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[1] Snow particle shape is an important factor affecting the development of blowing snow. In this paper, we established a numerical model of blowing snow development and compared the changes in numbers of endurance spherical, ellipsoidal, star, hexagonal prism, and cylindrical snow particles in the air with time and their transport rates with time and height during the development. The following are the major conclusions.(1) The effects of snow particle shapes on the numbers of endurance snow particles in the air and the transport rates of snow vary so dramatically, even in a few orders of magnitude, that snow particles should not be simplified as spheres or ellipsoids in simulation. (2) In the logarithmic wind field, the potential energy of spherical snow particles obtained from wind at higher heights is much greater than that of star snow particles at lower heights. Thus, the snow particles with greater energy can eject more snow particles when precipitating to the snow bed. (3) The five snow particles differ in their duration to reach dynamic equilibrium but not in the variation of the numbers of endurance snow particles in the air and the snow transport rates with time. (4) At dynamic equilibrium, the number of endurance snow particles in spherical, ellipsoidal, and star shapes and their heights and transport rates with time are at least one order of magnitude larger than those of the endurance snow particles in hexagonal prism and cylindrical shapes.

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Vacuum ultraviolet (VUV) lasers have demonstrated great potential as the light source for various spectroscopies, which, if they can be focused into a small beam spot, will not only allow investigation of mesoscopic materials and structures but also find application in the manufacture of nano-objects with excellent precision. In this work, we report the construction of a 177 nm VUV laser that can achieve a record-small (~0.76 μm) focal spot at a long focal length (~45 mm) by using a flat lens without spherical aberration. The size of the beam spot of this VUV laser was tested using a metal grating and exfoliated graphene flakes, and we demonstrated its application in a fluorescence spectroscopy study on pure and Tm3+-doped NaYF4 microcrystals, revealing a new emission band that cannot be observed in the traditional up-conversion process. In addition, this laser system would be an ideal light source for spatially and angle-resolved photoemission spectroscopy.

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An analytical method to validate local thermodynamic equilibrium (LTE) in laser-induced plasmas is reported in this article. A more universal and general than Maxwellian electron energy distribution function (EEDF) is...

Er3+-sensitized upconversion nanoparticles (UCNPs) have attracted great attention due to their tunable upconversion (UC) emissions, low cytotoxicity, high resistance to photobleaching and especially multiple effective excitation wavelengths. However, detailed energy conversion between Er3+ and Tm3+ ions in Y2O3 UCNPs is still a problem, especially under multi-wavelength and variable pulse width excitation. In this work, we successfully fabricated a series of Er3+-sensitized Y2O3 nanocrystals by a spray flame synthesis method with a production rate of 40.5 g h−1. The as-prepared UCNPs are a pure cubic phase with a mean size of 14 nm. Excited by both 980 and 808 nm lasers, the tunable upconversion luminescence (UCL) from Er3+ ions was achieved by increasing the Er3+ doping concentration, co-doping Tm3+ ions and extending excitation pulse-width. The investigations of the lifetimes and the laser power dependence of UC emissions further support the proposed mechanism, which provides guidance for achieving effective color control in anticounterfeiting and multiplexed labeling applications. In addition, the red UC emission at about 5 mm beneath the tissue surface was observed in an ex vivo imaging experiment under the excitation of 808 nm laser, indicating that the Y2O3:Er3+/Tm3+ UCNPs have great prospects in further biological applications.

We report on frequency down-conversion of dual-wavelength (DW) Raman fiber laser in a periodically poled lithium niobate-based optical parametric oscillator. The DW pump source was fixed at 1060 and 1111 nm that was obtained based on stimulated Raman scattering effect by combining a home-made linearly polarized 1060-nm fiber laser and 137m-long polarization-maintaining passive fiber. The total pump power went through three stages, in the latter two of which the 1111-nm wave appeared. In the entire experiment, the 1060-nm pump beam achieved parametric oscillation and generated 1626-nm signal beam and 3056-nm idler beam. The 1111-nm pump beam generated 3503-nm idler beam based on difference frequency generation (DFG) between itself and 1626-nm signal beam in the second stage. With power enhancement, it built independent parametric oscillation in the third stage and generated 1621-nm signal beam as well as 3530-nm idler beam. The DW idler power ranged from 3.94 to 7.78 W in the latter two stages. The power and efficiency characteristics in frequency conversion processes of 1060-and 1111-nm pump beams were also analyzed separately.