LIBS Basics, Part I: Measurement Physics and Implementation

Jan 01, 2014

Laser-induced breakdown spectroscopy (LIBS) is an emerging analytical method that has been the focus of substantial research over the last 25 years. The recent emergence of commercially available LIBS systems from major manufacturers is a sign that the technology is maturing. This column is the first of a three-part series focusing on major aspects of LIBS. This installment concentrates on the basics of the measurement and typical implementations. Part II will discuss the choices for LIBS hardware in detail, in particular lasers and spectrometers, and illustrate the trade-offs between cost, size, and performance. Part III will discuss LIBS analysis in some depth, exploring the various ways to go from a LIBS spectrum to a solution. Overall, this column series is intended to provide an overview for those considering implementation of LIBS to solve a particular analytical problem, and an introduction for those interested in learning more about LIBS.

Laser-induced breakdown spectroscopy (LIBS) has been the subject of a number of recent books (1,2) and numerous review papers (3–5). Widely referenced charts in the introduction of the Cremers and Radziemski book (1) and the first chapter of Noll's book (2) illustrate the dramatic increase in the annual number of LIBS papers from near zero through the 1970s to an annual rate of approximately 300–400 today. As an example, Figure 1 shows the annual rate of papers and patents containing "LIBS" or "laser-induced breakdown" in their titles from Google Scholar (6). Interestingly, the past few years may indicate a leveling in the publication rate, and the data can be closely modeled by the following logistic function:

Figure 1: Annual rate of publications and patents containing "LIBS" or "laser-induced breakdown," from Google Scholar. Accessed August 29, 2013.
Although it is too early to determine whether the leveling in the rate will be continued, if this trend holds the annual publication rate would peak around 500 per year, which is the equivalent of about three full monthly journals on an annual basis.

Clearly, there has been much progress in the science and application of LIBS. Today we increasingly see LIBS units in corporate laboratories and even controlling industrial processes. LIBS is deployed to take advantage of a number of positive attributes, which include minimal sample preparation, particularly compared with methods requiring digestion; speed of analysis; sensitivity to light elements, particularly compared with X-ray fluorescence (XRF); and "stand-off" ability in which the LIBS system is removed by distances of anywhere from millimeters to meters from the sample being measured. Because of these advantages there has been an explosion of interest in LIBS (see Figure 1) over a wide range of applications. However, LIBS is a complicated measurement, with special considerations related to the sample matrix and working hardware folded into the ablation process and the analytical laser plasma. Understanding the trade-offs between various component choices in a LIBS system, as well as the basic hardware arrangements, is key for a successful implementation of LIBS.