二次再现全息图

目前 ,光学防伪技术已广泛应用于钞票、信用卡、各种证件和高档商品上。全息术是一种被广泛认知的光学防伪技术 ,编码加密技术是提高它防伪功能的重要手段。二次再现全息图是根据全息图能够进行多次记录和多次再现的特点提出的一种加密全息图。在一定的照明条件下 ,它的再现光经过一个平面反射镜的反射返回到全息图 ,作为它的第二束照明光 ,这时能够再现出被加密的图像。它是由一个像全息图和一个参考光编码全息图组合而成的。一般情况下 ,二次再现全息图存在再现光路恢复困难的问题。利用低频光栅能够较好地解决这一问题 ,使二次再现全息图达到实用性的要求。该技术用于防伪产品可提高它的防伪力度。给出了详细的理论分析、制作方法和实验结果

Secondary reconstructed holograms

Optical security technology has been used widely in bank paper, credit cards, do cuments, value commodities, etc. Holography is known intimately as a kind of opt ical security technology. Encoding technology is a main method to enhance the an ti counterfeit capacity of holograms. According to the feature that a hologram can be multi recorded and multi reconstructed, a secondary reconstructed h ologram is presented. Under the specified lighting condition, its reconstructed light is reflected back by a mirror to illuminate the hologram again, and thus, another image is reconstructed. The secondary reconstructed hologram is composed of two elementary holograms--an image hologram and an encoded refe rence wave hologram. Generally, the reconstructing system of a secondary reconst ructed hologram is difficult to be restored. It can be easily solved with a low frequency grating. If it is used in the anti counterfeit domain, the technolo gy can dramatically enhance the anti counterfeit capacity of produces. The theo retical analysis and experimental results are given.