Abstract: 

Tunable diode laser spectroscopy provides a powerful approach to measure time-resolved absorption spectra of atoms and ions in laser-induced plasmas.  Previous research has focused primarily on low-pressure regimes, but recent advances have allowed measurements to be performed at atmospheric pressures, under ambient conditions, and with low concentration samples or on transitions with low oscillator strength.  I will present an overview of the experimental techniques and show results characterizing the time-resolved evolution of absorption lines of uranium in laser-induced plasmas.  Analysis of the results is used to determine spectral line-broadening parameters for uranium, many of which have not been previously measured.  We find that small pressure-broadening in uranium leads to narrow spectral lines in ambient laser-induced plasmas, which is promising for isotope-ratio measurements under these conditions.  The results from this work are valuable both for understanding the fundamental spectroscopy of uranium, and for improving the precision and accuracy of laser-induced plasma spectroscopy measurements including laser-induced breakdown spectroscopy (LIBS).

Bio:

Mark C. Phillips is currently a senior-level scientist at Pacific Northwest National Laboratory (PNNL), leading research and development of laser spectroscopy and sensing techniques for various applications.  While at PNNL, he developed high-performance external cavity quantum cascade laser systems for mid-infrared spectroscopy and sensing of trace gases, active hyperspectral imaging, and standoff detection of explosives.  He is currently leading an investigation into optical spectroscopy of uranium isotopes in laser-induced plasmas.  Prior to joining PNNL in 2005, he held a postdoctoral position at Sandia National Laboratory, researching semiconductor lasers and quantum optics.  He received a Ph.D. in physics in 2002 from the University of Oregon, where he worked in the lab of Hailin Wang researching quantum optics in semiconductor systems.