Journal of Computer and Communications, 2013, 1, 36-39
Published Online December 2013 (http://www.scirp.org/journal/jcc)
http://dx.doi.org/10.4236/jcc.2013.17009
Open Access JCC
Double-Pulse Remote Laser-Induced Breakdown
Spectroscopy Analysis of Magnesium Alloys
Lifeng Qi, Lanxiang Sun*, Zhibo Cong, Yong Xin, Yang Li
Lab. of Networked Control Systems, Shenyang Institute of Automation, Chinese Academy of Sciences, Shenyang, China.
Received August 2013
ABSTRACT
A self-built double-pulse remote Laser-Induced Breakdown Spectroscopy system in a collinear configuration was used
to investigate the magnesium alloys. The enhancement of the intensity was observed, about 4.7 times compared with
single pulse LIBS. The peak intensities of line Y II 366.4 nm and Zr I 468.7 nm were used in the calibration curves, and
the correlation coefficients were 0.9998 and 0.9547 respectively.
Keywords: Double Pulse ; LIBS; Remote; Magn e s ium Alloys
1. Introduction
The chemical elementary component analysis of metallic
alloys is very important for process control and quality
assessment in metallurgical processing. The dominant ana-
lytical tools applied nowadays are based on spectroscopic
techniques such as inductively coupled plasma-atomic
emission spectroscopy (ICP-AES), X-ray fluorescence
(XRF), etc. These techniques are mostly used in off-site
laboratories and require sample preparation which is time
consuming. Laser-induced breakdown spectroscopy (LIBS)
is a useful technique known as a spectrochemical tool for
detecting the chemical composition of a wide range of
materials such as metals, minerals, chemical substances,
and trace species without the need of sample preparation
and the analysis procedure is simple and fast [1]. It is a
potential powerful technique for the metal smelting in
real-time and online chemical analysisor monitoring. How-
ever, the lower sensitivity and precision than the other
elemental analysis methods is one of the major draw-
backs especially in remote detection [2]. To improve
LIBS, a lot of approaches have been proposed to enhance
the analytical performance [3-6], and the double pulse
LIBS (DP-LIBS) has been demonstrated by a number of
studies [7-11], which is a very efficient approach for en-
hancing the intensity of plasma emission and improve-
ment of the analytical capabilities of LIBS.
In this work, a self-built remote collinear DP-LIBS is
used to analyze the chemical component of magnesium
alloys and compare with the single pulse LIBS about the
intensity of p lasma light. The goal of this study is to con-
firm the effect of the intensity enhancement in remote
DP-LIBS and the probability of the remote DP-LIBS tech-
nique applied in metal smelting process.
2. Experimental
The experimental system in this study consisted of two
Nd:YAG lasers, which were characterized by a maxi-
mum repetition rate of 10Hz, a maximum energy of 200
mJ per pulse at 1064 nm, and a full width half maximum
(FWHM) of about 10 ns. A combination of half wave
plate and polarization beam splitter (PBS) was used to
adjustment the energy of the laser beams and alignment
the two laser beams in colline ar. The co llinear laser beams
were focused on the targets at 2.5 m by a combination of
four lenses. The emitted plasma radiation was collected
by a commercially available 12 inch Schmidt-Cassegrain
telescope, then focused into an optic fiber and guided to a
spectrometer (LIBS 2500) developed by Ocean Optics,
Inc. The delay time between the two lasers and the gate
delay time of the spectrometer was set and controlled by
a versatile digital delay/pulse generator (DG645). A sche-
matic of the experimental setup is shown in Figure 1. In
order to reduce the influence of Bremsstrahlung and free-
bound electronic recombination continuum radiation, the
gate delay time after the second laser pulse and the inte-
grate time of the spectrometer were respectively set 3 μs
and 1ms in all the measurements. For all the samples,
500 spectra were acquired and averaged into a single spec-
trum to reduce the spectral fluctuations.
All the magnesium alloy samples in this work were
*Corresponding a uthor.

Double-Pulse Remote Laser-Induced Breakdown Spectroscopy Analysis of Magnesium Alloys
Open Access JCC
37
Figure 1. Theschematic of the experimental setup.
provided by the institute of metal research, Chinese acade-
my of sciences. The average chemical compositions of
the samples are listed in Table 1.
3. Results
The delay time between the two laser pluses plays an
important role in the signal intensity of DP-LIBS [7,8,11].
Figure 2 shows the emission intensity for the Zr I line at
468.7 nm and Y II line at 366.4 nm of sample #56 as a
function of the delay time in DP-LIBS from 0 to 10 μs. It
can be seen that the signal intensity increases by the de-
lay time, maxima at about 6 μs. After 6 μs an almost
constant intensity is observed. Consequently, the delay
time between the laser pulses in DP-LIBS was fixed at 6
μs in this research.
Turned off the laser 1, just the laser 2 was on work for
a single pulse LIBS in this work. Figure 3 shows s ignif i-
cant enhancement in LIBS signal for collinear DP-LIBS
compared with single pulse LIBS. The energy of the both
laser pulses were fixed at 100 mJ in DP-LIBS, and the
energy in single pulse LIBS was fixed at 200 mJ for
keeping consistent for both single pulse and double pulse
LIBS. Sample #56 was chosen as sample for this study.
Observed from the data, it can be clearly seen that the
enhancement in signal intensity is about 4.7 times for
collinear DP-LIBS compared with the single pulse LIBS
of the Y II line at 366 .4 nm. In the remote LIBS system,
the higher laser energies are required for an effective
detection due to the larger propagating consumption of
the laser pulses and the plasma light in the free space [12].
Using the DP-LIBS, which allows lo wer lase r energy w ith
enhancement of the LIBS signal is an available technique
to improve the intensity and sensitivity in remote LIBS.
According to the standard concentrations of the mag-
nesium alloy samples in Table 1, the peak intensity of
line Y II 366.4 nm and Zr I 468.7 nm were selected for
Table 1. Average chemical compositions of the Mg-RE sam-
ples.
C
No.
Content w/%
Zn
Y
Zr
Gd
Mg
#56
6.12
1.14
0.58
residue
#138
3.79
2.22
0.5
residue
#139 4.75 1.41 0.53 residue
#118
2.1
0.32
9.32
residue
#132
0.48
2.7
0.4
9.44
residue
Figure 2. Intensity vs. gate delay time for the Y II 366.4nm
and Zr I 468.7nm (#56).
Figure 3. Comparison of DP-LIBS signalintensity with
single pulse LIBS for Y (#56).
the calibration curves, plotted as a function of the relative
concentration in a linear scale. In Figure 4, the calibra-
tion curve of Y II shows a near straight line, it was cal-
culated that the correlation coefficients of the ratio (R2) is
0.9998. Average relative error of calibration is less than

Double-Pulse Remote Laser-Induced Breakdown Spectroscopy Analysis of Magnesium Alloys
Open Access JCC
38
10% and the calibration curves that allow quantitative
analysis in unknown samples [13]. In Figure 5, the cali-
bration curve of Zr I is shown. The correlation coeffi-
cients of the ratio (R2) is 0.9547, slightly poor compared
with Y II at 366 .4 nm, which probably influenced by the
spectral peak overlapped with other elements such as Y,
Gd, etc.
4. Conclusion
In this experiment, 5 magnesium alloy samples have been
studied by a self-built remote DP-LIBS system. Com-
pared with single pulse LIBS, the emission line intensi-
ties was enhanced about 4.7 times in DP-LIBS. The cor-
relation coefficients of the calibration curves of Y II and
Zr I were 0.9998 and 0.9547 respectively. The results of
this study provide a potential DP-LIBS technique for
metal smelting in real-time online chemical analysis and
monitoring that used less energy to achieve enhanced
spectra, and the distance between the system and targets
Figure 4. Calibration curve for Y II 366.4 nm.
Figure 5. Calibration curve for Zr I 468.7 nm.
about 2.5 m. The long-range detection distance of the
LIBS system can be flexibility applied to the complex
high-temperature environment of metal smelting process.
5. Acknowledgements
This work has been supported by the Equipment Devel-
opment Programs of the Chinese Academy of Sciences
(Grant No. YZ201247), the National High-Tech Research
and Development Program of China (863 Program) (Grant
No. 2012AA040608) and the National Natural Science
Fund (Grant No. 61004131).
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