Sushil K. Kaura

Interferometric moiré pattern encoded security holograms

This paper describes a simple method for making interferometric moire pattern encoded security holograms. These security holograms contain multi-fold concealed and encoded anti-counterfeit security features which can only be decoded by using an encoded key hologram in the final reading process. The concealed codes in these holograms are recorded with an encoded feature, so that they remain invisible to the counterfeiters, thereby enhancing the anti-counterfeiting ability of security holograms. In the final reading process, a specific moire-like fringe pattern is formed on the security hologram only when a reconstructing beam generated from the encoded key hologram illuminates this hologram. Further, a careful spatial filtering results in the generation of a specific moire pattern in the observation plane and it disappears when perfectly repositioned. These can also be used as security codes for better protection against counterfeiting in embossed holograms. Recording schemes for the formation of such security holograms and typical experimental results have been presented.

Encoded reference wave security holograms with enhanced features

A simple and cost effective two-step method for making encoded reference wave security holograms with enhanced features, which are readable with an encoded key hologram, has been presented. In the final reading process, two spatially separated sharp focus spots (bright spots) emerge only when the security hologram is illuminated by the decoding, reconstructing beam, generated from the encoded key hologram. In addition these focused spots, upon divergence in the longitudinal direction, further generate variable interferometeric features, i.e. circular and linear interference fringe patterns contained respectively in them. Since the verification/identification pattern in these security holograms are variable interferometric features in addition to the spatially separated sharp focus spots, this type of security hologram is suitable for both visual as well as machine inspection. They can also be used as security codes for better protection against counterfeiting embossed holograms. Recording schemes for the formation of such security holograms and typical experimental results have been presented.

Full-view rainbow-reflection holograms

Abstract A simple method of recording full-view rainbow-reflection holograms on a single flat plate is described: only one white-light illuminating source is required in the reconstruction process. The hologram can be viewed from opposite sides, where each side of a three-dimensional object, with its original spatial relationship, is displayed in bright colours.

Realization of an optical interferometer based on holographic optics for real-time testing of phase objects

The paper describes a simple and cost effective method for the realization of an optical interferometer based on holographic optics, which use minimal bulk optical components. The optical arrangement in the proposed method involves a very simple alignment procedure and inexpensive holographic recording material is used in the formation of holographic optical elements. The proposed interferometer set-up is quite suitable for performing optical test studies on phase (transparent) objects in real-time. Recording schemes for the formation of holographic optical elements and the related technique for the realization of the interferometer set-up along with the experimental results have been presented.

Rainbow and full-field cylindrical fiber optic holograms

Simplified techniques of recording rainbow and full-field cylindrical holograms by using flexible fiber optic light beam delivery systems are described. The method used in recording full-fieId cylindrical holograms is similar to that of the conventional technique, where the object is kept at the centre of a cylinder and the hologram recording film is wrapped around the object forming a cylindrical shape. There are, however, some practical problems in realising these holograms: (a) proper illumination of the object and (b) achievement of a balanced intensity ratio between the object and the reference beams. These problems have conveniently been overcome by employing flexible multiple fiber optic beam delivery systems, where both front and the back sides of the object have been illuminated separately using a practically non-overlapping fiber optic end geometry coupled with an independent reference beam. Rainbow holograms in both one-step and two-step recording geometries have also been successfully realised, where the advantage of flexibility offered by fiber optic beam delivery system is gainfully utilised for providing the desired vertically inclined (overhanging) reference beam. Methods for recording inbuilt reference beam and large size rainbow holograms by the use of optical fibers in the recording geometries are also being studied.