Analysis of Carbon and Sulfur in Steel Samples Using Bench 

Top Laser-Induced Breakdown Spectroscopy (LIBS) 

by Frank C. De Lucia, Jr., Jennifer L. Gottfried, and Andrzej W. Miziolek 

ARL-TR-5000 October 2009 

Approved for public release; distribution is unlimited. 
NOTICES 

Disclaimers 

The findings in this report are not to be construed as an official Department of the Army position unless 

so designated by other authorized documents. 

Citation of manufacturer’s or trade names does not constitute an official endorsement or approval of the 

use thereof. 

Destroy this report when it is no longer needed. Do not return it to the originator. 
Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5066 

ARL-TR-5000 October 2009 

Analysis of Carbon and Sulfur in Steel Samples Using Bench 

Top Laser-Induced Breakdown Spectroscopy (LIBS) 

Frank C. De Lucia, Jr., Jennifer L. Gottfried, and Andrzej W. Miziolek 

Weapons and Materials Research Directorate, ARL 

Approved for public release; distribution is unlimited. 
ii

REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering 

and maintaining the data needed, and completing and reviewing the collection information. Send comments regarding this burden estimate or any other aspect of this collection of information, 

including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson 

Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to 

comply with a collection of information if it does not display a currently valid OMB control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 

1. REPORT DATE (DD-MM-YYYY)

October 2009 

2. REPORT TYPE 

Final 

3. DATES COVERED (From - To) 

June 13-June 16, 2009 

4. TITLE AND SUBTITLE 

Analysis of Carbon and Sulfur in Steel Samples Using Bench Top Laser-Induced 

Breakdown Spectroscopy (LIBS) 

5a. CONTRACT NUMBER 

5b. GRANT NUMBER 

5c. PROGRAM ELEMENT NUMBER 

6. AUTHOR(S) 

Frank C. De Lucia, Jr., Jennifer L. Gottfried, and Andrzej W. Miziolek 

5d. PROJECT NUMBER 

N/A 

5e. TASK NUMBER 

5f. WORK UNIT NUMBER 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 

U.S. Army Research Laboratory 

ATTN: RDRL-WMB-D 

Aberdeen Proving Ground, MD 21005-5066 

8. PERFORMING ORGANIZATION 

 REPORT NUMBER 

ARL-TR-5000 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 

US Army ARDEC, Benet Laboratories, Bldg. 115 

1 Buffington St. 

Watervliet, NY 12189 

10. SPONSOR/MONITOR’S ACRONYM(S) 

11. SPONSOR/MONITOR'S REPORT 

 NUMBER(S) 

12. DISTRIBUTION/AVAILABILITY STATEMENT 

Approved for public release; distribution is unlimited. 

13. SUPPLEMENTARY NOTES 

14. ABSTRACT 

Laser- induced breakdown spectroscopy (LIBS) has been used for steel analysis for many applications. LIBS was used to 

confirm that the steel sample of interest is the correct steel type using linear correlation. Next, we attempted to identify trace 

carbon and sulfur in the steel sample using a standard LIBS laboratory setup. However, the most intense carbon and sulfur 

emission occurs in the vacuum ultraviolet region and, therefore, needs specialized spectrometer equipment. Interference from 

steel lines and the trace amounts of sulfur and carbon prohibit the use of atomic emission lines in the more easily accessible 

ultraviolet-visible-near infrared emission region. 

15. SUBJECT TERMS

LIBS, steel analysis, correlation 

16. SECURITY CLASSIFICATION OF: 

17. LIMITATION 

OF ABSTRACT 

UU 

18. NUMBER 

OF PAGES 

18 

19a. NAME OF RESPONSIBLE PERSON

Frank C. De Lucia, Jr. 

a. REPORT 

Unclassified 

b. ABSTRACT 

Unclassified 

c. THIS PAGE 

Unclassified 

19b. TELEPHONE NUMBER (Include area code) 

410-306-0884 

Standard Form 298 (Rev. 8/98) 

Prescribed by ANSI Std. Z39.18 
iii

Contents 

List of Figures iv

List of Tables iv

1. Introduction 1

2. Experimental 1

3. Results and Discussion 3

4. Conclusions 8

5. References 9

List of Symbols, Abbreviations, and Acronyms 11

Distribution List 12 
iv

List of Figures 

Figure 1. LIBS spectra (single pulse, CCD spectrometer) of Benet Laboratories samples 1–

14 (red) and 4130 steel (blue). Several argon and iron lines saturate the detector. ........2

Figures 2a, 2b. LIBS spectra of Benet Laboratories samples and steel standards (a) region of 

strongest titanium atomic emission and (b) region of strongest chromium 

atomic emission. .....................................................................................................5

Figure 3. LIBS spectra of steel standards and organic residue reference in regions of carbon 

atomic emission. ..............................................................................................................6

Figure 4. LIBS spectra from the high resolution echelle spectrograph. .........................................7

Figure 5. LIBS spectra of 4130 steel and sulfur powder. ...............................................................8

List of Tables 

Table 1. Percentage of minor constituent elements in NIST steel standards. .................................2

Table 2. The r2 value for each sample with each steel standard. ....................................................3
1

1. Introduction 

The need to analyze steel samples for their chemical composition is important for process 

control. Most methods currently employed generally require multiple sample preparation steps 

and off-site analysis. Laser-induced breakdown spectroscopy (LIBS) requires no sample 

preparation, can simultaneously detect all elements, can be configured as a portable system (1–4) 

and can be used for real-time online steel analysis (5–9). Recently, Benet Laboratories was 

interested in seeing if LIBS could be used to determine slight discrepancies in the composition of 

steel parts, such as trace amounts of carbon. LIBS analysis of carbon in steel samples typically 

involves using atomic emission lines in the vacuum ultraviolet (VUV) region (10–18). 

Collecting emission in the VUV usually involves using specialized spectrometers and sample 

chambers in order to avoid absorption of the plasma emission due to the O2 Schumann-Runge 

band system (19). Also, the optics need to transmit light emission below 200 nm. Benet 

Laboratories provided several steel samples to the U.S. Army Research Laboratory (ARL) to see 

if a simple benchtop LIBS system could be used to detect carbon and sulfur emission in the 230–

1000 nm ultraviolet-visible-near infrared (UV-VIS-NIR) range, in order to avoid using the 

specialized equipment needed to collect emission in the VUV. We also needed to confirm that 

the samples provided were 4130 steel. 

2. Experimental 

The ARL benchtop LIBS system utilized a 300 mJ laser pulse from a Nd:YAG laser (Big Sky 

Laser, Quantel, CFR 400). The laser was focused by a convex lens (100 mm) through a pierced 

mirror onto the sample surface, creating a microplasma. An argon flow was directed across the 

plasma in order to enhance the signal further. The plasma emission was collected by a parabolic 

mirror and focused onto a seven fiber optic bundle where it was delivered to a seven channel 

charge-coupled device (CCD) spectrometer (Ocean Optics, LIBS2500+). The gate delay was 

1.25 s with a 1 ms integration time. We also used a double pulse Nd:YAG laser (Continuum, 

Surelite I-PIV) at 320 mJ per pulse for additional analysis. The laser pulses (separated by 1 s) 

passed through a flat pierced mirror and were focused by a 100 mm convex lens onto the sample 

surface. The plasma emission was collected by the lens and redirected by the flat mirror to a 

convex lens (50 mm) that focused the light onto a single 400 μ fiber. The fiber delivered the 

light to an echelle spectrograph (EMU-65, Catalina Scientific Instruments) with an electron 

multiplying charge-coupled device (EMCCD) (Andor iXon). The gate delay was 1.5 s with an 

integration time of 50 s. The echelle provided much higher resolution and dynamic range than 

the seven channel CCD spectrometer. 
2

Ten LIBS spectra were collected from each Benet Laboratories sample (no. 1, no. 2, no. 4, no. 5, 

no. 6, no. 8, no. 9, no. 10, no. 11, no. 12, no. 13, no. 14, and two base plate samples) and from 

various National Institute of Standards and Technology (NIST) steel standards, including 4130 

steel, a low alloy steel (1761a), and a stainless steel (C1296) using the single pulse laser system 

and the seven channel spectrometer. Ten additional spectra of the 1761a steel standard were 

collected using the double pulse system and the higher resolution echelle spectrometer. Table 1 

lists the minor constituent elements discussed in this report for each steel standard. For every 

sample (NIST standards and Benet samples) the first spectrum was removed from the data set as 

it was primarily used to clean the surface of any contaminants. The remaining spectra were used 

to calculate an average LIBS spectrum for each of the samples and standards. 

Table 1. Percentage of minor constituent elements in NIST steel standards. 

4130 

(%) 

1761a 

(%) 

C1296 

(%) 

Carbon 0.274 1.05 0.038 

Sulfur 0.014 0.037 0.013 

Chromium 0.91 0.222 27.9 

Titanium — 0.173 0.23 

The numbered samples and the 4130 steel sample are displayed in figure 1. The spectra are all 

very similar as expected since the majority of the atomic emission lines in the 200–500 nm 

region are due to iron atomic emission. The largest atomic emission lines from 600–950 nm are 

due to the argon bath gas. 

Figure 1. LIBS spectra (single pulse, CCD spectrometer) of Benet Laboratories samples 1–14 (red) 

and 4130 steel (blue). Several argon and iron lines saturate the detector. 
3

3. Results and Discussion 

We used linear correlation to determine if the Benet Laboratories samples were in fact 4130 

steel. Each individual numbered sample spectrum and the base plate spectra were correlated 

against each individual spectrum from the NIST steel standards (4130 steel, 1761a, and C1296) 

to determine the r2 value from the Pearson correlation coefficient 

  

    2 2

x x y y

x x y y r

   

    . (1) 

The r2

 value is used as a measure of the association between two spectra, where r2 = 1 indicates 

that the spectra are identical. We correlated each of the nine spectra from each sample from 

Benet Laboratories with each of the nine spectra from the three steel standards. There were a 

total of 81 correlation coefficients calculated for each sample. The average correlation is 

calculated for each sample and the error is determined for a 95% confidence limit. The 

correlation for each sample was closest to the 4130 steel and the 1761a steel. The samples do 

not correlate with C1296 at all. Table 2 shows the comparison of the correlations between the 

two standards. Overall, the majority of the samples correlate more closely with the 4130 steel. 

However, the correlation is extremely close for the two standards. Since the majority of each 

standard consists of iron it is not surprising that the numbered samples closely correlate with 

both standards. In order to definitively determine the best match, closer inspection of minor 

atomic emission peaks is necessary. The 1761a alloy contains titanium (0.173%), unlike the 

4130 steel standard. Prominent titanium atomic emission lines occur at 334.885, 336.099, 

337.262, and 338.325 nm. 

Table 2. The r2 value for each sample with each steel standard. 

4130 1761a C1296 

Sample r2 value r2 value r2 value 

1 0.968±0.004 0.955±0.003 0.719±0.005 

2 0.963±0.005 0.949±0.004 0.748±0.006 

4 0.959±0.004 0.946±0.003 0.729±0.004 

5 0.939±0.007 0.938±0.006 0.714±0.006 

6 0.957±0.004 0.951±0.004 0.736±0.005 

8 0.965±0.007 0.953±0.006 0.715±0.004 

9 0.959±0.004 0.952±0.003 0.714±0.005 

10 0.955±0.008 0.945±0.007 0.725±0.005 

11 0.897±0.014 0.895±0.012 0.721±0.006 

12 0.973±0.003 0.963±0.001 0.723±0.004 

13 0.953±0.008 0.946±0.006 0.727±0.005 

14 0.908±0.008 0.918±0.007 0.713±0.005 

Base plate 1 0.779±0.014 0.805±0.013 0.647±0.011 

Base plate 2 0.824±0.011 0.846±0.009 0.668±0.010 
4

In figure 2a, one can see that the numbered samples and the 4130 steel standard do not have 

prominent titanium lines compared to 1761a. However, the base plate samples clearly have 

higher titanium emission lines, thus higher titanium content. At 335.808 and 336.778 nm atomic 

emission lines due to chromium are much more prevalent in the numbered samples and the 4130 

steel compared to the 1761a standard and the base plate. The chromium content in 4130 steel 

and the 1761a standard is 0.91% and 0.222%, respectively. Again, the more prominent 

chromium peaks indicate that the numbered samples are 4130 steel. Figure 2b shows the most 

prominent chromium lines at 425.43 and 427.476 nm; the numbered samples and the 4130 steel 

have the highest emission due to chromium. The two base plate samples have higher chromium 

emission than the 1761a standard. From the correlations and the peak analysis, it is evident that 

the numbered samples are 4130 steel. However, the two base plate samples have higher titanium 

content and lower chromium content than 4130 steel and do not match well with the 1761a or 

C1296 steel. It should be noted that these are results from a limited study. Further investigation 

could involve selecting the key minor element emission peaks (not iron peaks) in 4130 steel. 

These same peaks would be selected in a variety of steel standards (more than used in this study) 

and these emission intensities would be used as inputs for a variety of chemometric techniques; 

principal components analysis, partial least squares, and partial least squares discriminant 

analysis, etc. By using more steel standards and minor emission lines particular to 4130 steel in 

the model, the matching of unknown samples to 4130 steel would be more robust. 

The spectrometer wavelength ranges available at ARL cover from 200–1000 nm. In this range 

the most prominent carbon line is at 247.8 nm. Other lines observed in organic samples are at 

833.515, 909.483, and 940.573 nm. Figure 3 displays the LIBS spectra from the 4130 steel, the 

1761a standard (has the highest % carbon content) and a residue of an organic material as a 

carbon reference. There was no carbon atomic emission at 833.515, 909.483, and 940.573 nm in 

any of the numbered samples or the standards as shown in figure 3. Unfortunately, an iron 

atomic line emits ~247.8 nm, interfering with any carbon emission that may be present. An 

attempt at generating a calibration line based on the intensity at 247.8 nm was still made using 

several carbon containing metal standards despite the potential interference. However, there was 

no linear correlation between the peak intensity and the known carbon concentration, indicating 

that the majority of the emission line in the spectra is due to the iron. 
5

Figures 2a, 2b. LIBS spectra of Benet Laboratories samples and steel standards (a) region of strongest 

titanium atomic emission and (b) region of strongest chromium atomic emission. 
6

Figure 3. LIBS spectra of steel standards and organic residue reference in regions of carbon atomic 

emission. 
7

We collected more LIBS spectra using the double pulse laser and the echelle spectrograph to 

improve the resolution. Figure 4 displays the spectra of the 1761a standard and the organic 

residue. We observe that the two peaks at ~248 nm do not overlap using the higher resolution 

spectrograph, further supporting the conclusion that the line in the steel standard is due to iron 

and not carbon. If any carbon emission is present then it is convoluted with the more prominent 

iron emission, making calibration all but impossible. 

Figure 4. LIBS spectra from the high resolution echelle spectrograph. 

The prominent sulfur emission lines in the ranges covered are observed at 869.47, 921.29, 

922.81, and 923.75 nm. We collected LIBS spectra of sulfur powder using the single pulse LIBS 

system and the seven channel spectrometer to use as a reference to compare to the steel samples. 

In figure 5, we show the spectra of the 4130 steel and the sulfur under argon. No sulfur emission 

is observed in the 4130 steel or any of the other numbered samples or standards. 
8

Figure 5. LIBS spectra of 4130 steel and sulfur powder. 

4. Conclusions 

As mentioned previously, the published literature for carbon and sulfur measurements in steel is 

conducted in the VUV (10, 11, 13, 15–18, 20). The advantage of using carbon and sulfur atomic 

emission peaks in this region is that the most prominent emission lines for carbon and sulfur are 

at 193.09 nm and 180.73 nm, respectively, compared to the lines used in the above study. They 

are also free of interference from the iron atomic emission lines, the most prevalent element in 

the steel samples. Successful calibration curves have been made in steel samples using these 

lines for sulfur and steel (10, 13, 17). The disadvantage of using these lines is air absorption in 

this region due to the O2 Schumann-Runge band system. The light collection pathway and the 

spectrometers must be purged with inert gases (such as nitrogen or argon) in order to obtain 

usable signals. Optics and gratings capable of transmitting and dispersing VUV light must also 

be acquired. We were unable to observe any carbon or sulfur emission in any of the steel 

samples in the UV-VIS-NIR; however other trace elements such as titanium and chromium were 

detected. In order to detect carbon or sulfur in steel, LIBS spectra should be collected in the 

VUV emission range, which requires specialized equipment and a more complex experimental 

setup. 
9

5. References 

1. DeLucia Jr., F. C.; Samuels, A. C.; Harmon, R. S.; Walters, R. A.; McNesby, K. L.; 

LaPointe, A.; Winkel Jr., R. J.; Miziolek, A. W. Laser-induced Breakdown Spectroscopy 

(LIBS): A Promising Versatile Chemical Sensor Technology for Hazardous Material 

Detection. IEEE Sensors Journal 5 2005, 681–689. 

2. Goujon, J.; Giakoumaki, A.; Piñon, V.; Musset, O.; Anglos, D.; Georgiou, E.; Boquillon, J. 

P. A Compact and Portable Laser-Induced Breakdown Spectroscopy Instrument for Single 

and Double Pulse Applications. Spectrochim. Acta, Part B 2008, 63, 1091–1096. 

3. Harmon, R. S.; DeLucia, F. C.; McManus, C. E.; McMillan, N. J.; Jenkins, T. F.; Walsh, M. 

E.; Miziolek, A. Laser-Induced Breakdown Spectroscopy - An Emerging Chemical Sensor 

Technology for Real-Time Field-Portable, Geochemical, Mineralogical, and Environmental 

Applications. Appl. Geochem. 2006, 21, 730–747. 

4. Munson, C. A.; Gottfried, J. L.; Snyder, E. G.; DeLucia Jr, F. C.; Gullett, B.; Miziolek, A. 

W. Detection of Indoor Biological Hazards Using the Man-Portable Laser Induced 

Breakdown Spectrometer. Appl. Opt. 2008, 47, G48–G57. 

5. Balzer, H.; Hoehne, M.; Noll, R.; Sturm, V. New approach to Online Monitoring of the Al 

Depth Profile of the Hot-Dip Galvanised Sheet Steel Using LIBS. Anal. Bioanal. Chem. 

2006, 385, 225–233. 

6. Noll, R.; Bette, H.; Brysch, A.; Kraushaar, M.; Moench, I.; Peter, L.; Sturm, V. LaserInduced Breakdown Spectrometry - Applications for Production Control and Quality 

Assurance In the Steel Industry. Spectrochim. Acta, Part B 2001, 56, 637–649. 

7. Sturm, V.; Schmitz, H. U.; Reuter, T.; Fleige, R.; Noll, R. Fast Vacuum Slag Analysis In a 

Steel Works By Laser-Induced Breakdown Spectroscopy. Spectrochim. Acta, Part B 2008, 

63, 1167–1170. 

8. Boué-Bigne, F. Laser-Induced Breakdown Spectroscopy Applications In the Steel Industry: 

Rapid Analysis of Segregation and Decarburization. Spectrochim. Acta, Part B 2008, 63, 

1122–1129. 

9. Hubmer, G.; Kitzberger, R.; Mörwald, K. Application of LIBS to the In-Line Process 

Control of Liquid High-Alloy Steel Under Pressure. Anal. Bioanal. Chem. 2006, 385, 219–

224. 

10 Aguilera, J. A.; Aragon, C.; Campos, J. Determination of Carbon Content in Steel Using 

Laser-Induced Breakdown Spectroscopy. Appl. Spectrosc. 1992, 46, 1382–1387. 
10

11. Aragon, C.; Aguilera, J. A.; Campos, J. Determination of Carbon Content in Molten Steel 

Using Laser-Induced Breakdown Spectroscopy. Appl. Spectrosc. 1993, 47, 606–608. 

12. Khater, M. A.; van Kampen, P.; Costello, J. T.; Mosnier, J. P.; Kennedy, E. T. TimeIntegrated Laser-Induced Plasma Spectroscopy In the Vacuum Ultraviolet for the 

Quantitative Elemental Characterization of Steel Alloys. J. Phys. D: Appl. Phys. 2000, 33, 

2252–2262. 

13. Sturm, V.; Peter, L.; Noll, R. Steel Analysis with Laser-Induced Breakdown Spectrometry 

in the Vacuum Ultraviolet. Appl. Spectrosc. 2000, 54, 1275–1278. 

14. Khater, M.; Costello, J.; Kennedy, E. Optimization of the Emission Characteristics of LaserProduced Steel Plasmas in the Vacuum Ultraviolet: Significant Improvements in Carbon 

Detection Limits. Appl. Spectrosc. 2002, 56, 970–983. 

15. Peter, L.; Sturm, V.; Noll, R. Liquid Steel Analysis with Laser-Induced Breakdown 

Spectrometry in the Vacuum Ultraviolet. Appl. Opt. 2003, 42, 6199–6204. 

16. Gruber, J.; Heitz, J.; Arnold, N.; Bauerle, D.; Ramaseder, N.; Meyer, W.; Hochortler, J.; 

Koch, F. In Situ Analysis of Metal Melts in Metallurgic Vacuum Devices By Laser-Induced 

Breakdown Spectroscopy. Appl. Spectrosc. 2004, 58, 457–462. 

17. Radivojevic, I.; Haisch, C.; Niessner, R.; Florek, S.; Becker-Ross, H.; Panne, U. 

Microanalysis by Laser-Induced Plasma Spectroscopy in the Vacuum Ultraviolet. Anal. 

Chem. 2004, 76, 1648–1656. 

18. Wormhoudt, J.; Iannarilli, F. J.; Jones, S.; Annen, K. D.; Freedman, A. Determination of 

Carbon in Steel by Laser-Induced Breakdown Spectroscopy Using A Microchip Laser and 

Miniature Spectrometer. Appl. Spectrosc. 2005, 59, 1098–1102. 

19. Pearse, R. W. B.; Gaydon, A. G. The Identification of Molecular Spectra, 4th ed.; John 

Wiley & Sons, Inc.: New York, 1976. 

20. Gonzalez, A.; Ortiz, M.; Campos, J. Determination of Sulfur Content in Steel by LaserProduced Plasma Atomic Emission Spectroscopy. Appl. Spectrosc. 1995, 49, 1632–1635. 
11

List of Symbols, Abbreviations, and Acronyms 

ARL U.S. Army Research Laboratory 

CCD charge-coupled device 

EMCCD electron multiplying charge-coupled device 

LIBS Laser-induced breakdown spectroscopy 

NIST National Institute of Standards and Technology

UV-VIS-IR ultraviolet-visible-near infrared 

VUV vacuum ultraviolet 
12

No. of 

Copies Organization

 1 DEFENSE TECHNICAL 

 (PDF INFORMATION CTR 

 only) DTIC OCA 

 8725 JOHN J KINGMAN RD 

 STE 0944 

 FORT BELVOIR VA 22060-6218 

 1 DIRECTOR 

 US ARMY RESEARCH LAB 

 IMNE ALC HRR 

 2800 POWDER MILL RD 

 ADELPHI MD 20783-1197 

 1 DIRECTOR 

 US ARMY RESEARCH LAB 

 RDRL CIM L 

 2800 POWDER MILL RD 

 ADELPHI MD 20783-1197 

 1 DIRECTOR 

 US ARMY RESEARCH LAB 

 RDRL CIM P 

 2800 POWDER MILL RD 

 ADELPHI MD 20783-1197 

 1 BENET LABORATORIES 

AMSTA CCB R 

 G VIGILANTE 

 1 BUFFINGTON ST BLDG 115 

 WATERVLIET NY 12189-4050 

 1 A3 TECHNOLOGIES LLC 

D WONG 

 1200 TECHNOLOGY DR STE Q 

 ABERDEEN MD 21001 

ABERDEEN PROVING GROUND

 1 DIR USARL 

 RDRL CIM G (BLDG 4600) 

 3 RDRL WMB D 

 F DE LUCIA 

 J GOTTFRIED 

 A MIZIOLEK