Ultra-low threshold lasing in silica whispering-gallery-mode microcavities with Nd³⁺:Gd 2 O 3 nanocrystals

WGM microresonators: sensing, lasing and fundamental optics with microspheres

“…For example, Yang and Vahala [25] used the sol-gel method to cover the surface of SiO 2 microspheres with a 1-μm thick erbium-doped layer from which 1530-nm lasing was observed with a threshold of 26 μW. Recently, Takashima et al [84] showed that by overcoating the sol gel layer with a layer of SiO 2 to a total thickness of 200 nm the coupling coefficient of the lasing emission into selected WGM can be increased from 0.039 to 0. old of 65 nW at 1050 nm was observed from a SiO 2 sphere coated with neodymium-doped gadolinium oxide nanocrystals [85]. In another novel approach, a SiO 2 microsphere was coated with a layer of erbium-doped phosphate glass.…”

On-chip whispering-gallery-mode microlasers and their applications for nanoparticle sensing

“…Rare-earth ions (e.g., Er 3+ , Nd 3+ , Yb 3+ , etc) and fluorescent dyes (e.g., rhodamine and Nile red) have been widely used as dopants in WGM resonators. They can be incorporated into the WGM resonator in different ways such as ion implantation 31,32 , coating by dipping a fabricated resonator in a solution with gain dopants [28][29][30] or by fabricating the resonator from an active medium doped substrate 33 .…”

“…The gain medium can be incorporated into resonator structures in three different ways: directly fabricating the resonator from an optically active material 26,27 , coating a passive resonator with an optically active gain medium [28][29][30] , and doping the passive resonator with gain medium using ion implantation 31,32 . An active resonator can operate either below or above the lasing threshold.…”

“…Optical microcavities sustaining Whispering Gallery Modes (WGMs) have gained an increasing popularity in developing state-of-the-art technologies ranging from sensing 1-24 , microlasers [25][26][27][28][29][30][31][32][33] , and modulators and filters for optical field [34][35][36][37][38][39][40] to cavity quantum electrodynamics 41,42 and opto-mechanics [43][44][45] . In a WGM resonator light is confined along the circular boundary of the cavity via total internal reflection.…”

Laser emission in Nd3+doped barium–titanium–silicate microspheres under continuous and chopped wave pumping in a non-coupled pumping scheme

“…The first laser action in a solid-state sphere was demonstrated by Baer [8] using Nd:YAG spheres with a diameter of 5 mm. Recently, laser emission has been achieved at visible and NIR wavelengths on various rare earth doped glass microspheres, from cryogenic [9] to room temperature in silica [10,11], ZBNA [12], or phosphate [13] glasses, using Nd 3+ or Er 3+ ions as gain dopant.…”