Enhancement of Nd:YAG LIBS emission of a remote target using a simultaneous CO_2 laser pulse

Abstract

For the first time to the best of our knowledge, a simultaneous 10.6 mum CO(2) laser pulse has been used to enhance the Laser Induced Breakdown Spectroscopy (LIBS) emission from a 1.064 mum Nd:YAG laser induced plasma on a hard target. The enhancement factor was on the order of 25 to 300 times, depending upon the emission lines observed. For an alumina ceramic substrate the Al emission lines at 308 nm and Fe impurity line at 278 nm showed an increase of 60x and 119x, respectively. The output energy of the Nd:YAG laser was 50 mJ/pulse focused to a 1 mm diameter spot to produce breakdown. The CO(2) laser pulse had a similar energy density of 40 mJ/mm(2). Timing overlap of the two laser pulses within 1 microsecond was important for enhancement to be observed. An observed feature was the differential enhancement between different elemental species and also between different ionization states, which may be helpful in the application of LIBS for multi-element analysis.

The importance of longer wavelength reheating in dual-pulse laser-induced breakdown spectroscopy

“…Currently, there is much research being conducted on techniques to improve the sensitivity of LIBS or to increase the spectral intensity, to compensate for signal degradation over standoff differences [2,3]. One technique for doing so is dualpulse LIBS (DP-LIBS), where laser plasmas are reheated shortly after their formation with a second laser pulse [4]. Previous dual-pulse studies, which utilized Nd:YAG lasers and their harmonics for both plasma formation and reheating, showed a signal enhancement factor of 2-12× [4,5].…”

“…One technique for doing so is dualpulse LIBS (DP-LIBS), where laser plasmas are reheated shortly after their formation with a second laser pulse [4]. Previous dual-pulse studies, which utilized Nd:YAG lasers and their harmonics for both plasma formation and reheating, showed a signal enhancement factor of 2-12× [4,5]. However, the reasons for the increased sensitivity have not been yet univocally ascertained, and a little effort has been made to understand the physics behind this emission enhancement.…”

“…Some of the explanations given for signal enhancement include a higher mass ablation [6][7][8][9], a larger plasma volume [8], the reheating of the plume [9,10], the lowering of the laser shielding effect [6], the heating of the target by the first pulse and the reduction in ambient density [11] preconditioning [12,13] or rekindling of the plume [14], and the confinement of the new plume by the first shock wave boundaries [15], etc. Recently, it has been demonstrated that IR laser reheating provides significant improvement in LIBS [4].…”

Flame-enhanced laser-induced breakdown spectroscopy

“…Many methods have been developed to improve the sensitivity of LIBS, such as, dualpulse excitation [8][9][10], spatial or magnetic confinement [11][12][13][14], microwave-assisted LIBS [15], and laser ablation combined with fast pulse discharge [16]. Generation of hightemperature and low-density plasmas in LIBS to improve the spectral resolution has also been achieved by introducing a second laser pulse to re-ablate the laser-induced particles with delays up to milliseconds [17].…”

Optimally enhanced optical emission in laser-induced breakdown spectroscopy by combining spatial confinement and dual-pulse irradiation

“…For instance, we [30] studied the enhancement of optical emission plasmas confined with the combination of spatial and magnetic confinements, resulting in a maximum enhancement factor of only 24 for pure metallic Cr sample. Killinger et al [31] reported the enhancement of plasmas using a simultaneous CO 2 laser pulse, resulting in an increase of 60x for the Al atomic lines at 308 nm. In this study, our aim was to further improve the enhancement effects by the spatial confinement and dual-pulse in LIBS.…”