Electron-beam Lithography
These types of hologram are created using highly sophisticated and very expensive electron-beam lithography systems. This kind of technology allows the creation of surface holograms with a resolution of up to 0.1 micrometres (254,000 dpi). This technique requires development of various algorithms for designing optical elements that shapes scattered radiation patterns. This type of hologram offers features like the viewing of four lasers at a single point, 2D/3D raster text, switch effects, 3D effects, concealed images, laser readable text and true colour images.
The various kinds of features possible in security holograms are mentioned below:
Concealed images
These usually take the form of very thin lines and contours. Concealed images can be seen at large angle light diffraction, and at one particular angle only.
Guilloché pattern (high resolution line patterns)
These are sets of thin lines of a complicated geometry (guilloché patterns) drawn with high resolution. The technology allows continuous visual changes of colour along each separated lines.
Kinetic images
They can be seen when the conditions of hologram observations are being changed. Turning or inclining the hologram allows the movements of certain features of the image to be studied.
Microtexts or nanotexts
Dot matrix holograms are capable of embedding microtext at various sizes. There are three types of microtexts in holograms: high contrast microtexts of size 50 – 150 micrometres; diffractive grating filled microtexts of size 50 – 150 micrometres low contrast microtexts. Microtexts of sizes smaller than 50 micrometres are referred to as nanotext. Nanotext with sizes of less than 50 micrometres can be observed with a microscope only.
CLR (Covert Laser Readable) image
Dot matrix holograms also support CLR imagery, where a simple laser device may be used to verify the hologram's authenticity. Computing CLR images is a complicated mathematical task that involves solving ill-posed problems. There are two types of CLR: Dynamic CLR and Multigrade CLR. Dynamic CLR is a set of CLR fragments that produce animated images on the screen as the control device moves along the hologram surface. Multigrade CLR images produce certain images on the screen of the controlling device, which differ in the first and minus first orders of laser light diffraction. As a variant, a hidden image which is both negative and positive, in plus one and minus one order respectively, may be created.
Computer-synthesized 2D/3D and 3D images
This technology allows 2D / 3D images to be combined with other security features (microtexts, concealed images, CLR etc.) - this combination effect cannot be achieved using any other traditional technologies of origination.
True colour images
True colour images are very effective decorative pictures. When synthesized by a computer, they may include microtexts, hidden images, and other security features, yielding attractive, high-security holograms.
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