Optics letters最新文献

This study investigates the temporal absorption behavior of single-layer HfO₂, SiO₂, and anti-reflective HfO₂/SiO₂ dielectric coatings under ultraviolet irradiation at 343 nm and 355 nm wavelengths, as a function of laser pulse duration ranging from 170 fs to 10 ps. Absorptance was measured using photothermal common-path interferometry and analyzed with rate equation-based numerical models. The results revealed that classical multiphoton absorption alone cannot fully account for the observed temporal absorptance dynamics. A simplified model indicated that absorption via intermediate defect states may significantly contribute to the nonlinear optical response, depending on both the pulse duration and the intrinsic material properties.

Optical microscopy is an essential tool in fields such as biology, material science, medicine, and nanotechnology, where resolution and contrast play a crucial role in sample analysis. Dark-field microscopy is fundamental for image contrast and edge enhancement, especially for nearly transparent or nanoscale samples. Dark-field microscopy, however, usually requires a bulky and expensive microscope setup. In this work, we demonstrate a miniaturized, millimeter-sized dark-field condenser fabricated by femtosecond two-photon polymerization 3D-printing. An annular absorbing aperture and a high-numerical aperture lens are combined on a glass substrate. This condenser provides an oblique illumination of the sample, necessary for dark-field imaging. We demonstrate excellent dark-field performance of the 3D-printed dark-field condenser by imaging USAF 1951 resolution test charts and on gold disks with diameters below 500 nm. Our work paves the way for the utilization of miniaturized microscopy techniques that can be rapidly prototyped for applications in medicine or biology. This could possibly lead to entire 3D-printed microscopes with enhanced dark-field imaging capability, for example, for microfluidic chips.

In this Letter, a configuration based on anisotropic photonic time crystals (APTCs) that implements a 2-bit binary encoder and logical operations is proposed. By exploiting the angle-sensitive wave amplification effect in APTCs, a tunable angle magnification window (AMW) is formed in the angular domain. Adjusting the parameters of the two temporal slabs of the APTC enables the positional shift of the AMW while maintaining its peak amplitude. Based on this physical mechanism, NOR and AND logic functions and a 2-bit binary encoder can be configured by detecting changes of transmittance in defined regions under four input combinations. A phase-encryption system is constructed using the APTC encoder and logic device. The accuracy of the results is verified through numerical simulations employing the transfer matrix method and the finite-difference time-domain method. The approach based on APTCs facilitates parallel implementation of encoding structures and logic design, providing a platform for photonic logic devices and information encryption technologies.

Measuring backscattered light spectra from biological tissue has strong potential to identify early signs of disease and injury. However, most devices that employ this method do not quantify changes in specific microscopic biophysical properties, such as the sizes and refractive indices of organelles. We employ analytical models using Mie Theory to quantify relationships between microscopic changes in turbid media and resulting changes to mesoscopic scattering parameters (scattering coefficient μ_s(λ), anisotropy g(λ), reduced scattering coefficient μ_s^'(λ)) from 400 to 1800 nm. The spectral lineshapes of μ_s(λ) and μ_s^'(λ) differ notably, due to the wavelength dependence of g(λ). However, these discrepancies may not substantially impact the sensitivity of μ_s^'(λ) to specific micro-scale changes. For a pancreatic cell nuclei model, cancer-relevant increases in nuclear size (~28%) and refractive index (~1.7%) raised μ_s(λ) amplitude at 1000 nm by >17-fold and decreased μ_s(λ) slope from 1000 to 1800 nm by ~15%, while increasing μ_s^'(λ) amplitude at 500 nm and slope from 500 to 1800 nm by ~15-fold and 12%, respectively. Characterizing relationships between microscopic and mesoscopic scattering parameters is a key step toward using backscattered light to quantify changes in specific micro-scale tissue components.

We present an optical active perception framework that enables autonomous instrument insertion through a trocar using robot-guided multi-view imaging. A low-cost RGB-D camera provides depth-guided viewpoint planning, while 3D Gaussian Splatting (3DGS) reconstructs a high-resolution trocar model from sparse multi-view RGB images with submillimeter fidelity, overcoming the practical limitations of commercial 3D optical sensing systems, such as stereo and structured-light cameras, in this constrained surgical scenario. Integrated with a 6-DOF robotic arm, the system estimates the trocar pose and aligns the instrument for insertion. Experiments on static and motion-simulated ex vivo porcine eyes achieve consistent submillimeter positional accuracy and angular accuracy on the order of a few degrees, sufficient for safe insertion given the narrow trocar clearance. These results establish the potential of 3DGS-based optical active perception for robotic microsurgical navigation.

Chalcogenide polymeric materials have emerged as promising, cost-effective alternatives to conventional infrared materials. In this Letter, we demonstrate the fabrication of micro-optics elements using a flexible chalcogenide polymer with an extended transparency window into the long-wave infrared region. Employing this thermoset S-DADS polymer, broadband infrared micro-optical components were fabricated via casting processes. Experimental results validate their functionality in IR imaging, wavefront sensing, and mechanically tunable beam shaping, which shows their potential for diverse infrared applications.

We present a light-driven inching random laser composed of a liquid crystal elastomer body and a random lasing tip region. Under optical illumination, the composite random laser undergoes bending deformation, enabling a remote-controlled motion on flat and blazed grating surfaces. The inching random laser is optically guided to a designated target position, where the integrated random-lasing tip generates emission characterized by a bandwidth collapse and a distinct lasing threshold. The light-driven inching random laser offers a promising platform for delivering intense optical signals at a desired location.

Graded index (GRIN) lenses are essential for in vivo imaging and endoscopy. Implantable probes made from short segments of standard GRIN fiber offer important benefits over commercial GRIN lenses; however, they struggle with aberrations. This study introduces a technique that combines structured speckle illumination with compressive sensing (CS) to enable aberration-free imaging with GRIN fiber-based probes. We develop a wave-optic mode-expansion model to simulate the propagation of coherent illumination and incoherent fluorescence response in an aberrated GRIN probe. Through numerical experiments involving sequential speckle illumination and CS for image reconstruction, we achieve high-resolution, aberration-free imaging throughout the entire field of view (FOV). In contrast to standard microscopy methods, the reconstructed image quality is independent of the fiber length. The proposed method opens avenues to minimally invasive single- and multisite deep brain microscopy.

The generation of tunable narrowband pulses is increasingly being pursued in terahertz science, for example, to study the nonlinear response of individual modes of solids and molecules. Here, we extend the chirp-and-delay method to achieve collinear phase-matched difference-frequency generation in the organic crystal N-benzyl-2-methyl-4-nitroaniline (BNA-S), which results in tunable narrowband terahertz pulses. In this configuration, the fundamental frequency of a Ti:sapphire amplifier is used-eliminating the need for optical parametric amplifiers typically required for THz generation in other organic crystals. Chirped-pulse excitation suppresses multiphoton absorption in BNA, improving stability and extending crystal lifetime. The source delivers THz transients tunable from ~0.25 THz to ~2 THz with adjustable spectral width.

Optical vortices have attracted significant interest due to their distinctive topological properties and wide-ranging applications, including free-space communication, quantum information, image analysis, and micromanipulation. Vortex formation can arise from the interaction of light with structured or anisotropic media, including chiral systems. Among the most effective platforms for generating optical vortex beams are optical valves and liquid crystal cells, which leverage molecular self-organization to produce complex light fields. We show, both experimentally and theoretically, that illuminating an optical valve with a donut-shaped beam generates a vortex rosette, consisting of a low-amplitude central vortex surrounded by a ring of interacting vortex-antivortex pairs. This structure imparts a nontrivial topological charge to the transmitted light, endowing it with novel characteristics akin to those of a q-plate. To elucidate the origin of these vortex rosettes, we derive an amplitude equation from first principles, offering insight into the underlying mechanisms driving their emergence.