Air Laser-based TErahertz SpectroScopy of Explosives 2 – ALTESSE 2
The identification and detection of energetic materials has become a major issue of dual research, both civil and military, for the safety of populations. An important area of ??research in this context is the ability to measure, with the least uncertainty, a set of spectral signatures characterizing explosives or suspicious materials at remote distance. Constructing a prototype instrument for this purpose assumes that it can emit radiation operating in an appropriate spectral range at intensities sufficiently high to interact with the material and to collect the scattered field away from the emitting source. We propose here to deepen the technique of identification by terahertz spectroscopy (THz) of military explosives as well as simulating products. THz waves offer a great selectivity on molecular transitions and many "fingerprints" of explosives belong to this spectral domain. With the new power laser sources available today, their remote identification can become operational in the short term.
The ANR / ASTRID project ALTESSE 1 (2015 - 2018) revealed the rich potential of a time-resolved THz spectroscopy using an air plasma formed by two-color femtosecond laser pulses based on the coherent detection of THz radiations issued from a target. Major scientific and technological breakthroughs have been achieved, such as proof of feasibility of a direct THz spectroscopy of explosives at a distance of 15 meters from the laser source, or the measurements of numerous lines of absorption of energetic materials populating the THz region up to the mean infrared (<60 THz). ALTESSE 1 has established the proof of concept of a detection by the ABCD ("Air-Biased Coherent Detection") method, consisting of extracting a THz wave from the second harmonic of a laser wave exciting the Kerr response of air in the presence of an external electric field. The project MATURATION ALTESSE 2 proposed here will focus on ways to render this technology more reliable and increase the THz emission by multi-color air plasmas for the implementation of a future demonstrator at the end of the project. We will complete our research with a quantitative study of the laser filamentation regime. We shall develop specific studies based on ab-initio simulations that will allow us to attribute the measured absorption lines to the molecular motions of the constituent chemical groups of the probed molecules. We shall carry out systematic measurements of the delivered THz energy and cross sections according to the samples considered. Finally, we shall organize laser experimental campaigns over propagation distances of 10 to 20 m from a more adapted laser source than that used at the end of the ALTESSE 1 project.
To carry out this work, four main partners will be involved: CEA-DIF, the Institut Lumière Matière of the University Lyon 1 (ILM), the company Amplitude Systèmes (AS) and the SME Imagine Optic (IO). The CEA-DIF will lead the project. It will manage the outsourcing of DTU / Fotonik for laboratory spectroscopy and filamentation experiments and that of ISL for explosive spectroscopy experiments over extended distances. ILM will conduct numerical and experimental studies on plasma optimization and the selectivity of the measured spectral signatures. Finally, the company AS will supply a laser system for the acquisition of explosive spectra over long distances> 10 m in filamentation regime controlled by means of adaptative optics (IO). The first 18 months of the project will be dedicated to laboratory studies in order to increase the emissivity potential of air plasmas in the THz domain. The last 18 months will be devoted to experiments aimed at making reliable THz spectroscopy at remote distances. The success of this project should pave the way for building a demonstrator.
Monsieur Luc BERGE (Commissariat à l'énergie atomique et aux énergies alternatives)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
ILM - CNRS INSTITUT LUMIERE MATIERE
IO IMAGINE OPTIC
CEA Commissariat à l'énergie atomique et aux énergies alternatives
AS AMPLITUDE SYSTEMES
Help of the ANR 499,936 euros
Beginning and duration of the scientific project: January 2020 - 36 Months