The diffraction theory was used to calculate the point spread function (PSF) of a typical Fresnel incoherent correlation holography (FINCH) system. It was found that the phase of the reconstructed image corresponds to the phase difference between the original points in two mutually perpendicular polarization directions. The experimental results show that the FINCH system with reasonable parameters can realize the phase-difference imaging of objects and measure the phase difference of cross-polarization directions in birefringent materials.We demonstrate a high sensitivity all-fiber spectroscopic methane sensor based on photothermal interferometry. With a 2.4-m-long anti-resonant hollow-core fiber, a 1654 nm distributed feedback laser, and a Raman fiber amplifier, a noise-equivalent concentration of $\sim4.3\;\rm ppb$ methane is achieved at the room temperature and pressure of $\sim1\;\rm bar$. The effects of temperature on the photothermal phase modulation as well as the stability of the interferometer are studied. By introducing a temperature-dependent compensation factor and stabilizing the interferometer at quadrature, signal instability of $\sim2.1\%$ is demonstrated for temperature variation from 296 to 373 K.In general, a spin-polarized light beam cannot couple its spin angular momentum (SAM) with intrinsic orbital angular momentum (IOAM) without spin reversal. Here we find that nonlinear media can give the spin-polarized photon an IOAM, as they travel in the media due to the nonlinear susceptibility along the transmission direction, which does not require spin reversal. To characterize this SAM-to-IOAM conversion process, we establish an evolution ray equation for photons carrying IOAM by reference to the Schrödinger equation. https://www.selleckchem.com/products/as601245.html We further reveal the inherent physics of such a phenomenon from a full-wave perspective and find that the vortex generation originates from the nonlinear-induced geometric phase.Differential phase optical time-domain reflectometry is subject to Rayleigh fading, which locally impedes proper phase extraction. We introduce in this Letter a reliability metric derived from the measured Jones matrix estimates of the fiber sensor to discriminate between true perturbations and false alarms caused by Rayleigh backscatter fading points. The proposed soft-decision metric is also of interest for further post-processing stages exploiting artificial intelligence based classifiers.Quantum emitters characterized by their emission colors constitute important elements in the design of modern nano-optics. Although we can change the emission colors of a quantum emitter by tailoring its chemical component, once selected, the color usually cannot be changed. It will be tempting to find out whether the emission color of an emitter could be tuned without touching its chemical component. In this Letter, we theoretically propose a strategy to externally tune the emission color of a model emitter by changing its electromagnetic environment. We found that the photonic local density of states (PLDOS) strongly affect the competition between various internal radiative and nonradiative channels, thus enabling a selective electronic state to dominate the emission spectrum. Indeed, quantitative calculations show that the emission color of a model emitter could be tuned from red to green and blue as the PLDOS increases. Moreover, due to direct correspondence between the emission color and PLDOS, the emitter can be potentially used as a sensor to characterize the local electromagnetic environment by its emission color at the nanoscale. This simple strategy may prove to be useful in the future design of various nano-optical devices.Terahertz imaging has recently attracted great attention owing to the abilities of high penetration and low ionizing damages. However, the low resolution and low contrast resulting from the diffraction limit and unwanted background illumination significantly hinder the extensive usage. In this Letter, we propose and numerically demonstrate a terahertz subwavelength imaging method capable of extracting only the edges and fine features of the targets. The underlying physics is the efficient transmission of the scattering evanescent waves related to key geometric information while blocking the propagating components. By exploiting the structurally induced plasmons in a bounded metallic waveguide, the transmission channel for evanescent waves is realized by hyperbolic metamaterials through periodically stacking dielectric layers. On this basis, high-contrast edge detection with a resolution up to $0.1\lambda$ is demonstrated at terahertz wavelengths. The proposed terahertz imaging method may find important applications in non-destructive testing, weak scattering object detection, and high-contrast microscopy.Sapphire fiber Bragg gratings (SFBGs) inscribed by using femtosecond laser point-by-point (PbP) technology typically have an extremely low reflectivity due to the limited cross-sectional area of refractive index modulations (RIMs) created in sapphire fiber. Hence, we propose and experimentally demonstrate a filamentation process for fabricating PbP SFBGs. This approach provides an efficient method for producing SFBGs at various Bragg wavelengths with a higher reflectivity, since the filament tracks could enlarge the cross-sectional area of RIMs. The influences of the pulse energy and the focal depth on the generation and morphology of the filament tracks were studied, and after optimizing these parameters, high-quality filament tracks with a length of 90 µm and a width of 1.4 µm were produced into sapphire fiber with a diameter of 100 µm. These filament tracks were precisely assembled in sapphire fiber, generating an SFBG with a reflectivity of 2.3%. The total fabrication time for this SFBG only requires $\sim1.1\;\rm s$. Subsequently, a wavelength-division-multiplexed (WDM) SFBG array consisting of five SFBGs was efficiently constructed. Moreover, the high-temperature response of the SFBG array was investigated and the experimental results showed that the SFBG array can withstand a high temperature of 1600°C. Such a WDM SFBG array could serve as quasi-distributed high-temperature sensor which will be promising in many areas, i.e., metallurgical, chemical, and aviation industries.