HOLOGRAM WITH RECORDING INFORMATION THAT IS INVISIBLE IN NORMAL STATE

摘要

PROBLEM TO BE SOLVED: To provide a volume phase type hologram whose recording information is invisible in a normal observation state. SOLUTION: The volume phase type hologram 1 has the tilt of interference fringes set so that at least a visible light component in diffracted light 5 from the interference fringes recorded in a hologram recording medium is totally reflected by the border surface between air and the hologram recording medium or a transparent layer laminated on its surface. To observe the recording information, a prism 3 having nearly the same refractive index with the hologram 1 is brought into contact with the hologram 1 and reproducing illumination light 4 is made incident at an angle exceeding the critical angle (a) or the diffracted light 5 is projected at an angle exceeding the critical angle (b).