NOPR Community:

Holographic optical elements encoded security holograms with enhanced features

2006-12-01T00:00:00Z

Title: Holographic optical elements encoded security holograms with enhanced features Authors: Kaura, Sushil K; Virdi, S P S; Aggarwal, A K Abstract: A simple and cost-effective two-step method for forming encoded security holograms with enhanced features is described in this paper. These security holograms contain enhanced encoded/concealed anti-counterfeit security Features, which can only be decoded using a key hologram in the final reading process. The encoded key hologram and the security hologram are in the form of special encoded complex holographic optical elements. When the security hologram is illuminated with the decoding beam, specific moire-like fringe patterns are formed on the security hologram and in addition several spatially separated bright focused spots are also generated from the security hologram. A careful spatial filtering of these bright spots results in specific moire patterns at different locations in the observation plane and moreover these patterns contain variable interferometric features. Further, these moire patterns disappear when the security hologram is perfectly repositioned and only the variable interferometric features are formed. Since these security holograms contain variable interferometric features in addition to the specific moire patterns and bright focused spots, thus making these holograms suitable for both visual and as well as machine inspection. Page(s): 896-902

Spectral analysis of Cu²⁺: B₂O₃-(TeO₂/CdO/ZnO)-Li₂O-AlF₃ glasses

2006-12-01T00:00:00Z

Title: Spectral analysis of Cu²⁺: B₂O₃-(TeO₂/CdO/ZnO)-Li₂O-AlF₃ glasses Authors: Reddy, B Sudhakar; Buddhudu, S Abstract: The development and optical spectral analysis of Cu²⁺ (0.5 mol %) doped three new glasses have been reported in the following composition: 10TeO₂-69.5 B₂O₃-10 Li₂O-10 AIF₃; 10ZnO-69.5 B₂O₃-10 Li₂O-10 AIF₃; 10ZnO-69.5 B₂O₃10 Li₂O-10 AIF₃. Due to the homogeneous distribution of Cu²⁺ ions, both CdO and ZnO containing glasses are found to be in bright blue colour, but a greenish blue colour has been noticed from the TeO₂ containing glass, the reason for this has been explained. Without the Cu²⁺ ions, the reference glasses have also been prepared and found them in good transparency with excellent resistance towards the moisture without any degradation on their surfaces. Based on the XRD profiles, amorphous nature of these glasses has been confirmed. Due to the presence of TeO₂, the UV transmission for the glass is found to be extended up to 300 nm compared with the other two glasses. Under an UV source (254 nm), a blue emission has been noticed from the surfaces of the glasses. From the measured absorption spectra of these copper glasses, a abroad absorption band (²B_1g → ²B_2g) at 800 nm and a weak absorption band (²B_1g → ²B_2g) at 387 nm have been measured to examine the effects of the CdO, ZnO and TeO₂ contents in the glasses studied. FTIR spectra of these glasses have also been analyzed to investigate the glass structures. Emission spectra of (0.5 mol %) Cu²⁺: B₂O₃-(TeO₂/CdO/ZnO)-Li₂O-AlF₃ have revealed two emissions at 415 and 438 nm with an excitation at 371 nm. Page(s): 887-895

Structural analysis and second-order non-linear optical activity of urea hydrogen peroxide adduct

2006-07-01T00:00:00Z

Title: Structural analysis and second-order non-linear optical activity of urea hydrogen peroxide adduct Authors: Das, Malyaj; Prasad, R; Sent, P Abstract: Urea hydrogen peroxide adduct is synthesized and characterized using UV and IR spectra. Second harmonic generation (SHG) efficiency has been determined experimentally in this adduct using pulsed Nd: YAG laser at 1064 nm wavelength. The efficiency is higher in the adduct as compared to urea. Geometry of the molecule was optimized using Austin Model 1 (AM1) semi-empirical technique. Our computations suggest two conformers of the adduct, both having no center of symmetry. Complete geometry of the molecule and the dipole moment calculations have been reported. It is concluded that increased dipole moment of one of the conformers of the adduct is responsible for the enhanced SHG efficiency of the adduct. Page(s): 554-558

Novel technique of pulse width modulator design using a ring oscillator

2006-06-01T00:00:00Z

Title: Novel technique of pulse width modulator design using a ring oscillator Authors: Sarkar, B C; Mandal, M K Abstract: A novel technique of pulse width modulation using a multiphase ring oscillator and a multiplexer-based digitally controlled phase shifter (DCPS) has been presented. The proposed circuit can produce 0 to 100 % variation of the width of the pulse train, depending on the control word applied to DCPS. Experimental results obtained in a prototype circuit confirm the design algorithm proposed in this work. Page(s): 473-477

NOPR Community:

Holographic optical elements encoded security holograms with enhanced features

Spectral analysis of Cu2+: B2O3-(TeO2/CdO/ZnO)-Li2O-AlF3 glasses

Structural analysis and second-order non-linear optical activity of urea hydrogen peroxide adduct

Novel technique of pulse width modulator design using a ring oscillator

Spectral analysis of Cu²⁺: B₂O₃-(TeO₂/CdO/ZnO)-Li₂O-AlF₃ glasses