Formation of circular fringes by interference of two boundary diffraction waves using holography

The theory of boundary diffraction waves (BDWs) is gaining importance due to its simplicity and physically appealing nature. The present work reports formation of circular fringes far away from the geometrically illuminated region by interference of two BDWs. One BDW is reconstructed from the hologram while the second is coming directly from the knife-edge. The uniqueness of the fringes is that their position can be controlled on the screen at will and fringes can be produced with bright as well as dark central fringe. These results could play an important role in understanding the nature of diffraction of light

Design and recording of holographic diffuser for controlled angular distribution of light

Now-a-days diffusers play a pivotal role in many applications. It is desirable in many applications that angular distribution of scattered light must be controlled in a particular manner. Present paper reports on design and recording of holographic diffusers for controlling the angular distribution of the scattered beam. Experimental results from recorded holographic diffuser have been compared with the conventional diffuser

Retrieval of infinite-fringe mode information from beam folding interferometer for direct phase visualization

A recently reported one-beam interferometer using beam folding is quite suitable for carrying out studies on phase objects in finite-fringe mode, but in its present form it is difficult to work with this interferometer in infinite-fringe mode for direct and quick phase visualization, which may be required for certain problems of physical interest. The present paper describes a modification to the beam folding interferometer, where interferometric fringes are superimposed onto a grating to get both finite- as well as infinite-fringe mode information of the test object

Interferometric moiré pattern encoded security holograms

This paper describes a simple method for making interferometric moiré 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 moiré-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 moiré 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

Folding mirror schlieren diffraction interferometer

We demonstrate the use of a mirror as a viewing diaphragm to generate a built-in diffracted reference beam in schlieren diffraction interferometry (SDI). The use of a mirror edge as a diffracting element instead of a conventional knife edge considerably enhances the contrast of the schlieren pattern, and it is shown to be equal to that of a phase knife edge. This increase in contrast is due to the fact that the otherwise unutilized diffracted beam in SDI is recombined in the described folding mirror geometr

Moiré Pattern Encoded Extended Fractional Fourier Transform Security Hologram

This paper describes a simple method for making extended fractional Fourier transform (EFRT) based Moiré pattern encoded security holograms. These security holograms contain multifold concealed and encoded anticounterfeit security features that can only be read through a key hologram and periodic patterns in the final reading process. The encoded features in these holograms are concealed and unknown to the counterfeiter. These features are encoded separately for each individual recording in angularly multiplexed extended fractional Fourier transform hologram (EFRTH). The principle of recording and reconstruction of the proposed security hologram along with experimental results are presented

A holographic dual-channel interferometer

A holographic, optics-based dual-channel interferometer with an in-built phase-shifting element is described. The interferometer can be used for testing two different phase objects simultaneously and independently. Additionally, a single object could be studied simultaneously in two different modes (e.g. finite and infinite fringe states) in this interferometer. The related geometry of the proposed interferometer along with experimental results is 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

Interferometry based security hologram readable with an encoded key hologram

A simple and cost-effective method for making security holograms has been presented, which incorporates holographic interferometry as verification feature in addition to spatially separated sharp focus spots. When the security hologram is illuminated with decoding reconstructing beam generated from an encoded key hologram, two spatially separated sharp focus spots emerge at the predefined positions and can be read through a photoelectric detector array. In addition, these focused spots upon divergence in longitudinal direction further generate specific kind of interferometric fringe patterns of random profile contained in them, which are suitable for further visual inspection. These machine-readable and visual verifiable features can be used for better counterfeit-resistant security codes in embossed holograms. Recording schemes for the formation of such security holograms and typical experimental results have been presente

Direct Visualization of Young’s Boundary Diffraction Wave

Experimental investigations on Young’s boundary diffraction wave are presented where a wavefront division interferometric scheme is used on diffracted wavefront to generate two-beam interference fringes in the geometrically shadow region. These fringes have good visibility and are observable in the whole space, strongly advocating the physical existence of Young’s boundary diffraction wave as a separate entity. Analysis of these fringes may provide vital information about the structure and nature of boundary diffraction wave e.g. existence in whole space, dependence of amplitude on obliquity factor etc