We here describe a nanosecond, multi-line laser source that preserves partial linear polarization after transmission through a 100-m large-core graded-index (GRIN) fiber. The system generates narrow emission lines between 473 and 600 nm, evenly spaced by the silica Raman shift of ∼440 cm -1 , from a Q-switched nanosecond pump coupled into the fiber. Despite multimode propagation, the cascaded beams emerge close to diffraction-limited Gaussian profiles due to nonlinear mode self-cleaning, while the residual pump remains multimodal. Across the emission lines, the degree of linear polarization (DoLP) ranges from 0.1 to 0.6 depending on the wavelength. As an application, we demonstrate single-shot, multiwavelength spectro-polarimetric reflectance, simultaneously measuring DoLP at all cascaded lines. To our knowledge, this is the first demonstration of wavelength-dependent polarization retention through a 100-m large-core GRIN fiber.

The research in the area of terahertz (THz) radiation is a subject of intense discussion in the international scientific community owing to its various applications in the fields of defense systems, security, interstellar studies, imaging, and agriculture. Although most of these applications have captured the attention of researchers in recent years, the development of a THz radiation source that meets specific requirements remains a challenging task. In this regard, the emission frequencies of terahertz quantum-cascade lasers (THz QCLs) can be fine-tuned by adjusting the thickness of the quantum well and the height of the barriers. The electron distribution among three periods of a hybrid active region design QCL structure is numerically simulated to estimate the optical gain spectra and electric field strength values. The results of the numerical simulations are compared with those of the experimental investigations by fabricating a 23 μm-thick active region THz QCL wafer by using the molecular beam epitaxy (MBE) technique. The wafer is split into six portions (A–F) to investigate the transport and the lasing properties. The electrical power dissipated at 10 K for the 23 μm-thick active region THz QCL stripe processed from the central portion (B) of the wafer is found to be approximately 56 W at the current density value of 0.53 kAcm−2. The thick active region THz QCL investigated in the present work operates in both pulsed and continuous-wave modes at the desired emission frequencies, which is a unique feature of the interlaced design. The optical output power of the 23 μm-thick active region THz QCL stripe compared to the 12 μm-thick active region is enhanced, attributed to improved mode confinement. Therefore, optimal performance in the pulsed mode can be achieved with thick active region THz QCL stripes fabricated near the center of the parent wafer. Nevertheless, thin active region THz QCLs are more suitable for continuous-wave operation due to reduced heat dissipation.

Precision glass molding (PGM) enables high-accuracy, efficient production of complex optical components, yet interfacial adhesion between mold and glass surfaces remains a significant barrier, impacting both quality and mold durability. This review comprehensively examines the factors influencing adhesion behavior, including the roles of material selection, surface wettability, process parameters, and thermodynamic principles in defining interfacial performance. Through a detailed analysis of anti-adhesion materials and optimized process strategies, such as controlled temperature, pressure, and atmospheric conditions, this work elucidates mechanisms that mitigate adhesion and extend mold life. Thermodynamic modeling, including work of adhesion calculations, provides a quantitative foundation for predicting interfacial behavior, offering guidance for material and process optimization in PGM applications. The findings provide a multi-dimensional framework for addressing adhesion challenges in PGM, setting the stage for enhanced efficiency and quality in precision optics manufacturing.

This study presents a novel approach for achieving high-quality and large-scale microscopic ghost imaging by integrating deep learning-based denoising with computational ghost imaging techniques. By utilizing sequenced random speckle patterns of optimized sizes, we reconstructed large noisy images with fewer patterns while successfully resolving fine details as small as 2.2 μm on a USAF resolution target. To enhance image quality, we incorporated the Deep Neural Network-based Noise2Void (N2V) model, which effectively denoises ghost images without requiring a reference image or a large dataset. By applying the N2V model to a single noisy ghost image, we achieved significant noise reduction, leading to high-resolution and high-quality reconstructions with low computational resources. This method resulted in an average Structural Similarity Index (SSIM) improvement of over 324% and a resolution enhancement exceeding 33% across various target images. The proposed approach proves highly effective in enhancing the clarity and structural integrity of even very low-quality ghost images, paving the way for more efficient and practical implementations of ghost imaging in microscopic applications.

The development of integrated photonic systems, both on-chip and fiber-based, has transformed quantum photonics by replacing bulky, fragile free-space optical setups with compact, efficient, and robust circuits. Photonic platforms incorporating fiber-connected sources of correlated and entangled photon pairs offer practical advantages, such as operation at room temperature, efficient integration with telecom infrastructure, and compatibility with mature and efficient semiconductor fabrication processes for cost-effective and large-scale optical circuits. The stability and scalability of integrated quantum photonics platforms have facilitated the generation and processing of quantum information in the temporal domain within a single spatial mode. Time-bin encoded states, known for their robustness against decoherence and compatibility with existing fiber-optic infrastructure, have shown to be an efficient paradigm for advanced applications like quantum secure communication, information processing, spectroscopy, imaging, and sensing. This review examines recent advancements in fiber- and chip-based platforms for generating non-classical states and their applications as quantum state processors in the time domain. We discuss the generation of pulsed quantum frequency combs using microring resonators and intra-cavity mode-locked laser schemes, enabling co- and cross-polarized quantum photonic states. Additionally, the versatility of these resonator chips for entanglement generation is emphasized, including two- and multi-photon time-bin entangled schemes. We highlight the development of time-bin entanglement analyzers in fiber architectures, featuring ultrahigh stability and post-selection-free capabilities, which enable precise and efficient characterization of two- and higher-dimensional time-bin entanglement. We also review scalable on-chip schemes for quantum key distribution, demonstrating low quantum bit error rates and compatibility with higher-dimensional quantum communication protocols. Further, methods for enhancing temporal resolution in detection schemes, crucial for time-bin encoding, are presented, such as the time-stretch sampling technique using electro-optic modulation. These innovations, relying on readily available, telecom-based fiber-optic components, provide practical, scalable, and cost-effective solutions for advancing quantum photonic technologies. Looking forward, time-bin encoding is expected to play a pivotal role in the advancement of quantum repeaters, distributed quantum networks, and hybrid light-matter systems, advancing the realization of globally scalable quantum technologies.

IntroductionApart from discussing general issues related to the application of freeform telescopes, this work presents a design of ultra-compact high-resolution freeform telescope dedicated to CubeSat application associated with Earth surface imaging from Low Earth Orbit (LEO), providing high resolution (Ground Sampling Distance, GSD <5 m) and 20 km width of the observed Earth strip.MethodsThe telescope was designed in a three-mirror off-axis configuration according to the <0.5U volume constraint. Freeform surfaces were described by shifted polynomial equations. In order to prevent optimization falling into numerous local minima of multi-variate merit function, the new design strategy was proposed. The optical design commercial software was supplemented by add-on responsible for dynamically modifying the set of variables in the loop during the optimization process.ResultsThe designed 250 mm f/4.9 telescope meets the assumed operational and volumetric criteria. It fits into the volume of 5 × 10 × 10 cm cuboid. It is diffraction limited across the whole (3o) field of view.DiscussionFreeform optics design technology was successfully applied to design a miniature space telescope. The proposed design algorithm proved to be computationally efficient. It enabled to obtain the excellent imaging of the designed telescope, which from mathematical perspective becomes a challenging multi-variable optimization task, unattainable with the standard optimization procedures included in the commercial optical design software.

The advent of X-ray Free Electron Lasers (XFELs) has opened unprecedented opportunities for advances in the physical, chemical, and biological sciences. With their state-of-the-art methodologies and ultrashort, and intense X-ray pulses, XFELs propel X-ray science into a new era, surpassing the capabilities of traditional light sources. Ultrafast X-ray scattering and imaging techniques leverage the coherence of these intense pulses to capture nanoscale structural dynamics with femtosecond spatial-temporal resolution. However, spatial and temporal resolutions remain limited by factors such as intrinsic fluctuations and jitters in the Self-Amplified Spontaneous Emission (SASE) mode, relatively low coherent scattering cross-sections, the need for high-performance, single-photon-sensitive detectors, effective sample delivery techniques, low parasitic X-ray instrumentation, and reliable data analysis methods. Furthermore, the high-throughput data flow from high-repetition rate XFEL facilities presents significant challenges. Therefore, more investigation is required to determine how Artificial Intelligence (AI) can support data science in this situation. In recent years, deep learning has made significant strides across various scientific disciplines. To illustrate its direct influence on ultrafast X-ray science, this article provides a comprehensive overview of deep learning applications in ultrafast X-ray scattering and imaging, covering both theoretical foundations and practical applications. It also discusses the current status, limitations, and future prospects, with an emphasis on its potential to drive advancements in fourth-generation synchrotron radiation, ultrafast electron diffraction, and attosecond X-ray studies.

IntroductionSeveral population-based clinical studies suggest that increased Pulse Wave Velocity (PWV) is highly associated with increased cardiovascular disease (CVD) mortality, which is one of the leading causes of death worldwide. Current methods for CVD detection are invasive, expensive, and contact methods, which are not friendly for skin-sensitive patients.MethodsIn this study, we investigated the use of remote photoplethysmography (rPPG) on the neck region using a high-speed camera (2000 frames per second (fps)) to resolve the drawbacks of CVD detection and overcome the limitations of current PWV measurement techniques. Pearson correlation and cross-correlation were used for signal processing and generating the projection map of potential major vessels. A reference signal is selected for the region of interest based on peak value and modulation depth variation. The signal distance and pulse transit time (PPT) between the local and reference signals were calculated using the cross-correlation method and then fitted into a linear regression model for PWV calculation.ResultsThe results revealed areas on the neck that positively and negatively correlated with the selected reference signals, potentially representing the distribution of the main neck vessels - carotid artery and jugular vein- and, consequently, the upstream and downstream blood circulation directions.DiscussionThis research implies the feasibility of touchless estimation of local PWV using a high-speed camera, expanding the potential applications of remote photoplethysmography in aiding the diagnosis of CVD.

In this paper, the authors explore the potential of an exotic multi-graphene layer/Si nanowire (MGL/SiNW) pin device as a switch in the THz frequency domain. The device is developed by the incorporation of multiple SiNWs into its intrinsic region. In contrast, cap and bottom layers are developed by the incorporation of multiple graphene layers. The electrical characterization of the proposed exotic pin device is carried out by developing a quantum-rectified Schrodinger–Poisson drift-diffusion (QRSP-DD) model. The developed QRSP-DD model is validated by analyzing experimental and simulation observations under similar operating conditions. After establishing its validity, the same model in conjunction with the PSpice simulator is used to obtain the switching characteristics of MGL/SiNW pin-based series-shunt and shunt single-pole single-throw (SPST), single-pole double-throw (SPDT), and single-pole multiple-throw (SPMT) switches in the THz frequency domain. The analysis proves that the MGL/SiNW pin-based SPMT switch offers low resistance (0.56 Ω), high isolation (91.15 dB), and low insertion loss (0.007 dB) at 5 THz frequency compared to its SiNW counterpart.

Introduction: This work presents a prototype electromagnetic actuation deformable mirror (DM) assembly with stress-resilient face sheet design.Methods: The DM face sheet design includes slender micromachined silicon pillars that are integrated with a silicon face sheet to reduce unpowered face sheet surface distortion caused by actuator adhesion stress.Results: The assembled deformable mirror prototype allowed bi-directional actuation with total stroke exceeding 20 μm. A two-step control method was used to improve the prototype dynamic performance, allowing settling time on the order of 1 ms. Prescribed references shapes were made on the prototype deformable mirror using closed-loop control.Discussion: While the simplified DM produced in this work has only 19 actuators and therefore has limited capacity to control complex shapes, the design and fabrication processes described and demonstrated in this work provide a promising approach to development of high-stroke magnetic DMs.