a host matrix — normally a binder such as cellulose acetate propionate in a solvent such as acetone — contains a radiation - polymerizable photopolymer — normally a monomer like dipentaerythritol pentaacrylate in combination with a crosslinker like 1 - vinyl - 2 - pyrrolidinone , an initiator like n - phenyl glycine , and / or a photosensitizer like camphor quinine — that is initially uniformly doped with a stable dye — typically rhodamine b and / or bodipy red — that photoinitiates photopolymerization . upon selective exposure of certain regions of the matrix by radiation , most normally laser light radiation , the dye will initially migrate and redistribute itself to radiatively - exposed regions until , dye migration being substantially complete , photopolymerization will occur , locking the migrated dye in place at a relatively higher concentration at the selectively exposed regions . the dye therein stably located can be optically detected by , preferably , light - radiation - stimulated fluorescence . the medium thus serves as an optical memory , including of the volume type , that can be reliably permanently written quickly and inexpensively at high density .