Publications

Abstract not provided.

We present the results of a three year LDRD project which has focused on the development of novel, compact, ultraviolet solid-state sources and fluorescence-based sensing platforms that apply such devices to the sensing of biological and nuclear materials. We describe our development of 270-280 nm AlGaN-based semiconductor UV LEDs with performance suitable for evaluation in biosensor platforms as well as our development efforts towards the realization of a 340 nm AlGaN-based laser diode technology. We further review our sensor development efforts, including evaluation of the efficacy of using modulated LED excitation and phase sensitive detection techniques for fluorescence detection of bio molecules and uranyl-containing compounds.

A discussion on an active gas imager that can potentially improve system performance and reliability in Smart Leak Detection and Repair covers conventional single-wavelength imaging; differential imaging; methane detection; modification for detecting fugitive emissions relevant to refineries and chemical plants; and system description. This is an abstract of a paper presented at the AWMA's 99th Annual Conference and Exhibition (New Orleans, LA 6/20-23/2006).

In optical firing sets, laser light is used to supply power to electronics (to charge capacitors, for example), to trigger electronics (such as vacuum switches), or in some cases, initiate explosives directly. Since MEMS devices combine electronics with electro-mechanical actuators, one can integrate safe and arm logic alongside the actuators to provide all functions in a single miniature package. We propose using MEMS-activated mirrors to make or break optical paths as part of the safe and arm architecture in an optical firing set. In the safe mode, a miniature (∼1 mm diameter) mirror is oriented to prevent completion of the optical path. To arm the firing set, the MEMS mirrors are deflected into the proper orientation thereby completing the optical path required for system functionality (e.g., light from a miniature laser completes the path to an optically triggered switch). The optical properties (i.e. damage threshold, reflectivity, transmission, absorption and scatter) of the miniature mirrors are critical to this application. Since Si is a strong absorber at the wavelengths under consideration (800 to 1064 nm), high-reflectivity, high-damage-threshold, dielectric coatings must be applied to the MEMS devices. In this paper we present conceptual MEMS-activated mirror architectures for performing arming and safing functions in an optical firing set and report test data which shows that dielectric coatings applied to MEMS-mirrors can withstand the prerequisite laser pulse irradiance. The measured optical damage threshold of polysilicon membranes with high-reflectivity multilayer dielectric coatings is ∼ 4 GW/cm 2, clearly demonstrating the feasibility of using coated MEMS mirrors in firing sets.

Continuing use of explosives by terrorists throughout the world has led to great interest in explosives detection technology, especially in technologies that have potential for standoff detection. This LDRD was undertaken in order to investigate the possible detection of explosive particulates at safe standoff distances in an attempt to identify vehicles that might contain large vehicle bombs (LVBs). The explosives investigated have included the common homogeneous or molecular explosives, 2,4,6-trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), cyclonite or hexogen (RDX), octogen (HMX), and the heterogeneous explosive, ammonium nitrate/fuel oil (ANFO), and its components. We have investigated standard excited/dispersed fluorescence, laser-excited prompt and delayed dispersed fluorescence using excitation wavelengths of 266 and 355 nm, the effects of polarization of the laser excitation light, and fluorescence imaging microscopy using 365- and 470-nm excitation. The four nitro-based, homogeneous explosives (TNT, PETN, RDX, and HMX) exhibit virtually no native fluorescence, but do exhibit quenching effects of varying magnitude when adsorbed on fluorescing surfaces. Ammonium nitrate and fuel oil mixtures fluoresce primarily due to the fuel oil, and, in some cases, due to the presence of hydrophobic coatings on ammonium nitrate prill or impurities in the ammonium nitrate itself. Pure ammonium nitrate shows no detectable fluorescence. These results are of scientific interest, but they provide little hope for the use of UV-excited fluorescence as a technique to perform safe standoff detection of adsorbed explosive particulates under real-world conditions with a useful degree of reliability.

Abstract not provided.

We report results from Yb-doped fiber amplifiers seeded with two microchip lasers having 0.38-ns and 2.3-ns pulse durations. The shorter duration seed resulted in output pulses with a peak power of > 1.2 MW and pulse energy of 0.67 mJ. Peak power was limited by nonlinear processes that caused breakup and broadening of the pulse envelope as the pump power increased. The 2.3-ns duration seed laser resulted in output pulses with a peak power of >300 kW and pulse energy of > 1.1 mJ. Pulse energies were limited by the onset of stimulated Brillouin scattering and ultimately by internal optical damage (fluences in excess of 400 J/cm 2 were generated). In both experiments, nearly diffraction-limited beam profiles were obtained, with M 2 values of < 1.2. Preliminary results of a pulse-amplification model are in excellent agreement with the experimental results of the amplifiers operating in the low-to-moderate gain-depletion regime.

Abstract not provided.

Optical firing sets need miniature, robust, reliable pulsed laser sources for a variety of triggering functions. In many cases, these lasers must withstand high transient radiation environments. In this paper we describe a monolithic passively Q-switched microlaser constructed using Cr:Nd:GSGG as the gain material and Cr4+:YAG as the saturable absorber, both of which are radiation hard crystals. This laser consists of a 1-mm-long piece of undoped YAG, a 7-mm-long piece of Cr:Nd:GSGG, and a 1.5-mm-long piece of Cr 4+:YAG diffusion bonded together. The ends of the assembly are polished flat and parallel and dielectric mirrors are coated directly on the ends to form a compact, rugged, monolithic laser. When end pumped with a diode laser emitting at ∼807.6 nm, this passively Q-switched laser produces ∼1.5-ns-wide pulses. While the unpumped flat-flat cavity is geometrically unstable, thermal lensing and gain guiding produce a stable cavity with a TEM00 gaussian output beam over a wide range of operating parameters. The output energy of the laser is scalable and dependent on the cross sectional area of the pump beam. This laser has produced Q-switched output energies from several μJ per pulse to several 100 μJ per pulse with excellent beam quality. Its short pulse length and good beam quality result in high peak power density required for many applications such as optically triggering sprytrons. In this paper we discuss the design, construction, and characterization of this monolithic laser as well as energy scaling of the laser up to several 100 μJ per pulse.

Abstract not provided.

The Defense Advanced Research Projects Agency (DARPA) has recognized that biological and chemical toxins are a real and growing threat to troops, civilians, and the ecosystem. The Explosives Components Facility at Sandia National Laboratories (SNL) has been working with the University of Montana, the Southwest Research Institute, and other agencies to evaluate the feasibility of directing honeybees to specific targets, and for environmental sampling of biological and chemical ''agents of harm''. Recent work has focused on finding and locating buried landmines and unexploded ordnance (UXO). Tests have demonstrated that honeybees can be trained to efficiently and accurately locate explosive signatures in the environment. However, it is difficult to visually track the bees and determine precisely where the targets are located. Video equipment is not practical due to its limited resolution and range. In addition, it is often unsafe to install such equipment in a field. A technology is needed to provide investigators with the standoff capability to track bees and accurately map the location of the suspected targets. This report documents Light Detection and Ranging (LIDAR) tests that were performed by SNL. These tests have shown that a LIDAR system can be used to track honeybees. The LIDAR system can provide both the range and coordinates of the target so that the location of buried munitions can be accurately mapped for subsequent removal.

This report summarizes the development of sensor particles for remote detection of trace chemical analytes over broad areas, e.g residual trinitrotoluene from buried landmines or other unexploded ordnance (UXO). We also describe the potential of the sensor particle approach for the detection of chemical warfare (CW) agents. The primary goal of this work has been the development of sensor particles that incorporate sample preconcentration, analyte molecular recognition, chemical signal amplification, and fluorescence signal transduction within a ''grain of sand''. Two approaches for particle-based chemical-to-fluorescence signal transduction are described: (1) enzyme-amplified immunoassays using biocompatible inorganic encapsulants, and (2) oxidative quenching of a unique fluorescent polymer by TNT.