Applied optics最新文献

Eu³⁺-activated GaGd₂SbO₇ phosphors were synthesized via the solid-state reaction method. XRD confirmed the formation of a single-phase cubic pyrochlore structure, with Eu³⁺ occupying high-symmetry Gd³⁺ sites. Under 266 nm excitation, both host-related broadband emission and sharp Eu³⁺4f-4f transitions were observed. Increasing Eu³⁺ concentration enhanced energy transfer efficiency with optimal luminescence at 30 mol% Eu³⁺. Under 394/466 nm excitation, comparable intensities of the ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transitions confirm centrosymmetric site occupancy. The phosphors demonstrated an internal quantum efficiency of 88.19%, high color purity (>88%), strong thermal stability (71.6% intensity retention at 450 K), and a relatively high activation energy of 0.27 eV. Compared with previously reported Eu³⁺-based red phosphors, the Eu³⁺-activated GaGd₂SbO₇ phosphors provide efficient excitation under both near-UV and blue light, highlighting their promise as a competitive candidate for high-power warm-white LEDs and other solid-state lighting applications.

Traditional vibration frequency measurement methods using stereo vision systems (SVS) often require explicit extraction of vibration signal time histories, rely on complex image processing algorithms, and depend on optical cues (e.g., markers or speckling) or techniques like edge and feature detection to track small movements on the target surface. These limitations increase implementation complexity and reduce adaptability to diverse scenarios. This paper introduces the SVS/ML method, a straightforward approach combining stereo vision techniques with machine learning (ML) for accurate and robust vibration frequency measurement. Unlike conventional methods, SVS/ML eliminates the need for explicit time history extraction and simplifies the tracking process. Experimental results comparing SVS/ML with reference methods employing industrial-grade sensors and known excitation sources demonstrate that the proposed method directly generates pixel-level vibration frequency maps with minimal error, achieving comparable accuracy to industrial-grade sensors. Moreover, SVS/ML exhibits strong robustness in both laboratory and field conditions, producing results that are ready-to-use without additional post-processing. These advantages make the method highly suitable for practical engineering applications, including structural health monitoring and machinery diagnostics.

A scheme to generate multi-octave linear frequency modulation (LFM) signals based on an optoelectronic recirculating frequency shift loop (RFSL) is proposed and demonstrated by simulation. In optoelectronic RFSL, the Mach-Zehnder modulator (MZM) driven by the initial narrowband LFM signal operates in the CS-DSB pattern to generate ±1st-order optical sidebands. The two sets of frequency components beat in a photodetector and generate an LFM signal with a doubled bandwidth. Then, the generated signal is used to replace the initial LFM signal and fed to the MZM to close the loop. As the circulating turn increases, the loop can output a multi-octave LFM signal. In addition, this scheme can easily suppress the influence of laser phase noise, thereby ensuring the signal performance. In a proof-of-concept simulation, the loop generates an 8.39 GHz LFM signal by using the initial LFM signal with a bandwidth of 0.524 GHz. Its bandwidth has increased by 16 times, resulting in the time-bandwidth product increasing to 8590. The bandwidth and center frequency of the generated LFM signals can also be adjusted by changing the parameters of the initial LFM signal and the bandwidth of the electrical band-pass filter. By selecting lasers with linewidths of 1 kHz, 1 MHz, and 0.1 GHz to change phase noise, the phase noise performance of the generated signals remains unchanged, indicating that the system effectively suppresses the laser phase noise.

Laser damage of optical components can be a limiting factor in scaling the energetics of high-peak and average power laser systems. Specifically for optical coatings, damage under nanosecond pulsed irradiation is initiated by pre-existing defects in the coating layers, including those that cause discontinuities in the structure, like craze lines. Crazing or cracking in a multilayer dielectric optical coating is induced when the overall coating stress is sufficiently tensile, and is an occasionally observed issue when employing more porous deposition techniques like electron-beam evaporation. In this study, electron-beam high-reflectors were fabricated utilizing process parameters that are known to induce crazing based on prior processing history to systematically evaluate the impact of crazing on reflector damage performance for 1064 and 355 nm lasers. The crazing that was observed was apparently nucleated at nodular defects. When the cross-section of these nodules was investigated, it was observed that there were cracks into the fused silica substrate of approximately 5 µm in depth. The craze lines were irradiated with 1064 and 355 nm light at fluences slightly above the onset of damage initiation fluence of the coating. The 1064 nm irradiated sub-apertures exhibit laser damage but with no spatial correlation with the craze line, whereas the 355 nm irradiated area exhibited many damage sites along the craze line. Finite-difference time-domain electric-field simulations were conducted, and ∼2× field amplification in hafnia was observed for the 355 nm wavelength case. The laser damage can be attributed to a slight electric-field intensification coincidental with an area where UV damage-prone precursors are known to occur. The 355 nm laser damage in uncoated fused silica substrates has been previously correlated to initiate through localized UV absorption at the broken silica bonds in the tips of fractures.

Gold nanoparticles (AuNPs) exhibit significant potential in photothermal therapy and bioimaging due to their localized surface plasmon resonance (LSPR) effect and biocompatibility. However, the formation of a protein corona on the nanoparticle surface in blood can substantially alter their optical properties, yet a systematic analysis of its influence remains limited. To address this, this study established a gold-protein corona core-shell structure model and systematically investigated the modulation mechanisms of PC parameters (thickness and complex refractive index) on the optical responses of AuNPs in blood environments using Mie scattering theory. The results demonstrate dynamic spectral responses under varying PC parameters, with maximum redshifts of 23.11 and 42.57 nm observed in absorption and scattering peaks, respectively. Compared to pure AuNP systems, the formation of a PC reduced both absorption and scattering efficiencies. Under a fixed PC refractive index, absorption and scattering efficiencies exhibited a negative correlation with increasing PC thickness. Conversely, a constant PC thickness led to reduced scattering and absorption with elevated refractive indices. At a PC refractive index of 1.30 and a thickness equivalent to 1.4 times the core diameter, the maximum attenuation amplitudes of absorption and scattering efficiencies reached 93.9% and 95.6%, respectively, compared to pure AuNPs. For a PC containing absorbing media, absorption and scattering peaks remained stable regardless of the medium's absorption capacity. The absorption efficiency increased by up to 14.6%, while the scattering efficiency decreased by 12.2%. This study establishes the first quantitative model linking PC parameters to LSPR responses in blood environments, to our knowledge, providing theoretical insights for optimizing photothermal therapy efficiency and developing PC detection technologies based on LSPR shifts.

This study investigates the propagation characteristics of pin-like vortex beams (PLVBs) traversing plasma sheath turbulence, employing the random phase-screen method. We compare the transmission performances of PLVBs with conventional Laguerre-Gaussian beams (LGBs) in terms of intensity dispersion, detection probability of orbital angular momentum, bit error rate (BER), and channel capacity. Our results show that PLVBs outperform LGBs in plasma sheath turbulence, with detection probabilities 9%-12.5% higher and BER 0.03-0.067 lower across propagation distances ranging from 0.1 to 0.4 m. Additionally, PLVBs exhibit enhanced channel capacity compared to LGBs, demonstrating the superior robustness of PLVBs against plasma sheath turbulence. We further examine the impact of the beam modulation parameter and wavelengths on the performance of PLVBs, revealing that the higher beam modulation parameter and longer wavelengths reduce BER and increase channel capacity. These findings suggest the potential of PLVBs as robust candidates for optical communication in turbulent plasma environments.

Micro-electro-mechanical system (MEMS) gyroscopes based on the Coriolis principle have numerous potential applications, including industrial automation, motion control, inertial navigation, and automotive systems. In this paper, we present a novel (to our knowledge) micro-opto-electro-mechanical system (MOEMS) gyroscope design based on the grating-waveguide mode coupling effect. This diffraction phenomenon enables highly sensitive displacement detection, even nanoscale shifts in the grating elements induce a dramatic change in optical diffraction efficiency, exhibiting anomalous diffraction behavior. Using RSoft software, we systematically simulate and investigate the influence of sub-wavelength grating parameters on diffraction efficiency and determine the optimal geometric configuration. Furthermore, we conduct a comprehensive tolerance analysis to evaluate the impact of fabrication accuracy on diffraction intensity. Finally, we develop a Simulink-based system model for the gyroscope. The designed system achieves a structural sensitivity of 0.09 nm/°/s, an optical diffraction sensitivity of 0.679 mW/nm, and a photoelectric conversion sensitivity of 44.5 mV/mW, yielding a total sensitivity of 2.72 mV/°/s. The proposed sub-wavelength grating MOEMS gyroscope not only addresses critical limitations of conventional MEMS gyroscopes but also demonstrates strong potential for inertial-grade MEMS gyroscopes with unprecedented precision.

The bi-orthogonal edge wavefront sensor (WFS) is, to our knowledge, a new wavefront sensor based on the Foucault knife-edge test. In this paper, we show by calculating sensitivity with the spatial frequency of Fourier modes that the bi-orthogonal edge WFS has higher photon and read noise sensitivity than the pyramid, roof, 3-sided, and cone WFS for both low-order (gradient) and high-order (Hilbert) modes. We propose the use of other (nonlinear) transmittance functions in the transition region of the amplitude masks of the bi-orthogonal edge WFS and show that this can be used to either increase the sensitivity or the dynamic range of the low-order modes. We demonstrate a relative improvement in closed-loop Strehl of up to 8% in turbulent conditions by using a nonlinear sigmoid function compared to a linear transmittance curve.

Cancer has become a major threat to human health, with precise cellular morphology analysis critical for diagnosis and grading. Deep learning-based automatic cell segmentation is emerging as a key tool in computer-aided pathology. However, distortion and blur in digital pathology images often degrade segmentation model performance. To address this, we propose the frequency-domain resolution network, which maps images to the frequency domain, processes amplitude and phase information independently, and employs a fusion strategy to restore clear images. This approach surpasses traditional spatial-domain methods, enhancing image detail and structural feature restoration. Using these generated images, we perform nucleus extraction and segmentation, incorporating a pyramid pooling module to optimize accuracy. Experimental results show our method achieves superior resolution-enhancement reconstruction and cell segmentation, demonstrating significant potential and academic value.

The Airy light-sheet is known for its unique properties, such as non-diffraction, self-acceleration, and self-healing, making it valuable in imaging and particle manipulation. However, most existing scattering studies focus on symmetric spherical particles using analytical models, overlooking irregular particles commonly found in biological systems. In this work, we develop a finite-difference time-domain (FDTD) framework to construct a two-dimensional Airy light-sheet using the vector angular spectrum method and the total-field/scattered-field (TF/SF) technique. The reconstructed Airy light-sheet in FDTD agrees well with theoretical predictions. We further analyze near-field scattering from two representative models-the square-shaped particle and the red blood cell particle under varying parameters. This study provides a flexible tool for structured light interaction with irregular particles, expanding FDTD applications in biophotonics and optical trapping.