Abstract

Optical index gratings are radiation-induced periodic spatial variations in an active medium’s dielectric constant. These structures are responsible for numerous active optical processes and are of central interest to nonlinear optics. In this paper these concepts are extended to superconducting thin films. Notably, theory asserts that optical index gratings can be created in thin film superconducting structures from coherently interfering laser beams. The presence of the optical interference pattern gives rise to pair-splitting processes that generate quasiparticle (qp) population gratings. In turn, these qp gratings establish conductivity gratings within the thin-film super-conductor, that are active for frequencies below the pair-splitting frequency. Since the conductivity has both real and imaginary parts, both phase and amplitude gratings are established in the superconducting thin film. We examine the steady-state and transient dynamics of these index gratings and show that they form quite rapidly, on the order of 0.5 ns for Nb superconducting thin films. Furthermore, it is shown that the existence of these optical index gratings can be verified by measuring the angle resolved transmittance and reflectance of millimeter waves. In particular, our theoretical analysis shows that well-defined off-specular peaks, corresponding to the grating diffraction orders, appear.

© 1991 Optical Society of America