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.
Point source diffraction and its use in an encoder.
Diffraction from a point light source (a laser diode) was studied. The diffraction images were found to be magnified without using a lens and to move corresponding to the displacement of the slit aperture. A digital encoder using this diffraction is proposed to obtain very high resolution without a lens.
The General Theory of Relativity
THE WORD “SPECIAL” IN “SPECIAL THEORY OF RELATIVITY” means that the theory is restricted to those frames of reference for which the law of inertia holds, that is, inertial frames of reference.* Einstein sometimes referred to them as Galilean frames of reference. At first glance, it does not seem reasonable to expect that the principle of relativity can be extended to non-inertial frames. The reasons are fairly obvious. The principle of relativity that we have been using states that the laws of physics have the same form in all frames of reference to which the principle applies. In other words there should be no way to determine by an experiment which of two frames of reference is in motion relative to the other.