Flowing lattices of bubbles as tunable, self-assembled diffraction gratings

We demonstrate tunable, fluidic, two-dimensional diffraction gratings based on a microfluidic platform comprising a flow-focusing bubble generator and flowing, regular lattices of bubbles formed by dynamic self-assembly. The structure of these lattices can be tuned with switching times of less than ten seconds by changing the pressures and rates of flow applied to the device. These diffraction gratings exhibit high stability (over hours of operation if properly designed and operated). For our devices, we achieved tunable ranges in pitch from 12 to 51 mu m, corresponding to first-order diffraction angles from 3.2 degrees to 0.7 degrees for light with a wavelength of 632 nm.