Three-dimensional sensing of arbitrarily shaped nanoparticles by whispering gallery mode resonators.

Whispering-gallery-mode (WGM) microresonators are a promising platform for highly sensitive, label-free detection and probing of individual nano-objects. Our work expands these capabilities by providing the analysis tools required for three-dimensional (3D) characterization of arbitrarily shaped nanoparticles. Specifically, we introduce a theoretical model that describes interactions between nanoparticles and WGM resonators, taking into account effects that were often not considered, such as the elliptical polarization of the transverse-magnetic (TM) mode, the possible non-spherical shape of the nanoparticle, its finite size, and the open-system nature of the modes. We also introduce a self referencing measurement method that allows the extraction of information from measurements done at arbitrary positions of the nanoparticles within the WGM. We verify our model by experimentally probing a single Tungsten-disulfide (WS2) nanotube with a silica microtoroid resonator inside a scanning electron-microscope (SEM) and perform 3D characterization of the nanotube.

Analysis of continuous wave diode pumped cesium laser with gas circulation: experimental and theoretical studies.

Analysis of the operation of flowing-gas low power DPALs is crucial for designing high power devices. In particular, the comparison between the measured and calculated temperature rise in the laser cell makes it possible to estimate the contribution of the quenching of the alkali atoms electronic states to the gas heating. Here we report on an experimental and theoretical study of continuous wave flowing-gas Cs DPAL with He and CH4 buffer gases, flow velocities of 1-4 m/s and pump powers of 30-65 W. In the calculations we used a 3D computational fluid dynamics model, solving the fluid mechanics and kinetics equations relevant to the laser operation. Maximum CW output power of 24 W with a slope efficiency of 48% was obtained. The experimental and theoretical values of the power and gas temperature are in good agreement. The lasing power was not affected by the flow velocity at this range of pump power and the gas temperature rise was only several degrees. It was found that the best agreement between the measured and calculated temperature rise is achieved for quenching cross-section ~0.05 Å2.

Flowing-gas diode pumped alkali lasers: theoretical analysis of transonic vs supersonic and subsonic devices.

We examine transonic diode pumped alkali laser (DPAL) devices as a simpler alternative to supersonic devices, suggested by B.D. Barmashenko and S. Rosenwaks [Appl. Phys. Lett. 102, 141108 (2013)], where complex hardware, including supersonic nozzle, diffuser and high power mechanical pump, is required for continuous closed cycle operation. Three-dimensional computational fluid dynamics modeling of transonic (Mach number M ~0.9) Cs and K DPALs, taking into account the kinetic processes in the lasing medium is reported. The performance of these lasers is compared with that of supersonic (M ~2.5) and subsonic (M ~0.2) DPALs. For Cs DPAL the maximum achievable power of transonic device is lower than that of supersonic, with the same resonator and Cs density at the laser section inlet, by only ~3% implying that supersonic operation mode has only small advantage over transonic. On the other hand, for subsonic laser the maximum power is by 7% lower than in transonic, showing larger advantage of transonic over subsonic operation mode. The power achieved in supersonic and transonic K DPALs is higher than in subsonic by ~80% and ~20%, respectively, showing a considerable advantage of supersonic device over transonic and of transonic over subsonic.