Droplet lasers: a review of current progress

Abstract

Abstract. It is perhaps surprising that something as fragile as a microscopic droplet could possibly form a laser. In this article we will review some of the underpinning physics as to how this might be possible, and then examine the state of the art in the field. The technology to create and manipulate droplets will be examined, as will the different classes of droplet lasers. We discuss the rapidly developing fields of droplet biolasers, liquid crystal laser droplets and explore how droplet lasers could give rise to new bio and chemical sensing and analysis. The challenges that droplet lasers face in becoming robust devices, either as sensors or as photonic components in lab on a chip devices is assessed.

Microlasers Enabled by Soft‐Matter Technology

“…On the basis of the above work, it has been expected that a liquid droplet can also act as a suitable cavity for lasers. It would be interesting to see lasing emission from a structure as fragile as a droplet . However, due to the inherent property of any fluid, a droplet generally cannot be formed on a conventional substrate without spreading.…”

“…In the literature, there have been several review articles on organic lasers with the main focus on conducting polymers . Furthermore, organic lasers also are partly covered in a number of review papers dedicated to specific laser structures such as optofluidic lasers, droplet lasers, whispering gallery mode lasers . However, none of them is specifically devoted to soft‐matter lasers.…”

Optically Transportable Optofluidic Microlasers with Liquid Crystal Cavities Tuned by the Electric Field

“…Among the various liquid-based photonic components, self-assembled optical cavities formed by liquid droplets, which are shaped into virtually perfect spheres by surface tension, have been at the forefront of optofluidics research for over three decades. − Such droplets, surrounded by an optically less dense medium, can exploit total internal reflection of light to confine light waves with precisely defined frequencies in the form of electromagnetic resonances known as whispering gallery modes (WGMs) . These optical resonances, which are spatially localized to the proximity of the droplet surface and whose frequencies are determined by the droplet size and refractive indices inside and outside the droplet, possess high quality factors ( Q -factors) up to 10 8 .…”

“…These optical resonances, which are spatially localized to the proximity of the droplet surface and whose frequencies are determined by the droplet size and refractive indices inside and outside the droplet, possess high quality factors ( Q -factors) up to 10 8 . Thus, they can readily support lasing action in pumped droplet-based optofluidic cavities containing a suitable gain medium. ,,− …”

Whispering Gallery‐Mode Microdroplet Tensiometry

“…To excite the WGMs, light is either coupled into the spherical cavity via an evanescent field or the cavity is doped with a fluorescent dye. Droplets are frequently used as WGM microcavities and lasers in various forms, [22] for example, in air, [23] on a superhydrophobic surface, [24,25] embedded in a solid, [26,27] or dispersed in another liquid. [28,29] Lasing has been also demonstrated in natural and injected droplets inside live cells.…”