Formation of a Diffractional Grating by Magnetic Lithograph

A new method to make an optical diffraction grating has been developed using the Bitter method. A periodic magnetic pattern like 0101 ... is written in a magnetic memory medium, and a magnetic fluid is used as magnetic toner to visualize this pattern. To enhance the contrast of the grating, an interfacial active agent in the magnetic fluid is destroyed by a certain organic solvent, and a DC magnetic bias field is applied to the memory medium to thicken the pattern. When a transparent grating is required, Au film is deposited on it as a parting agent after the formation of a magnetic toner pattern. After separation of the epoxy resin film from the memory medium, Au film is chemically etched. A sharp diffraction image is observed by projecting a laser diode onto the diffraction grating. Using this method, an optical grating can easily be made even on a convex or concave surface.