We develop a multi-color microfluidic droplet-based dye laser in which the frequency of lasing can be switched rapidly. The system includes a microfluidic droplet generator, capable of generating trains of droplets of fluid containing a dye capable of lasing, and suspended in a second transparent fluid. These droplets of dye pass through a section of the microchannel where they are optically excited to cause lasing.

We also develop a method for on-demand generation of single droplet containing different contents of dye. This method allows for an arbitrary sequence of different dye droplets to be programmed in a microchannel, and therefore the sequence of the color of the lasing output.