Picosecond laser ablation system with process control by optical coherence tomography

Piotr Targowski; Roman Ostrowski; Jan Marczak; Marcin Sylwestrzak; Ewa A. Kwiatkowska

doi:10.1117/12.827286

10 July 2009 Picosecond laser ablation system with process control by optical coherence tomography

Piotr Targowski, Roman Ostrowski, Jan Marczak, Marcin Sylwestrzak, Ewa A. Kwiatkowska

Proceedings Volume 7391, O3A: Optics for Arts, Architecture, and Archaeology II; 73910G (2009) https://doi.org/10.1117/12.827286
Event: SPIE Europe Optical Metrology, 2009, Munich, Germany

Abstract

In this contribution we describe an apparatus for precise laser ablation of delicate layers, like varnish on pictures. This specific case is very demanding. First of all any changes in colour of remaining varnish layer as well as underneath paint layers are unacceptable. This effect may be induced photochemically or thermically. In the first case strong absorption of the radiation used will eliminate its influence on underlying strata. The thermal effect is limited to so called heat affected zone (HAZ). In addition to colour change, a mechanical damage caused by overheating of the structure adjacent to ablated region should be considered also. All kinds of treads must be carefully eliminated in order to make laser ablation of varnish commonly accepted alternative to chemical and/or mechanical treatments [1]. Since the varnish ablation process is obviously irreversible its effective monitoring is very important to make it safe and trusted. As we showed previously [2-6] optical coherence tomography (OCT) originated from medicine diagnostic method for examination and imaging of cross-sections of weakly absorbing objects can be used for this task. OCT utilises infrared light for non-invasive structure examination and has been under consideration for the examining of objects of art since 2004 [7-10]. In this case the in-depth (axial) resolution is obtained by means of interference of light of high spatial (to ensure sensitivity) and very low temporal coherence (to ensure high axial resolution). In practice, IR sources of bandwidths from 25 to 150 nm are utilised. Resolutions obtained range from 15 down to 2 μm in the media of refracting index equal 1.5. In this contribution we expand application of OCT to space resolved determination of ablation rates, separately for every point of examined area. Such data help in better understanding of the ablation process, fine tuning the laser and finally permit increase of the safety of the ablation process.

Citation Download Citation

Piotr Targowski, Roman Ostrowski, Jan Marczak, Marcin Sylwestrzak, and Ewa A. Kwiatkowska "Picosecond laser ablation system with process control by optical coherence tomography", Proc. SPIE 7391, O3A: Optics for Arts, Architecture, and Archaeology II, 73910G (10 July 2009); https://doi.org/10.1117/12.827286

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