Paul Ruffin

Detection of residual traces of explosives by surface enhanced Raman scattering using gold coated substrates produced by nanospheres imprint technique

Explosives detection for national and aviation security has been an area of concern for many years. In order to improve the security in risk areas, much effort has been focused on direct detection of explosive materials in vapor and bulk form. New techniques and highly sensitive detectors have been extensively investigated and developed to detect and identify residual traces that may indicate an individuals recent contact with explosive materials. This paper reports on the use and results of Surface Enhanced Raman Scattering (SERS) technique, to analyze residual traces of explosives in highly diluted solutions by using low-resolution Raman spectroscopy (LRRS). An evaluation of the detection sensitivity of this technique has been accomplished using samples of explosives such as Trinitrotoluene(TNT), Cyclotrimethylenetrinitramine (RDX) and HMX evaluated at different concentrations. Additionally, different SERS substrates have been studied in order to achieve the best enhancement of the Raman spectrum for residual amounts of materials. New substrates produced by gold-coated polystyrene nanospheres have been investigated. Two different sizes of polystyrene nanospheres, 625nm and 992nm, have been used to produce nanopatterns and nanocavities on the surface of a glass slide which has been coated with sputtered gold. Results from homemade substrates have been compared to a commercial gold-coated substrate consisting of an array of resonant cavities that gives the SERS effect. Sample concentration, starting from 1000ppm was gradually diluted to the smallest detectable amount. Raman spectrum was obtained using a portable spectrometer operating at a wavelength of 780nm.

Short Distance Standoff Raman Detection of Extra Virgin Olive Oil Adulterated with Canola and Grapeseed Oils

A short distance standoff Raman technique is demonstrated for detecting economically motivated adulteration (EMA) in extra virgin olive oil (EVOO). Using a portable Raman spectrometer operating with a 785 nm laser and a 2-in. refracting telescope, adulteration of olive oil with grapeseed oil and canola oil is detected between 1% and 100% at a minimum concentration of 2.5% from a distance of 15 cm and at a minimum concentration of 5% from a distance of 1 m. The technique involves correlating the intensity ratios of prominent Raman bands of edible oils at 1254, 1657, and 1441 cm–1 to the degree of adulteration. As a novel variation in the data analysis technique, integrated intensities over a spectral range of 100 cm–1 around the Raman line were used, making it possible to increase the sensitivity of the technique. The technique is demonstrated by detecting adulteration of EVOO with grapeseed and canola oils at 0–100%. Due to the potential of this technique for making measurements from a convenient distance, the short distance standoff Raman technique has the promise to be used for routine applications in food industry such as identifying food items and monitoring EMA at various checkpoints in the food supply chain and storage facilities.

Middle-IR supercontinuum generations and applications

In this paper, the two different mechanisms of supercontinuum generation in single crystal sapphire fibers according to fiber lengths longer and shorter than dispersion length are theoretically and experimentally investigated. When the fiber length is shorter than the dispersion length, self-phase modulation is the dominant factor for supercontinuum broadening. A broad spectrum ranging from near-IR (1.2 μm) to the lower end of mid-IR (2.8 μm) is obtained. But, when the fiber length is longer than dispersion length, soliton-related dynamics with self-phase modulation is the dominant factor for supercontinuum. We further demonstrate that supercontinuum in a sapphire fiber can extend beyond the range of silica fibers by showing the spectrum from 2 μm to 3.2 μm. Also, we successfully apply the supercontinuum source generated from a sapphire fiber to IR spectroscopy. The spectra of pseudo-TNT chemical measured using our own supercontinuum source is in good agreement with those obtained by FTIR. Supercontinuum generation using a sapphire fiber, which has high damage threshold and broad transmission ranges can be used in many applications such as IR spectroscopy, broadband LADAR, remote sensing, and multi-spectrum free space communications.

An investigation on fiber optic gyroscopes using microstructured fibers

In this paper, we review currently available fiber-optic gyroscope (FOG) technologies and major noise factors limiting the performance of FOGs. We investigate possible solutions to noise factors including Rayleigh backscattering, Kerr effect, Faraday, and Shupe effects. Based on these solutions, we present the possible design of an interferometric FOGs employing microstructured fibers. A supercontinuum source can minimize Rayleigh backscattering and Kerr effect by reducing the coherence length of FOGs. Also, by using a photonic bandgap fiber with hollow core, Kerr, Faraday and Shupe effects can be minimized.

Gold/silver coated nanoporous ceramic membranes: a new substrate for SERS studies

Surface Enhanced Raman Scattering (SERS) is a recently discovered powerful technique which has demonstrated sensitivity and selectivity for detecting single molecules of certain chemical species. This is due to an enhancement of Raman scattered light by factors as large as 1015. Gold and Silver-coated substrates fabricated by electron-beam lithography on Silicon are widely used in SERS technique. In this paper, we report the use of nanoporous ceramic membranes for SERS studies. Nanoporous membranes are widely used as a separation membrane in medical devices, fuel cells and other studies. Three different pore diameter sizes of commercially available nanoporous ceramic membranes: 35 nm, 55nm and 80nm are used in the study. To make the membranes SERS active, they are coated with gold/silver using sputtering techniques. We have seen that the membranes coated with gold layer remain unaffected even when immersed in water for several days. The results show that gold coated nanoporous membranes have sensitivity comparable to substrates fabricated by electron-beam lithography on Silicon substrates.

Innovative Smart Micro Sensors for Army Weaponry Applications

Micro sensors offer the potential solution to cost, size, and weight issues associated with smart networked sensor systems designed for environmental/missile health monitoring and rocket out-gassing/fuel leak detection, as well as situational awareness on the battlefield. In collaboration with the University of Arkansas (Fayetteville), University of Alabama (Tuscaloosa and Birmingham), Alabama A&M University (Normal), and Streamline Automation (Huntsville, AL), scientists and engineers at the Army Aviation & Missile Research, Development, and Engineering Center (AMRDEC) are investigating several nano-based technologies to solve the problem of sensing extremely small levels of toxic gases associated with both chemical warfare agents (in air and liquids) and potential rocket motor leaks. Innovative techniques are being devised to adapt voltammetry, which is a well established technique for the detection and quantification of substances dissolved in liquids, to low-cost micro sensors for detecting airborne chemical agents and potential missile propellant leakages. In addition, a surface enhanced Raman scattering (SERS) technique, which enhances Raman scattered light by excitation of surface plasmons on nanoporous metal surfaces (nanospheres), is being investigated to develop novel smart sensors for the detection of chemical agents (including rocket motor out-gassing) and potential detection of home-made explosive devices. In this paper, results are delineated that are associated with experimental studies, which are conducted for the aforementioned cases and for several other nano-based technology approaches. The design challenges of each micro sensor technology approach are discussed. Finally, a comparative analysis of the various innovative micro-sensor techniques is provided.

Recent advances on multiple channel unequally spaced optical phased array for ultrafast LADAR

In this paper, we experimentally verify that previously proposed idea of unequally spaced optical phased array can greatly reduce grating-lobes. As the verification purpose of our previous numerical design, a laser beam is passed through unequally-spaced slits, whose spacings are the same as the previous design. Interference patterns formed after both 4- and 8-channel slits clearly show that the grating-lobes can be greatly minimized. To realize the beam steering possible, optical waveguides array, which has unequally spaced design at the output ends is fabricated. The phase of each beam can be varied using fibers array wound around PZT tubes before each beam is coupled into the waveguides array. Interference patterns formed after the outputs of both 4- and 8-channel waveguides array show that the gratinglobes can be greatly reduced using unequally spaced optical phased array technique.

MEMS-based phased arrays for army applications

The Army Aviation and Missile Research, Development, and Engineering Center (AMRDEC) initiated a research and development project several years ago to develop Micro Electro-Mechanical Systems (MEMS)-based phased arrays to provide rapid beam steering for sensors, optical and Radio Frequency (RF) missile seekers, and RF communication links. In particular, the joint AMRDEC/Army Research Laboratory (ARL) project, which leverages low-cost phased array components developed under the Defense Advanced Research Projects Agency (DARPA) Low Cost Cruise Missile Defense (LCCMD) project, is developing RF switches, phase shifters, and passive phased sub-arrays to provide a fast scanning capability for pointing, acquisition, tracking, and data communication; and rugged, optical MEMS-based phased arrays to be employed in small volume, low-cost Laser Detection and Ranging (LADAR) seekers. The current status of the project is disclosed in this paper. Critical technical challenges, which include design and fabrication of the RF switches and phase shifters, design and fabrication of micro lens arrays, control of beam steering, scanning angular resolution and array losses, are discussed. Our approach to overcoming the technical barriers and achieving required performance is also discussed. Finally, the validity of a MEMS technology approach against competing low cost technologies is presented.

High efficiency IR supercontinuum generation and applications

In this paper, we have reviewed our recent works on IR supercontinuum generation (SCG) and its applications. First, we provide a brief review on the physical mechanism of the supercontinuum generation. Second, the advance of SCG in single crystal sapphire fibers is reviewed and introduced. In particular, we discussed how to fabricate thinned sapphire fiber and use it for high efficiency SCG. Finally, experimental results of chemical analysis with supercontinuum source are reviewed.

Recent advances on IR supercontinuum source and its applications

In this paper, we have reviewed our recent works on IR supercontinuum generation (SCG) and its applications. First, we provide a brief introduction on the motivations of the proposed effort. Second, the work of SCG in single crystal sapphire fibers is reviewed. Third, in addition to single crystal sapphire fibers, the method, the process, and the results of fabricating other IR waveguides are presented. Fourth, a quantitative simulation on the supercontinuum generation with the new IR waveguide is provided, which shows that it is possible to generate SCG beyond 5 microns. To the best knowledge of authors, this is the longest SCG reported so far. Finally, more experimental results of chemical analysis with supercontinuum source are presented.