Research at the Laser Cleaning (LC) group is developing novel laser ablation methodologies in order to meet a number of diverse conservation and cleaning challenges.

Highlights of this activity are:

1. The initiation of a Bilateral collaboration between IESL-FORTH and the Conservation department of the PALACE MUSEUM in Beijing, CHINA with the aim to organize a common Laser Technology Joint Laboratory on Cultural Heritage with the name “NIKI” currently under the "One belt, One road initiative".
2. The development of a prototype laser system and methodology for the removal of pollution encrustation from the Parthenon Sculptures, which ensures safe and controlled cleaning without discoloration side-effects. This methodology is being applied since 2002 in a number of sculptures at the Athenian Acropolis Monuments (i.e. the West Frieze, metopes and pedimental sculptures of the Parthenon, the >Frieze of the Athena Nike Temple, and the roof of the Caryatids’ porch in the Erechtheion).
   Since 2011 it has been also included in the regular conservation practice of the Acropolis Museum and along these lines an advanced laser laboratory has been set up on the visitors’ floor where the Caryatids are exhibited. Removal of pollution accumulations from their surface takes place in this laboratory while visitors can follow live the cleaning process is carried out. Further synergies between the Acropolis Museum and IESL-FORTH have been planned in the context of an “open common laboratory” in which modern laser-based diagnostic and imaging techniques will be used for expanding the knowledge and deciding the best conservation practices for the exhibits.

Current research and activities aimed at:

• elucidation of laser induced side-effects in Cultural Heritage applications e.g. yellowing of stonework and pigments’ discoloration,
• optimisation of laser-assisted removal of polymeric over-layers from paintings,
• monitoring and control of the cleaning intervention through optical and laser-based techniques (spectral, optoacoustic, non-linear imaging, laser spectroscopies, holographic interferometry, etc.),
• realization of laser cleaning projects on important CH objects and monuments in the lab or in-situ.

Additionally, the implementation of laser technology to other challenges in Heritage Conservation is investigated.

Recently research efforts have been focused on the restoration of cracks and other pathologies found on the surface of glazed ceramics using laser irradiation; cracked glazed surfaces have been restored on the principle of laser-induced local and controlled melting of the existing glaze material (Restoration of vitreous surfaces using laser technology).

The main direction of the optical imaging activity is to develop new methods for the non-contact, non-invasive, in-situ examination and continuous inspection of CH objects. Applications include:

• mapping of varnish and paint layers,
• stratigraphic analysis and visualization of under-drawings,
• assessment of past conservation treatments,
• real time monitoring of cleaning interventions etc.,

on the basis of reflectance imaging and spectroscopy. The goal of this research is to investigate, quantify and expand the potential applications of spectral imaging on CH objects, while continuous technical developments both in hardware and software target to improve analytical capabilities.

Recently, a novel technique, Photoacoustic Imaging, predominantly developed in the context of biomedical research, has been applied on CH objects. The photoacoustic signal can overcome limitations of light and offer substantially improved detection sensitivity at high spatial resolution. The technique has been proved to be capable of uncovering “hidden” features in multi-layered CH objects such as paintings and determining the thickness of thin layers thus providing micrometric precision stratigraphic information. Finally, the potential of applying the photoacoustic signal for the in situ and real-time monitoring of laser cleaning interventions is currently investigated.

Laser Spectroscopic Analysis is necessary and sometimes vital for the examination of CH objects, since it provides information not only for their constituents but also for deterioration materials, pollutants and other substances that have developed throughout time on the objects and may lead to their aesthetic and structural decline. 

Timely and accurate detection of these deterioration materials can lead to proper conservation and restoration treatments, which can safeguard and actually save the CH objects. Moreover, a series of questions can be answered such as the authenticity of artworks, style of the painter, etc, aiding the art historians to extract important information about the artist and his/her era. Furthermore, spectroscopic techniques can be applied to monitor various processes related to the protection of CH objects, such as the controlled removal of unwanted layers/encrustations, etc. using either laser radiation or any other conventional tools and methods.

PhoHS laboratory of IESL-FORTH has many years of expertise in a series of laser spectroscopic techniques, such as LIBS, LIF, Raman, SERS as well as spectroscopic techniques that use other light sources like LED-IF and Diffuse Reflectance. Along with the laboratory setups, compact/portable laser-based analytical instruments have been developed for in situ and field-deployable applications combining different spectroscopies in hybrid arrangements.

Laser Interferometry for Structural Diagnostics. The main direction of this activity is to investigate deformation, deterioration and fracture mechanisms in order to evaluate the structural condition of materials and systems.

The remote optical sensing of almost invisible defects and alterations, which allows their location, measurement and exact positioning within the structure of the object,  as well as their monitoring through

• environmental and climate changes,
• conservation treatments,
• natural or provoked ageing,
• transportation or handling

are among the objectives of this research group.

This is achieved by the effective transfer of interferometric techniques and know-how to CH applications (artworks and monuments) and the continuous inspiration, design, development and implementation of new experimental processes, methodologies and instruments in order to exploit the full potential of laser metrology.

Since 2012 PhoHS at IESL-FORTH organises a series of training activities inviting conservators, conservation scientists, and other Heritage disciplines for an exciting journey to Crete to become acquainted with the latest developments on non-invasive optical technologies and explore their field applications in Cultural Heritage research and conservation.

The aim of OPTO-CH summer courses is to introduce participants to the applications of advanced laser-based technologies in Heritage Science. Lectures from experts on modern laser diagnostic and analytical techniques and laser cleaning methodologies are combined with practical demonstrations and laboratory hands-on sessions. Field experiments on-site at a selected monument in Crete are organised in order to demonstrate the applicability of the techniques in practice.

Further info at https://opto-ch.iesl.forth.gr/