Border security challenges and immigration issues are increasing considerably in recent years. Counterfeiting and fraudulent use of identity and other travel documents are posing serious threats and safety concerns worldwide, ever since the advancement of computers, photocopiers, printers and scanners. Considering the current scenario of illegal migration and terrorism across the world, advanced technologies and improved security features are essential to enhance border security and to enable smooth transits. In this paper, we present a novel dual waveguide based invisible fluorescence security feature and a simple validation system to elevate and strengthen the security at border controls. The validation system consists of an LED (light emitting diode) as excitation source and an array photodetector which helps in the simultaneous detection of multiple features from the fluorescence waveguides. The fluorescence waveguides can be embedded into the identity document as micro-threads or tags which are invisible to the naked eye and are only machine readable. In order to improve the sensitivity, rare earth fluorescence materials are used which absorb only specific ultraviolet (UV) or visible (VIS) wavelengths to create corresponding fluorescent emission lines in the visible or infrared wavelengths. Herein, we present the preliminary results based on the fluorescence spectroscopic studies carried out on the fabricated rare earth doped waveguides. The effect of different rare earth concentrations and excitation wavelengths on the fluorescence intensity were investigated.
The past three years have seen a global increase in explosive-based terror attacks. The widespread use of improvised explosives and anti-personnel landmines have caused thousands of civilian casualties across the world. Current scenario of globalized civilization threat from terror drives the need to improve the performance and capabilities of standoff explosive trace detection devices to be able to anticipate the threat from a safe distance to prevent explosions and save human lives. In recent years, laser-induced breakdown spectroscopy (LIBS) is an emerging approach for material or elemental investigations. All the principle elements on the surface are detectable in a single measurement using LIBS and hence, a standoff LIBS based method has been used to remotely detect explosive traces from several to tens of metres distance. The most important component of LIBS based standoff explosive trace detection system is the telescope which enables remote identification of chemical constituents of the explosives. However, in a compact LIBS system where Cassegrain telescope serves the purpose of laser beam delivery and light collection, need a design optimization of the telescope system. This paper reports design optimization of a Cassegrain telescope to detect explosives remotely for LIBS system. A design optimization of Schmidt corrector plate was carried out for Nd:YAG laser. Effect of different design parameters was investigated to eliminate spherical aberration in the system. Effect of different laser wavelengths on the Schmidt corrector design was also investigated for the standoff LIBS system.
Surface plasmon resonance (SPR) is a rapid and sensitive technique used for probing the biomolecular interactions in real time. Several new approaches have been suggested to improve the sensitivity of SPR sensors over the last two decades. Most of them are based on creating or patterning nanostructures/nanomaterials in order to enhance the sensitivity. Graphene offers several advantages due to its special optical and structural properties. Herein, we propose a new angular interrogated dual wavelength based differential detection approach for graphene based SPR sensing to increase the sensitivity. Reflectivity of the p-polarized incident light has been calculated using the N-layer model for the most common Kretschmann configuration. Sensitivity of the SPR with and without graphene layers has been calculated for single and dual wavelength based approaches. Computational results show that the proposed graphene SPR sensor has (1 + 0.4 L) η times higher sensitivity than the conventional gold thin film based SPR sensors. Further, increasing the number of graphene layers, L, improves the sensitivity. Where, η represents the enhanced sensitivity due to increased binding/adsorption of biomolecules on graphene over a gold thin film. Sensitivity analysis has been carried out for a refractive index (Δn) = 0.005 with L = 1 to 10.