Direct Evidence of the role of He Triplet Metastable Excited State in Excitation Process of Laser-Induced He Gas Plasma.
Direct Proof of the Role of He Triplet over He Singlet Metastable State in Excitation Process of
Laser-Induced He Gas Plasma
Hery Suyanto1, Rinda Hedwig2, Zener Sukra Lie2,3, Koo Hendrik Kurniawan3, Kiichiro Kagawa4
1Department
of Physics, Faculty of Mathematics and Natural Sciences, Udayana University, Kampus Bukit Jimbaran, Denpasar 80361, Bali, Indonesia
2Department of Computer Engineering, Bina Nusantara University, 9 K.H. Syahdan, Jakarta 14810, Indonesia
3Research Centre of Maju Makmur Mandiri Foundation, Jakarta, Indonesia 11630
4Fukui Science Education Academy, Takagi Chuo 2 chome, Fukui 910-0804, Japan
The experiment investigate the excitation process of He emission through He I 587.6 nm and He I
Abstract
667.8 nm emission lines. For this study, both laser in figure1 operated and the result as shown in figure 3.
A time resolved spectroscopic study is performed on He plasma in a special orthogonal
double pulse experiment employing an ns laser for the He plasma generation and a ps laser
He emission by electron
bombardment
Starting of ps Laser
Induced emission area
1 div = 1 μs
Starting of ns Laser
for target ablation. The study is focused on the most dominant He I 587.6 nm (triplet) and He I
667.8 nm (singlet) emission lines responsible for the previously proposed He assisted
excitation mechanism. The result reveals a transient enhancement of He I 587.6 nm emission
in concomitance with the delayed target ablation, signifying the effect of He atom
bombardment by electrons ejected from the target. The maximum enhancement is achieved
Starting of ps Laser
Fig.3.
with the optimal 5 s delay of target ablation following the He plasma generation in the
double pulse LIBS experiment.
Oscilloscope trace of He I 587.6 nm (μs) Oscilloscope trace of He I 587.6 nm (μs)
Oscilloscope trace of He I 587.6 nm (μs)
He gas plasma
He gas plasma
Background
Target plasma
due to ps laser
Target plasma
due to ps laser
The advantages of using helium ambient gas in LIBS has been widely reported in the
published literatures (1-7), that are for emission enhancement, to suppress the signal
Actually, put mask
background and to decrease the limit of detection. These results can be explained to be
ns laser
closely related to the crucial role of helium metastable excited state which serves as a
temporary energy reservoir for exciting of the ablated atom through penning effect (8-12).
Unfortunately , the identification of the specific He metastable excited state has rarely been
reported. This study focused to investigate the excitation process of He emission through He
I 587.6 nm (triplet) and He I 667.8 nm (singlet) emission lines.
Experimental Set up and Methods
ns laser
Z-axis
the signal in Fig. 3(b)
1
He gas
plasma
ps laser as a source of fast electron
2
ps laser
target
plasma
X-axis
He* (metastable) + e- He+ + e-
He+ + e- He** (triplet) He + h (587.6 nm)
He** (singlet) He + h (667.8 nm)
pico second
Nd:YAG laser
Emission
computer
vacuum
pump
fiber
mask
signal in Fig. 3(a) = signal in Fig. 3(c).
gain of the He emission due to bombardment of the He atoms by the fast electrons
ns laser
He gas
motor
ps laser
Fig. 3(a) shows the oscilloscope recorded time profile of He I 587.6 nm emission intensity associated
with transition from the 3d triplet states of the metastable excited He atoms when only the ns
laser is switched on.
Fig. 3(b) is the same He I 587.6 nm time profile recorded with the ps laser switched on 3 μs after the
generation of the He gas plasma.
Fig. 3(c) shows the same emission intensity time profile when only the picosecond laser is sent onto
the target.
recombination
OMA
Spectrograph
PMT
oscilloscope
We
observed
the
induced
emission of 587.6 nm and 667.8
nm using oscilloscope trace
Figure 1. Experimental Set up : The Orthogonal double pulse LIBS
Induced emission intensity (counts)
nano second
Nd:YAG laser
ns + ps laser
700
600
Induced emission of of He I 587.6 nm
(Triplet)
500
400
Induced emission of He I 667.8 nm
(Singlet)
300
200
100
0
0
5
10
15
20
Time delay between ns and ps laser (µs)
Figure 4. Induced emission intensities versus time delay of ps laser with respect to the ns laser irradiation.
Figure 4. The resulted time profiles obtained from the two modes of measurements are
substracted (Fig 3b – fig 3.a) for each delay time and then integrated to give the amount of the
Results and Discussion
associated intensity enhancement effect.
The first experiment was focused on the He plasma spectrum in order to sort out the
metastable excited states most relevant to the He assisted excitation process. For this study,
Conclusions
only the ns Nd-YAG laser in Fig.1 was operated to generate He gas plasma and emission
1. By the ns laser irradiation, hot He plasma is produced resulting He ions and electrons.
spectrum was measured with OMA system resulted as shown Fig. 2.
Time integrated spectrum, low resolution
With time, they recombine and mostly following to triplet path emitting 587.6 nm emission,
587.6 nm (Triplet)
then finally triplet metastable state is produced.
2. Thus, we conclude He triplet metastable state is the major in the He gas plasma
667.8 nm (Singlet)
Singlet and triplet lines are comparable
Figure 2. Emission spectrum oh He from Laser-induced He
gas plasma and He discharge Lamp
References
1. K.H. Kurniawan, T. Kobayashi, K. Kagawa, Effect of different atmospheres on the excitation
process of TEA-CO2 laser-induced shock wave plasma, Appl. Spectrosc. 46, 581 (1992), and
references therein.
2. M. Kuzuya, H. Matsumoto, H. Takechi, O. Mikami, Effect of laser energy and atmosphere on
the emission characteristics of laser-induced plasma, Appl. Spectrosc. 47, 1659 (1993), and
references therein.
3. M.R. Joseph, N. Xu, V. Majidi, Time-resolved emission characteristics and temperature
profiles of laser-induced plasmas in helium, Spectrochim. Acta B 49, 89 (1994), and
references therein.
4. M. Tran, Q. Sun, B.W. Smith, J.D. Winefordner, Determination of F, Cl, and Br in solid
organic compounds by laser-induced plasma spectroscopy, Appl. Spectrosc. 55, 739 (2001).
5. Other references can be obtained from the authors
www.postersession.com
He＊
www.postersession.com
Laser-Induced He Gas Plasma
Hery Suyanto1, Rinda Hedwig2, Zener Sukra Lie2,3, Koo Hendrik Kurniawan3, Kiichiro Kagawa4
1Department
of Physics, Faculty of Mathematics and Natural Sciences, Udayana University, Kampus Bukit Jimbaran, Denpasar 80361, Bali, Indonesia
2Department of Computer Engineering, Bina Nusantara University, 9 K.H. Syahdan, Jakarta 14810, Indonesia
3Research Centre of Maju Makmur Mandiri Foundation, Jakarta, Indonesia 11630
4Fukui Science Education Academy, Takagi Chuo 2 chome, Fukui 910-0804, Japan
The experiment investigate the excitation process of He emission through He I 587.6 nm and He I
Abstract
667.8 nm emission lines. For this study, both laser in figure1 operated and the result as shown in figure 3.
A time resolved spectroscopic study is performed on He plasma in a special orthogonal
double pulse experiment employing an ns laser for the He plasma generation and a ps laser
He emission by electron
bombardment
Starting of ps Laser
Induced emission area
1 div = 1 μs
Starting of ns Laser
for target ablation. The study is focused on the most dominant He I 587.6 nm (triplet) and He I
667.8 nm (singlet) emission lines responsible for the previously proposed He assisted
excitation mechanism. The result reveals a transient enhancement of He I 587.6 nm emission
in concomitance with the delayed target ablation, signifying the effect of He atom
bombardment by electrons ejected from the target. The maximum enhancement is achieved
Starting of ps Laser
Fig.3.
with the optimal 5 s delay of target ablation following the He plasma generation in the
double pulse LIBS experiment.
Oscilloscope trace of He I 587.6 nm (μs) Oscilloscope trace of He I 587.6 nm (μs)
Oscilloscope trace of He I 587.6 nm (μs)
He gas plasma
He gas plasma
Background
Target plasma
due to ps laser
Target plasma
due to ps laser
The advantages of using helium ambient gas in LIBS has been widely reported in the
published literatures (1-7), that are for emission enhancement, to suppress the signal
Actually, put mask
background and to decrease the limit of detection. These results can be explained to be
ns laser
closely related to the crucial role of helium metastable excited state which serves as a
temporary energy reservoir for exciting of the ablated atom through penning effect (8-12).
Unfortunately , the identification of the specific He metastable excited state has rarely been
reported. This study focused to investigate the excitation process of He emission through He
I 587.6 nm (triplet) and He I 667.8 nm (singlet) emission lines.
Experimental Set up and Methods
ns laser
Z-axis
the signal in Fig. 3(b)
1
He gas
plasma
ps laser as a source of fast electron
2
ps laser
target
plasma
X-axis
He* (metastable) + e- He+ + e-
He+ + e- He** (triplet) He + h (587.6 nm)
He** (singlet) He + h (667.8 nm)
pico second
Nd:YAG laser
Emission
computer
vacuum
pump
fiber
mask
signal in Fig. 3(a) = signal in Fig. 3(c).
gain of the He emission due to bombardment of the He atoms by the fast electrons
ns laser
He gas
motor
ps laser
Fig. 3(a) shows the oscilloscope recorded time profile of He I 587.6 nm emission intensity associated
with transition from the 3d triplet states of the metastable excited He atoms when only the ns
laser is switched on.
Fig. 3(b) is the same He I 587.6 nm time profile recorded with the ps laser switched on 3 μs after the
generation of the He gas plasma.
Fig. 3(c) shows the same emission intensity time profile when only the picosecond laser is sent onto
the target.
recombination
OMA
Spectrograph
PMT
oscilloscope
We
observed
the
induced
emission of 587.6 nm and 667.8
nm using oscilloscope trace
Figure 1. Experimental Set up : The Orthogonal double pulse LIBS
Induced emission intensity (counts)
nano second
Nd:YAG laser
ns + ps laser
700
600
Induced emission of of He I 587.6 nm
(Triplet)
500
400
Induced emission of He I 667.8 nm
(Singlet)
300
200
100
0
0
5
10
15
20
Time delay between ns and ps laser (µs)
Figure 4. Induced emission intensities versus time delay of ps laser with respect to the ns laser irradiation.
Figure 4. The resulted time profiles obtained from the two modes of measurements are
substracted (Fig 3b – fig 3.a) for each delay time and then integrated to give the amount of the
Results and Discussion
associated intensity enhancement effect.
The first experiment was focused on the He plasma spectrum in order to sort out the
metastable excited states most relevant to the He assisted excitation process. For this study,
Conclusions
only the ns Nd-YAG laser in Fig.1 was operated to generate He gas plasma and emission
1. By the ns laser irradiation, hot He plasma is produced resulting He ions and electrons.
spectrum was measured with OMA system resulted as shown Fig. 2.
Time integrated spectrum, low resolution
With time, they recombine and mostly following to triplet path emitting 587.6 nm emission,
587.6 nm (Triplet)
then finally triplet metastable state is produced.
2. Thus, we conclude He triplet metastable state is the major in the He gas plasma
667.8 nm (Singlet)
Singlet and triplet lines are comparable
Figure 2. Emission spectrum oh He from Laser-induced He
gas plasma and He discharge Lamp
References
1. K.H. Kurniawan, T. Kobayashi, K. Kagawa, Effect of different atmospheres on the excitation
process of TEA-CO2 laser-induced shock wave plasma, Appl. Spectrosc. 46, 581 (1992), and
references therein.
2. M. Kuzuya, H. Matsumoto, H. Takechi, O. Mikami, Effect of laser energy and atmosphere on
the emission characteristics of laser-induced plasma, Appl. Spectrosc. 47, 1659 (1993), and
references therein.
3. M.R. Joseph, N. Xu, V. Majidi, Time-resolved emission characteristics and temperature
profiles of laser-induced plasmas in helium, Spectrochim. Acta B 49, 89 (1994), and
references therein.
4. M. Tran, Q. Sun, B.W. Smith, J.D. Winefordner, Determination of F, Cl, and Br in solid
organic compounds by laser-induced plasma spectroscopy, Appl. Spectrosc. 55, 739 (2001).
5. Other references can be obtained from the authors
www.postersession.com
He＊
www.postersession.com