Filament-Based Laser-Induced Breakdown Spectroscopy for the Standoff Detection of Radiological Materials

An improved method is needed for the detection of radiological materials for nuclear nonproliferation and safety. Current techniques using laser-induced breakdown spectroscopy (LIBS), while robust, are limited in range due to pulse energy and diffraction. Furthermore, atmospheric broadening of the spectral lines reduces the sensitivity of the detection scheme, such as optical emission spectroscopy, to measure the isotopic content of radiological materials at standoff distances. We have proposed the use of femtosecond laser pulses that can form stable filament s air overcoming diffraction and the high energy requirement. They can, thus, deliver high intensity for ablation to interrogate radiological materials or target samples at long distances. We have experimentally demonstrated the utility and potential of optical filaments for LIBS at range. The ablation plasma from femtosecond pulses and optical filaments show remarkably different characteristics from a nanosecond laser plasma that seem to suggest that atmospheric broadening is less critical for femtosecond and filament LIBS in air. We have also demonstrated a new technique to increase the range and intensity of filaments for long range propagation. We plan to combine optical emission spectroscopy with laser absorption spectroscopy (LAS) to investigate the plume dynamics of laser ablation plasmas from nanosecond, femtosecond laser pulses and optical filaments over a broad spectral range. This will enable us to select the best spectral range for laser interrogation of radiological materials at standoff distances. Commercial Applications and Other Benefits: The proposed technology will allow the precise and accurate measurements of radiological materials using LIBS and LAS. These techniques can also be applied for other atmospheric monitoring and light detection and ranging (LIDAR) applications.