Polarization-resolved laser-induced breakdown spectroscopy

Department of Chemistry, University of Illinois, Chicago, Illinois 60607-7061, USA.
Optics Letters (Impact Factor: 3.29). 03/2009; 34(4):494-6. DOI: 10.1364/OL.34.000494
Source: PubMed


It is shown that plasma polarization measurements can be used to enhance the sensitivity of laser-induced breakdown spectroscopy (LIBS). The polarization of the plasma emission is used to suppress the continuum with only slight attenuation of the discrete atomic and ionic spectra. The method is demonstrated for LIBS detection of copper and carbon samples ablated by pairs of femtosecond laser pulses.

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    • "Improvements in the sensitivity of LIBS can be achieved by enhancing the signal strength or reducing the background noise. Recent advancements with femtosecond (fs) laser based LIBS and polarization resolved LIBS showed sharp reduction in background continuum noise, but the technology of a handheld fs laser system is still far away [2] [4] [5]. Among the various methods proposed for improving the detection sensitivity of LIBS, double-pulse (DP) excitation is more promising [6] [7] [8] [9] [10] [11]. "
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    ABSTRACT: Dual-pulse (DP) laser-induced breakdown spectroscopy (LIBS) provides significant improvement in signal intensity as compared to conventional single-pulse LIBS. We investigated collinear DPLIBS experimental performance using various laser wavelength combinations employing 1064 nm, 532 nm, and 266 nm Nd:YAG lasers. In particular, the role of the pre-pulse laser wavelength, inter-pulse delay times, and energies of the reheating pulses on LIBS sensitivity improvements is studied. Wavelengths of 1064 nm, 532 nm, and 266 nm pulses were used for generating pre-pulse plasma while 1064 nm pulse was used for reheating the pre-formed plasma generated by the pre-pulse. Significant emission intensity enhancement is noticed for all reheated plasma regardless of the pre-pulse excitation beam wavelength compared to single pulse LIBS. A dual peak in signal enhancement was observed for different inter-pulse delays, especially for 1064:1064 nm combinations, which is explained based on temperature measurement and shockwave expansion phenomenon. Our results also show that 266 nm:1064 nm combination provided maximum absolute signal intensity as compared to 1064 nm:1064 nm or 532 nm:1064 nm.
    Full-text · Article · May 2013 · Spectrochimica Acta Part B Atomic Spectroscopy
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    • "The polarization was found to be strongest at short wavelengths, increasing to over 90% below 350 nm. Later studies showed this effect to be a general phenomenon, occurring also for metals [4] [5] and dielectrics [5]. Subsequently, Liu et al. [6] and Majd et al. [7] reported that a polarized continuum is generated also by nanosecond (ns) pulses, using, respectively, the 532nm second harmonic and the 1.064 μm fundamental frequency of a Nd: YAG laser. "
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    ABSTRACT: Polarization of the plasma luminescence produced by both nanosecond and femtosecond laser ablation of Si(111) was analyzed under different conditions of fluence and detection geometry. It is shown that the luminescence is partially polarized and is directed in the plane of the crystal. The time evolution of the plasma emission signal was also investigated with the use of a streak camera. The mechanism for polarization is proposed to be preferential reflection of s-polarized light (i.e., light polarized normal to the plane of laser incidence) by the melted surface, in agreement with the Fresnel equations. Earlier reports of much stronger polarization are shown to be erroneous.
    Full-text · Article · Aug 2012 · Spectrochimica Acta Part B Atomic Spectroscopy
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    • "Corroborating evidence is provided by our femtosecond experiments , in which we observed high values of P for silicon [1], copper [2] and graphite [2] at 800 nm. The insensitivity to material and wavelength (but not necessarily to pulse duration) suggests that the polarization depends more on the properties of the plasma than of the underlying substrate. "
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    ABSTRACT: Several studies have appeared in the past two years reporting that the continuum emission produced by the laser ablation of solid materials is strongly polarized. In a paper that appears to conflict with these findings, Asgill et al. report that they did not observe a significant amount of polarization produced by nanosecond laser excitation of nitrogen gas and laser ablation of copper and steel ( M.E. Asgill, H.Y. Moon, N. Omenetto, D.W. Hahn, Investigation of polarization effects for nanosecond laser-induced breakdown spectroscopy, Spectrochim. Acta Part B (2010) xxx–xxx [7]). Here we show that the apparent discrepancy is resolved when laser fluence and polarization are taken into account. Using a 532nm Nd:YAG laser to ablate Al samples in air, we find that the degree of polarization, P, of the continuum is greater for s- vs. p-polarized excitation and that P decreases with increasing fluence. We show that P would be 60% is obtained at low fluences with s-polarized excitation. We also confirm that at high fluence the polarization of the discrete emission is much smaller than that of the continuum.
    Preview · Article · Feb 2011 · Spectrochimica Acta Part B Atomic Spectroscopy
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