Evaporation of levitating microdroplets containing nanoparticles: luminescent Gd2O3:Er3+, illumination with 805 nm laser from below via optical fiber

Microdroplets of suspension were levitated in a linear quadrupole trap and studied similarly as described e.g. in Y. Shopa et al., JQSRT 296 (2023), but illumination with an 805 nm diode laser (CW, ~1.5 W), which excited luminescence by up-conversion, was provided (vertically) from below via a 200 micrometer-core fiber for circularization. Its polarization was p. In some experiments, the droplet was additionally illuminated with a 512 nm diode laser with p polarisation. The suspended phase consisted of nanoparticles of Gd2O3:Er3+ of several concentrations. The continuous phase consisted of diethylene (2EG). Ther was also experiment on pure tetraethylene (4EG) glycol for comparison. In several experiments the 805 nm laser power was modulated. The data is divided into the folders correspondingly. Two groups of spectral lines were (usually) visible (green (stronger) and red). We followed the temporal evolution of several selected lines, both in luminescence and in scattering at right angle (usually 538, 548, 553, 562, 633, 654, 661, 675, 682, 783, 806 nm): files *-Spectra.csv, where * (in hh_mm_ss format) always denotes the time of measurement file creation. Simultaneously the shadow image of the droplet was recorded (non-coherent light, 633 nm LED) - in some cases, a movie: *_Shadow-*.avi is provided. The droplet radius was measured by fitting an ellipse to the shadow edge. The ellipse parameters temporal evolution are stored in *-Shadow.pdf files: time, mean diameter (mean of the ellipse axes), long axis rotation, X and Y of the centre, long and short axis, border length, X and Y of “the centre of mass” of the border, fitting error. The microdroplet's vertical position was stabilised with a DC field. The corresponding voltage variation and other stabilisation system parameters are stored in *.csv files: KeyStab: 0 – stabilisation off, 2 – on, k_PID – proportionality parameter of the software voltage regulator, freq – trapping AC field frequency. In some cases, partially concurrently light was collected at a right angle with a PMT for the green 512 or 806 nm laser. The photon count rate is stored in *-CRM.csv files. Time stored in corresponding files was synchronised. In-focus movies (see readme.txt for details) of the evaporating microdroplet were recorded for certain experiments to illustrate its evolution – no synchronisation is available. It must be kept in mind that the observed image is for the most part laser speckle. The "Laser on/off" pertains to the 806 nm laser. Further details can be found in the readme.txt files in the corresponding folder. (No)_th_spectrum.csv represents the ith recorded spectrum from the corresponding experiment. The parameters of the Gd2O3:Er3+ samples can be found in the .ppt file.

悬浮液微滴被囚禁于线性四极阱中，研究方法参照Y. Shopa等人于2023年发表于《JQSRT》第296卷的相关工作。本次实验采用805 nm二极管激光器（连续波，功率约1.5 W）进行照明，该激光器通过上转换过程激发发光，照明光束经200 μm芯径光纤从下方垂直入射以实现光斑圆形化，其偏振态为p偏振。
部分实验中，还会额外使用512 nm二极管激光器对微滴进行照明，其偏振态同样为p偏振。
分散相为不同掺杂浓度的Gd₂O₃:Er³⁺纳米颗粒，连续相为二甘醇（2EG）。此外还开展了纯四甘醇（4EG）的对照实验。
部分实验中对805 nm激光器的功率进行了调制，相关数据按实验分组存储于对应文件夹中。
实验中通常可观测到两组光谱谱线：强度较高的绿光波段谱线与红光波段谱线。我们追踪了若干选定谱线的时间演化过程，涵盖发光与直角散射信号两类，涉及的波长通常为538、548、553、562、633、654、661、675、682、783、806 nm。相关光谱数据存储于*-Spectra.csv文件中，其中通配符*采用hh_mm_ss格式，代表数据文件的创建时刻。
实验同时记录了微滴的阴影图像（采用非相干光，即633 nm LED光源），部分实验还提供了对应视频文件，格式为*_Shadow-*.avi。通过将椭圆拟合至微滴阴影边缘来计算微滴半径，椭圆参数的时间演化数据存储于*-Shadow.pdf文件中，包含的参数包括：测量时刻、平均直径（椭圆两轴的平均值）、长轴旋转角、图像中心的X/Y坐标、长轴与短轴长度、阴影边缘周长、阴影边缘的质心X/Y坐标以及拟合误差。
实验通过直流电场稳定微滴的垂直位置，相关电压变化数据与稳控系统的其他参数存储于*.csv文件中，其中各参数含义为：KeyStab：0代表未开启稳控，2代表开启稳控；k_PID为软件电压调节器的比例参数；freq为囚禁交流电场的频率。
部分实验中，还通过光电倍增管（PMT）同步采集了512 nm或806 nm绿光激光器的直角散射光信号，光子计数率数据存储于*-CRM.csv文件中，各对应文件中的时间戳已完成同步。
部分实验中录制了蒸发微滴的焦内视频，详细说明参见对应文件夹中的readme.txt文件，该视频用于展示微滴的演化过程，未进行时间同步。需要注意的是，观测到的图像绝大部分为激光散斑（laser speckle）。文中提及的“激光器开启/关闭”指的是806 nm激光器的工作状态。
更多详细信息可查阅对应文件夹下的readme.txt文件。(No)_th_spectrum.csv文件代表对应实验中第i次记录的光谱数据。Gd₂O₃:Er³⁺样品的相关参数可从同名.ppt文件中获取。