Laser Induced Breakdown Spectroscopy (LIBS)

Luis Mair, winter semester 2018/19

Laser Induced Breakdown Spectroscopy (LIBS) is a virtually non-destructive analysis method that uses laser spectroscopy to determine the elementary constituents of a substance.

Principle of the Testing Method

At the beginning of the triggered measurement, the sample is hit by a short laser pulse (Nd:YAG laser). This laser pulse has a wavelength of 1064 nm and lasts for a period of a few nanoseconds. ^[1] The power density on the surface of the sample can be more than 1 GW / cm² ^[2] and leads to extremely high temperatures up to some 10,000 degrees Celsius. This turns a portion of the material of the sample into a plasma. ^[3] Upon cooling of the plasma and its excited constituents, the stored energy is emitted as radiation at discrete frequencies and wavelengths. The radiation is split into the different wavelengths and detected by a spectrometer. The spectral distribution of each element is unique. As a result, on the one hand, the elements constituting the sample and, on the other hand, the percentage of each element in the sample can be determined.

Application

To analyze a sample, the device can be placed on the surface as well as at some distance, depending on the type of device. Subsequently, the measurement is started by a trigger. The discovered elements and their percentage distribution can be read immediately from the display of the device. In addition, the device can provide information on the expected deviations. The device is immediately ready for use again. ^[4]
The simple basic principle enables small, powerful and portable test equipment for real-time, on-site, and in-situ analysis. ^[5]

Advantages and Limits of the Application

A big advantage of LIBS is its simple and fast process. Within a few seconds, the measurement device can be attached to test specimens, the measurement can be triggered, and the result can be read directly. ^[6] In particular, by the extremely low material consumption in the measurement (10^-9 g up to 10^-12 g) ^[7] and the generation of a small crater with a diameter of several 10 µm ^[8], the method can be referred to as a virtually non-destructive testing method.

Further advantages compared to other measuring methods: The test specimens do not require preparation before the measurement. ^[9] The testing devices can be small, portable and powerful at the same time. ^[10]

However, it should be noted that the method covers only a small part of the surface of the entire test specimen and is therefore limited, especially in case of inhomogeneous specimens with regions of different material composition.

Application Areas

Typical applications are analysis of aluminum alloys, sorting of components during recycling of scrap and detection of explosive residues. A special form of application can be found in forensics.

• LIBS Analysis of Aluminum Alloys ^[11]

Aluminum, as the second most important material for the industry after steel, is the base for a variety of alloys. The two characteristic spectral lines in LIBS for aluminum are easy to determine. In the single pulse spectrum of aluminum alloys, the other components are barely visible or invisible. For better detection, a double pulse spectrum is generated and measured. Here, the intensities of the radiation are higher, and the wavelength of the radiation can be better studied. Thus, the components of the alloy can be determined more precisely, and manufacturing quality can be secured.

• Element Analysis during Sorting of Scrap ^[12]

An omnipresent problem in elementary analysis in the sorting of scrap is coated, contaminated or otherwise dirty material. For example, the materials may be painted, oxidized, or covered by a dirt layer. Nevertheless, to make an analysis possible, a high-performance laser can be prefixed to a LIBS. This removes the interfering layers and exposes the actual specimen. Subsequently, as already described, the composition of the materials is determined by means of a classic LIBS. Now a sorting of the components of the scrap can take place. The short duration of a single measurement allows speeds of conveyor belts up to 3 m/s ^[13]. Special requirements are placed on the presorting for the recycling of steel. Low levels of manganese, chromium and copper should ensure the quality of the melted again steel.

• Detection of Explosive Residues ^[14]

Special requirements are placed on the detection of explosives and their residues. The sensitivity and selectivity of the LIBS devices used must be higher than the ones of most other applications. Particularly in the search for very small amounts of residues of explosives already the first measurement can lead to removal of the residues to be detected. Most military explosives consist of hydrogen, carbon, nitrogen and oxygen. In principle, explosives have high ratios of nitrogen and oxygen to hydrogen and carbon. The measurement of this ratio allows a statement about the energetic potential of the substance. A special challenge in measuring these elements is the atmosphere. Since this has very high levels of nitrogen and oxygen, the measurement can be greatly influenced. The relevant quantities must be determined separately and deducted accordingly from the results of the measurement of the residues of explosives.

• Forensic Applications ^[15]

Forensics also includes examples of LIBS applications. Fragments of automobile glass can be identified and assigned to their origin. Similarly, residues of gunpowder can be detected and used as evidence.

Literature

• Donges, A., Noll, R.: Laser Measurement Technology. Fundamentals and Applications. Springer publ., Berlin Heidelberg (2015), p. 324.
• Gottfried, J.L., De Lucia, Jr.F.C., Harmon, R.S., Munson, C.A., Winkel, R.J., Miziolek, A.W.: Detection of Energetic Materials and Explosive Residues With Laser-Induced Breakdown Spectroscopy: I. Laboratory Measurements. Weapons and Materials Research Directorate, ARL (2007). pp. 2-6.
• Gottfried, J.L., De Lucia, Jr.F.C.: Laser-Induced Breakdown Spectroscopy: Capabilities and Applications. Weapons and Materials Research Directorate, ARL (2010). pp. 1-10.
• Jarvikivi, M.: What is Laser Induced Breakdown Spectroscopy (LIBS)?, Blog post. Website of Hitachi High-Technologies Corporation, 2018, January 3. Retrieved 2018, January 19, from https://hha.hitachi-hightech.com/en/blogs-events/blogs/2018/01/03/what-is-libs/.
• Musazzi, S., Perini, U. (eds.): Laser-Induced Breakdown Spectroscopy. Theory and Applications. Springer publ., Berlin Heidelberg (2014), pp. 59-189.
• SECOPTA analytics GmbH.: MopaLIBS. Elementanalyse in der Schrottsortierung. (n.d.). Retrieved 2018, January 19, from https://www.secopta.de/produkte/mopa-libs.
• SECOPTA analytics GmbH.: Recycling von Stahl. Stahlschrotte zum Wiedereinschmelzend sicher nach Legierung unterscheiden. (n.d.). Retrieved 2018, January 19, from https://www.secopta.de/applikationen/recycling.
• SECOPTA analytics GmbH.: Technologie. LIBS-Laser Induced Breakdown Spectroscopy. (n.d.). Retrieved 2018, January 19, from https://www.secopta.de/unternehmen/technologielibs.

References

1. Gottfried, J.L., De Lucia, Jr.F.C.: Laser-Induced Breakdown Spectroscopy: Capabilities and Applications. Weapons and Materials Research Directorate, ARL (2010). p. 1.
2. Gottfried, J.L., De Lucia, Jr.F.C., Harmon, R.S., Munson, C.A., Winkel, R.J., Miziolek, A.W.: Detection of Energetic Materials and Explosive Residues With Laser-Induced Breakdown Spectroscopy: I. Laboratory Measurements. Weapons and Materials Research Directorate, ARL (2007). p. 6.
3. Jarvikivi, M.: What is Laser Induced Breakdown Spectroscopy (LIBS)?, Blog post. Website of Hitachi High-Technologies Corporation, 2018, January 3. Retrieved 2018, January 19, from https://hha.hitachi-hightech.com/en/blogs-events/blogs/2018/01/03/what-is-libs/.
4. Jarvikivi, M.: What is Laser Induced Breakdown Spectroscopy (LIBS)?, Blog post. Website of Hitachi High-Technologies Corporation, 2018, January 3. Retrieved 2018, January 19, from https://hha.hitachi-hightech.com/en/blogs-events/blogs/2018/01/03/what-is-libs/.
5. SECOPTA analytics GmbH.: Technologie. LIBS-Laser Induced Breakdown Spectroscopy. (n.d.). Retrieved 2018, January 19, from https://www.secopta.de/unternehmen/technologielibs.
6. Jarvikivi, M.: What is Laser Induced Breakdown Spectroscopy (LIBS)?, Blog post. Website of Hitachi High-Technologies Corporation, 2018, January 3. Retrieved 2018, January 19, from https://hha.hitachi-hightech.com/en/blogs-events/blogs/2018/01/03/what-is-libs/.
7. Gottfried, J.L., De Lucia, Jr.F.C.: Laser-Induced Breakdown Spectroscopy: Capabilities and Applications. Weapons and Materials Research Directorate, ARL (2010). p. 2.
8. Donges, A., Noll, R.: Laser Measurement Technology. Fundamentals and Applications. Springer publ., Berlin Heidelberg (2015), p. 324.
9. Musazzi, S., Perini, U. (eds.): Laser-Induced Breakdown Spectroscopy. Theory and Applications. Springer publ., Berlin Heidelberg (2014), p. 59.
10. Gottfried, J.L., De Lucia, Jr.F.C.: Laser-Induced Breakdown Spectroscopy: Capabilities and Applications. Weapons and Materials Research Directorate, ARL (2010). p. 2.
11. Musazzi, S., Perini, U. (eds.): Laser-Induced Breakdown Spectroscopy. Theory and Applications. Springer publ., Berlin Heidelberg (2014), pp. 177ff.
12. SECOPTA analytics GmbH.: MopaLIBS. Elementanalyse in der Schrottsortierung. (n.d.). Retrieved 2018, January 19, from https://www.secopta.de/produkte/mopa-libs.
13. SECOPTA analytics GmbH.: Recycling von Stahl. Stahlschrotte zum Wiedereinschmelzend sicher nach Legierung unterscheiden. (n.d.). Retrieved 2018, January 19, from https://www.secopta.de/applikationen/recycling.
14. Gottfried, J.L., De Lucia, Jr.F.C., Harmon, R.S., Munson, C.A., Winkel, R.J., Miziolek, A.W.: Detection of Energetic Materials and Explosive Residues With Laser-Induced Breakdown Spectroscopy: I. Laboratory Measurements. Weapons and Materials Research Directorate, ARL (2007). p. 2f.
15. Gottfried, J.L., De Lucia, Jr.F.C.: Laser-Induced Breakdown Spectroscopy: Capabilities and Applications. Weapons and Materials Research Directorate, ARL (2010). p. 10.