Microlasers have experienced tremendous development in the past decade and become an essential part in laser evolution, as miniature lasers provide strong optical confinement and feature greatly enhanced light–matter interactions. Among all the configurations, whispering gallery mode (WGM) microcavities and microlasers exhibit outstanding optical performances with high quality factors and small mode volumes, thus ensuring low lasing thresholds. In addition, some unique properties inherent to WGM cavities, like bi‐directional propagation and an evanescent field that spans several hundred nanometers across the boundary, can be exploited for novel applications. Therefore, designing and engineering innovative WGM microcavities and microlasers has attracted increasing research interest. The fundamentals and characteristics of WGM are introduced here, and then the developments and current status of WGM microcavities and microlasers are reviewed in terms of the evolution of fabrication techniques and built‐up materials. In particular, the melting of glassy materials in early studies, top‐down and bottom‐up approaches with semiconductors, coating structures, as well as flexible, soft microresonators in recent years are presented. Finally, the application prospects of microlasers including the wavelength manipulation, sensing and microresonator coupling, are discussed.

The newly engineered ternary CdZnS/ZnS colloidal quantum dots (CQDs) are found to exhibit remarkably high photoluminescence quantum yield and excellent optical gain properties. However, the underlying mechanisms, which could offer the guidelines for devising CQDs for optimized photonic devices, remain undisclosed. In this work, through comprehensive steady-state and time-resolved spectroscopy studies on a series of CdZnS-based CQDs, we unambiguously clarify that CdZnS-based CQDs are inherently superior optical gain media in the blue spectral range due to the slow Auger process and that the ultralow threshold stimulated emission is enabled by surface/interface engineering. Furthermore, external cavity-free high-Q quasitoroid microlasers were produced from self-assembly of CdZnS/ZnS CQDs by facile inkjet printing technique. Detailed spectroscopy analysis confirms the whispering gallery mode lasing mechanism of the quasitoroid microlasers. This tempting microlaser fabrication method should be applicable to other solution-processed gain materials, which could trigger broad research interests.

Engineering photonic devices from liquid has been emerging as a fascinating research avenue. Reconfigurably tuning liquid optical micro-devices are highly desirable but remain extremely challenging because of the fluidic nature. In this article we demonstrate an all-liquid tunable whispering gallery mode microlaser floating on a liquid surface fabricated by using inkjet print technique. We show that the cavity resonance of such liquid lasers could be reconfigurably manipulated by surface tension alteration originated from the tiny concentration change of the surfactant in the supporting liquid. As such, remarkable sensing of water-soluble organic compounds with a sensitivity of free spectral range as high as 19.85 THz / (mol · mL−1) and the detectivity limit around 5.56 × 10−3 mol · mL−1 is achieved. Our work provides not only a novel approach to effectively tuning a laser resonator but also new insight into potential applications in biological, chemical and environmental sensing.

This work demonstrates mass production of printable multi-color lasing microarrays based on uniform hemispherical microcavities on a distributed Bragg reflector using inkjet technique. By embedding two different organic dyes into these prints, optically pumped whispering gallery mode microlasers with lasing wavelengths in green and red spectral ranges are realized. The spectral linewidth of the lasing modes is found as narrow as 0.11 nm. Interestingly, dual-color lasing emission in the ranges of 515-535 nm and 585-605 nm is simultaneously achieved by using two different dyes with certain ratios. Spectroscopic measurements elucidate the energy transfer process from the green dye (donor) to the red one (acceptor) with an energy transfer efficiency up to 80% in which the nonradiative Förster resonance energy transfer dominates. As such, the acceptor lasing in the presence of donor exhibits a significantly lower (∼2.5-fold) threshold compared with that of the pure acceptor lasing with the same concentration. © 2015 AIP Publishing LLC

Ultra‐low threshold stimulated emission is demonstrated upon both one‐ and two‐photon pumping from quaternary alloyed Cd(1−x)ZnxSe(1−y)Sy/ZnS quantum dots (QDs) in the green region for the first time. Moreover, an all‐solution‐processed whispering gallery mode laser is produced by coating Cd(1−x)ZnxSe(1−y)Sy/ZnS QDs on a self‐assembled hemisphere. These results represent a significant progress in green lasers and hold great potential in addressing the “green gap” challenge.