In this paper, we present a remote time-based free technique for fiber-based coherence optical frequency transfer system. At the remote site, the thermal noise of the optical equipment is corrected along with the link phase noise caused by environmental effect. In this system, an 1×2 AOM is applied at the remote site, with the 1st light being used to interface with remote users while the 0th light is used to establish an active noise canceling loop. By using this technique, a 10 MHz commercial oscillator, used as a time base at the remote site, is independent of the Rubidium clock at the local site. We constructed an experimental system on a 150 km fiber spool based on this technique for verification. After compensation, the overlapping Allan deviation of the transfer link is 7.42×10-15 at 1 s integration time and scales down to 1.07×10-18 at 10,000 s integration time. The uncertainty of the optical frequency launched into the fiber link and the reference light is a few 10-19 . It greatly reduces the time-base requirements and costs of the users while not damaging transfer accuracy at the same time. Meanwhile, these results show great potential for transferring ultra-stable optical frequency signals to remote sites, especially for point-to-point users and point-to-multi-users.

This paper presents a method to expedite multi-wavelength photoelasticity for efficient stress analysis. By modulating two slightly different-wavelength illumination beams and simultaneously capturing dark-field and bright-field images, our approach acquires four essential polarized images. Spatial filtering of Fourier transforms streamlines inner stress computation, enabling multi-wavelength photoelasticity with a single detector exposure. Theoretical foundations are outlined, and proof-of-principle experiments validate feasibility with a measurement error below 6.4%. The high measurement speed, determined by the detector's frame rate, facilitates dynamic sample measurements at video frequency, offering promising advancements in materials stress analysis.

In this paper, we have experimentally demonstrated a high power and high brightness narrow-linewidth fiber amplifier seeded by an optimized fiber oscillator. In order to improve the temporal stability, the fiber oscillator consists of a composite FBG-based cavity with an external feedback structure. By optimizing the forward and backward pumping ratio, nonlinear effects and SRS-induced mode distortion of the fiber amplifier are suppressed comprehensively, accompanying with the simultaneous improvement of beam quality and output power. Furthermore, the TMI threshold is also improved by ~1.0 kW by coiling the gain fiber with a novel curvature shape. Finally, a 6 kW narrow linewidth laser is achieved with beam quality (M2) of ~1.4. The laser brightness has doubled comparing to the results before optimization. At the maximum output power,. To the best of our knowledge, it is the highest brightness narrow linewidth fiber laser based on one-stage MOPA structure.

Double cone ignition (DCI) [Zhang et al., Phil. Trans. R. Soc. A 378: 20200015 (2020)] was proposed recently as a novel path for direct-drive inertial confinement fusion (ICF) using high power lasers. In this scheme, plasma jets with both high density and high velocity are required for collisions. Here we report preliminary experimental results obtained at the Shenguang-II upgrade laser facility, employing a CHCl shell in a gold cone irradiated with a two-ramp laser pulse. The CHCl shell was pre-compressed by the first laser ramp to a density of 3.75 g/cm3 along the isentropic path. Subsequently, the target was further compressed and accelerated by the second laser ramp in the cone. According to the simulations, the plasma jet reached a density of up to 15 g/cm3, while measurements indicated a velocity of 126.8 ± 17.1 km/s. The good agreements between experimental data and simulations are documented.

Power scaling in conventional broad-area (BA) lasers often leads to the operation of higher-order lateral modes, resulting in a multiple-lobe far-field profile with large divergence. Here, we report an advanced sawtooth waveguide (ASW) structure integrated onto a wide ridge waveguide. It strategically enhances the loss difference between higher-order modes and the fundamental mode, thereby facilitating high-power narrow-beam emission. Both optical simulations and experimental results illustrate the significant increase in additional scattering loss of the higher-order modes. The optimized ASW lasers achieve an impressive output power of 1.1 W at 4.6 A at room temperature, accompanied by a minimal full width at half maximum (FWHM) lateral divergence angle of 4.91°. Notably, the far-field divergence is reduced from 19.61° to 11.39° at the saturation current, showcasing a remarkable 42% improvement compared to conventional BA lasers. Moreover, the current dependence of divergence has been effectively improved by 38%, further confirming the consistent and effective lateral mode control capability offered by our design.

We report on a high-efficiency, high-power tandem Ho:YAG single-crystal fiber (SCF) laser in-band pumped by a Tm-doped fiber laser (TDFL) at 1907 nm. In addition to the uniform heat distribution resulting from the large surface-to-volume ratio of this fiber-like thin crystal rod, the long gain region provided by the tandem layout of two SCFs enables high lasing efficiency and power handling capability. More than 100 W output power is achieved at 2.1 μm, corresponding to a slope efficiency of 70.5% and an optical-to-optical efficiency of 67.6%. To the best of our knowledge, this is the highest output power and efficiency ever reported from the SCF lasers in the 2-μm spectral range.

In this study, we investigated the influence of fiber parameters on stimulated Raman scattering (SRS) and identified a unique pattern of SRS evolution in the counter tandem pumping configuration. Our findings revealed that the SRS threshold in counter-pumping is predominantly determined by the length of the output delivery fiber rather than the gain fiber. By employing counter tandem pumping scheme and optimizing fiber parameters, a 10 kW fiber laser was achieved with beam quality M2 of 1.92. No mode instability (MI) or severe SRS limitation were observed. To our knowledge, this study achieved the highest beam quality in over 10 kW fiber lasers based on conventional double-clad Yb-doped fiber.

In this Letter, we innovatively present general analytical expressions for arbitrary n-step phase-shifting Fourier single-pixel imaging (FSI). We also design experiments capable of implementing arbitrary n-step phase-shifting FSI, and compare the experimental results, including image quality, for 3-6 steps phase-shifting cases without loss of generality. These results suggest that, compared to the 4-step method, these FSI approaches with a higher number of steps exhibit enhanced robustness against noise while ensuring no increase in data acquisition time. These approaches provide us more strategies to perform FSI for different steps, which could offer guidance in balancing the tradeoff between image quality and the number of steps encountered in the application of FSI.

The hologram, which is formed by phases coupled through cascade devices for secret information sharing, still carries a cracking risk. We propose a liquid crystal planar doublet as the information carrier, and new holograms generated by the new coupled phases when the relative displacements of the different liquid crystal layers change. The designed geometrical phases are generated by an optimized iterative restoration algorithm, and each holographic image formed by these phases is readable. This scheme achieves an increase in the capacity of the stored secret information and provides more misdirection, which is expected to have potential value in optical steganography and storage.

The existing single crystals slicing techniques result in significant material wastage, and the heightened cost of premium-quality thin disk crystals. Here we first report an approach for vertical slicing of large-size single crystal gain materials by ultrafast laser. By employing aberration correction techniques, the optimization of the optical field distribution within the high-refractive-index crystal enables the achievement of a continuous laser-modified layer with a thickness of less than 10 μm, oriented perpendicular to the direction of the laser direction. The compressed focal spot facilitated crack initiation, enabling propagation under external forces, ultimately achieving the successful slicing of a Ф12 mm crystal. The surface roughness of the crystal thin disk is less than 2.5 μm. The results illustrate the potential of low loss slicing strategy for single crystals fabrication and pave the way for the future development of thin disk lasers.