Metal nanomaterials have been widely used to generate photoacoustic (PA) signals because of their high optical absorption characteristics. However, the PA conversion efficiency of metal nanomaterials is limited by the single-wavelength absorption at the resonant peak. To mitigate this issue, a three-layer ultrathin film containing a thin PDMS layer sandwiched between two ultrathin chromium films is proposed. This kind of film structure can attain high optical absorbance (>80%) through the visible light range (450-850 nm). The optical absorption characteristics can be easily modulated by varying the thickness of the PDMS layer. Under the same excitation condition, the PA signal generated by this film structure is twice that of an only Cr film and three times that of an only Au film. This film structure is easily fabricated and can operate with lasers having different central wavelengths or even white light sources, leading to its applications in many fields, including photoacoustic communications and audio transducers.We present a holmium-doped all-fiber master oscillator power amplifier (MOPA) system operating at 2108 nm targeting optical frequency conversion applications. The MOPA delivers pulses of 0.52 mJ energy at 10 kHz repetition rate after three amplification stages, with a close to square-shaped temporal profile of 50 ns duration, diffraction-limited beam quality and linear polarization. Challenges with achieving high gain and efficiency in the final amplification stage are discussed and attributed to quenching effects inferred from measurements of non-saturable absorption in the holmium fibers. Using this MOPA, we demonstrate a mid-IR conversion efficiency of 59% by direct pumping of a ZnGeP2 optical parametric oscillator.We investigate the topological skin effect in a ring resonator array which can be mapped into the square root of a Su-Schrieffer-Heeger (SSH) model with non-Hermitian asymmetric coupling. The asymmetric coupling is realized by integrating the same amount of gain and loss into the two half perimeters of linking rings that effectively couple two adjacent site rings. Such a square-root topological insulator inherits the properties from its parent Hamiltonian, which has the same phase transition points and exhibits non-Bloch features as well. We show the band closing points for open chain are different from that of periodic chain as a result of the skin effect. Moreover, the square-root insulator supports multiple topological edge modes as the number of band gaps is doubled compared to the original Hamiltonian. The full-wave simulations agree well with the theoretical analyses based on a tight-binding model. The study provides a promising approach to investigate the skin effect by utilizing ring resonators and may find potential applications in light trapping, lasers, and filters.We experimentally demonstrate an ultra-low-noise pre-amplification using a non-degenerate phase-sensitive amplifier (ND-PSA) with an optically dispersion-unmanaged link. Chromatic dispersion (CD) compensation is required for phase-sensitive amplification after fiber transmission. In the conventional transmitter configuration for ND-PSAs in which phase-conjugated light (idler light) is optically generated, it is necessary to optically compensate for the CD, for example, by using dispersion-compensating fibers. In this work, we propose an ND-PSA scheme using a digitally generated idler and CD pre-equalization by means of digital signal processing. We conduct an unrepeated transmission over a 200-km single-mode fiber with a 10-Gbaud 64QAM signal using the periodically poled LiNbO3-based PSA. https://www.selleckchem.com/products/740-y-p-pdgfr-740y-p.html The experimental results demonstrate that the proposed ND-PSA scheme provides a low-noise pre-amplification that outperforms the EDFA without optical CD compensation.A novel method to control the parameters of a chiral fiber grating structure is proposed. Mode couplings are controlled in real time during the twisting fabrication process. This chiral grating structure can satisfy the phase-matching condition for generating high-quality orbital angular momentum (OAM) beams, with an order mode of conversion efficiency over 99.9%. Both theoretical analysis and experimental results of this OAM mode conversion have been investigated, with good agreement. The results demonstrate a dual-OAM beam converter with a charge of ±1 for the right- and left-handed CLPGs, respectively. The high-quality OAM beam generated in this twisted single-mode fiber process may find excellent applications in optical communications.Flexible gradually tapered metal waveguides (GTMWs) are fabricated by an inner plating silver film in a polycarbonate (PC) capillary for the transmission and imaging at 0.3 THz. It was demonstrated theoretically and experimentally that GTMWs have lower transmission losses and smaller additional losses of bending, comparing with thin constant bore metal waveguides (CBMWs). Measured losses of 1.95 dB and 2.45 dB were obtained for a 1 m long GTMW with bore size varying from 2.6 mm to 1.6 mm under straight and one circle bending configuration. Measured losses were 4.48 dB/m and 7.78 dB/m for 1.6 mm bore CBMW under the same straight and bend configurations. Owing to higher energy concentration at the output, a larger penetration ability of output wave can be achieved by GTMW, which is beneficial for imaging application. A scanning imaging system was established using fabricated waveguides as the probes. Measured results show that the air slits of the order of wavelength can be clearly distinguished. An imaging system with a GTMW probe also has better performances due to lower bending loss and improved coupling efficiency.The widely used lenslet-bound definition of the Shack-Hartmann wavefront sensor (SHWS) dynamic range is based on the permanent association between groups of pixels and individual lenslets. Here, we formalize an alternative definition that we term optical dynamic range, based on avoiding the overlap of lenslet images. The comparison of both definitions for Zernike polynomials up to the third order plus spherical aberration shows that the optical dynamic range is larger by a factor proportional to the number of lenslets across the SHWS pupil. Finally, a pre-centroiding algorithm to facilitate lenslet image location in the presence of defocus and astigmatism is proposed. This approach, based on the SHWS image periodicity, is demonstrated using optometric lenses that translate lenslet images outside the projected lenslet boundaries.