Optics and Laser Technology最新文献

An all-optical method for precisely measuring of residual stress in the submillimeter depth of shot-peened structures is proposed, based on laser-induced Rayleigh waves. First, a finite element analysis is conducted to elucidate the correlation between Rayleigh wave velocity and surface roughness. The velocity of Rayleigh waves in a stress-relieved, shot-peened specimen is then established as a baseline, effectively eliminating the influence of microstructural alterations such as grain refinement and work hardening on the Rayleigh wave velocity. By numerically simulating velocity variations across different stress levels, the acoustoelastic constant of Rayleigh waves in TB6 titanium alloy is accurately determined. Additionally, the optimized frequency of Rayleigh waves is identified, enabling the precise measurement of average residual stress within the shot-peening depth. In this study, the complex interaction between surface roughness and microstructural changes on Rayleigh wave velocity is rigorously controlled through meticulous experimental design, ensuring accurate residual stress measurements using an all-optical approach. The average residual stress, quantified using laser-induced Rayleigh waves under varying shot-peening intensities, aligns closely with results from X-ray diffraction and blind hole drilling methods, demonstrating the high efficacy and reliability of the proposed methodology.

The large area and uniform laser-induced periodic surface structure has a wide range of industrial application potential. The effect of the laser beam scanning velocity and laser fluence on the large-area fabrication of Laser-Induced Periodic Surface Structures (LIPSS), on 50 nm thickness a-Si thin films, is investigated. The results show that the formation and crystallization changes of LIPSS structure are obviously related to the scanning speed and laser fluence. In addition to surface morphology, the crystallinity of polycrystalline silicon can also be controlled by laser parameters. Based on these results, we applied direct laser induced periodic surface structuring to drive the phase transition from amorphous silicon into polycrystalline silicon. And prepare the periodic fringe structure of polycrystalline silicon with good crystallization and regular structure. By changing the polarization direction of the incident laser, the periodic surface structure with specific orientation can be obtained, and the surface of the material can be endowed with significant optical properties. When the prepared polycrystalline silicon periodic structure samples with different orientations are put into dark field microscope, the different color effects of the samples can be observed.

Polycarbonate (PC) and cyclic olefin copolymers (COC) are extensively employed in optical lenses due to their exceptional optical properties. However, mechanical clamping forces connecting lenses to each other and barrel within the camera module assembly (CMA) can lead to image quality degradation. Laser welding of plastics has emerged as an innovative technique for addressing this issue. Picosecond laser welding has successfully achieved joints between PC to PC, PC to COC, and COC to COC under optical contact (OC) and non-optical contact (NOC) conditions. Comprehensive analyses of weld zone morphology and mechanical properties have revealed diffusion bonding as the mechanism for joint formation and brittle fracture as the mechanism for fracture. By contrasting the requirements of camera module assembly with these plastic joints, the joint bonding strength is deemed adequate. However, numerous challenges and limitations hinder the advancement of laser plastic welding within the CMA field. Pertinent suggestions have been provided to address these obstacles, including the optimization of welding parameters, utilization of a high-NA focal system, and surface polishing of materials. The implementation of improved laser welding techniques is expected to significantly contribute to the future development of CMA.

We demonstrate here high-efficiency self-frequency-shifted soliton generation in standard single-mode fiber (SMF). Pulse with 80.96-MHz repetition rate passing through a length of 5.5-m fiber, Raman soliton with an energy of as much as 4.8 nJ was generated by pump pulse with an energy of 5.7 nJ, corresponding to an efficiency of nearly 85 %. Wavelength shifting of Raman soliton is fully investigated by controlling the input pulse energy, fiber length, and polarization state, resulting over 440 nm wavelength tuning range 1600–2040 nm. As the length of SMF is shortened to 0.5 m, Raman soliton pulses with energy and pulse duration of 3 nJ, 80 fs at 1700 nm and 6 nJ, 75 fs at 1820 nm are generated respectively, and the output average power keeps stable with a root-mean-square value of 0.7 % in four hours measurement. The proposed demonstration provides an easy-to-build, stable, high efficiency tunable laser source for multiphoton imaging.

Self-filamentation of laser beams is widely used in glass scribing. However, the scribing speed is usually limited due to a small transverse damage zone of the modifications. Therefore, the processing time could be improved by forming controllable cracks. In this paper, we demonstrate a polarization-based control of cracks formed using burst regime. To the best of our knowledge, this is the first time a volumetric laser-induced crack control by polarization is reported inside fused silica. This research also includes a comparative study of MHz and GHz burst regimes on modification lengths and positions. The GHz burst is shown to be more advantageous over the MHz regime, as it allows forming more uniform modifications with longer cracks. However, both MHz and GHz bursts are eligible for controllable crack formation. At the polarization-controlled regime modification longitudinal lengths reached up to 1 mm and transverse lengths up to 32 μm. These results indicate that filamentation scribing using bursts has the potential to increase the scribing speeds up to tens of meters per second.

Obtaining high power, high beam quality, and high efficiency laser sources has always been one of the important development goals in solid-state laser technology. However, up to now, hundred-watt TEM₀₀ mode (large-volume) beams directly from simple solid-state lasers without liquid cooling are not available. To overcome these challenges, here we propose a new approach based on the principle of low thermal effect and the power superposition method. By doing so, at room temperature, a 131 W TEM₀₀ mode is obtained from the simplest Nd:YAG laser. Importantly, the laser can work stably for a long time (root mean square: 0.307 % over 3 h), and the gain medium is cooled by a fan. This demonstration promises to upgrade high-power and high beam quality applications for solid-state laser sources.

This study demonstrated a femtosecond laser dual-beam interference direct writing (DBIDW) method for fabricating high-quality nanogratings on silicon. The nanogratings had Λ/2, Λ/3, and Λ/4 periods, with Λ slightly smaller than the laser wavelength. The grating stripes exhibited extremely smooth and straight edges, with an average line edge roughness (LER) of 2.23 nm and a difference in structural orientation angle (DSOA) of 2.3°. The formation mechanism involves interference enhancement inducing nanoplasma formation in periodic stripes, while local asymmetric enhancement by surface plasmons significantly increases light intensity inside the nanogrooves. This method greatly reduces thermal effects and debris deposition, offering significant advantages for high-efficiency, low-cost, large-area nanolithography.

During laser cladding, the in-situ synthesis of ceramic particles in the coatings can further enhance the performance of the coatings. However, current research lacks a method to predict and optimize the in-situ synthesized composite coatings. Therefore, in this paper, laser power, scanning speed, powder feeding speed, overlap rate, and the content of Ti and B₄C mixed powder were used as experimental factors to optimize the powder utilization, surface flatness, and microhardness of the coatings. The random forest optimized by the osprey optimization algorithm was used as the predictive model and the unified non-dominated sorting genetic algorithm III was used for optimization. The microhardness of the optimized coatings was enhanced due to the in-situ synthesized TiB₂/TiC particles, and the particles were dispersed within the composite coating. The powder utilization of the composite coating under the optimum process parameters was 72.18%, the surface flatness was 81.96% and the microhardness was 712.3 HV_1.0. The relative errors were all lower than 3%, and the hardness was 5.76% higher than that of the substrate. Therefore, this method can provide a reference for the optimization of process parameters for in-situ synthesized composite coatings.

Laser shock interface bonding force detection technology has significant advantages in assessing the bonding strength of adhesively bonded composite structures. However, current research methods rely on dynamic monitoring of the shock process combined with post-impact microscopic imaging for damage status determination. This approach presents challenges such as a cumbersome process, difficulty in standardizing damage scales, inconsistency between laboratory and field data types and their physical meanings, and limited generalizability of test results. This paper establishes a “mass-spring-damper” response theory model for laser-shocked composite plate structures and introduces a new damage characterization parameter, R. This parameter reflects the residual vibrational energy post-impact and can serve as a threshold indicator for damage determination. By establishing a relationship between laser parameters and the R value, the model facilitates rapid identification of damage stages and quantifies internal damage status with the established threshold model. The model accuracy is validated using laser shock data from two sets of T300 composite laminates. This method addresses the challenges of direct quantification and unified assessment across parameters, providing a reliable basis for parameter selection in engineering applications.

Multicomponent plasmonic nanostructures exhibit enhanced resonant coupling and unique energy dissipation mechanisms, demonstrating out-standing application potential. However, the controllable fabrication of multicomponent plasmonic nanostructures in terms of composition, shape, and size, remains highly challenging. In this paper, we propose a method for controllable fabrication of multicomponent plasmonic nanocavity arrays through femtosecond laser directly writing. Based on the optically induced mechanical spallation effect, in-situ controllable direct writing of Au-Ag nanocavities was achieved and the size could be tuned within the range of 700 nm to 20 μm in diameter and 300 nm to 1.3 μm in height. The Au-Ag nanocavity structure showing a limit detection concentration of 10^-14 M of rhodamine (R6G) and an enhancement factor of 1.27 × 10⁸. Furthermore, the structure exhibited excellent physical and chemical stability, with a maxi-mum relative standard deviation of 3.02 % after exposure to air two months. In addition, other kinds of metal (Ag-Al) were also fabricated successfully, revealing highly universality of the fabrication method and making the method highly promising for widely applications.