PURPOSE: To improve visible ray transmittance and heat ray reflectivity by mosaic-likely arranging diffraction gratings of various reflecting wave length territories, and reflecting heat rays of a wide territory of wave length more then a specific wave length.
CONSTITUTION: Douser plates 2 in which square windows of a few cm side are mosaic-likely formed, are stuck on both sides of sensitive material 1 used for hologram and the like. Next, glass blocks 3 having end faces of desired angle are stuck on the plates 2. Next, parallel laser beams are projected from the end faces of the blocks 3, and the respective incident rays are interfered with each other in the sensitive material 1 so as to form interference fringes. Further, another plate 2 of which opening window parts are reversed and the blocks having the end faces of different angle are used, so as to similarly form interference fringes of different grating intervals. A territory in which the peak of diffraction efficiency is shown against wave length territories having various reflecting wave length is formed, and heat ray transmittance rate over wave length of 800nm is lowered. Hereby, because wave length is selected by utilizing diffraction, visible ray transmittance can be improved, and a heat ray reflecting membrane for a wide wave length territory can be easily formed.
