This paper introduces Firefly, an optical lithography origination system that has been developed to produce holographic masters of high quality. This mask-less lithography system has a resolution of 418 nm half-pitch, and generates holographic masters with the optical characteristics required for security applications of level 1 (visual verification), level 2 (pocket reader verification) and level 3 (forensic verification). The holographic master constitutes the main core of the manufacturing process of security holographic labels used for the authentication of products and documents worldwide. Additionally, the Firefly is equipped with a software tool that allows for the hologram design from graphic formats stored in bitmaps. The software is capable of generating and configuring basic optical effects such as animation and color, as well as effects of high complexity such as Fresnel lenses, engraves and encrypted images, among others. The Firefly technology gathers together optical lithography, digital image processing and the most advanced control systems, making possible a competitive equipment that challenges the best technologies in the industry of holographic generation around the world. In this paper, a general description of the origination system is provided as well as some examples of its capabilities.
The optical characteristics of Diffractive Optical Elements are determined by the properties of the photosensitive
film on which they are produced. When working with photoresist plates, the most important property is the
change in the plate's topography for different exposures. In this case, the required characterization involves a
topographic measurement that can be made using digital holography. This work presents a digital holography
system in which a hologram's phase map is obtained from a single recorded image. The phase map is calculated
by applying a phase-shifting algorithm to a set of images that are created using a digital phase-shifting/tilteliminating
procedure. Also, the curvatures, introduced by the imaging elements used in the experimental setup,
are digitally compensated for using a polynomial fitting-method. The object's topography is then obtained from
this modified phase map. To demonstrate the proposed procedure, the topography of patches exposed on a
Shipley 1818 photoresist plate by microlithography equipment-which is currently under construction-is shown.
Spatial filtering techniques are used in the analysis of interferograms and off-axis digital holograms to obtain the
phase information from an optical field. The masks applied for the selection of the virtual image order in the
frequency space usually have regular shapes and are located by hand. Therefore, they create artifacts that hide
some details in the obtained phase, especially when holograms from objects with sharp edges are reconstructed.
In this work, a novel algorithm that automatically calculates and locates the mask separating the spectral orders
is presented. This new method uses a distance criterion between the maximum values in the amplitude spectrum
as a clustering parameter. The values for the distance parameter are changed and the results are analyzed for a
simulated image-plane hologram. As an example of the algorithm application, a digital hologram obtained from
one USAF-1951 test target is reconstructed and the phase of the test target element is obtained.
Off-Bragg reconstruction of volume holographic grating is known to result in an attenuation of the diffracted beam intensity. In this letter we demonstrate that contrary to the disseminated believe a strong increase of the diffracted beam intensity can be observed when an angular deviation between the grating and reconstruction beam takes place in the direction perpendicular to the dispersion plane. The effect of such `anomalous' behavior of the diffracted beam intensity is studied experimentally.
The theoretical and experimental study of the diffraction efficiency of a volume transmission diffraction grating when illuminated by an arbitrary direction reconstruction beam was realized. It was found that on the contrary of what is usually expected, the diffraction efficiency could be increased by a rotation of the grating around its K vector, although the exact Bragg condition is no longer satisfied. Theoretically, the diffraction efficiency can be increased up to 100% for any grating, if we discard the reflection on the grating boundary, and absorption on the holographic media.
Here a method for data storage by means of multiplexing 3D holograms is considered. The method consists in shifting the recording material with respect to a reference speckle wave. The experimental data on the dependence of the diffraction efficiency of the hologram with respect to the shift is presented. The general scheme of data storage in 3D-speckle shift hologram is considered and presented. It's shown that this kind of hologram substantially outperforms all other types for the number of cells (pixels) in which information can be stored. At the same time, the noises that are inherent in a 3D-speckle shift hologram restrict the density of the information storage.
We have shown the vortex structure of the dislocation appearing in a laser beam passing through a Gaussian lens induced in a cubical, non-linear media during self-action. We make such studies using focusing and defocusing Gaussian lenses both theoretically and experimentally.