Abstract
We introduce tunable optofluidic microlasers based on active optical resonant cavities formed by optically stretched, dye-doped emulsion droplets confined in a dual-beam optical trap. To achieve tunable dye lasing, optically pumped droplets of oil dispersed in water are stretched by light in the dual-beam trap. Subsequently, resonant path lengths of whispering gallery modes (WGMs) propagating in the droplet are modified, leading to shifts in the microlaser emission wavelengths. Using this technique, we present all-optical, almost reversible spectral tuning of the lasing WGMs and show that the direction of tuning depends on the position of the pump beam focus on the droplet. In addition, we study the effects of temperature changes on the spectral position of lasing WGMs and demonstrate that droplet heating leads to red-tuning of the droplet lasing wavelength.
Highlights
Liquid droplets have been long recognized and studied for their peculiar optical properties [1]
We introduce tunable optofluidic microlasers based on active optical resonant cavities formed by optically stretched, dye-doped emulsion droplets confined in a dual-beam optical trap
We have presented tunable optofluidic dye microlasers based on active optical resonant cavities formed by optically trapped microdroplets of fluorescently stained immersion oil emulsified in water
Summary
Liquid droplets have been long recognized and studied for their peculiar optical properties [1]. Dye lasing [5], stimulated Raman scattering [6], and Raman lasing [7] in microdroplets have been demonstrated at low threshold pump powers Apart from their significance for the fundamental physics research, microdroplets are well suited to another important line of applications that benefit from the sensitivity of the WGMs to the microdroplet size as well as the refractive indices of the droplet liquid and the surrounding medium. Because of the Gaussian transversal intensity profile of both beams, high refractive index objects (e.g. oil droplets suspended in water) are pulled toward the beams axis and, subsequently, move along this axis to the location where the radiation pressures of both beams just balance each other At this position, the objects are stably confined and their stretching in the optical field of the two beams can be studied. We characterize the effects of changes of the droplet and immersion medium temperature on the spectral position of lasing WGMs and show that these thermally induced spectral shifts are caused by simultaneous changes of the droplet size and refractive index of both the droplet and the host medium resulting from the droplet heating by the stretching laser beam
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