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Analyzing Metals
with Handheld
Laser-Induced Breakdown Spectroscopy (LIBS)
M
etal producers, inspectors, and recyclers are
under constant pressure to increase both the vol-
ume and quality of tested materials. Because
testing in non-laboratory settings has become common—
close to the production line, in situ, or at chemical facilities
or handling yards—testing is regularly performed with
portable instrumentation.
Technicians and operators who must use this equipment
are seeking faster and more comprehensive analysis from
tools that minimize damage to tested goods. One such
method—laser-induced breakdown spectroscopy (LIBS)—
is an established technology that provides nearly instanta-
neous and virtually nondestructive analysis with minimal or
no sample preparation and without an ionizing radiation
source. LIBS is now taking its first leap into the field of metal
analysis via handheld equipment.
Laser-induced breakdown spectroscopy
Accurate metal analysis in the field has been tradition-
ally performed using handheld x-ray fluorescence (XRF)
and mobile optical emission spectroscopy (OES) instru-
ments. LIBS has long been available in a benchtop form,
which until recently was limited to lab-
oratories for metal analysis.
Today, LIBS can be found as a
standalone handheld analyzer and
it is becoming a viable and eco-
nomical option for high-volume
metal alloy analysis.
LIBS is an atomic emission
spectroscopy technique capable
of analyzing any element in any
physical state. It is limited only by
the instrument’s laser power, sen-
sitivity, and spectrometer wave-
length range. The technology
combines the speed and ease of XRF—without a radiation
source—and the expanded elemental range of OES while
minimizing sample preparation and damage. Drawing on
the strengths of established portable XRF and OES tech-
nologies, the handheld LIBS instrument quickly and accu-
rately analyzes metals using a laser-based spectrometer,
which is virtually nondestructive.
How it works
LIBS is an atomic emission technique whereby the in-
strument’s laser—commonly a neodymium-doped yttrium
aluminum garnet (ND:YAG) laser—fires a series of
nanosecond-long pulses through a small focusing lens onto
the sample. The focused beam ablates a tiny amount of the
sample’s surface and subsequently ionizes the removed ma-
terial to create a plasma. The plasma expands as it is bom-
barded by the laser and excites electrons in the plasma’s
constituent atoms. As electrons relax and atoms return to
a stable state, they emit photons that are characteristic of
the element and electron transitions. The spectrometer
uses a scanning monochromator (e.g., Czerny-Turner), a
prism, or grating to disperse light. A photomultiplier or
charge-coupled device (CCD) detector
array collects emitted radiation over a de-
fined wavelength range, typically between
170-1100 nm.
Making LIBS portable
Laboratory LIBS instruments have
been available since the early 1960s.
ADVANCED MATERIALS & PROCESSES •
APRIL 2014
24
TECHNICAL SPOTLIGHT
Fig. 1 —
mPulse is a handheld portable scrap metal analyzer
that enables one-second analysis results used in the field to
sort scrap metal.
Fig. 2 —
The portable mPulse LIBS analyzer allows faster
sorting and metal grading.