LIBS : L aser I nduced B reakdown S pectroscopy LIBS is an analytical method by which one can determine (qualitatively and quantitatively) the elemental composition of solid, liquid or gas samples. LIBS  focused laser pulses  vaporize, atomize and excite the sample  plasma emission  collect, disperse and analyze light  atomic spectral lines determine the elemental composition

How does LIBS compare with other analytical methods?  Different types of samples  Little sample preparation  No (chemical) waste  Micro-LIBS  Portability  Rapid  NDT What is LIBS used for? Environmental monitoring to measure soil contamination Detect toxic metals Study the chemical compositions in liquids Study the chemical compositions in polymers In forensics and military applications Biomedical studies of bones and teeth Art restoration (or conservation), by analyzing pigments and/or precious and ancient metals

LIBS for coin compositional determination Experimental set-up Nd-YAG 3 rd harmonic prism dichroic mirror personal computer monochromator mirror collecting lens Rotating sample holder sample PDA Movie

LIBS for coin compositional determination 10% iron in KBr (calibration pellet) Fe I Fe I Fe I Fe I Br II Fe I Fe I Fe I Fe I Fe I Br I Br II Fe I Fe I Fe I Br I Data: Å

LIBS spectra for (solid) one side of a 25 Fils Bahrain coin and (dashed) the other side of the same coin. Notice how the spectra are almost identical!!

LIBS spectra for (solid) a 10-Hallalah Saudi coin, (dashed) 20 cent Euro coin and (dotted) a game token, in the Å region. There are similarities between the three spectra; for example, all have Fe peaks 4228 Å. The game token has more iron and nickel than the other (real) currencies. The game token does not contain copper 4180, 4275 & 4377 Å). The real currencies do contain copper!! The Euro coin does not have the 4201 & 4401Å Ni peaks.

Photographs of the four coins used in the experiments (a) before and (b) after 30 seconds of laser irradiation. The coins show no apparent destruction due to LIBS. (a)(b)

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LIBS for coin compositional determination Experimental Results 1.PDA Calibration 2.Apply LIBS to coins a.Check repeatability b.Look for coin signatures c.Reliability (same results in different regions!!) d.NDT

grating mirror 1024 diodes PDA ~ optical multi-channel analyzer With a Photo-Diode Array (PDA), one can simultaneously detect the intensity of many “different” wavelengths.

Is LIBS absolutely NDT? LIBS as NDT?

Good general references on LIBS Also, check Applied Optics vol 42 (30), Oct (theme issue)

LIBS for coin compositional determination Conclusions  LIBS spectra are repeatable.  LIBS gives consistent/ reliable results in different regions.  Coins have iron.  Game token has no copper.  20 cent Euro coin is nickel-free.  We can distinguish between “different” currencies using LIBS.  The spectra of the Saudi 10-Hallalah and the Bahrain 25 Fils are very similar.  At the macroscopic level, LIBS procedure can be NDT.

Sample matrix Morphology Power [energy per pulse & pulse width] dependence Atmosphere type and pressure Shot to shot energy fluctuation Depends on photon energy [esp. plasma absorption] Complications in Using LIBS