New embossed hologram originating technique, producing effects which are not possible to reproduce with commonly used image-matrix Kinemax type equipment was developed. Thus, Geola Digital Ltd. is launching a series of unique equipment devoted to embossed holograms originating. Equipment allows one to produce master-holograms containing simultaneously achromatic and true colour deep 3D images. Such images are perfectly viewable while illuminated with light sources situated in front of the hologram or at its back. The Originators also can produce and with higher precision all effects achievable with commonly used image-matrix originators. Therefore, an ultimate goal to have one Originator assuring all security features from Level 1 to Level 4 is achieved. Moreover, pulsed laser employed in Geola's originators enable one to produce whole holograms windows quickly, employing an optical holograms recombination instead of mechanical one.
New combined embossed hologram originating technique was developed by the international team of holography experts. The technique merges deep 3D holographic images with commonly used hologram security features. Deep 3D images were first recorded on photoresist with Geola's holographic printer containing their proprietary pulsed laser. Optical security features were then overexposed onto the photoresist plates containing latent images of deep 3D scenes. The photoresist plates with several exposures (containing optical security features and deep 3D images) were developed. Embossed holograms, containing such effective public security features as full colour 3D images, guilloches, rainbow patterns were manufactured. Manufactured embossed holograms also contained such optical security features as microtext and laser readable hidden image.
It is well known fact that holograms can be recorded either by continuous wave (CW) laser, or by single pulse coming from pulsed laser. However, multi-pulse or multiple-exposure holograms were used only in interferometry as well as for information storage. We have used Geola's single longitudinal mode pulsed RGB laser to record Denisyuk type holograms. We successfully recorded objects situated at the distance of more than 30cm, employing the multi-pulse working regime of the laser. To record Denisyuk hologram we have used 50 ns duration 440, 660nm wavelength and 35ns duration 532nm wavelength laser pulses at the repetition rate of 30Hz. As photosensitive medium we have used Slavich-Geola PFG-03C glass photoplate. Radiations with different wavelengths were mixed into "white" beam, collimated and directed onto the photoplate. For further objects illumination an additional flat silver coated mirror was used.
Direct write digital holography technique (DWDH) using a single 440-nm pulsed laser exposure has been proposed to record master holograms on commercially available positive-tone photoresist systems based on a mixture of diazonaphthoquinone and novolac resin (DNQ-novolac) of different thicknesses. The DNQ-novolac nanocomposite doped with copper nanoparticles (CuNPs) films was also used. The method for numerical evaluation of hologram quality based on reflected beam diffraction intensity measurements was proposed and verified. It was found that all investigated photoresist nanocomposites were sensitive enough to record holographic structures at low single pulse laser exposures (from 3.3 to 18.0 mJ/cm2). Moreover, doping DNQ-novolac nanocomposite with CuNPs s increases its sensitivity to pulsed laser exposure by more than 30%. The potential of single pulsed laser exposures to record high quality master holograms on commercially available and metal nanoparticles doped photoresists with at least five times lower exposures values as compared to the continuous-wave laser exposures usually used to expose photoresist materials in holographic applications, opens the possibility to use pulsed lasers for quick master-originals origination for embossed holograms applying a DWDH technique or analog methods.
Direct write digital holography technique (DWDH) using single pulsed exposures of 440nm pulsed laser has been applied to record master holograms on commercially available photoresists (ma-P1200 and Shipley 1800 series) of different thickness. Method for numerical evaluation of hologram quality, based on diffraction intensity measurement (reflected beam), was proposed and verified. It was found that all investigated photoresists: ma-P1205, ma-P1225 and S1805, were sensitive enough to record holographic structures at low single pulse laser exposures from the range 3.3 ÷ 19.5 mJ/cm2 . Best quality holograms with well – structured holopixels (hogels) were observed on 0.67 μm thick ma- P1205 photoresist exposed to 11.4 mJ/cm2 and on 0.65 μm thick S1805 photoresits exposed to 13 mJ/cm2, where corresponding measured diffraction intensity had its maximum value. In the case of thicker photoresists (ma-P1225, 3.33 μm), comparable quality of the hogel structure was found in the interval 9.8 – 13 mJ/cm2.
Investigation has shown a potential of single pulsed laser exposures to record good quality master holograms on commercially available photoresists applying at least 5 times lower exposures values as compared to CW laser exposures usually used to expose photoresist materials in holographic applications. That opens a possibility to use pulsed lasers for quick origination of master-originals for embossed holograms applying DWDH technique or analogue methods.
The Direct Write Digital Holography (DWDH) technique has been used to print master-original holograms for embossed applications using a 440nm pulsed laser. Holograms were recorded on both Silver Halide photo-plates and Shipley photoresist photo-plates. Shipley photoresist consistently exhibited a sensitivity to pulsed radiation several times better than that observed on exposure to CW radiation. In addition, image quality of the recorded holograms using pulsed radiation appeared very similar to that obtainable with CW exposure. The clear implication is that pulsed lasers emitting at 440nm can replace the CW HeCd lasers currently used for the origination of embossed holograms. Master-original holograms recorded with the DWDH technique are able to record deep 3D imagery. The origination technique described allows the production of master-original holograms with achromatic or full colour images. In addition the DWDH technique allows one to combine achromatic and full colour images on one hologram. As a proof of concept, embossing matrix shims were produced from our master-original holograms and embossed holograms were stamped.
A one-step digital holographic printing system based on RGB pulsed-laser technology is described. The system is capable of writing full-color composite digital reflection holograms and composite digital holographic optical elements up to a size of 1.0 m×1.5 m at hogel sizes ranging from 0.4 to 2 mm. We also show how the same pulsed-laser technology may be used to generate fast high-quality copies of such holograms. Both silver halide and photopolymer materials are used.
We report on creation of frequency doubled E-O Q-switched Nd:YAG laser lasing Single Longitudinal and Transversal
mode radiation at 1319 nm (4F3/2 to 4I11/2 transition) at repetition rate of 10 Hz. By means of linear resonator stable redlight
pulses were obtained at 660 nm having Emax = 5mJ output energy and τ = 50 ns (FWHM) pulse duration by using
NCPM LBO crystal as an extra-cavity frequency doubler. Laser design incorporates particularly made fast negative
feedback loop controls for pulse buildup control. It allowed obtaining much more stable laser performance as well as
much shorter Optical Jitter and fast pulse buildup time. To best our knowledge, these are the first time such pulse energy,
rep rate Transversal and Longitudinal mode structure ever achieved in compact flashlamp pumped E-O Q-Switched laser
operating at 1319 nm.
Investigated H1-H2 transfer analogue and digitally printed reflection holograms suitability for autostereoscopic projection displays. Proved that reflection hologram, having part of replayed image in front of its surface may be used as autostereoscopic display. Assembled 3D streaming images projection device, incorporating digitally printed reflection hologram. Given recommendation for digitally printed holograms use as 3D projection screens.
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