Three-dimensionally modulated graded-index diffractive elements by thermal ion exchange in glass Salmio, Risto-Pekka ; Saarikoski, Henri ; Saarinen, Jyrki ; Westerholm, Jan ; Turunen, Jari Abstract Publication: Optics Letters Pub Date: May 1997 DOI: 10.1364/OL.22.000591 Bibcode: 1997OptL...22..591S