Dynamic Stark effect on Fraunhofer-type absorption in DP LIBS

LEV NAGLI, Ariel University, Petah Tikva, Israel (nagli@post.tau.ac.il)

LIBS demonstrates considerable potential in various applications, including the diagnostics of raw materials. Traditional LIBS diagnostics employ LIP emission spectra, which display emission lines of the targeted elements. Notably, the strongest LIBS lines, often resonant, are subject to self-absorption effects at higher element concentrations]. Alternatively, Fraunhofer-type absorption in DP LIBS has been suggested as an analytical approach for detecting elements at medium and high concentrations.^1,2 The essence of the FTA in DP LIBS is that the second laser pulse, fired inside preliminary created plasma microseconds after the first, generates a plasma plume whose initial tens of nanoseconds are akin to a solar configuration. A hot, compact plasma core is surrounded by a much colder plasma formed by the initially generated plasma. The light from the hot center passes through the cold outer shell, partly absorbed by atoms and ions in the ground (or close to the ground) states. As a result, dips detected in the continuum radiation of the DP LIBS are similar to Fraunhofer lines observed in the solar spectrum. When 2^nd laser is polarized, the FTA lines are split and polarized when observed in the backward direction. Effects exist only in the presence of the 2^nd laser pulse.

but 7ns after 2^nd laser pulse.   Effects are attributable to the Dynamic Stark Effect (DSE) induced by the electric field of the second laser pulse within the first pulse-created plasma.

 

[1] L. Nagli, M. Gaft, I. Gornushkin, Fraunhofer-type absorption lines in double-pulse laser-induced plasma, Apl. Optics, 51 (2012) B201-B212.

DOI: 10.1364/AO.51.00B201.

[2]  L. Nagli, M. Gaft, Fraunhofer-type absorption line splitting and Polarization in

confocal double-pulse laser-induced plasma, Spectrochimica Acta Part B 88 (2013) 127–135.

DOI: 10.1016/j.sab.2013.06.009.