Guenther Dausmann

Copy-proof machine-readable holograms for security application

The most frequently used optical security features to protect documents and goods against counterfeiting are various types of rainbow holograms and diffractive optical variable devices (OVDs). Although these features offer a fair degree of security and most known falsifications are rather crude imitations it is still possible to copy them with all hidden and visible information. In our opinion it would be helpful to have copy proof holograms containing a machine readable feature to achieve a doubtfree verification at point of sale and other sites. We present our work towards the development of a copy proof and machine readable hologram with an optically encoded security feature.

Method for production of a one-step large-format holographic multistereogram

A method for producing a large format (multiple square meters) holographic multistereogram on the high sensitive photoresist REFO 200 M will be presented. The basic images are acquired by video, movie film or generated by computer systems. They will be used to drive a light modulator. On examples it will be shown that this light modulator can be photographic film, a LCD screen or a scanning system. This method requires a high number of multiple exposures on the recording medium. This requirement and a possible solution will be discussed as the main subject of this paper.

Making blazed holograms with the new REFO-125 photoresist

A new photoresist (REFO-125) is developed especially for holography as well as diffractive optics. It is at least twice as sensitive as conventional photoresists in the spectral range of 350 nm - 520 nm. Using this resist holographic gratings with blazed surface relief profiles have been produced which show diffraction efficiencies of up to 90% for the blaze wavelengths. A theoretical model has been successfully used to determine the holographic recording geometries for various configurations of blazed gratings of transmission or reflection type. Experimental results show that the REFO-125 photoresist allows great modulation depths which are necessary especially for blazed transmission gratings.