Laser Ablation Induced Photoacoustics (LAIP) applied to material characterization

G. M. BILMES; D. J. O. ORZI; F. ALVIRA

Santiago de Compostela

Conferencia; ICO 23; 2014

International Committee for Optics

Laser ablation is a process of removing material from a surface, abruptly expelled out, when it is irradiated with a laser pulse of suitable fluence and short duration. During ablation, also light is emitted (plasma formation), as well as a shock wave that produces a sound appreciated as a ?crack?. Laser Ablation Induced Photoacoustics (LAIP) is a technique that measures the acoustic signal generated during the ablation processes of a surface, performed with a pulsed laser. Acoustic detection was used in several previous works for monitoring the laser ablation process. In this work we make a summary of different applications of LAIP that we performed for material characterization. In these applications, the ablationprocess can be produced using lasers with pulse duration from nanoseconds to femtoseconds, and the measurements are performed by using a simple and cheap electret microphone.We show applications to surface cleanliness determination, which include the development of a method and instruments for on-line real time measurements; for the identification of the ablation threshold fluence of substrates, coatings, thin films, and different types of dirt (i.e. produced by paints, inks and hand?manipulation); for evaluation of the laser fluence that produces damage in a material (i.e. for laser cleaning); for the identification of the focal plane of a focused laser beam (i.e. in laser micromachining) and for the measurement of surface coating thickness.Fig 1 shows an example of the acoustic determination of the Laser ablation thresholds fluence (F0) of soot dirt deposited on an antique rag paper manuscript. F0 have been determined as the abscissa of the linear regression plots (linear region) of the acoustic signal as a function of laser fluence.