Colloquium: Sivanandan Harilal

    Thursday, September 21, 2017 - 3:30pm - 5:00pm
    Meinel 307

    Isotopic analysis of solids using optical spectroscopy of laser-produced plasmas


    Currently, isotopic analysis of nuclear materials is predominantly laboratory based (mass spectroscopy) which is time consuming and not useful for field applications. Optical spectroscopic methods (emission, absorption, fluorescence) in conjunction with laser ablation sampling have the potential to overcome these limitations with capabilities for in-field, rapid, and non-contact analysis. Laser-induced breakdown spectroscopy (LIBS) is a proven technology for standoff detection of all elements in the periodic table, however, spectral and instrumental broadening affect its performance for isotopic analysis. On the other hand, laser-absorption spectroscopy provides spectral resolution for isotopic analysis, but it requires orthogonal beam interrogation geometry.  Laser-induced fluorescence (LIF) spectroscopy incorporates aspects of both atomic absorption and emission and is capable of overcoming limitations of both emission and absorption spectroscopy methods for isotopic analysis. In LIF spectroscopy, like atomic absorption, the ground state atoms in the plasma plume are excited by a tunable laser.  However, instead of directly monitoring the amount of light absorbed in the process, the emission resulting from the decay of the excited atoms by the source is measured.  In this work, we demonstrate measuring isotopic analysis of various solid samples by employing 2D fluorescence spectroscopy (2DFS) of ns/fs laser ablation plumes up to atmospheric pressure levels from a stand-off distance. For performing LIF of LA plumes, we used a narrow-band CW laser to probe absorption from selected atomic transitions.  The high spectral resolution provided by the LIF measurement allows isotopic peaks to be easily separated even if they overlap in the emission spectra.

    Speaker Bio(s): 

    Dr. Sivanandan Harilal is a chief scientist at Pacific Northwest National Laboratory.  Before joining PNNL in 2014, he was a faculty member at School of Nuclear Engineering, Purdue University (2008-2014) and research scientist at University of California San Diego, CA (2001-2007).  At PNNL he is responsible for developing laser-based standoff detection tools for national security applications.  He is also one of the lead persons for the development of plasma sources for next generation lithography, which is essential for keeping Moore’s law intact. He has authored or co-authored over 175 peer-reviewed publications and book chapters in optical spectroscopy, laser-plasma, plasma diagnostics, EUV lithography, plasma applications etc. He is a senior member of OSA, SPIE, and IEEE. Currently he serves as associated editor of Optics Letters and guest editor of IEEE Transactions of Plasma Science.