Identification of chemical species using eye-safe laser pulses is becoming of wide interest for both biology and security purposes. Many instruments are designed to this purpose exploiting the high selectivity and sensitivity of the Raman spectroscopy. A laser pulse is sent to a target, and its Raman echo (usually from the Stokes band) is collected by some optics, dispersed and analyzed by a detector. Being the Raman cross sections usually very small, when compliance with the regulations about exposure to laser radiations is requested, each step of the acquisition chain must be optimized in order to lose less photons as possible from the target to the detector. In this work we will discuss some of these aspects with a main focus on the maximization of the laser dose and the detector signal-to-noise.
Lidar fluorosensors, i.e. laser radars based on laser induced fluorescence (LIF), have been extensively operated by the Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) to real-time monitoring of water bodies. LIF spectra contain unique signatures of phytoplankton pigments, chromophoric dissolved organic matter and dispersed impurities (crude oils). In this paper, we present technological innovations and oceanographic campaigns carried out by the Diagnostics and Metrology Laboratory (FSN-TECFIS-DIM) of ENEA. In particular, the lidar fluorosensors developed in 2017 within the RITMARE and RIMA projects will be described, and the preliminary results of the High North 18 and Flex 2018 campaigns will be reported.
We report the results of Raman investigation performed at stand-off distance between 6-10 m with a new apparatus, capable to detect traces of explosives with surface concentrations similar to those of a single fingerprint. The device was developed as part of the RADEX prototype (RAman Detection of EXplosives) and is capable of detecting the Raman signal with a single laser shot of few ns (10<sup>-9</sup> s) in the UV range (wavelength 266 nm), in conditions of safety for the human eye. This is because the maximum permissible exposure (MPE) for the human eye is established to be 3 mJ/cm<sup>2</sup> in this wavelength region and pulse duration. Samples of explosives (PETN, TNT, Urea Nitrate, Ammonium Nitrate) were prepared starting from solutions deposited on samples of common fabrics or clothing materials such as blue jeans, leather, polyester or polyamide. The deposition process takes place via a piezoelectric-controlled plotter device, capable of producing drops of welldefined volume, down to nanoliters, on a surface of several cm<sup>2</sup>, in order to carefully control the amount of explosive released to the tissue and thus simulate a slight stain on a garment of a potential terrorist. Depending on the type of explosive sampled, the detected density ranges from 0.1 to 1 mg/cm<sup>2</sup> and is comparable to the density measured in a spot on a dress or a bag due to the contact with hands contaminated with explosives, as it could happen in the preparation of an improvised explosive device (IED) by a terrorist. To our knowledge the developed device is at the highest detection limits nowadays achievable in the field of eyesafe, stand-off Raman instruments. The signals obtained show some vibrational bands of the Raman spectra of our samples with high signal-to-noise ratio (SNR), allowing us to identify with high sensitivity (high number of True Positives) and selectivity (low number of False Positives) the explosives, so that the instrument could represent the basis for an automated and remote monitoring device.
In the last decades there have been several terroristic attacks with improvised explosive devices (IED) that have raised the need for new instrumentation, for homeland security applications, to obtain a reliable and effective fight against terrorism. Public transportation has been around for about 150 years, but terroristic attacks against buses, trains, subways, etc., is a relatively recent phenomenon . Since 1970, transportation has been an increasingly attractive target for terrorists. Most of the attacks to transport infrastructures take place in countries where public transportation is the primary way to move. Terrorists prefer to execute a smaller-scale attack with certainty of success rather than a complex and demanding operation to cause massive death and destruction. . Many commonly available materials, such as fertilizer, gunpowder, and hydrogen peroxide, can be used as explosives and other materials, such as nails, glass, or metal fragments, can be used to increase the amount of shrapnel propelled by the explosion. The majority of substances that are classified as chemical explosives generally contain oxygen, nitrogen and oxidable elements such as carbon and hydrogen . The most common functional group in military explosives is NO2. That functionality can be attached to oxygen (ONO<sub>2</sub>) in the nitrate esters (PETN), to carbon (C-NO<sub>2</sub>) in the nitroarenes (TNT) and nitroalkanes (Nitromethane), and to nitrogen (N-NO<sub>2</sub>) as in the nitramines (RDX). Some organic peroxides, such as TATP and HMTD, are popular amongst terrorists because they are powerful initiators that can be easily prepared from easily available ingredients. Azides are also powerful primary explosives commonly used as initiators (commercial detonators) in civilian and military operations, therefore they could be potentially used by terrorists as initiators for IEDs.
Accurate knowledge of gas composition in volcanic plumes has high scientific and societal value. On the one hand, it gives information on the geophysical processes taking place inside volcanos; on the other hand, it provides alert on possible eruptions. For this reasons, it has been suggested to monitor volcanic plumes by lidar. In particular, one of the aims of the FP7 ERC project BRIDGE is the measurement of CO<sub>2</sub> concentration in volcanic gases by differential absorption lidar. This is a very challenging task due to the harsh environment, the narrowness and weakness of the CO<sub>2</sub> absorption lines and the difficulty to procure a suitable laser source. This paper, after a review on remote sensing of volcanic plumes, reports on the current progress of the lidar system.