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Single-atomic-layered materials are important for future electronics. They allow optoelectronic devices to be fabricated at the single-atomic layer level. A single-atomic-layered two-dimensional (2D) transition metal dichalcogenide (TMD) film is usually composed of randomly orientated single-crystalline domains, and the size distribution of the domains on a large-area film has a significant impact on the applications of the film, but the impact is difficult to characterize. We report an approach to evaluate the size of the single-crystalline domains by measuring the second-harmonic generation divergence caused by the domains of different orientations. Using this method, domain size mapping on an 8×8mm2 region of a continuous MoS2 film is achieved. This method provides a fast and efficient way of domain size characterization across a large area in a non-destructive and transfer-free manner for single-atomic-layered TMD films.Synthetic aperture radar can measure the phase of a microwave with an antenna, which cannot be directly extended to visible light imaging due to phase lost. In this Letter, we report an active remote sensing with visible light via reflective Fourier ptychography, termed coherent synthetic aperture imaging (CSAI), achieving high resolution, a wide field-of-view (FOV), and phase recovery. A proof-of-concept experiment is reported with laser scanning and a collimator for the infinite object. Both smooth and rough objects are tested, and the spatial resolution increased from 15.6 to 3.48 µm with a factor of 4.5. The speckle noise can be suppressed obviously, which is important for coherent imaging. Meanwhile, the CSAI method can tackle the aberration induced from the optical system by one-step deconvolution and shows the potential to replace the adaptive optics for aberration removal of atmospheric turbulence.We report on the use of a 61 beamlets coherent beam combination femtosecond fiber amplifiers as a digital laser source to generate high-power orbital angular momentum beams. Such an approach opens the path for higher-order non-symmetrical user-defined far field distributions.Low-loss conversion among a complete and orthogonal set of optical modes is important for high-bandwidth quantum and classical communication. In this Letter, we explore tunable impedance mismatch between coupled Fabry-Perot resonators as a powerful tool for manipulation of the spatial and temporal properties of optical fields. In the single-mode regime, frequency-dependent impedance matching enables tunable finesse optical resonators. Introducing the spatial dependence of the impedance mismatch enables coherent spatial mode conversion of optical photons at near-unity efficiency. We experimentally demonstrate a NIR resonator whose finesse is tunable over a decade, and an optical mode converter with efficiency >75% for the first six Hermite-Gauss modes. We anticipate that this new perspective on coupled multimode resonators will have exciting applications in micro- and nano-photonics and computer-aided inverse design.Many optoelectronic devices embedded in a silicon photonic chip, like photodetectors, modulators, and attenuators, rely on waveguide doping for their operation. However, the doping level of a waveguide is not always reflecting in an equal amount of free carriers available for conduction because of the charges and trap energy states inevitably present at the Si/SiO2 interface. In a silicon-on-insulator technology with 1015cm-3p-doped native waveguides, this can lead to a complete depletion of the core from free carriers and to a consequently very high electrical resistance. This Letter experimentally quantifies this effect and shows how the amount of free carriers in a waveguide can be modified and restored to the original doping value with a proper control of the chip substrate potential. A similar capability is also demonstrated by means of a specific metal gate integrated above the waveguide that allows fine control of the conductance with high locality level. This paper highlights the linearity achievable in the conductance modulation that can be exploited in a number of possible applications.Phase retrieval is a numerical procedure concerned with the recovery of a complex-valued signal from measurements of its amplitude. We describe a generalization of this method for multi-wavelength data acquired in a coherent diffractive imaging experiment. It exploits the wavelength-dependent scaling of the support domain to recover separate reconstructions for each wavelength, providing new possibilities for coherent diffractive imaging experiments. Limitations on the number of wavelengths are discussed through adaptation of the constraint ratio, and the method's performance is investigated as a function of the source spectrum, sample geometry, and degree of complexity through numerical simulations.The physical properties of each transducer element play a vital role in the quality of images generated in optoacoustic (photoacoustic) tomography using transducer arrays. Thorough experimental characterization of such systems is often laborious and impractical. A shortcoming of the existing impulse response correction methods, however, is the assumption that all transducers in the array are identical and therefore share one electrical impulse response (EIR). In practice, the EIRs of the transducer elements in the array vary, and the effect of this element-to-element variability on image quality has not been investigated so far, to the best of our knowledge. We hereby propose a robust EIR derivation for individual transducer elements in an array using sparse measurements of the total impulse response (TIR) and by solving the linear system for temporal convolution. Thereafter, we combine a simulated spatial impulse response with the derived individual EIRs to obtain a full characterization of the TIR, which we call individual synthetic TIR. Correcting for individual transducer responses, we demonstrate significant improvement in isotropic resolution, which further enhances the clinical potential of array-based handheld transducers.Light absorption by in-water suspended natural particles in the near-infrared radiation (NIR; 780-3000 nm) region has received little attention. Minerogenic matter is thought to be one source for NIR light absorption in aquatic environments. Here, mass-specific particulate light absorption coefficients of several particulate single minerals and mineral samples for the spectral range of 200-2500 nm are presented. The current methodology allows very sensitive measurements of particle suspension with a detection limit of about 2×10-6m2g-1 for the mass-specific absorption coefficient. Except for one, all mineral materials examined possessed significant light absorption throughout the full spectral range considered. The spectra revealed absorption features of specific elements (like iron) and from water structures (H2O, O-H bonds) in the mineral or crystal structure that have been known from reflectance measurements of minerals. The specific absorption in the NIR was as high as 0.02m2g-1 for laterite earths samples, but also below the detection limit for a steatite sample in a narrow spectral region (1600-1800 nm). The specific absorption by mineral particles in the NIR was, hence, highly variable from strong absorbing black minerals (magnetite) to low absorbing white clays. The information in the absorption coefficient spectrum can be used not only to identify specific mineral in natural particle assemblages but also to quantify their contribution to total particulate absorption in the NIR.Laser triangulation method is widely used in online precision measurement owing to its advantages of being fast, accurate, and dynamic, and having large-scale measurement capability. To improve the accuracy of laser triangulation, the scan depth, inclination angle, rotation angle, and deflection angle are defined. Then, a spatial pose error model and an experimental model for laser measurement error are established. Next, error analysis experiments are conducted, and the influence of spatial pose parameters on the error is analyzed. Further, error proofreading experiments on the surface characteristics of the measured workpiece, including the material, surface roughness, and color, are completed, and their influences on the error are analyzed. Based on the experimental data, an error correction model based on support vector regression is established. Measurement strategies are formulated considering multi-factor constraints such as optical path interference, mechanical interference, scan depth of field, measurement angle, and measurement path. The tooth profile of a cycloid gear is taken as the measurement object, then the measurement path planning is performed, and the error correction model is used to correct the measured data. The accuracy of the results agrees well with the result of a fully automatic computer numerical control (CNC)-controlled P 65 precision measuring center.We present a simple and robust technique for measuring the nonlinear refractive index. The principle is based on an iterative phase retrieval algorithm with a pump-probe system. Different strong phase modulations are intentionally introduced into the probe beam, and corresponding diffraction intensity patterns are recorded. The recordings are used in the phase retrieval algorithm to reconstruct the pump-induced phase on the probe beam. The nonlinear refractive index is then extracted from the reconstructed phase. The reconstruction method offers a straightforward procedure and a simple lensless setup. Simulations validate the proposed method. The effects of different characteristics of the pump and probe beams on the quality of reconstructions are investigated. The obtained results demonstrate that the reconstructions are accurate even for the probe beams with complex-valued fields and non-Gaussian pump beams; it removes the requirement for smooth fields of the pump and probe beams. The validity of the method in noisy conditions is also shown.An all-subwavelength grating waveguide-based sensing structure for figure of merit (FOM) improvement on a silicon-on-insulator platform is proposed and demonstrated. this website Four racetrack resonators are applied to narrow the spectrum from the drop port of a single racetrack resonator for lower full width at half-maximum, and the FOM is therefore higher through the spectrum-narrowing operation. Numerical simulation and analysis illustrate that the proposed structure is able to raise the FOM more than twice compared to a single racetrack resonator, and a high FOM of 1850.57/refractive index unit is achieved.In this paper, a study is made of the refractive index structure parameter Cn2, as derived from angle-of-arrival (AOA) measurements made on the beam after propagation along a 16 km slant path across the Chesapeake Bay. These measurements are compared with Cn2 estimates derived from the Navy Atmospheric Vertical Surface Layer Model (NAVSLaM), which are based upon prevailing meteorological conditions. Correlation coefficients for the reported data vary between 0.64 and 0.9. Despite the Chesapeake Bay theoretically being a difficult location for employing a Monin-Obukhov similarity theory-based model such as NAVSLaM, the agreement between the AOA Cn2 measurements and the NAVSLaM Cn2 estimates was, in many cases, good. A possible explanation of this agreement between the modeled and measured Cn2 values is that the large air-water temperature differences encountered provided such strong forcing for the NAVSLaM model that any potential violations of the Monin-Obukhov similarity theory assumptions had only a secondary influence on the Cn2 estimates.
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