Stand-off Detection at the DLR Laser Test Range Applying Laser-Induced Breakdown Spectroscopy

The DLR laser test range at Lampoldshausen allows for optical measurements under daylight conditions at distances up to 130 m. This infrastructure is very suitable for the development of stand-off detection systems of biological, chemical and explosive hazardous substances. In a first step, laser-induced breakdown spectroscopy (LIBS) has been introduced to this test site. A basic LIBS set-up and first LIBS spectra of selected samples are presented. A Nd:YAG laser beam was focussed by a Cassegrain type telescope onto different samples at distances exceeding 50 m. The light of the generated plasma plume was collected by a Newtonian telescope, and analyzed by a gated broadband CCD-spectrometer system. The Nd:YAG laser yields pulse energies up to 800 mJ at a wavelength of 1064 nm and a pulse width of 8 ns. Optionally the second and third harmonics can be extracted. LIBS spectra from 10 nm layers of gold on a silicon wafer were recorded. In addition, LIBS spectra from black powder were measured, and compared to the spectrum of potassium nitrate, which is a main component of black powder and shows very characteristic emission. LIBS spectra of the above samples have also been acquired with an excitation laser wavelength in the eye-safe region. Recorded spectra are measured as a function of the laser wavelength, pulse energy, and energy density on the target and are compared to the literature

Remote Raman detection of chlorine with deep UV excitation wavelengths

Deep ultraviolet Raman spectroscopy measurements have been performed at the German Aerospace Center (DLR) to detect chlorine gas. In this study a remote Raman set up was optimized to detect chlorine gas at a distance of 60 cm. Several ultraviolet laser wavelengths (224, 232, 235 nm respectively, 2.5 mJ/pulse at 10 Hz) were changed to experimentally observe the highest possible signal to noise ratio. For each tested excitation wavelength, chlorine spectra were successfully detected. Detection limits in acquisition times for a 0.36 bar chlorine sample are discussed. A possible solution to avoid spectral overlapping of the background material with the sample is presented

Multispectral LIF-Based Standoff Detection System for the Classification of CBE Hazards by Spectral and Temporal Features

Laser-induced fluorescence (LIF) is a well-established technique for monitoring chemical processes and for the standoff detection of biological substances because of its simple technical implementation and high sensitivity. Frequently, standoff LIF spectra from large molecules and bio-agents are only slightly structured and a gain of deeper information, such as classification, let alone identification, might become challenging. Improving the LIF technology by recording spectral and additionally time-resolved fluorescence emission, a significant gain of information can be achieved. This work presents results from a LIF based detection system and an analysis of the influence of time-resolved data on the classification accuracy. A multi-wavelength sub-nanosecond laser source is used to acquire spectral and time-resolved data from a standoff distance of 3.5 m. The data set contains data from seven different bacterial species and six types of oil. Classification is performed with a decision tree algorithm separately for spectral data, time-resolved data and the combination of both. The first findings show a valuable contribution of time-resolved fluorescence data to the classification of the investigated chemical and biological agents to their species level. Temporal and spectral data have been proven as partly complementary. The classification accuracy is increased from 86% for spectral data only to more than 92%

Application of Standoff LIF to Living and Inactivated Bacteria Samples

To minimize the impact of an airborne bio-agent output, sensitive, specific and swift detection and identification are essential. A single method can hardly meet all of these requirements. Point sensors allow highly sensitive and specific identification but are localized and comparatively slow. Most laser-based standoff systems lack selectivity and specificity but provide real-time detection and classification in a wide region with additional information about location and propagation. A combination of both methods allows benefiting from their complementary assets and may be a promising solution to optimize detection and identification of hazardous substances. Here, we present progress for an outdoor bio-detector based on laser-induced fluorescence (LIF) developed at the DLR Lampoldshausen. After excitation at 280 and 355 nm, bacteria species express unique fluorescence spectra. Upon deactivation, the spectral features change depending on the applied method

EDX Remote Detection on NATO SET-237 Samples

Ultraviolet Raman spectroscopy measurements have been performed at DLR Lampoldshausen to detect NATO SET-237 standard samples of RDX. The goal was to quantify the minimum requirements for an unambiguous identification in remote detection (60 cm distance) arrangement using simple and robust spectroscopic equipment on well-defined distribution of explosives on surfaces. Therefore, Raman spectra of RDX have been acquired for different sample concentrations (50, 250, and 1000 μg/cm2 respectively) and under several laser energies (1.5, 3.0 and 5.0 mJ/pulse respectively) at 355 nm excitation wavelength. The lowest producible surface concentration (50 µg/cm2) was detected with excitation energy of 3 mJ/pulse in the described configuration. The presented Raman spectra are also discussed in terms of future applications

Remote Raman Spectroscopy of Explosive Precursors

Deep ultraviolet Raman spectroscopy measurements have been performed at the German Aerospace Center (DLR) with the aim of detecting traces (µg range) of explosive precursors. In this study a backscattering Raman system was set up and optimized to detect urea, sodium perchlorate, ammonium nitrate, and sodium nitrate at a 60 cm short-range remote detection. Sample were tested at 264 nm ultraviolet laser excitation wavelength to experimentally observe any possible trace over textiles samples. For each colored sample textile, Raman spectra were acquired and no background fluorescence interference was observed at this laser excitation wavelength. Detection limits and system sensitivity with an acquisition times up to 3 seconds for microgram traces are presented

Ultraviolet Raman Spectroscopy for Remote Detection of Chlorine Gas

As a primary material frequently used in industry, chlorine is relatively easy to obtain and available even in large quantities. Despite its high toxicity, molecular chlorine is readily available since it is an essential educt in the chemical industry. Over the past decades, numerous accidents involving injured and dead victims have occurred. Furthermore, it was already misused as a warfare agent at the beginning of the last century with still reported attacks. Early detection, localization, and monitoring of sources and cloud movements are essential for protecting stationary facilities, mobile operations, and the public. In contrast to most chemical hazardous materials, where it is possible to detect them by vibrational spectroscopic methods (e.\,g., passive hyper-spectral absorption technologies in the infrared), halogens are inactive to infrared absorption. Raman-based technologies rely on changes in the polarizability of the molecule and provide vibrational-spectroscopic access to such diatomic molecules and therefore close the gap in infrared detection capabilities. Here we present a straightforward approach for a standoff Raman detector in a backscattering configuration. This paper uses a simplified model to discuss optimum excitation wavelengths in achievable detection ranges. We validate the model by spontaneous (vibrational) Raman spectroscopic measurements between 20 and 60~m standoff distance. We also briefly discuss detection performances and technical and physical aspects as prospects of system design.Comment: 6th International Conference on Frontiers of Diagnostic Technologies, 6 page

Compact setup for standoff laser induced breakdown spectroscopy of radioactive material

Radioactive materials present a major threat and can cause severe direct and long term injuries to humans as experienced i.e. in the Fukushima and Chernobyl nuclear plant catastrophes. Furthermore, intended use of radiological dispersal devices may spread radioactive materials over large areas. Detecting these hazards and investigating the status of contaminated areas a remote standoff determination of nuclear fission products would serve as a helpful tool for first responders and damage control teams. Laser induced breakdown spectroscopy (LIBS) offers a unique possibility for the identification of nuclear fission products and can be able to distinguish different isotopes of the same species. Within this scope and based on experiences with a high power / long distance (> 100 m) LIBS setup a compact and low power setup is presented. The compactness allows for handheld operation as well as mounted on a small robot or on an unmanned aerial vehicle (UAV) an advanced setup could be controlled remotely and would be able to safely determine radioactive materials

Standoff laser induced fluorescence of living and inactivated bacteria

Biological hazards, such as bacteria, represent a non-assessable threat in case of an accident or a terroristic attack. Rapid detection and highly sensitive identification of released, suspicious substances at low false alarm rates are challenging requirements which one single technology cannot cope with. It has been shown that standoff detection using laser-induced fluorescence (LIF) can provide information on the class of bioorganic substances in real-time1. In combination with traditional, highly sensitive, but non-standoff methods, the time for identification of the threat can be optimized. This work is aimed at the selectivity of LIF technology for different bacterial strains. A second important aspect examines how to deal with inactivated bacteria and how their fluorescence signature changes after deactivation. LIF spectra of closely and more distantly related bacterial strains are presented as well as spectra of bacteria treated by different inactivation methods