Revealing a one-dimensional optically cloaked surface using the spin Hall effect of light

The realization of an optical cloak that can hide a target object is no longer fiction, yet distinguishing the optically cloaked surface from our illusion remains an open problem. Here, the detection of a one-dimensional optically cloaked surface is presented by leveraging the spin Hall effect of light, the microscopic and transverse splitting of linearly polarized light at an optical interface into two circular polarizations. We first derive an analytical formula for the spin Hall shift at a planar surface with a linear phase gradient and demonstrate that the spin Hall effect of light at the cloaked surface differs from that at its perceived image. The theoretical description and numerical computation are generalized for a curved surface with a nonlinear phase gradient. Two approaches for examining optically cloaked surfaces are presented, in which the unknown incident angle and phase gradient are successfully reproduced. This work suggests the potential of the spin Hall effect of light in various applications, including anti-counterfeiting and security.