A diode-pumped mode-locked (ML) Tm,La:CaF2 crystal laser is reported in this paper. This laser system delivers stable continuous-wave ML pulses, achieving a maximum output power of 143 mW at a fundamental frequency of 96.2 MHz. Moreover, the signal-to-noise ratio in the stabilized single-pulse regime reaches as high as 75 dB. The central wavelengths of the laser are located at 1886.5 and 1886.7 nm, which further advances the development of ultrafast lasers in the water absorption band of 1.8–1.9 µm.

The exceptional temporal and spatial photon confinement properties of whispering gallery mode (WGM) microcavities render them ideally suitable for nonlinear frequency conversion. Here, we present a reliable packaged microcavity device with vibration isolation, air tightness, temperature adaptability, and quality factors greater than 2 billion that can serve as a compact and stable platform for soliton optical comb generation. Low-noise soliton combs can be initiated with a repetition rate of 24.98 GHz at wavelengths near 1550 nm with 4 mW threshold power. Our work provides innovative solutions for investigating and manufacturing miniature, economical, and robust microcomb devices.

In this Letter, we provide a novel maximum a posteriori probability detection-based decision-directed carrier phase estimation (MAP-DDCPE) algorithm. The introduced probability-aware maximum a posteriori probability (MAP) detection avoids the decision errors brought by an ununiform probability distribution, which enhances the phase-tracking ability for the probabilistic shaping (PS) signals. With the proposed MAP-DDCPE, we experimentally demonstrate the 96-channel transmission that delivers 40-GBaud polarization division multiplexing (PDM) PS-64-ary quadrature amplitude modulation (64QAM) signals over the 2-km nested anti-resonant nodeless fiber (NANF). We believe the PS-assisted broadband NANF transmission enabled by the MAP-DDCPE is a promising solution for large-capacity optical communication.

For bicolor regulation in laser protection compatible with visible light stealth, a metal–dielectric–enhanced reflection asymmetric Fabry–Perot structure is proposed that has high reflectance at the laser wavelength and the color control of the visible spectrum. The six-layer reflection enhancement unit is composed of an Al metal mirror, SiO2, Ta2O5, and an ultrathin Nb metal layer. The synergistic relationship between the background color and laser wavelength reflectance was analyzed and simulated. Six different colors from blue to red with high reflectance at 1064 nm laser wavelength up to 97.84% were prepared. The thin films can withstand 2535 W cm-2 power density continuous irradiation for 60 s without being destroyed. Moreover, a symmetrical structure presents the spectrum consistency from both directions, which makes the potential to be applied to the laser protective coatings. The blue symmetrical microreflector sample was prepared and sprayed on the nonplanar models to demonstrate the actual application effect. This simple and efficient scheme provides an innovative technical approach in the field of surface laser protection.

Coherent lidar (CL) addresses existing constraints in CL data products by enabling simultaneous observation of multiple meteorological parameters such as cloud height, extinction coefficient, aerosol concentration, and wind field evaluation. A detailed analysis of CL echo signals was performed at a wavelength of 1550 nm, enabling accurate measurements of cloud height and aerosol concentration. Extensive data analyses and validation tests were conducted, aligning them with a 532 nm direct aerosol lidar (AL). The assessments of the aerosol extinction coefficient demonstrated notable consistency. This underscores the potential of advanced CL for providing prolonged and consistent observations across diverse meteorological conditions.

In traditional sensing, each parameter is treated as a real number in the signal demodulation, whereas the electric field of light is a complex number. The real and imaginary parts obey the Kramers–Kronig relationship, which is expected to help further enhance sensing precision. We propose a self-Bayesian estimate of the method, aiming at reducing measurement variance. This method utilizes the intensity and phase of the parameter to be measured, achieving statistical optimization of the estimated value through Bayesian inference, effectively reducing the measurement variance. To demonstrate the effectiveness of this method, we adopted an optical fiber heterodyne interference sensing vibration measurement system. The experimental results show that the signal-to-noise ratio is effectively improved within the frequency range of 200 to 500 kHz. Moreover, it is believed that the self-Bayesian estimation method holds broad application prospects in various types of optical sensing.

We demonstrate an effective and optimal strategy for generating spatially resolved longitudinal spin angular momentum (LSAM) in optical tweezers by tightly focusing the first-order spirally polarized vector (SPV) beams with zero intrinsic angular momentum into a refractive index stratified medium. The stratified medium gives rise to a spherically aberrated intensity profile near the focal region of the optical tweezers, with off-axis intensity lobes in the radial direction possessing opposite LSAM (helicities corresponding to σ = + 1 and -1) compared to the beam center. We trap mesoscopic birefringent particles in an off-axis intensity lobe as well as at the beam center by modifying the trapping plane and observe particles spinning in opposite directions depending on their location. The direction of rotation depends on the particle size with larger particles spinning either clockwise or anticlockwise depending on the direction of spirality of the polarization of the SPV beam after tight focusing, while smaller particles spin in both directions depending on their spatial locations. Numerical simulations support our experimental observations. Our results introduce new avenues in spin–orbit optomechanics to facilitate novel yet straightforward avenues for exotic and complex particle manipulation in optical tweezers.

Holographic microscopy has emerged as a vital tool in biomedicine, enabling visualization of microscopic morphological features of tissues and cells in a label-free manner. Recently, deep learning (DL)-based image reconstruction models have demonstrated state-of-the-art performance in holographic image reconstruction. However, their utility in practice is still severely limited, as conventional training schemes could not properly handle out-of-distribution data. Here, we leverage backpropagation operation and reparameterization of the forward propagator to enable an adaptable image reconstruction model for histopathologic inspection. Only given with a training dataset of rectum tissue images captured from a single imaging configuration, our scheme consistently shows high reconstruction performance even with the input hologram of diverse tissue types at different pathological states captured under various imaging configurations. Using the proposed adaptation technique, we show that the diagnostic features of cancerous colorectal tissues, such as dirty necrosis, captured with 5× magnification and a numerical aperture (NA) of 0.1, can be reconstructed with high accuracy, whereas a given training dataset is strictly confined to normal rectum tissues acquired under the imaging configuration of 20× magnification and an NA of 0.4. Our results suggest that the DL-based image reconstruction approaches, with sophisticated adaptation techniques, could offer an extensively generalizable solution for inverse mapping problems in imaging.

The unique phase profile and polarization distribution of the vector vortex beam (VVB) have been a subject of increasing interest in classical and quantum optics. The development of higher-order Poincaré sphere (HOPS) and hybrid-order Poincaré sphere (HyOPS) has provided a systematic description of VVB. However, the generation of arbitrary VVBs on a HOPS and a HyOPS via a metasurface lacks a unified design framework, despite numerous reported approaches. We present a unified design framework incorporating all design parameters (e.g., focal lengths and orders) of arbitrary HOPS and HyOPS beams into a single equation. In proof-of-concept experiments, we experimentally demonstrated four metasurfaces to generate arbitrary beams on the fifth-order HOPS (nonfocused and tightly focused, NA 0.89), 0-2 order, and 0-1 order HyOPS. We showed HOPS beams’ propagation and focusing properties, the superresolution focusing characteristics of the first-order cylindrical VVBs, and the different focusing properties of integer-order and fractional-order cylindrical VVBs. The simplicity and feasibility of the proposed design framework make it a potential catalyst for arbitrary VVBs using metasurfaces in applications of optical imaging, communication, and optical trapping.

Two-photon microscopy provides sectioned excitation, but in practical settings, it often suffers from contrast limitations. Here, we report the observation of a strong acousto-optic modulation of two-photon excited fluorescence. Harnessing this effect yields enhanced image detail and contrast and improves optical sectioning in deep brain tissue in vivo. Ultrasound-modulation assisted multiphoton imaging (UMAMI) is compatible with standard multiphoton microscopes, without requiring changes to the optical path or image acquisition parameters.