316
R. Das et al.
Fig. 5 Normal LIBS (blue) and NELIBS (red) spectra of brass over different spectral windows
NPs coated LIBS spectrum shows an average enhancement of LIBS intensity up to 4
times than the conventional LIBS spectrum. In order to investigate the broadening of
the spectral lines during NELIBS, the most intense lines of Cu I 324.77 nm and Zn I
481.07 nm in the spectrum have been selected and compared with conventional LIBS.
The line widths of these lines in both cases were found to be 0.26 and 0.45 nm (±0.02
nm), respectively. The observation suggests that there is no broadening induced on
the spectral lines during nanoparticle treated measurements. Apart from Cu and Zn
emission lines, two medium intense Ag I lines (328.07 and 338.28 nm) observed in
the NELIBS spectrum, ensuring the presence of Ag nanoparticles on the surface.
Figure 5 illustrates the LIBS and NELIBS spectra of brass at higher wavelength
region. Contrary to the LIBS spectrum, two intense lines are observed in the NELIBS
spectrum at 588.99 589.59 nm which are contributed by the colloidal nanoparticles
solution (containing sodium as a stabilizer). The silver and sodium lines observed
in the spectra confirm the presence of nanoparticles on the substrate. Apart from the
major elements, the spectrum also manifests a weak Hα line at 656.27 nm, nitrogen,
and oxygen triplets at 742.36, 744.23, 746.83 nm, and 777.19, 777.41, 777.54 nm,
respectively, as shown in Fig. 5. The observed emission lines from the light elements
arise from the surrounding atmosphere since the Rayleigh region is relatively high
here due to the large focal length system used for focusing the laser pulse. Apart
from the detection of light elements, the interesting observation here is that the
intensity of light elements is also enhanced during the nanoparticle treated LIBS
measurements. The increase in the intensity of light elements is probably due to the
larger volume of the plasma as described by De Giacomo [36]. However, a detailed
investigation is needed for this observation. This observation highlights one of the
promising advantages of LIBS for detecting light elements (C, H, O, and N) over
other analytical techniques such as XRF, ICP-MS, etc.
To examine the temporal behavior of nanoparticle-coated LIBS emission lines, a
set of the spectrum was recorded as a function of gate delay by keeping a constant
gate width of 4 µs and energy 90 mJ. Figure 6 shows the temporal evolution of
two Cu (324.75, 521.84 nm) and Zn (472.28, 481.11 nm) lines in transient plasma of
R. Das et al.
Fig. 5 Normal LIBS (blue) and NELIBS (red) spectra of brass over different spectral windows
NPs coated LIBS spectrum shows an average enhancement of LIBS intensity up to 4
times than the conventional LIBS spectrum. In order to investigate the broadening of
the spectral lines during NELIBS, the most intense lines of Cu I 324.77 nm and Zn I
481.07 nm in the spectrum have been selected and compared with conventional LIBS.
The line widths of these lines in both cases were found to be 0.26 and 0.45 nm (±0.02
nm), respectively. The observation suggests that there is no broadening induced on
the spectral lines during nanoparticle treated measurements. Apart from Cu and Zn
emission lines, two medium intense Ag I lines (328.07 and 338.28 nm) observed in
the NELIBS spectrum, ensuring the presence of Ag nanoparticles on the surface.
Figure 5 illustrates the LIBS and NELIBS spectra of brass at higher wavelength
region. Contrary to the LIBS spectrum, two intense lines are observed in the NELIBS
spectrum at 588.99 589.59 nm which are contributed by the colloidal nanoparticles
solution (containing sodium as a stabilizer). The silver and sodium lines observed
in the spectra confirm the presence of nanoparticles on the substrate. Apart from the
major elements, the spectrum also manifests a weak Hα line at 656.27 nm, nitrogen,
and oxygen triplets at 742.36, 744.23, 746.83 nm, and 777.19, 777.41, 777.54 nm,
respectively, as shown in Fig. 5. The observed emission lines from the light elements
arise from the surrounding atmosphere since the Rayleigh region is relatively high
here due to the large focal length system used for focusing the laser pulse. Apart
from the detection of light elements, the interesting observation here is that the
intensity of light elements is also enhanced during the nanoparticle treated LIBS
measurements. The increase in the intensity of light elements is probably due to the
larger volume of the plasma as described by De Giacomo [36]. However, a detailed
investigation is needed for this observation. This observation highlights one of the
promising advantages of LIBS for detecting light elements (C, H, O, and N) over
other analytical techniques such as XRF, ICP-MS, etc.
To examine the temporal behavior of nanoparticle-coated LIBS emission lines, a
set of the spectrum was recorded as a function of gate delay by keeping a constant
gate width of 4 µs and energy 90 mJ. Figure 6 shows the temporal evolution of
two Cu (324.75, 521.84 nm) and Zn (472.28, 481.11 nm) lines in transient plasma of