The paper Fabrication of Optical Microstructures with Gradient Refractive Index by Two-Photon Laser Lithography written by M.D. Aparin, T.G. Baluyan, M.I. Sharipova, M.A. Sirotin, E.V. Lyubin, I.V. Soboleva, V.O. Bessonov, and A.A. Fedyanin has been published in Bulletin of the Russian Academy of Sciences: Physics.