Bermanmccormick3193

A near-infrared spectrometer based on offset fused multimode fiber (MMF) is investigated in this study. see more The light spectrum is recovered by analyzing the speckle images when light is passing through the MMF. In order to generate adequate speckles, a polarization maintaining fiber (PMF) and a 30 cm long MMF are fused with a vertical offset. Seven different offset displacements are implemented in the fiber fusion. The follow-up experiments show that the fiber offset fusion has a significant influence on the spectral correlation and the resolution. Larger offset fusion can excite more high-order modes in the MMF, and it greatly improves the spectrometer's performance. The simulation results also show that more modes are excited in MMF, and the increase of mode number leads to lower correlation coefficients of the neighboring spectral channels. However, large offset fusion increases the fusion and the insertion loss of the whole system, which may bring difficulties in the low-light cases. In addition, an image denoising algorithm based on dynamic threshold filtering and a spectral reconstruction algorithm originated from complete orthogonal decomposition were used to remove the speckle pattern noise and recover the spectrum. The final speckle-based spectrometer has a spectral resolution of 0.6∼0.016nm depending on the different offset fusions.An efficient method is proposed to measure the topological charge (TC) of terahertz (THz) vortex beams with a focal hyperbolic (FH) lens at 0.1 THz. The FH lens is designed and fabricated by 3D printing. The diffraction fringes acquired in the focal plane of the FH lens can judge the number and sign of the TC. Furthermore, after the horizontal or vertical measurement curve is recorded by rotating the FH lens to a suitable angle, the TC value can then be simply and effectively identified. The TC value of the experiment measurement reaches 5. The experiment results are in excellent accord with the simulation.We report on a temperature sensor based on an optical fiber with nanostructured cladding fabricated by graphene nanoparticles (G-NPs) deposited onto a chemically etched no-core fiber (NCF). The basic structure of this sensor comprises a single-mode-no-core-single-mode (SNCS) fiber section concatenation. The sensing head is the NCF segment where the modal interference is highly sensitive to temperature variations. The influence of the NCF diameter on the sensitivity of the sensor has been investigated. The obtained results revealed that the sensor with an etched NCF diameter of 60 µm coated with G-NPs embedded in polyvinyl alcohol exhibits a maximum sensitivity of -0.104nm/∘C in the temperature range of 25-235°C, which is approximately six times higher than that of the basic structure without coating. To the best of our knowledge, this is the first demonstration of a temperature sensor based on an etched NCF coated with graphene-polyvinyl alcohol thin film.Oceanographic lidar can provide remote estimates of the vertical distribution of suspended particles in natural waters, potentially revolutionizing our ability to characterize marine ecosystems and properly represent them in models of upper ocean biogeochemistry. However, lidar signals exhibit complex dependencies on water column inherent optical properties (IOPs) and instrument characteristics, which complicate efforts to derive meaningful biogeochemical properties from lidar return signals. In this study, we used a ship-based system to measure the lidar attenuation coefficient (α) and linear depolarization ratio (δ) across a variety of optically and biogeochemically distinct water masses, including turbid coastal waters, clear oligotrophic waters, and calcite rich waters associated with a mesoscale coccolithophore bloom. Sea surface IOPs were measured continuously while underway to characterize the response of α and δ to changes in particle abundance and composition. The magnitude of α was consistent with the diffuse attenuation coefficient (Kd), though the α versus Kd relationship was nonlinear. δ was positively related to the scattering optical depth and the calcite fraction of backscattering. A statistical fit to these data suggests that the polarized scattering properties of calcified particles are distinct and contribute to measurable differences in the lidar depolarization ratio. A better understanding of the polarized scattering properties of coccolithophores and other marine particles will further our ability to interpret polarized oceanographic lidar measurements and may lead to new techniques for measuring the material properties of marine particles remotely.To continuously monitor, identify, and classify a wide range of areas all day and satisfy the hyperspectral remote sensing requirements in disaster reduction, environment, agriculture, forestry, marine, and resource areas, the authors participated in a pre-research program for full spectrum hyperspectral detection in geostationary orbit. As part of the program, the authors designed a cryogenic infrared spectrometer working at the diffraction limit. Such spectrometer complied with prism dispersion, exhibiting a 120 mm long slit, 2.5-5 µm band range, and 50 nm minimum spectral resolution. The spectrometer should overtake a temperature variation of 143 K for its assembly temperature at 293 K and the working temperature at 150 K. Low-temperature invar and carbon fiber were adopted as the framework material. The spectrometer was composed of two reflective Zerodur mirrors and one CaF2 Fery prism. Compensation mounts were developed for the reflective mirrors, while a spring-loaded autocentering cryogenic lens mount was designed for a CaF2 prism. CaF2 material exhibits a large linear expansion coefficient, making its mount difficult to design. The alignment requirements of the system were described, and the calculations that ensure the lenses undergo both appropriate stresses and temperature differences were presented. Structural thermal optical performance analysis was also conducted to assess the degradation in optical performance caused by temperature variation to verify the overall optomechanical design.