OSA's Digital Library

Energy Express

Energy Express

  • Editor: Christian Seassal
  • Vol. 20, Iss. S6 — Nov. 5, 2012
  • pp: A1011–A1018
« Show journal navigation

Utilization of moderate cylindrical confinement for precision improvement of laser-induced breakdown spectroscopy signal

Zhe Wang, Zongyu Hou, Siu-lung Lui, Dong Jiang, Jianmin Liu, and Zheng Li  »View Author Affiliations


Optics Express, Vol. 20, Issue S6, pp. A1011-A1018 (2012)
http://dx.doi.org/10.1364/OE.20.0A1011


View Full Text Article

Acrobat PDF (1995 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

Moderate cylindrical cavity was used to regularize the laser-induced plasma for signal strength enhancement and precision improvement in laser-induced breakdown spectroscopy (LIBS). A polytetrafluoroethylene (PTFE) plate of 1.5 mm thickness with diameter of 3 mm was fabricated. It was placed closely on a sample surface and a laser pulse was shot through the center of the hole to the sample. Using coal as samples, it was verified that the configuration both enhanced the spectral line intensity and reduced shot-to-shot fluctuation, showing its great potential in improving the precision of LIBS analysis.

© 2012 OSA

1. Introduction

Laser-induced breakdown spectroscopy (LIBS) is a spectrometry technology based on measuring the atomic emission of a plasma induced by a high power laser pulse. LIBS have numerous advantages. It can study samples of any physical form (powder, liquid, solid, gas, etc.). Sample preparation is simple and the analysis is fast. Therefore, LIBS find its application in many real-time and online chemical assays or monitoring [1

1. J. D. Winefordner, I. B. Gornushkin, T. Correll, E. Gibb, B. W. Smith, and N. Omenetto, “Comparing several atomic spectrometric methods to the super stars: special emphasis on laser induced breakdown spectrometry, LIBS, a future super star,” J. Anal. At. Spectrom. 19(9), 1061–1083 (2004). [CrossRef]

, 2

2. R. E. Russo, X. Mao, H. Liu, J. Gonzalez, and S. S. Mao, “Laser ablation in analytical chemistry-a review,” Talanta 57(3), 425–451 (2002). [CrossRef] [PubMed]

].

Due to fluctuations of various factors such as the laser energy and laser-sample interaction, the precision of LIBS analysis is always of concern. Efforts have been spent on system improvement and spectral processing algorithms to solve the problem. Researchers have proposed various methods to enhance the signal stability like the multiple pulse excitation technique [3

3. V. I. Babushok, F. C. DeLucia Jr, J. L. Gottfried, C. A. Munson, and A. W. Miziolek, “Double pulse laser ablation and plasma: Laser induced breakdown spectroscopy signal enhancement,” Spectrochim. Acta, B At. Spectrosc. 61(9), 999–1014 (2006). [CrossRef]

6

6. M. Weidman, M. Baudelet, S. Palanco, M. Sigman, P. J. Dagdigian, and M. Richardson, “Nd:YAG-CO2 double-pulse laser induced breakdown spectroscopy of organic films,” Opt. Express 18(1), 259–266 (2010). [CrossRef] [PubMed]

], introduction of inert gas [7

7. Q. L. Ma, V. Motto-Ros, W. Q. Lei, M. Boueri, X. S. Bai, L. J. Zheng, H. P. Zeng, and J. Yu, “Temporal and spatial dynamics of laser-induced aluminum plasma in argon background at atmospheric pressure: Interplay with the ambient gas,” Spectrochim. Acta, B At. Spectrosc. 65(11), 896–907 (2010). [CrossRef]

], and usage of spectra normalization method [8

8. N. B. Zorov, A. A. Gorbatenko, T. A. Labutin, and A. M. Popov, “A review of normalization techniques in analytical atomic spectrometry with laser sampling: From single to multivariate correction,” Spectrochim. Acta, B At. Spectrosc. 65(8), 642–657 (2010). [CrossRef]

11

11. L. Li, Z. Wang, T. Yuan, Z. Hou, Z. Li, and W. Ni, “A simplified spectrum standardization method for laser-induced breakdown spectroscopy measurements,” J. Anal. At. Spectrom. 26(11), 2274–2280 (2011). [CrossRef]

].

Currently, confinement has been proved to be an effective approach for signal enhancement [12

12. R. Hedwig, “Confinement effect in enhancing shock wave plasma generation at low pressure by TEA CO2 laser bombardment on quartz sample,” Spectrochim. Acta, B At. Spectrosc. 58(3), 531–542 (2003). [CrossRef]

22

22. X. K. Shen, J. Sun, H. Ling, and Y. F. Lu, “Spectroscopic study of laser-induced Al plasmas with cylindrical confinement,” J. Appl. Phys. 102(9), 093301–093305 (2007). [CrossRef]

]. A plasma confined by a cavity wall is physically different from a free expanding plasma. Firstly, the expansion of the plasma is guided and bounded by the cavity wall so that the plasma temperature (T) and electron density (ne) may vary from those in free expansion. Secondly, the shockwave reflected from the cavity wall may reheat and maintain the plasma at a higher temperature. Different cavity configurations were studied for their confinement effects. Hedwig et al. created a cavity (1 mm in diameter and 1 mm in depth) by shooting laser pulses repeatedly on a quartz sample. Results showed that the cavity enhanced the spectra line intensity [12

12. R. Hedwig, “Confinement effect in enhancing shock wave plasma generation at low pressure by TEA CO2 laser bombardment on quartz sample,” Spectrochim. Acta, B At. Spectrosc. 58(3), 531–542 (2003). [CrossRef]

]. Zeng et al. fabricated truncated cone cavities in the sample surface and the cavity was of 0.5 mm in depth with different diameters (80 μm, 165 μm, and 490 μm). Results showed that the cavity enhanced T and ne as well as the spectral line intensity [19

19. X. Zeng, S. S. Mao, C. Liu, X. Mao, R. Greif, and R. E. Russo, “Plasma diagnostics during laser ablation in a cavity,” Spectrochim. Acta, B At. Spectrosc. 58(5), 867–877 (2003). [CrossRef]

]. Guo et al. put a hemispherical cavity of 11 mm diameter onto the steel target and measured a 12-fold enhancement in manganese atomic line signal. The hemispherical cavity was fabricated from aluminum, with a polished internal surface and with a 2 mm hole at the top for laser incoming and plasma emission outcoming [20

20. L. B. Guo, C. M. Li, W. Hu, Y. S. Zhou, B. Y. Zhang, Z. X. Cai, X. Y. Zeng, and Y. F. Lu, “Plasma confinement by hemispherical cavity in laser-induced breakdown spectroscopy,” Appl. Phys. Lett. 98(13), 131501 (2011). [CrossRef]

]. Popov et al. used a cylinder cavity of dimension 4 mm by 4 mm to confine plasmas generated from soil, steel and aluminum samples. The limit of detection (LOD) was improved by two to five times for different elements [15

15. A. M. Popov, F. Colao, and R. Fantoni, “Enhancement of LIBS signal by spatially confining the laser-induced plasma,” J. Anal. At. Spectrom. 24(5), 602–604 (2009). [CrossRef]

, 21

21. A. M. Popov, F. Colao, and R. Fantoni, “Spatial confinement of laser-induced plasma to enhance LIBS sensitivity for trace elements determination in soils,” J. Anal. At. Spectrom. 25(6), 837–848 (2010). [CrossRef]

]. Yeates et al. diagnosed the evolution of a plasma confined by a rectangular cavity via ICCD imaging and Langmuir probes [23

23. P. Yeates and E. T. Kennedy, “Spectroscopic, imaging, and probe diagnostics of laser plasma plumes expanding between confining surfaces,” J. Appl. Phys. 108(9), 093306–093312 (2010). [CrossRef]

]. Shen et al. used the cylindrical pipes of various diameters as cavities and showed that the signal enhancement could be explained by the change of plasma temperature [22

22. X. K. Shen, J. Sun, H. Ling, and Y. F. Lu, “Spectroscopic study of laser-induced Al plasmas with cylindrical confinement,” J. Appl. Phys. 102(9), 093301–093305 (2007). [CrossRef]

]. However, the researches on the confinement effect reported so far mainly focused on the mechanism and the intensity enhancement, but rarely on the signal repeatability for LIBS measurement as described above. Only Popov et al. studied the signal precision but with a even higher relative standard deviation (RSD) when the cavity was introduced [21

21. A. M. Popov, F. Colao, and R. Fantoni, “Spatial confinement of laser-induced plasma to enhance LIBS sensitivity for trace elements determination in soils,” J. Anal. At. Spectrom. 25(6), 837–848 (2010). [CrossRef]

].

The main objective of the present work is to seek the possibility of improving the stability of the LIBS signal using spatial confining the plasma while keeping the advantage of signal enhancement. Ideally, to obtain a high repeatable LIBS signal, the laser induced plasma should have the same morphology. Yet, due to the variation of surface condition as well as laser surface interaction, the propagation of the laser induced plasma would be affected in different way, resulting in different plasma morphology and generating relatively higher measurement uncertainty than other technologies such as inductive coupled plasma /optical emission spectroscopy (ICP-OES). Spatial confinement is possible applicable to modulate the laser induced plasma to obtain more repeatable spectra.

2. Basic logics

Figure 1
Fig. 1 Plasma morphology (a) without and (b) with cavity confinement.
explains the basic ideas of using a confinement for plasma morphology modulate. Without the cavity wall (Fig. 1(a)), the propagation of the plasma from a same sample is affected by the surface condition (roughness), laser-sample interaction, and ambient environment and the resulted plasma morphology can differ from pulse to pulse. Furthermore, this uncontrollable behavior can change the plasma temperature, electron density, and specie density which result in additional uncertainty of LIBS signal.

Theoretically, plasma expanded axisymmetrically. With the presence of an axisymmetrical cavity (Fig. 1(b)), the propagation of a plasma is confined inside the hollow cavity. Although variation in laser-sample interaction, the roughness of the sample surface and other factors still affect the expansion of the plasma, due to the compression of the reflection of shockwave, the size and shape of the plasma could be more stable between different laser pulses. That is, there is possible that a more stable and homogeneous plasma with lower measurement uncertainty can be obtained. However, as mentioned above, there was no research reporting the improvement with the application of confinement. It was hypothesized that the undesirable effect was resulted from either too small confinement [12

12. R. Hedwig, “Confinement effect in enhancing shock wave plasma generation at low pressure by TEA CO2 laser bombardment on quartz sample,” Spectrochim. Acta, B At. Spectrosc. 58(3), 531–542 (2003). [CrossRef]

14

14. M. Corsi, G. Cristoforetti, M. Hidalgo, D. Iriarte, S. Legnaioli, V. Palleschi, A. Salvetti, and E. Tognoni, “Effect of laser-induced crater depth in laser-induced breakdown spectroscopy emission features,” Appl. Spectrosc. 59(7), 853–860 (2005). [CrossRef] [PubMed]

, 19

19. X. Zeng, S. S. Mao, C. Liu, X. Mao, R. Greif, and R. E. Russo, “Plasma diagnostics during laser ablation in a cavity,” Spectrochim. Acta, B At. Spectrosc. 58(5), 867–877 (2003). [CrossRef]

], in which the plasma touches the confinement material, or too large confinement [15

15. A. M. Popov, F. Colao, and R. Fantoni, “Enhancement of LIBS signal by spatially confining the laser-induced plasma,” J. Anal. At. Spectrom. 24(5), 602–604 (2009). [CrossRef]

, 16

16. L. B. Guo, W. Hu, B. Y. Zhang, X. N. He, C. M. Li, Y. S. Zhou, Z. X. Cai, X. Y. Zeng, and Y. F. Lu, “Enhancement of optical emission from laser-induced plasmas by combined spatial and magnetic confinement,” Opt. Express 19(15), 14067–14075 (2011). [CrossRef] [PubMed]

, 20

20. L. B. Guo, C. M. Li, W. Hu, Y. S. Zhou, B. Y. Zhang, Z. X. Cai, X. Y. Zeng, and Y. F. Lu, “Plasma confinement by hemispherical cavity in laser-induced breakdown spectroscopy,” Appl. Phys. Lett. 98(13), 131501 (2011). [CrossRef]

, 21

21. A. M. Popov, F. Colao, and R. Fantoni, “Spatial confinement of laser-induced plasma to enhance LIBS sensitivity for trace elements determination in soils,” J. Anal. At. Spectrom. 25(6), 837–848 (2010). [CrossRef]

], in which the reflected shockwave is not able to regularize the plasma due to energy dissipation, or the utilization of asymmetric confinement [4

4. L. B. Guo, B. Y. Zhang, X. N. He, C. M. Li, Y. S. Zhou, T. Wu, J. B. Park, X. Y. Zeng, and Y. F. Lu, “Optimally enhanced optical emission in laser-induced breakdown spectroscopy by combining spatial confinement and dual-pulse irradiation,” Opt. Express 20(2), 1436–1443 (2012). [CrossRef] [PubMed]

, 23

23. P. Yeates and E. T. Kennedy, “Spectroscopic, imaging, and probe diagnostics of laser plasma plumes expanding between confining surfaces,” J. Appl. Phys. 108(9), 093306–093312 (2010). [CrossRef]

]. With a suitable cavity diameter and shape, it was applicable to improve signal precision using confinement. Besides, the confinement by the cavity wall may re-shape the plasma such that the elongated plume becomes optically thinner with respect to the light collection optics, which is beneficial to reduce the self-absorption effects.

Furthermore, the reflected shockwave from the cavity wall would reheat the plasma, resulting in an increase in the plasma temperature, electron density, as well as signal strength, which would also be helpful to improve the measurement precision as explained below:

Under the local thermodynamic equilibrium (LTE) condition, for an atomic emission induced by an electron transition from an upper energy level i to a lower energy level j, the emitted line intensity, I, can be expressed by [24

24. R. Mavrodineanu, ed., “Flame Spectroscopy” (John Wiley & Sons, New York, 1965).

]:
IijI=Fns(11+R)giIexp(EiI/(kT))UI(T)AijI,
(1)
where R can be calculated by the Saha equation [25

25. H. R. Griem, ed., “Plasma Spectroscopy” (McGraw-Hill Inc., New York, 1964).

]:
R=nIInI=2neUII(T)UI(T)(2πmekT)1.5h3eEionΔEionkT.
(2)
In the equations, the superscripts I and II refer to atomic and ionic states, while the subscripts i refers to the upper energy level and j refers to the lower energy level of the transition. nI and nII, are the number density of the neutral atom and the ion at the first ionization stage, respectively. The rest of the parameters are: F – gain factor of the instrument; A – transition probability; g – degeneracy; U(T) – partition function; Ei – upper level energy of excitation; Eion – ionization energy of ground state atoms; ΔE – the ionization potential lowering factor with a typical value on the order of 0.1 eV; ns – specie number density; h – Planck constant; k – Boltzmann constant.

In this case, the carbon line C(I) 193.09 nm is chosen for illustration. Using Eq. (1) and (2), the intensity of this carbon line at different plasma conditions can be calculated (Fig. 2
Fig. 2 Theoretical intensity distribution of C(I)193.09nm at different plasma conditions. The intensities are normalized by their maximum value.
). Within the simulation range of T from 7000 to 25000 K and ne from 1.5 × 1017 to 3 × 1018 cm−3, it can be observed that the intensity peaks at around T = 17000K and ne = 3 × 1018 cm−3, i.e., the red region or the region near the ridge. Far away from the ridge, the intensities can be extremely sensitive to a slightly change of T or ne. In the blue region, however, the intensity is too low. In practice, if a plasma can be engineered such that its condition maintains at the red region, then the emission signal would be maximized and become more stable. In other words, the LIBS measurement will have a higher precision.

It should be noted that Fig. 2 is derived from theory. In reality, the optimal emission state can shift due to many factors such as the sample matrix or the ambience which alter the emission characteristic. Moreover, with our current LIBS apparatus, the spectrum was recorded for one millisecond and during the recorded time, the plasma temperature and electron density shifted greatly, weaken the relationship shown above to some extent. The emphasis of this simulation is only to show the non-linearity characteristic of the emission stability with the plasma temperature and electron number density.

3. Experimental setup

The plasma generated using the current device is about 1-2 mm, and therefore to avoid direct contact of plasma and cavity. The diameter of the cylindrical cavity was chosen as 3 mm. The cylindrical cavity was drilled in a 1.5 mm thick polytetrafluoroethylene (PTFE) plate. Eleven holes were drilled on the plate. The plate was fixed closely on the pellet surface so that they would move simultaneously on a motorized sample stage in the sample chamber. The laser beam could be aimed to the center of the cavity with the help of the imaging camera of the LIBS system. The ambience condition was air at normal pressure. In the study, a spectrum was sampled from each of the 10 different locations for one experimental setting. Therefore, each setting could be completed with one pellet. This could minimize undesired signal variations due to different samples and the ambient condition. The recorded spectrum was background subtracted before processing. For each setting, the experiment was repeated three times, that is to say, three pellets.

4. Results and discussion

In this study, the laser energy was the only variable. It affected not only the plasma temperature and electron density, but also the ablated mass, and the size, lifetime, and propagation speed of the plasma. These characteristics could be directly or indirectly modified by the cavity wall. Two laser energy settings were chosen: 130 mJ and 80 mJ. The former was similar to the energies adopted in our other coal studies [27

27. M. Dong, J. Lu, S. Yao, J. Li, J. Li, Z. Zhong, and W. Lu, “Application of LIBS for direct determination of volatile matter content in coal,” J. Anal. At. Spectrom. 26(11), 2183–2188 (2011). [CrossRef]

, 28

28. J. Feng, Z. Wang, L. West, Z. Li, and W. D. Ni, “A PLS model based on dominant factor for coal analysis using laser-induced breakdown spectroscopy,” Anal. Bioanal. Chem. 400(10), 3261–3271 (2011). [CrossRef] [PubMed]

], while the latter served as comparison purpose as the confinement effect was expected to be weaker at a lower ablation energy. Ten spectra were collected from each pellet and three pellets were studied for each setting. Thus, unless otherwise stated, the results presented in this section were an average of 30 data points.

4.1 Spectral intensity, plasma temperature, and electron number density

Carbon is the common element of interest in coal analysis. Two carbon lines, C(I) 193.09 nm and C(I) 247.856 nm, were studied. Figure 4
Fig. 4 Spectra showing the C(I) 193.09nm and C(I) 247.856nm lines. Laser energy was (a) 80 mJ and (b) 130 mJ
shows the enhancement of the emission by the cavity at the two energy settings. For both settings, the signal enhancement of the carbon lines can be readily observed. Table 1

Table 1. Average Line Intensity of 193 nm (a.u.) under Different Conditions

table-icon
View This Table
| View All Tables
summarizes the average intensities and their average standard deviations under different conditions, where the intensity means the peak area of a characteristic line and the average standard deviation was the average of three standard deviations from three repeated experiments. As Fig. 4(b) suggests that the C(I) 247.856 nm line could be saturated, only the intensities of C(I) 193.09 nm line were listed. The enhancement was more than two times in the cavity configuration. In addition, the profile of line C(I) 247.856 nm showed some saturation, therefore line C(I)193.09 nm was utilized for analyses in the present work.

The enhancement could also be seen from the changes of plasma temperature, T, and electron density, ne, two common parameters to explain LIBS’s phenomena. Here, the temperature was obtained from the Boltzmann plots of six aluminum lines (237.312nm, 257.509nm, 308.215nm, 309.271nm, 394.401nm, 396.152nm), while the electron number density was calculated from the full width at half maximum (FWHM) of Hα line,Δλ1/2with [25

25. H. R. Griem, ed., “Plasma Spectroscopy” (McGraw-Hill Inc., New York, 1964).

, 29

29. C. Aragon and J. Aguilera, “Characterization of laser induced plasmas by optical emission spectroscopy: A review of experiments and methods,” Spectrochim. Acta, B At. Spectrosc. 63(9), 893–916 (2008). [CrossRef]

]:
ne(cm3)=C(T,ne)(Δλ1/2)3/2.
(3)
C(T,ne) is a weak function of T and ne, and can be obtained from Ref [25

25. H. R. Griem, ed., “Plasma Spectroscopy” (McGraw-Hill Inc., New York, 1964).

]. Table 2

Table 2. Plasma Parameters under Different Conditions

table-icon
View This Table
| View All Tables
lists the average plasma parameters and their average standard deviation for different settings. For both energy settings, the plasma temperature was higher when there was a cavity. This confirmed that the increment of temperature caused by the cavity could be a reason for intensity improvement.

The electron density, however, remained unchanged with the laser energy in the case of without cavity. This confirmed the free expansion characteristic of the plasma when no cavity was introduced. When the cavity was added, the cavity wall and the reflected shockwave helped to cage the plasma and made it smaller, so the electron densities were much higher.

According to the McWhirter criterion [29

29. C. Aragon and J. Aguilera, “Characterization of laser induced plasmas by optical emission spectroscopy: A review of experiments and methods,” Spectrochim. Acta, B At. Spectrosc. 63(9), 893–916 (2008). [CrossRef]

], a higher electron number density can help the plasma reach the LTE condition. Since LTE condition is a basic assumption for quantitative analysis, it is necessary to investigate whether the cavity can help the plasma to reach LTE condition. According to Ref [30

30. G. Cristoforetti, A. De Giacomo, M. Dell'Aglio, S. Legnaioli, E. Tognoni, V. Palleschi, and N. Omenetto, “Local Thermodynamic Equilibrium in Laser-Induced Breakdown Spectroscopy: Beyond the McWhirter criterion,” Spectrochim. Acta, B At. Spectrosc. 65(1), 86–95 (2010). [CrossRef]

], the LTE condition can be considered to be satisfied when the relaxation time is much shorter than the expansion time of the plasma and the diffusion length during the relaxation time is much shorter than plasma diameter. Table 3

Table 3. Relaxation Time and Diffusion Length under Different Conditions

table-icon
View This Table
| View All Tables
shows the relaxation time trel and the diffusion length λ. The trel and λ were calculated using the average value in Table 2 according to the method in Ref [30

30. G. Cristoforetti, A. De Giacomo, M. Dell'Aglio, S. Legnaioli, E. Tognoni, V. Palleschi, and N. Omenetto, “Local Thermodynamic Equilibrium in Laser-Induced Breakdown Spectroscopy: Beyond the McWhirter criterion,” Spectrochim. Acta, B At. Spectrosc. 65(1), 86–95 (2010). [CrossRef]

].

For a typical laser induced plasma, the expansion time is about 10−6~10−5s and the plasma diameter is about several millimeter [30

30. G. Cristoforetti, A. De Giacomo, M. Dell'Aglio, S. Legnaioli, E. Tognoni, V. Palleschi, and N. Omenetto, “Local Thermodynamic Equilibrium in Laser-Induced Breakdown Spectroscopy: Beyond the McWhirter criterion,” Spectrochim. Acta, B At. Spectrosc. 65(1), 86–95 (2010). [CrossRef]

]. Table 3 clearly shows that the cavity can shorten the relaxation time and diffusion length, which can help to ensure the LTE condition. This may help to improve the accuracy of quantitative analysis of LIBS. It need to be pointed out that due to the compression effect of the reflected shock wave, the plasma with a cavity was expected to be slimmer, which will reducing the significance of the great reduction in diffusion length to some extent. In our future work, the plasma size will be investigated to further evaluate the significance of the diffusion length reduction.

4.2 Relative standard deviation of the line intensity

Repeatability of measurements is a key issue in LIBS applications and is the main focus of this study. The RSD is an indicator to assess the signal stability. Table 4

Table 4. RSD (%) of the C(I) 193 nm of Each Experiment Setting

table-icon
View This Table
| View All Tables
shows the RSD of the C(I) 193 nm line of each experiment and the standard deviation of the RSD, where the standard deviation was calculated from the three RSD of three repeated experiments.

At the laser pulse energy of 80 mJ, the RSD of the signal were decreased from 5.2 to 4.1 when a confinement was added. When the laser energy was increased to 130 mJ, the RSD of the signal were decreased from 12.2 to 7.8. The improvement of RSD may be attributed to the following: 1) the temperature and the electron density was pushed to a certain range such that the intensity was less sensitive to T and ne, such as the “ridge” in Fig. 2; 2) the shockwave reflected from the cavity wall regulates the expansion process of the plasma to makes the plasma more stable and homogeneous; 3) the confinement effect may reduce the signal sensitivity to morphologic effect.

In addition, the standard deviation of the RSD was also much reduced when a cavity was added. This further indicated that the cavity not only improve the pulse-to-pulse signal repeatability, but also improve the sample-to-sample repeatability.

The results proved the applicability of the utilization of cavity to enhance signal strength as well as to improve signal stability. It was also noticed that laser energy, delay time, and other parameters such as the cavity diameter/thickness, the confinement shape, and the material of the cavity change final effect of signal repeatability improvement. Systematic studies of the energy-dependent, spatial and temporal variation of LIBS plasma are planned to further investigate the mechanism and effects of the moderate confinement.

5. Conclusions

Moderate cylindrical cavity was used to confine and regularize the laser induced plasma. Compared to the cases without cavity, the line intensity was enhanced due the increase in plasma temperature and electron density. More important, the uncertainty of the signal can be reduced by the confinement as shown in our experiments. That is, the confinement effect shows great potentials to improve precision of LIBS analysis. Yet further studies were required to understand the role of the cavity and the reactions between the shockwave and the plasma. Other parameters, such as the delay and integration time of the spectrometer or the dimension of the cavity, were also critical, and should be investigated in detail as well in future studies.

Acknowledgment

The authors are grateful for the financial support from National Natural Science Foundation of China (No. 51276100).

References and links

1.

J. D. Winefordner, I. B. Gornushkin, T. Correll, E. Gibb, B. W. Smith, and N. Omenetto, “Comparing several atomic spectrometric methods to the super stars: special emphasis on laser induced breakdown spectrometry, LIBS, a future super star,” J. Anal. At. Spectrom. 19(9), 1061–1083 (2004). [CrossRef]

2.

R. E. Russo, X. Mao, H. Liu, J. Gonzalez, and S. S. Mao, “Laser ablation in analytical chemistry-a review,” Talanta 57(3), 425–451 (2002). [CrossRef] [PubMed]

3.

V. I. Babushok, F. C. DeLucia Jr, J. L. Gottfried, C. A. Munson, and A. W. Miziolek, “Double pulse laser ablation and plasma: Laser induced breakdown spectroscopy signal enhancement,” Spectrochim. Acta, B At. Spectrosc. 61(9), 999–1014 (2006). [CrossRef]

4.

L. B. Guo, B. Y. Zhang, X. N. He, C. M. Li, Y. S. Zhou, T. Wu, J. B. Park, X. Y. Zeng, and Y. F. Lu, “Optimally enhanced optical emission in laser-induced breakdown spectroscopy by combining spatial confinement and dual-pulse irradiation,” Opt. Express 20(2), 1436–1443 (2012). [CrossRef] [PubMed]

5.

D. K. Killinger, S. D. Allen, R. D. Waterbury, C. Stefano, and E. L. Dottery, “Enhancement of Nd:YAG LIBS emission of a remote target using a simultaneous CO2 laser pulse,” Opt. Express 15(20), 12905–12915 (2007). [CrossRef] [PubMed]

6.

M. Weidman, M. Baudelet, S. Palanco, M. Sigman, P. J. Dagdigian, and M. Richardson, “Nd:YAG-CO2 double-pulse laser induced breakdown spectroscopy of organic films,” Opt. Express 18(1), 259–266 (2010). [CrossRef] [PubMed]

7.

Q. L. Ma, V. Motto-Ros, W. Q. Lei, M. Boueri, X. S. Bai, L. J. Zheng, H. P. Zeng, and J. Yu, “Temporal and spatial dynamics of laser-induced aluminum plasma in argon background at atmospheric pressure: Interplay with the ambient gas,” Spectrochim. Acta, B At. Spectrosc. 65(11), 896–907 (2010). [CrossRef]

8.

N. B. Zorov, A. A. Gorbatenko, T. A. Labutin, and A. M. Popov, “A review of normalization techniques in analytical atomic spectrometry with laser sampling: From single to multivariate correction,” Spectrochim. Acta, B At. Spectrosc. 65(8), 642–657 (2010). [CrossRef]

9.

D. W. Hahn and N. Omenetto, “Laser-Induced Breakdown Spectroscopy (LIBS), Part II: Review of Instrumental and Methodological Approaches to Material Analysis and Applications to Different Fields,” Appl. Spectrosc. 66(4), 347–419 (2012). [CrossRef] [PubMed]

10.

Z. Wang, L. Li, L. West, Z. Li, and W. Ni, “A spectrum standardization approach for laser-induced breakdown spectroscopy measurements,” Spectrochim. Acta, B At. Spectrosc. 68, 58–64 (2012). [CrossRef]

11.

L. Li, Z. Wang, T. Yuan, Z. Hou, Z. Li, and W. Ni, “A simplified spectrum standardization method for laser-induced breakdown spectroscopy measurements,” J. Anal. At. Spectrom. 26(11), 2274–2280 (2011). [CrossRef]

12.

R. Hedwig, “Confinement effect in enhancing shock wave plasma generation at low pressure by TEA CO2 laser bombardment on quartz sample,” Spectrochim. Acta, B At. Spectrosc. 58(3), 531–542 (2003). [CrossRef]

13.

K. H. Kurniawan, M. Pardede, T. J. Lie, H. Niki, K. Fukumoto, T. Maruyama, K. Kagawa, and M. O. Tjia, “Crater effects on H and D emission from laser induced low-pressure helium plasma,” J. Appl. Phys. 106(6), 063303–063306 (2009). [CrossRef]

14.

M. Corsi, G. Cristoforetti, M. Hidalgo, D. Iriarte, S. Legnaioli, V. Palleschi, A. Salvetti, and E. Tognoni, “Effect of laser-induced crater depth in laser-induced breakdown spectroscopy emission features,” Appl. Spectrosc. 59(7), 853–860 (2005). [CrossRef] [PubMed]

15.

A. M. Popov, F. Colao, and R. Fantoni, “Enhancement of LIBS signal by spatially confining the laser-induced plasma,” J. Anal. At. Spectrom. 24(5), 602–604 (2009). [CrossRef]

16.

L. B. Guo, W. Hu, B. Y. Zhang, X. N. He, C. M. Li, Y. S. Zhou, Z. X. Cai, X. Y. Zeng, and Y. F. Lu, “Enhancement of optical emission from laser-induced plasmas by combined spatial and magnetic confinement,” Opt. Express 19(15), 14067–14075 (2011). [CrossRef] [PubMed]

17.

X. Zeng, X. Mao, S. S. Mao, S.-B. Wen, R. Greif, and R. E. Russo, “Laser-induced shockwave propagation from ablation in a cavity,” Appl. Phys. Lett. 88(6), 061502–061503 (2006). [CrossRef]

18.

X. Zeng, X. Mao, S. S. Mao, J. H. Yoo, R. Greif, and R. E. Russo, “Laser-plasma interactions in fused silica cavities,” J. Appl. Phys. 95(3), 816–822 (2004). [CrossRef]

19.

X. Zeng, S. S. Mao, C. Liu, X. Mao, R. Greif, and R. E. Russo, “Plasma diagnostics during laser ablation in a cavity,” Spectrochim. Acta, B At. Spectrosc. 58(5), 867–877 (2003). [CrossRef]

20.

L. B. Guo, C. M. Li, W. Hu, Y. S. Zhou, B. Y. Zhang, Z. X. Cai, X. Y. Zeng, and Y. F. Lu, “Plasma confinement by hemispherical cavity in laser-induced breakdown spectroscopy,” Appl. Phys. Lett. 98(13), 131501 (2011). [CrossRef]

21.

A. M. Popov, F. Colao, and R. Fantoni, “Spatial confinement of laser-induced plasma to enhance LIBS sensitivity for trace elements determination in soils,” J. Anal. At. Spectrom. 25(6), 837–848 (2010). [CrossRef]

22.

X. K. Shen, J. Sun, H. Ling, and Y. F. Lu, “Spectroscopic study of laser-induced Al plasmas with cylindrical confinement,” J. Appl. Phys. 102(9), 093301–093305 (2007). [CrossRef]

23.

P. Yeates and E. T. Kennedy, “Spectroscopic, imaging, and probe diagnostics of laser plasma plumes expanding between confining surfaces,” J. Appl. Phys. 108(9), 093306–093312 (2010). [CrossRef]

24.

R. Mavrodineanu, ed., “Flame Spectroscopy” (John Wiley & Sons, New York, 1965).

25.

H. R. Griem, ed., “Plasma Spectroscopy” (McGraw-Hill Inc., New York, 1964).

26.

J. Feng, Z. Wang, Z. Li, and W. Ni, “Study to reduce laser-induced breakdown spectroscopy measurement uncertainty using plasma characteristic parameters,” Spectrochim. Acta, B At. Spectrosc. 65(7), 549–556 (2010). [CrossRef]

27.

M. Dong, J. Lu, S. Yao, J. Li, J. Li, Z. Zhong, and W. Lu, “Application of LIBS for direct determination of volatile matter content in coal,” J. Anal. At. Spectrom. 26(11), 2183–2188 (2011). [CrossRef]

28.

J. Feng, Z. Wang, L. West, Z. Li, and W. D. Ni, “A PLS model based on dominant factor for coal analysis using laser-induced breakdown spectroscopy,” Anal. Bioanal. Chem. 400(10), 3261–3271 (2011). [CrossRef] [PubMed]

29.

C. Aragon and J. Aguilera, “Characterization of laser induced plasmas by optical emission spectroscopy: A review of experiments and methods,” Spectrochim. Acta, B At. Spectrosc. 63(9), 893–916 (2008). [CrossRef]

30.

G. Cristoforetti, A. De Giacomo, M. Dell'Aglio, S. Legnaioli, E. Tognoni, V. Palleschi, and N. Omenetto, “Local Thermodynamic Equilibrium in Laser-Induced Breakdown Spectroscopy: Beyond the McWhirter criterion,” Spectrochim. Acta, B At. Spectrosc. 65(1), 86–95 (2010). [CrossRef]

OCIS Codes
(300.6210) Spectroscopy : Spectroscopy, atomic
(300.6365) Spectroscopy : Spectroscopy, laser induced breakdown

ToC Category:
Spectroscopy

History
Original Manuscript: September 10, 2012
Revised Manuscript: October 23, 2012
Manuscript Accepted: October 25, 2012
Published: November 2, 2012

Citation
Zhe Wang, Zongyu Hou, Siu-lung Lui, Dong Jiang, Jianmin Liu, and Zheng Li, "Utilization of moderate cylindrical confinement for precision improvement of laser-induced breakdown spectroscopy signal," Opt. Express 20, A1011-A1018 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-S6-A1011


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. J. D. Winefordner, I. B. Gornushkin, T. Correll, E. Gibb, B. W. Smith, and N. Omenetto, “Comparing several atomic spectrometric methods to the super stars: special emphasis on laser induced breakdown spectrometry, LIBS, a future super star,” J. Anal. At. Spectrom.19(9), 1061–1083 (2004). [CrossRef]
  2. R. E. Russo, X. Mao, H. Liu, J. Gonzalez, and S. S. Mao, “Laser ablation in analytical chemistry-a review,” Talanta57(3), 425–451 (2002). [CrossRef] [PubMed]
  3. V. I. Babushok, F. C. DeLucia, J. L. Gottfried, C. A. Munson, and A. W. Miziolek, “Double pulse laser ablation and plasma: Laser induced breakdown spectroscopy signal enhancement,” Spectrochim. Acta, B At. Spectrosc.61(9), 999–1014 (2006). [CrossRef]
  4. L. B. Guo, B. Y. Zhang, X. N. He, C. M. Li, Y. S. Zhou, T. Wu, J. B. Park, X. Y. Zeng, and Y. F. Lu, “Optimally enhanced optical emission in laser-induced breakdown spectroscopy by combining spatial confinement and dual-pulse irradiation,” Opt. Express20(2), 1436–1443 (2012). [CrossRef] [PubMed]
  5. D. K. Killinger, S. D. Allen, R. D. Waterbury, C. Stefano, and E. L. Dottery, “Enhancement of Nd:YAG LIBS emission of a remote target using a simultaneous CO2 laser pulse,” Opt. Express15(20), 12905–12915 (2007). [CrossRef] [PubMed]
  6. M. Weidman, M. Baudelet, S. Palanco, M. Sigman, P. J. Dagdigian, and M. Richardson, “Nd:YAG-CO2 double-pulse laser induced breakdown spectroscopy of organic films,” Opt. Express18(1), 259–266 (2010). [CrossRef] [PubMed]
  7. Q. L. Ma, V. Motto-Ros, W. Q. Lei, M. Boueri, X. S. Bai, L. J. Zheng, H. P. Zeng, and J. Yu, “Temporal and spatial dynamics of laser-induced aluminum plasma in argon background at atmospheric pressure: Interplay with the ambient gas,” Spectrochim. Acta, B At. Spectrosc.65(11), 896–907 (2010). [CrossRef]
  8. N. B. Zorov, A. A. Gorbatenko, T. A. Labutin, and A. M. Popov, “A review of normalization techniques in analytical atomic spectrometry with laser sampling: From single to multivariate correction,” Spectrochim. Acta, B At. Spectrosc.65(8), 642–657 (2010). [CrossRef]
  9. D. W. Hahn and N. Omenetto, “Laser-Induced Breakdown Spectroscopy (LIBS), Part II: Review of Instrumental and Methodological Approaches to Material Analysis and Applications to Different Fields,” Appl. Spectrosc.66(4), 347–419 (2012). [CrossRef] [PubMed]
  10. Z. Wang, L. Li, L. West, Z. Li, and W. Ni, “A spectrum standardization approach for laser-induced breakdown spectroscopy measurements,” Spectrochim. Acta, B At. Spectrosc.68, 58–64 (2012). [CrossRef]
  11. L. Li, Z. Wang, T. Yuan, Z. Hou, Z. Li, and W. Ni, “A simplified spectrum standardization method for laser-induced breakdown spectroscopy measurements,” J. Anal. At. Spectrom.26(11), 2274–2280 (2011). [CrossRef]
  12. R. Hedwig, “Confinement effect in enhancing shock wave plasma generation at low pressure by TEA CO2 laser bombardment on quartz sample,” Spectrochim. Acta, B At. Spectrosc.58(3), 531–542 (2003). [CrossRef]
  13. K. H. Kurniawan, M. Pardede, T. J. Lie, H. Niki, K. Fukumoto, T. Maruyama, K. Kagawa, and M. O. Tjia, “Crater effects on H and D emission from laser induced low-pressure helium plasma,” J. Appl. Phys.106(6), 063303–063306 (2009). [CrossRef]
  14. M. Corsi, G. Cristoforetti, M. Hidalgo, D. Iriarte, S. Legnaioli, V. Palleschi, A. Salvetti, and E. Tognoni, “Effect of laser-induced crater depth in laser-induced breakdown spectroscopy emission features,” Appl. Spectrosc.59(7), 853–860 (2005). [CrossRef] [PubMed]
  15. A. M. Popov, F. Colao, and R. Fantoni, “Enhancement of LIBS signal by spatially confining the laser-induced plasma,” J. Anal. At. Spectrom.24(5), 602–604 (2009). [CrossRef]
  16. L. B. Guo, W. Hu, B. Y. Zhang, X. N. He, C. M. Li, Y. S. Zhou, Z. X. Cai, X. Y. Zeng, and Y. F. Lu, “Enhancement of optical emission from laser-induced plasmas by combined spatial and magnetic confinement,” Opt. Express19(15), 14067–14075 (2011). [CrossRef] [PubMed]
  17. X. Zeng, X. Mao, S. S. Mao, S.-B. Wen, R. Greif, and R. E. Russo, “Laser-induced shockwave propagation from ablation in a cavity,” Appl. Phys. Lett.88(6), 061502–061503 (2006). [CrossRef]
  18. X. Zeng, X. Mao, S. S. Mao, J. H. Yoo, R. Greif, and R. E. Russo, “Laser-plasma interactions in fused silica cavities,” J. Appl. Phys.95(3), 816–822 (2004). [CrossRef]
  19. X. Zeng, S. S. Mao, C. Liu, X. Mao, R. Greif, and R. E. Russo, “Plasma diagnostics during laser ablation in a cavity,” Spectrochim. Acta, B At. Spectrosc.58(5), 867–877 (2003). [CrossRef]
  20. L. B. Guo, C. M. Li, W. Hu, Y. S. Zhou, B. Y. Zhang, Z. X. Cai, X. Y. Zeng, and Y. F. Lu, “Plasma confinement by hemispherical cavity in laser-induced breakdown spectroscopy,” Appl. Phys. Lett.98(13), 131501 (2011). [CrossRef]
  21. A. M. Popov, F. Colao, and R. Fantoni, “Spatial confinement of laser-induced plasma to enhance LIBS sensitivity for trace elements determination in soils,” J. Anal. At. Spectrom.25(6), 837–848 (2010). [CrossRef]
  22. X. K. Shen, J. Sun, H. Ling, and Y. F. Lu, “Spectroscopic study of laser-induced Al plasmas with cylindrical confinement,” J. Appl. Phys.102(9), 093301–093305 (2007). [CrossRef]
  23. P. Yeates and E. T. Kennedy, “Spectroscopic, imaging, and probe diagnostics of laser plasma plumes expanding between confining surfaces,” J. Appl. Phys.108(9), 093306–093312 (2010). [CrossRef]
  24. R. Mavrodineanu, ed., “Flame Spectroscopy” (John Wiley & Sons, New York, 1965).
  25. H. R. Griem, ed., “Plasma Spectroscopy” (McGraw-Hill Inc., New York, 1964).
  26. J. Feng, Z. Wang, Z. Li, and W. Ni, “Study to reduce laser-induced breakdown spectroscopy measurement uncertainty using plasma characteristic parameters,” Spectrochim. Acta, B At. Spectrosc.65(7), 549–556 (2010). [CrossRef]
  27. M. Dong, J. Lu, S. Yao, J. Li, J. Li, Z. Zhong, and W. Lu, “Application of LIBS for direct determination of volatile matter content in coal,” J. Anal. At. Spectrom.26(11), 2183–2188 (2011). [CrossRef]
  28. J. Feng, Z. Wang, L. West, Z. Li, and W. D. Ni, “A PLS model based on dominant factor for coal analysis using laser-induced breakdown spectroscopy,” Anal. Bioanal. Chem.400(10), 3261–3271 (2011). [CrossRef] [PubMed]
  29. C. Aragon and J. Aguilera, “Characterization of laser induced plasmas by optical emission spectroscopy: A review of experiments and methods,” Spectrochim. Acta, B At. Spectrosc.63(9), 893–916 (2008). [CrossRef]
  30. G. Cristoforetti, A. De Giacomo, M. Dell'Aglio, S. Legnaioli, E. Tognoni, V. Palleschi, and N. Omenetto, “Local Thermodynamic Equilibrium in Laser-Induced Breakdown Spectroscopy: Beyond the McWhirter criterion,” Spectrochim. Acta, B At. Spectrosc.65(1), 86–95 (2010). [CrossRef]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.

Figures

Fig. 1 Fig. 2 Fig. 3
 
Fig. 4
 

« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited