Search Results (344)

Spaceborne spectrometers are key optical payloads for global and regional greenhouse gas (GHGs) monitoring. With the increasing demands for high-precision and high-efficiency monitoring, spectrometers are required to provide a wide swath, high spatial resolution, and high spectral resolution. However, existing spaceborne grating spectrometers still face a trade-off between swath width and spatial resolution. To address this issue, this paper presents the optical design and fabrication of an immersed-grating spectrometer for GHG monitoring. The proposed spectrometer achieves a swath width of 100 km and a spatial resolution of 3 km × 3 km while providing high spectral resolution. It operates in four channels centered at 0.76, 1.61, 2.06, and 2.30 μm, covering the O₂-A band and the main absorption bands of CO₂ and CH₄, with corresponding spectral resolutions of 0.04, 0.07, 0.09, and 0.10 nm, respectively. The four channels share a common slit, which reduces system volume and inter-channel spatial registration errors. Immersed gratings are used as the core dispersive elements, enabling high spectral resolution in a compact optical configuration. To correct the smile and anamorphic beam compression induced by high-angular-dispersion immersed gratings, a prism-based simultaneous correction method is proposed. Based on this method, the initial parameters of the dispersion module are determined, and the optical design of the spectrometer is completed. Large-sized immersed gratings with high groove density are precisely fabricated using holographic lithography and ion-beam etching, after which the spectrometer is aligned and tested. The test MTF at the Nyquist frequency of the spatial dimension exceeds 0.72, indicating good imaging quality. The test spectral resolution of the four channels is all better than the design value, and the maximum smile and trapezoidal distortion are both within one pixel. This spectrometer provides an effective technical solution for achieving wide-swath, high-spatial-resolution, and high-spectral-resolution GHG monitoring under constraints imposed by detector size, signal-to-noise ratio, and payload size and mass. Full article

Ultraviolet remote sensing systems generally encounter the technical limitation of insufficient effective signal energy. Optical systems featuring a lightweight and compact layout are emerging as the mainstream research and development trend in this field. Varied-line-space (VLS) gratings can simultaneously achieve effective aberration correction and beam focusing in ultraviolet spectral imaging systems, enabling fewer system components and a simplified optical layout. On this basis, the modulation mechanisms of the groove distribution of planar VLS gratings for aberration correction and dispersion manipulation in the non-vacuum ultraviolet (non-VUV) band are thoroughly investigated. We elaborate on the theories concerning the line density function of VLS gratings based on phase distribution, and implement global optimization for the parameters of holographic gratings. The overall optical performance of the grating system is evaluated via ray tracing, which verifies the capability of VLS gratings to improve spectral resolution. We further perform optical design, device fabrication, and experimental validation using VLS gratings with a central groove density of 300 lp/mm. A spectral resolution of 0.345 nm is finally realized at the central wavelength of 300 nm. This work not only enriches the fundamental theories of VLS grating systems but also demonstrates that VLS gratings can significantly boost the aberration correction performance of ultraviolet spectrometers while adopting only a small number of optical elements. The theoretical conclusions are validated by measured data, and a complementary research framework integrating theoretical analysis and experimental testing is established. This study offers novel design ideas for hyperspectral and high-spatial-resolution spectral imaging systems. Full article

Metasurfaces enable versatile wavefront control, but passive designs struggle with multichannel dynamic switching, while active approaches often introduce complexity and require external power. Here, we propose a rotation-driven multifunctional metasurface holographic encryption scheme based on a cascaded architecture of two single-layer dielectric metasurfaces. By mechanically rotating one metasurface relative to the other, dynamic switching of holographic images across multiple predefined focal planes is achieved without any external energy supply. The encryption information is encoded into a multidimensional key space, defined by three independently controllable physical dimensions: rotation angle (4 states), incident polarization (3 states), and imaging distance (3 states), offering up to 36 theoretical key combinations. These parameters constitute distinct and independently controllable dimensions within the key space, substantially enhancing resistance to unauthorized access. As a proof-of-concept demonstration, full-wave simulations confirm faithful reconstruction of four independent images under four representative key combinations at a fixed operating frequency. This passive, mechanically reconfigurable approach offers a practical and secure pathway for three-dimensional dynamic displays and holographic encryption, with obvious advantages in simplicity, cost, and integrability over active tuning methods. Full article

This paper focuses on the significant potential of specific optical non-invasive methods, such as digital holographic microscopy, digital speckle pattern interferometry, and digital holographic interferometry, as scientific and technological tools for retrieving physical and biomechanical parameters embedded in the optical phase of laser-illuminated biomedical samples. These techniques take advantage of the laser speckle phenomena observed when non-specular surfaces are illuminated, enabling whole-field measurements and reconstruction of 3D images. Their versatility in implementation and application has led to advances in various fields of research and has broadened our understanding in both the basic and applied sciences. In clinical environments, the aforementioned quantitative optical studies are particularly valuable for understanding the behavior of biological samples, as they allow precise characterization of deformations, displacements, stress, strain, refractive index, and morphological features. Applications presented span from soft to hard tissues at both micro- and macro-scales, with results obtained from vocal cords, skin tissues, melanoma cells, and teeth. Furthermore, this overview provides a general perspective of some current speckle-based approaches and their growing relevance in biomedical research. Full article

Since the invention of lasers, coherent imaging has been widely employed in digital holographic microscopy. Improving the resolution of the image field remains a key challenge for achieving high-precision measurements. However, due to the high coherence of the laser, the resolution of the wavefront at the image plane depends not only on the radius of curvature of the illumination wavefront, but also on the observation position and direction. Existing theoretical approaches, which provide only approximate calculations of the amplitude distribution of the image field, are insufficient for practical applications. In this study, a theoretical framework for calculating the complex wavefield at the image plane is established, and analytical expressions describing the spectral distribution as functions of observation position and direction are derived. The proposed theory is experimentally validated using digital holographic microscopy. The results show good agreement between theory and experiment, demonstrating that the proposed approach accurately characterizes the spectral and resolution variations in the image field. These findings provide a solid theoretical foundation for the optimal design of digital holographic microscopy systems and illumination wavefields. Full article

The pervasive contamination of aquatic environments by microplastic particles necessitates the development of rapid, cost-effective and field-deployable detection methodologies to complement established but laboratory-bound spectroscopic techniques such as Fourier-transform infrared and Raman microscopy. The demand for field-suitable methods with a broad accessibility comes from researchers themselves. In this review we systematically examine recent advances in optical methods for microplastics identification with a particular emphasis on birefringence as a key diagnostic feature of partially crystalline synthetic polymers. In particular, we analyze three complementary technological directions: liquid crystal-based sensors that exploit orientational order disruptions at interfaces for label-free microplastics detection; polarization holographic imaging combined with machine learning for high-throughput particle classification; and on-chip polarization light microscopy enabling compact and portable analyzing systems. Liquid crystal platforms demonstrate exceptional sensitivity to submicron particles and enable real-time visualization of microplastics aggregation at aqueous interfaces, though they currently lack polymer-specific chemical identification. Conversely, smart polarization holography integrated with Stokes polarimetry and deep learning algorithms achieves over 90% accuracy in distinguishing microplastics from natural particles while processing up to 10,000 particles per minute. Emerging on-chip polarized light microscopy offers a pathway toward miniaturized, low-cost devices suitable for field applications. By synthesizing insights from foundational studies, this review identifies convergent interdisciplinary trends—particularly the integration of artificial intelligence with multimodal optical imaging—and outlines persistent challenges including standardization, interference from natural organic matter, and the transition from laboratory prototypes to robust field-deployable instruments. The systematization of birefringence-based approaches aims to guide future research towards integrated monitoring systems capable of addressing water quality concerns. Full article

In situ marine particle-field observation by parallel phase-shifting digital holography (PPSDH) produces long image sequences under real deployment conditions, but exhaustive full-frame reconstruction and segmentation are computationally expensive when many frames are low contrast and particle-like targets occupy sparse regions. This paper presents a training-free two-stage selective-processing workflow for a 9521-frame coastal South China Sea PPSDH campaign. Stage 1 uses an amplitude-derived contrast metric as a campaign-specific pruning rule to form a retained-frame pool, and Stage 2 combines coarse reconstruction, candidate filtering, valid-field gating, and ROI merging for ROI-restricted reconstruction and segmentation. Stage 1 retained 6970 frames, corresponding to 73.2% of the full sequence. On a balanced 120-frame benchmark, Stage 2 achieved a spatial-support reduction ratio of 49.9% ± 12.0%, and the complete workflow provided a 5.66-fold end-to-end speedup relative to a matched full-frame baseline. The efficiency gain was accompanied by a measurable fidelity cost, with a baseline-matched correspondence rate of 0.612 and a count-based yield gap of 0.287, mainly associated with small or weak targets within the selected ROI support. These results show that the proposed workflow can support computation-aware review of real marine PPSDH particle fields by efficiently prioritizing informative frames and particle-like regions for downstream visual assessment. Full article

Accurate axial localization of microparticles is a key requirement in in-line digital holography (ILDH), particularly under noisy conditions and for weakly scattered objects. This work presents experimental and simulated benchmarking of three widely used focus metrics: maximum intensity, complex amplitude, and Kurtosis. Experimental holograms of microparticles with different diameters were recorded using a compact ILDH system, while simulated holograms of a 10 µm particle were generated. Numerical reconstruction was performed using a Fresnel convolution approach with FFT-based propagation over a range of axial distances. The performance of each focus metric was evaluated based on peak definition, robustness to coherent noise, and consistency across particle sizes and configurations. The results show that both maximum intensity and Kurtosis provide consistent and reliable axial localization, with very similar behavior across all cases. In contrast, the complex amplitude metric is more sensitive to noise and exhibits larger fluctuations in the axial response. These results indicate that simple intensity-based metrics can achieve accurate localization under moderate signal-to-noise conditions, while higher-order statistical metrics improve robustness in more challenging scenarios. This work provides practical guidelines for selecting autofocus criteria in ILDH systems for particle imaging and holographic metrology. Full article

Modern wound care is challenged by the emergence of antibiotic-resistant bacterial strains, causing the need for advanced dressing materials that provide infection control while promoting healing. Although polyacrylamide (PAAm) hydrogels are widely investigated due to their biocompatibility, their lack of intrinsic antibacterial activity and poor mechanical properties restrict their clinical use. To overcome these limitations, this study proposes a natural–synthetic hydrogel that combines PAAm with TEMPO-oxidized cellulose nanofiber (TOCNF) functionalized silver nanoparticles (AgNPs). The synthesis is performed through the polymerization of the synthetic monomer in the presence of the TOCNF–AgNPs, the nanofibrillar cellulose simultaneously serving as a reducing and stabilizing agent for AgNPs, and as a plasticizer for the PAAm network. Morpho-structural analysis of the hybrid precursor (TOCNF–AgNPs) revealed two populations of AgNPs, offering a cumulative effect between rapid bacterial penetration and a prolonged ionic reservoir, while maintaining the stability of the system. The subsequent incorporation of the hybrid into PAAm matrix resulted in tunable swelling kinetics and mechanical properties. Wettability and surface stiffness improve with the increase in hybrid content. The antibacterial effect was confirmed by a colony-counting assay for formulations with higher AgNPs content, exhibiting inhibitory metabolic activity against several pathogenic strains. These results suggest that PAAm/TOCNF–AgNPs (PTA) nanocomposites represent a promising mechanically adaptive candidate for wound-care applications. Full article

Volume phase holographic gratings (VPHGs) are high-performance dispersive elements characterized by high diffraction efficiency and low noise. When used as dispersive components in imaging spectrometers for CO₂ detection, they can significantly enhance instrument performance, detection capability, and measurement accuracy. However, for short-wave infrared (SWIR) applications requiring high dispersion and operational efficiency, traditional design approaches struggle to effectively balance the trade-offs among multidimensional diffraction performance metrics, resulting in low optimization efficiency. Furthermore, as spectrometers require dispersive elements, established fabrication methods lack robust methodologies for producing large-area VPHGs. To address these gaps, we developed both a design approach and a fabrication process for VPH gratings tailored to CO₂ detection. On the design front, we propose a novel method that integrates a multi-objective simulated annealing optimization algorithm with Kogelnik’s coupled-wave theory. The optimized gratings achieve diffraction efficiencies of 95.35% (TE polarization) and 82.21% (TM polarization) across the target spectral range, with polarization sensitivity maintained below 6.57%. For fabrication, we developed holographic plate fabrication via a blade-coating technique coupled with an optimized aging protocol. A medium-to-large aperture holographic recording and exposure system with a wavefront error better than λ/25 RMS was developed. Post-processing conditions were systematically optimized based on experimental diffraction efficiency measurements, enabling the successful fabrication of VPHGs. It is explicitly noted that the experimental validation of the fabricated VPHGs is limited to the 1.620–1.630 μm wavelength range, while the full target design range of 1.620–1.650 μm has not been experimentally verified in this work. This work provides a valuable reference for the selection of dispersive elements for next-generation CO₂ detection satellites. The designed gratings fully meet application requirements, while the established fabrication process lays a solid foundation for the production of high-performance VPHGs. Full article

Lensless digital holography provides a simple, low-cost imaging platform with a large field of view (FOV) and quantitative phase capability, making it attractive for biomedical imaging, microstructure inspection, and large area imaging. However, the achievable FOV is still limited by sensor size, and in-line reconstruction suffers from twin-image artifacts that degrade image quality. To overcome these limitations, this study proposes an extended FOV lensless digital holography method that combines hologram stitching with multi-depth phase retrieval. Multiple holograms acquired from laterally shifted FOVs are stitched to form an extended hologram, while holograms recorded at multiple axial depths are used to suppress twin-image artifacts and improve reconstruction fidelity. Experimental results show that the proposed method effectively expands the imaging area, enhances effective resolution by integrating complementary diffraction information from different FOVs, and improves image contrast and feature visibility. This approach enables extended FOV, resolution enhancement, and high-quality holographic imaging while preserving the simple lensless digital holography architecture. Full article

Non-Line-Of-Sight (NLOS) Terahertz (THz) radar 3D imaging leverages electromagnetic wave propagation characteristics such as reflection, diffraction, scattering, and penetration to detect, locate, and image hidden targets in occluded environments. It holds significant potential for applications in autonomous driving, disaster rescue, and urban warfare. However, uncertainties introduced by reflecting surfaces and occluding objects in practical NLOS scenarios, such as phase errors, aperture shadowing, and multipath effects, lead to issues like blurred imaging and increased artifacts in radar imaging. To address these challenges, this study proposes a 3D learning imaging method for NLOS THz radar based on a holographic imaging operator, leveraging the adaptive optimization properties of deep unfolding networks and prior environmental perception. First, a 3D imaging model for NLOS THz radar in the Looking Around Corner (LAC) scenario is established. A holographic imaging operator is introduced to enhance imaging efficiency and reduce computational complexity. Second, a high-precision NLOS 3D imaging network is constructed based on the Fast Iterative Shrinkage/Thresholding Algorithm (FISTA) framework. Utilizing features specific to NLOS scenes and designing algorithm parameters as functions of network weights, the method achieves high-precision and high-efficiency in the 3D reconstruction of NLOS targets. Finally, a near-field NLOS radar imaging platform operating at 121 GHz (within the sub-THz regime) is developed. Experimental validations in the LAC scenario are performed on targets, including metal letters “E”, a metal resolution chart, and a pair of scissors. The results demonstrate that the proposed method significantly improves 3D imaging precision, achieving a two-orders-of-magnitude increase in computational speed over traditional imaging algorithms. Full article

High-throughput and compact volume phase holographic (VPH) grating transmission spectrometers are widely employed in scientific research, agriculture, and industrial applications. Conventional transmission spectrometers generally adopt a fixed configuration and therefore have limitations in simultaneously achieving high spectral resolution and broad wavelength coverage. To address the limited tunability of transmission spectrometers, this work presents the theoretical analysis and experimental validation of a transmission spectrometer incorporating a novel catadioptric grating assembly, which consists of a transmitting VPH and a planar reflector. A catadioptric system is a combination of reflective (catoptric) and refractive (dioptric) elements. In the proposed configuration, a VPH grating and a plane mirror arranged at a fixed 90° angle form the catadioptric dispersion module. Synchronous rotation of this assembly enables wavelength scanning. The structure ensures that the diffracted ray along the optical axis of the imaging lens maintains the Bragg condition across the scanning range, thereby preserving maximum diffraction efficiency. The optical configuration and structural parameters of the spectrometer were theoretically derived, and a prototype spectrometer with an f-number of 1.8 employing a 2400 g/mm grating was constructed. Measurements demonstrate that, when the rotation angle is tuned from 30.5° to 50.5°, the accessible spectral range covers from 410 nm to 650 nm. Spectral response measurements using a tungsten–halogen light source confirm that the spectrometer maintains an acceptable diffraction efficiency across the entire tuning range. The measured spectral resolution is 0.1 nm at 626 nm with a 2400 g/mm grating and 0.18 nm with a 1500 g/mm grating. The spectrometer was further applied to fiber-enhanced gas Raman spectroscopy, where it successfully resolved the closely spaced Raman peaks of CH₄ and C₂H₆ that are difficult to distinguish using conventional compact spectrometers. These results demonstrate that the proposed tunable catadioptric spectrometer simultaneously provides excellent wavelength tunability and high spectral resolution. Full article

We propose a field-transformation-based framework for generating phase-only light-field holograms from a single RGB image. The method establishes an explicit pipeline from monocular scene inference to holographic wavefront synthesis, without requiring multi-view capture or task-specific hologram-network training. First, we construct a layered occlusion RGB-D model from the input image using monocular depth estimation, connectivity-based layer decomposition, and occlusion-aware inpainting, which provides a lightweight 3D prior for sparse-view rendering in the small-parallax regime. Second, we transform the rendered sparse RGB-D light field into a target complex wavefront on the recording plane through local frequency mapping, thereby bridging explicit scene geometry and wave-optical field construction. Third, we optimize the phase-only hologram under multi-plane amplitude constraints using a geometrically consistent initial phase and an error-driven adaptive depth-sampling strategy, which improves convergence stability and reconstruction quality under a limited computational budget. Numerical experiments show that the proposed method achieves better depth continuity, occlusion fidelity, and lower speckle noise than representative layer-based and point-based methods, and improves the average PSNR and SSIM by approximately 3 dB and 0.15, respectively, over Hogel-Free Holography. Optical experiments further confirm the physical feasibility and robustness of the proposed framework. Full article

Oral squamous cell carcinoma (OSCC) remains a major clinical challenge, highlighting the need for novel therapeutic strategies. Natural bioactive compounds such as curcumin (Cu) and cordycepin (Co) have shown anticancer potential; however, their effects on cancer cell morphology and behavior remain incompletely characterized. This study assessed the individual and combined effects of Cu and Co on oral squamous cell carcinoma cells (OECM-1) and normal human gingival epithelial cells (HGEpiC) over 24 and 48 h. Metabolic activity, membrane integrity, oxidative stress, apoptosis, and inflammatory responses were evaluated using MTT, LDH, ROS-H₂O₂, caspase 3/7, and NO assays. Label-free digital holographic microscopy enabled real-time monitoring of morphology, motility, and proliferation. Both compounds induced ROS-mediated cytotoxicity, but responses were notably more pronounced in OECM-1 than in HGEpiC cells. Real-time morphological profiling revealed distinct response patterns: Co primarily exerted cytostatic effects, whereas Cu induced cell shrinkage, impaired motility, and inhibited cell division. The combination treatment (CC) largely reflected Cu-driven morphological and functional changes, with Co coexisting without counteracting Cu’s effects. Taken together, these findings reveal compound-specific mechanisms of action for Cu and Co in OSCC therapy. Full article