Once a nonlinear metasurface is made, its response is usually fixed. If you want to know how to get around this, have a look at our latest work in Nanophotonics. Together with the group of Mikko Huttunen and our colleagues at the University of Eastern Finland, we placed two inside a multi-pass cell and let the pump pass multiple times. By rotating one metasurface relative to the other, the nonlinear geometric (Pancharatnam–Berry) phase adds a tunable phase delay to the second-harmonic signal (SHG), which lets us continuously and reversibly shift the phase-matching peaks across a 900–970 nm pump range, simply by mechanical rotation.
Congratulations to all co-authors, especially Madona for her hard work and all the collaborators for this nice piece of work.