Laser Induced Breakdown Spectroscopy (LIBS) is a robust chemical
analysis technique that has found application in a range of
areas where rapid, remote and semi-quantitative analysis of
chemical composition is needed. The technique in its essential
form is quite simple. Light is used to ionize a small portion
of the analyte and the spectral emission (characteristic of
the electronic energy levels) from the species in the resulting
plasma is collected to determine the chemical constituents.
Most often the light comes from a laser since high photon fluxes
can be obtained readily with this type of light source. By focusing
the light from the laser to a small spot, highly localized chemical
analysis can be performed.
As a result of the simplicity of the experimental technique,
LIBS has found application in a variety of fields including
the following:
1. Environmental (air quality monitoring; soil, sediment,
and mineral analysis; waste stream analysis (plastics, sludge,
etc.))
2. Life Sciences and Cultural/Conservation (biological materials;
pharmaceutical analysis; tissue analysis; pigment analysis;
archeometallurgy; ceramic and glass analysis)
3. Materials Analysis and Industrial (precious alloys; steels
and other alloys; semiconductors; nuclear industry; superconductors).
LIBS has been demonstrated and is currently being used in
a variety of sensor/diagnostic roles in these areas. With
advances in instrumentation related to laser source size and
spectrometer unit performance and portability, there are emerging
roles for LIBS that could not be explored previously. LIBS
is being recognized as a versatile analytical method for environmental
chemical analysis. LIBS offers real-time monitoring capabilities
with high analytical sensitivity and selectivity. James Spicer’s
laboratory in the Materials Science Department at Johns Hopkins
University is pursuing the application of LIBS toward the
detection of explosives and explosive-related compounds (ERCs)
in the condensed phase with the ultimate goal of detecting
land mines in the environment.
Example of a Single Shot LIBS Spectra of an Explosive
Comp B- Grain Slice
(63% RDX, 36% TNT, 1% Wax)
Other advances in instrumentation such as the ready availability
of femtosecond laser sources allow for more refined approaches
to LIBS that could lead to better performance of LIBS sensors.
At Johns Hopkins University, a Spectra Physics Tsunami femtosecond
laser coupled to a regenerative amplifier serves as the light
source for plasma generation.
The benefits of using femtosecond pulses include:
• Ultrafast excitation can improve the material interaction
• Ultrafast absorption of energy reduces post ejection
interactions
• Heat affected zone is confined to smaller region -
less vaporization of substrate
• Potential for highly selective desorption-ionization
Spectra
Physics Spitfire: regenerative amplifier JHU©2003
