Year
2012
Abstract
It has been suggested that laser-induced breakdown spectroscopy (LIBS) is a viable approach for efficient detection and characterization of nuclear materials relevant for nuclear forensics. LIBS utilizes an intense laser pulse to generate plasma on the surface of a target. The light from the plasma is collected and spectrally analyzed to determine elemental and, in some cases, isotopic composition of the target material. Such a technique could be utilized for identifying interdicted nuclear materials or for performing post-detonation analysis rapidly and without the need for sample preparation or destruction. Research of LIBS has shown that many advantages exist when using femtosecond pulses compared to nanosecond or picoseconds laser pulses, but the characteristics of plasmas generated on the surface by such ultrashort laser pulses are not as well understood. Using a Mach-Zehnder interferometer that uses femtosecond laser pulses as a probe, we are working to improve our understanding of the time evolution of ultrashort laser-induced plasmas generated for LIBS analysis. Using a fast Fourier transform method to extract phase information from the reconstructed interferogram, followed by an inverse Abel transformation, the radially symmetric refractive index and electron density distribution of the laser-produced plasma can be calculated. Further, by varying the interferometer probe pulse delay, the time evolution of the electron density distribution in the plasma can be observed. These “snapshots” of the plasma at different stages of formation could provide valuable information regarding the mechanisms of plasma formation and evolution.