With the surface prepared for coating as described, further steps are necessary to achieve a strong bond to the fundamentally weak polymer crosslinked groups. A process that promotes chemical bonding of O, C, or CH groups to metal oxides is the key to obtaining a strong bond. An activated electron or ion plasma in contact with the surface serves this purpose. Ar is used to first abrade the surface and O 2 is admitted before deposition begins. As a further initiator of bonding strength, many AR designs include a very thin layer of a metal oxide such as chromium oxide.
Polymeric materials are ideal for creating molded mirror substrates of complex shapes.
Generally, the rms surface roughness requirements are not as rigid as for refractive optics. More than one deposition technique has been tried in the search to economize the coating deposition process without sacrificing durability or yield. Sputtering can deposit a fundamentally harder, more adherent coating, but other problems, such as layer stress and higher cost for lower batch throughput, reduce this potential benefit. Thus, standard thermal deposition technology is currently in place in the coating of ophthalmic lenses. 5-layer AR stack.