72 research outputs found
High-power laser experiment forming a supercritical collisionless shock in a magnetized uniform plasma at rest
We present a new experimental method to generate quasi-perpendicular supercritical magnetized collisionless shocks. In our experiment, ambient nitrogen (N) plasma is at rest and well-magnetized, and it has uniform mass density. The plasma is pushed by laser-driven ablation aluminum (Al) plasma. Streaked optical pyrometry and spatially resolved laser collective Thomson scattering clarify structures of plasma density and temperatures, which are compared with one-dimensional particle-in-cell simulations. It is indicated that just after the laser irradiation, the Al plasma is magnetized by a self-generated Biermann battery field, and the plasma slaps the incident N plasma. The compressed external field in the N plasma reflects N ions, leading to counter-streaming magnetized N flows. Namely we identify the edge of the reflected N ions. Such interacting plasmas form a magnetized collisionless shock
In situ observations of freezing processes of single micrometer-sized aqueous ammonium sulfate droplets in air
The freezing processes of single micrometer-sized aqueous ammonium sulfate droplets levitated in air were observed by means of laser trapping and spectroscopy techniques. Single micrometer-sized aqueous ammonium sulfate droplets were levitated by radiation pressure in air. When a levitated droplet was cooled below 213 K, a supercooled droplet was turned from the liquid to solid state. To the best of our knowledge, this is the first observation of the freezing processes of single micrometer-sized supercooled aqueous solution droplets in air by means of laser trapping and spectroscopy techniques
Laser trapping and picosecond time-resolved spectroscopy of water droplets in air : cavity-enhanced spontaneous emission of Ru(bpy)3Cl2
Whispering gallery mode (WGM) resonances were observed in the emission spectrum of Ru(bpy)3^[2+] (bpy = 2,2'-bipyridine) in a single laser-trapped water droplet levitated in air. The emission decay profiles of Ru(bpy)3^[2+] in the water droplets comprised fast and slow decay components. The emission lifetime of the slow decay component was independent of the diameter of the droplet, and corresponded to the value in a bulk aqueous solution. On the other hand, the emission lifetime of the fast decay component decreased with decreasing the droplet diameter, which could be ascribed to the cavity-enhanced spontaneous emission. The decrease in the emission lifetime of the fast decay component as a function of the droplet diameter was explained on the basis of cavity quantum electrodynamic (QED) effects. It was shown that the mode characteristic of WGM resonances and the enhancement factor of the radiative rate of Ru(bpy)3^[2+] were controlled by the size of the water droplet
In situ Quantification of Ammonium Sulfate in Single Aerosol Droplets by Means of Laser Trapping and Raman Spectroscopy
Noncontact levitation in air of single micrometer-sized water droplets containing ammonium sulfate was successful by a laser trapping technique. The trapping laser beam was also used simultaneously as an excitation light source for the Raman spectroscopy of trapped droplets. Raman scattering of the symmetric stretching vibration of the SO42− anion and the OH stretching vibrations of H2O were observed at 980 and 3420 cm−1, respectively. The intensity ratio of these two Raman peaks was linearly proportional to the ammonium sulfate concentration in water. Therefore, the in situ quantification of ammonium sulfate in single aerosol droplets was achieved by means of laser trapping and Raman spectroscopy. To the best of our knowledge, this study is the first experimental observation of the independence of ammonium sulfate concentrations of aerosol water droplets to those of the mother solutions under constant relative humidity conditions.This research was supported by JST, PRESTO and Grand-in-Aid for Scientific Research (A) (No. 23245015) from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan
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