“…This technology utilizes the birefringence/polarization effect of the bulk anisotropic nanogratings and polarization/interference effects in their multiple layers with overall retardance approaching wavelength scale [ 2 , 5 ], rather than its common irreversible densification- [ 6 ] or void-related refractive-index modulation [ 7 ]. These underlying effects provide additional flexibility in terms of the design, internal arrangement, and spatial scales of laser-inscribed functional optical elements and the ongoing progress of this technology [ 1 , 2 , 3 , 4 , 5 ]. Meanwhile, many conjugate physical processes—(non)linear laser focusing [ 8 ], nanoplasmonic arrangements [ 9 ], and nanoscale material transport mechanisms [ 10 ]—in the focal region during material/refractive-index nanograting formation are still poorly understood.…”