Saturable plasmonic metasurfaces for laser mode locking
Plasmonic metasurfaces are artificial 2-D sheets of plasmonic unit cells repeated in a subwavelength array, which give rise to unexpected wave properties that do not exist in nature. In the linear regime, their applications in wavefront manipulation for lensing, holography or polarization control have been intensively studied. However, applications in the nonlinear regime have been rarely reported. Considering the growing demand for saturable absorbers—a special class of nonlinear devices in which transparency (or absorption) depends on light intensity—for ultrafast lasers and neuromorphic circuits, scientists from France, China and Brazil have developed plasmonic metasurfaces providing a remarkably efficient saturable absorption which can be tuned with the polarization of light.