training the YOLOv8 model with tailored techniques for each group, and integrating the results to produce the final output. Experiments conducted on the benchmark ARCADE dataset demonstrate that our proposed method outperforms traditional approaches, highlighting its potential in vascular segmentation tasks and providing a strong foundation for future advancements in stenosis detection.

Recently popular GeSn photodetectors struggle with β -Sn defects, a weak directness in the bandgap, and reduced optical confinement. To address these issues, we proposed a GeSnC-based multi-quantum well (MQW) heterojunction p-i-n photodetector for SWIR spectrum (780 – 3000 nm) sensing. Different parameters like responsivity, photocurrent, and dark current were analyzed with varying numbers of quantum wells. Noise parameters like NEP, detectivity, and SNR were also calculated for further analysis. The proposed device exhibited an extended photodetection up to 2900 nm and a prominent I ph /I dark of 3.0088 x 10 4 for N = 9 at 300K. At reverse bias, V r = 2V, simulations predicted a maximum SR of 1.39 A/W at 2000 nm and 0.6 A/W at 2700 nm at 300K. Detectivity of 4.14x10 9 Jones and NEP of 1.43x10 −13 W/Hz 1/2 for N = 9 at 2700 nm were found. The SNR and LDR were calculated to be 95.21 dB and 82.46 dB for N = 9 at 2700 nm. The proposed device gained a high 3dB bandwidth of 45.7 GHz. Thus, the obtained results indicate that Ge 1− x − y Sn x C y is a promising candidate for realizing high-performance, high-speed photodetectors with improved CMOS compatibility for sensing applications in the SWIR spectrum.

The study of the laser-induced molecular plasma produced during the ablation of boron carbide as a medium for high-order harmonic generation is reported. The efficiency of harmonics generation in this laser-induced plasma is compared with the plasma produced on the surfaces of boron and carbon targets at the intensities of heating and driving pulses of 2 × 1010 and 3 × 1014 W/cm2, respectively. The stability of harmonic emission from boron carbide plasma was notably better compared with the boron and carbon plasmas. The influence of laser-induced plasma formation, the role of ablated components, the delay between heating and driving pulses, and the characteristics of converting pulses on the harmonic efficiency and harmonic cut-off in boron carbide plasma are studied.