Wavelength tunability in an all-fiber passively mode-locked laser is studied in both the anomalousand normal-dispersion regimes, by employing a fiber-type birefringence filter. An all-fiber birefringence filter composed of a polarization-maintaining fiber, an inline polarizer, and a polarization controller is implemented, exhibiting continuous wavelength tunability across the fiber-optic telecommunication band around 1560 nm, by adjusting the incident polarization state. The integration of a fiber-type filter into an all-fiber mode-locked laser enables a compact, wavelength-tunable pulsed laser that operates stably in both the anomalous- and normal-dispersion regimes of the laser cavity. The mode-locked laser exhibits maximum tuning ranges of 21.9 nm and 29.9 nm in the anomalous- and normal-dispersion regimes, with pulse durations of 810 fs and 15.7 ps, respectively.
To address the issue of projection-data truncation in photon-counting computed tomography (CT), arising from a sample exceeding the effective field of view of the detector, a dual-domain collaborative truncation-artifact correction network based on the Swin transformer is proposed. First, an edge-extrapolation module is designed in the projection domain, which employs a multiscale feature-fusion approach to extrapolate the edge information of truncated sinograms. Second, a reconstruction algorithm is utilized to simultaneously process both the truncated projection data and the extrapolated projection data, thereby achieving dual-channel information fusion. Finally, an artifact-correction module is constructed in the image domain to capture the transition from detailed features to global structural features within the dual-channel information, thus realizing the correction of truncation artifacts. Experimental results demonstrate that the proposed network can effectively extrapolate truncated data, suppress the interference of truncation artifacts on reconstructed images, and render the corrected images more consistent with real data. Compared to the state-of-the-art dual-Swin method, the results obtained by the proposed method exhibit a 6.4% improvement in peak signal-to-noise ratio (PSNR) and a 6.3% improvement in structural similarity index measure (SSIM).
We investigate how structural disorder governs ultrafast photoinduced transport in thin-film silicon, by comparing polycrystalline silicon (poly-Si) and hydrogenated amorphous silicon (a-Si:H) using optical pump-terahertz (THz) probe spectroscopy. The pump-induced THz transmittance is converted to the complex photoconductivity spectra, which are analyzed with the Drude-Smith model to quantify carrier backscattering and localization. Time-domain transients reveal distinct relaxation kinetics: Poly-Si is described by a single dominant relaxation (tau = 26.34 ps), whereas a-Si:H requires a biexponential response with a faster relaxation time (tau 1 = 1.452 ps) and a slower component (tau 2 = 38.087 ps). In the frequency domain, both materials exhibit non-Drude-like shapes with suppressed low-frequency conductivity, but the degree and evolution of the Drude-Smith backscattering parameter differ, consistent with grain-boundary-limited transport in poly-Si and defect-driven localization in a-Si:H. These results demonstrate that time-resolved THz conductivity affords a quantitative, contact-free analysis to compare disorder-controlled carrier dynamics in technologically relevant silicon phases.
Instant photography has regained attention due to its physical tangibility and analog aesthetics; However, it is still limited to two-dimensional imaging. This study presents the structural design and experimental verification of a three-dimensional (3D) instant photography system based on integral photography (IP). IP records both spatial and angular light-ray information using a micro lens array (MLA), enabling glasses-free 3D image reconstruction. Although instant photographic film provides high angular sampling density owing to its submicrometer-scale photosensitive grains, conventional IP-based systems suffer from alignment errors between the MLA and film, as well as inherent depth inversion caused by ray-geometry inversion between recording and observation stages. To address these limitations, an integrated MLA-film structure is proposed to maintain fixed geometric alignment, and a dihedral corner reflector array (DCRA) is introduced to compensate for depth inversion and achieve orthoscopic reconstruction. The structure was designed to ensure compatibility with roller-based chemical development processes. To isolate optical performance from mechanical and chemical variables, a UV-sensitive photosensitive medium was employed. The experimental results demonstrated stable motion parallax, reduced image distortion, and successful orthoscopic 3D reconstruction, confirming the feasibility of instant photography as a physical 3D recording medium.
This research presents an approach to the design, simulation, and fabrication of a controllable offaxis diffractive optical element. The primary objective is to enhance nonlinear optical systems by offering a cost-effective and versatile solution capable of operating across a range of wavelengths. Utilizing an integrated structural technique, the diffractive optical element is meticulously designed and simulated through Fourier-optics methods. Fabrication is executed using a writing laser lithography system, ensuring precision and reliability. An experimental setup is established to rigorously assess the optical performance of the fabricated diffractive optical element. The primary advantages of this off-axis diffractive optical element are compactness, durability, and an economical manufacturing process, particularly for larger dimensions. Furthermore, its versatility allows application at various wavelengths, including xrays, gamma rays, and ultraviolet light, making it an invaluable component for advanced nonlinear optical systems.
