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Laser-assisted particle removal has acquired a growing importance in last few years, finding applications in several fields ranging from microelectronics to conservation and restoration of materials having cultural or historical interest. Recently new ‘indirect’ laser cleaning techniques such as ‘shock’ and ‘verso’ laser cleaning have been developed. Here we present a simple laser cleaning mechanical model in order to associate cleaning efficiency to surface deformation characteristics during cleaning pulse and apply it to examine the behaviour of ‘verso’ laser cleaning which has experimentally shown promising results on cellulosic (paper and cotton) materials.

Polyethylene glycol (PEG) is a polymer with technologically important applications, especially as a biomaterial. Several biomedical applications (such as tissue engineering, spatial patterning of cells, anti-biofouling and biocompatible coatings) require the application of high quality PEG thin films. In order to have a good adhesion to substrate chemically modified polymer molecules have been used, but for some “in vivo” applications it is essential to deposit a film with the same chemical and structural properties of bulk PEG. Pulsed Laser Deposition (PLD) technique in generally able to produce high quality thin films but it is inadequate for polymer/organic molecules. MAPLE (Matrix Assisted Pulsed Laser Evaporation) is a recently developed PLD based thin film deposition technique, particularly well suited for organic/polymer thin film deposition. Up to now MAPLE depositions have been carried out mainly by means of modified PLD systems, using excimer lasers operating in UV: using of less energetic radiations can minimize the photochemical decomposition of the polymer molecules. We have used a deposition system explicitly designed for MAPLE technique connected to a Q-switched Ng:YAG pulsed laser which can be operated at different wavelengths ranging from IR to UV in order to optimise the deposition parameters. The capability of MAPLE technique to deposit PEG has been confirmed and preliminary results show that visible (532nm wavelength) radiation gives better results with respect to UV (355nm) radiation. Despite usually UV wavelengths have been used and even if more systematic tests must be performed, it is important to underline that the choice of laser wavelength plays an important role in the application of MAPLE thin film deposition technique.

The use of pulsed laser radiation in order to remove extraneous materials from a solid substrate, i.e. the Laser Cleaning/Ablation (LC/LA) technique, in recent years has found an increasing interest in several fields ranging from microelectronics to cultural heritage. Within latter field the most common application is the removal of undesired surface layers (e.g. fungi, bacteria, pollution crusts, corrosion layers, surface treatments, etc.) from artifacts of both inorganic (stones, metals, glasses, etc.) and organic (wood, paper, parchment, textiles, etc.) materials. In order to achieve good results the operating parameters (i.e. laser beam wavelength, fluence, pulse repetition rate, etc.) must be set to avoid damaging the substrate to be preserved and to efficiently remove undesired material. Therefore a correct application of the LC/LA technique requires a good knowledge of the effects of laser radiation interaction with both the substance to be removed and the substrate. A lot of experimental work has been carried out and several papers have been written describing several more or less general techniques and some specific applications. The aim of the present work is to summarize and present in an organic manner the LC/LA techniques applied to cultural heritage from both a theoretical and an application point of view. In the first section we briefly describe the main (Laser Ablation, Dry Laser Cleaning, Steam Laser Cleaning) and some other specific (Angular Laser Cleaning, Laser Induced Buckling/Detaching, Laser Shock Cleaning, Verso Laser Cleaning) techniques. In the second section we first summarize the basic physical problems (laser heating, thermo-elastic wave generation, particle - surface adhesion/removal) whose knowledge is required to fully understand the LC/LA. After that we present some models for the description of main LC/LA techniques. Third section is devoted to a review of LC/LA applications in the field of cultural heritage with the aim to collect and summarize the large amount of experimental work carried out in recent years.

Symposium O - Materials aspects of art characterization, conservation and restoration - O/P.20.

http://www.ressign.com/UserBookDetail.aspx?bkid=340&catid=116

Series in Optics and Optoelectronics.

s: D/PI.48 http://www.emrs-strasbourg.com/files/pdf/2002_SPRING/02_Prog_Dv2.pdf

Matrix-Assisted Pulsed Laser Evaporation (MAPLE) is a deposition technique, developed from Pulsed Laser Deposition (PLD) especially well suited for producing organic/polymeric thin films, which can take advantage from using Nd:YAG laser. Depending on the relative values of light absorption coefficients of the solvent and of the molecules to be deposited, laser energy is directly absorbed by the solvent or is transferred to it, providing a softer desorption mechanism with respect to PLD. In PLD ultraviolet laser radiation is commonly used, but in MAPLE, since easily damaged molecules are usually involved, the use of Nd:YAG laser offers the advantage to allow selecting laser wavelength from ultraviolet (266 nm or 355 nm, corresponding to 4.66 eV or 3.49 eV photon energies, resp.) to visible (532 nm, 2.33 eV) to infrared (1064 nm, 1.17 eV). In this paper, the MAPLE technique is described in details, together with a survey of current and possible future applications for both organic and biomaterial deposition taking into account the advantages of using an Nd:YAG laser. Beside other results, we have experimental confirmation that MAPLE applications are not limited to transparent molecules highly soluble in light absorbing solvent, thus allowing deposition of poorly soluble light absorbing molecules suspended in a light transparent liquid.