The interaction of an electromagnetic wave with a noncentrosymmetric crystal is not necessarily time reversible, and the departure from reversality may be seen in nonlocal (wave-vector linear) phenomena. However, relativistic symmetry with respect to simultaneous time and space inversion is always preserved in optics.
© 1995 Optical Society of America
Yu. P. Svirko and N. I. Zheludev, "Reversality of optical interactions in noncentrosymmetric media," Opt. Lett. 20, 1809-1811 (1995)