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• An improved model capable of analyzing the effects of ambient gas on laser polishing is proposed. • Mass transfer, solutocapillary force, and chemical reaction are added to the model. • Convection is the main mass transfer mechanism in the molten pool, not diffusion. • The solutocapillary force always acts in the opposite direction to the melt flows. • The dissolved oxygen enhances the thermocapillary force driving the melt to flow inward. Laser polishing, as an effective surface finishing process, is significantly affected by ambient gas. Previous studies on the contribution of ambient gas to laser polishing mostly focused on experiments, but rarely on numerical simulations. Given this, this paper proposes an improved model capable of analyzing the effects of ambient gas on the laser-polished surface's morphology evolution mechanisms, by expanding an existing laser polishing model with the influences of mass transfer, solutocapillary forces, and chemical reactions. Argon and air were used as ambient gasses for comparison. Through this model, the surface morphology evolution of laser polishing in air was compared with that in argon in terms of the velocity field, temperature field, concentration field, melt surface velocity, molten pool surface profile, and surface forces. The respective contributions of chemical reaction heat, oxygen mass flux, mass transfer, and surface forces were also presented. Furthermore, the numerical model was verified on 304 stainless steel from the perspectives of polished surface roughness, molten pool depth, and oxygen element distribution. [Display omitted] [ABSTRACT FROM AUTHOR]

• Melting analysis of DNA methylation based on laser-emission in a Fabry-Pérot microcavity was proposed. • DNA molecules were distinguished by the melting temperature from the laser-based melting curves. • The method of laser slope was proposed to discriminate DNA molecules at a constant temperature. • Five mixes of methylated and non-methylated DNA samples were discriminated by the laser slope. In this paper, we first analyzed the DNA methylation by using the method of laser-based melting in a Fabry-Pérot (FP) microcavity. Pumped with an external intensity, four types of artificially synthesized DNA sequences with/without cytosine methylation in each strand were first analyzed and distinguished by the melting temperatures of the laser-based high-resolution melting (HRM) curves. Meanwhile the dependance of the laser threshold on the melting temperature for each sample was investigated; the experimental result indicates that, by optimizing the pump intensity, a lower melting temperature can be obtained for each sample. On the other hand, by setting the melting temperature at an optimized value, the samples can be distinguished by the laser behaviors above the threshold; this provides a new way for DNA analysis, and cannot be realized in the fluorescence-based melting analysis. For example, the four types of DNA samples were distinguished with an obvious difference in the laser slope coefficients when the melting temperature was set at 60 °C. Finally, five mixes of methylated and non-methylated DNAs with different mole percentages were analyzed by the laser slope coefficients. [ABSTRACT FROM AUTHOR]

Keywords: biological lasers; cell phenotyping; deep learning; laser modes; microcavities; single cells EN biological lasers cell phenotyping deep learning laser modes microcavities single cells 1 1 1 11/23/21 20211118 NES 211118 In article number 2101421, Zhen Qiao, Yu-Cheng Chen and co-workers demonstrate the biological function of complex laser modes by exploiting deep learning technology. Biological lasers, cell phenotyping, deep learning, laser modes, microcavities, single cells Brain cells extracted from rat were classified through hyperspectral imaging of cell laser modes, offering new prospects for single cell analysis and biophotonic applications. [Extracted from the article]

• Simulation and modeling on laser polishing in melting and transition regimes. • Mechanism of surface topography evolution in laser polishing is revealed. • Contributions of surface forces and material removal in laser polishing are analyzed. • Thermocapillary force affected by surface-active component results in a bulge structure on the polished surface. • Surface roughness prediction is tried through the established model with a maximum error of 14.9%. Previous studies on the mechanism of laser polishing were limited to the melting regime, this paper proposed a numerical model for the melting and transition regimes of laser polishing, which coupled heat transfer, fluid flow, and material vaporization. Based on the model, the evolution of the temperature and velocity fields of the molten pool in laser polishing was presented. And the mechanism of surface topography evolution was revealed from the perspective of surface forces (capillary force, thermocapillary force, and recoil pressure), fluid velocity, and material removal. Furthermore, the corresponding relationships between surface forces, fluid velocity, and surface topography were determined. The contributions of surface forces and vaporization front velocity in laser polishing were investigated, and the reason for the formation of the bulge structure and the influence of laser power on it were analyzed. And the velocity direction change points which have a great influence on the surface evolution were found, and the method to determine the positions of these points was proposed. Besides, the surface roughness prediction after laser polishing was tried through the numerical model, and the maximum error between the predicted results and the experimental results is 14.9%. Therefore, this model can be used to optimize process parameters. [ABSTRACT FROM AUTHOR]

A new method of surface structuring by laser remelting with the help of surface tension (mainly thermocapillary force and solutocapillary force) and volume expansion was proposed. A multiphysics coupled numerical model was proposed for this surface structuring method, in which the calculation of surface tension and solutocapillary force is improved. Using the established numerical model, the formation mechanism of the surface structure was explored from the aspects of surface tension, fluid flow, volume expansion, and surface profile evolution. The reason why the surface structure changes from a "W" shape to an "A" shape was explained, and the contributions of thermocapillary force, solutocapillary force, and volume expansion to the surface structure were investigated. The effects of laser power, scanning speed, and beam diameter on the surface profile of the surface structure were studied by experiments, which indicates that the desired surface structure can be obtained by adjusting the process parameters. All the experimental results were simulated by the established numerical model, and the simulation results are in good agreement with the experimental results, indicating that the numerical model is effective and available. • A new surface structuring by laser remelting was proposed. • The function between main chemical elements and the surface tension was established. • A multiphysics coupled model for the surface structuring was established and verified. • The contributions of thermocapillary force, solutocapillary, and volume expansion was investigated. • The formation mechanism of the surface structure was revealed. [ABSTRACT FROM AUTHOR]

We demonstrate a concatenated fuzzy matching algorithm to restrain local strong regions for the spatial beam shaping of a focused laser with quasi-near-field characteristics on the cross section in the focusing light path. Considering that the light field is redistributed according to the spatial angular spectrum after the laser beam is converged, modulations increasing with the propagation distance will decrease the smoothness of the beam. An effective algorithm for the spatial beam shaping of such focused laser is discussed by establishing the cascaded correspondence between the light field in the front stage and the later stage. The results show that the fluence contrast reduces from 37.2% to 21.4%, and the intensity modulation from 3.33:1–1.86:1. Meanwhile, the low-frequency components corresponding to local large-scale strong regions of the light field in the PSD distribution are effectively suppressed. A more regular spatial intensity profile of the focused laser is finally obtained. [ABSTRACT FROM AUTHOR]