IR and UV pulsed lasers: application on artworks

Our laboratory has a Polaris III pulsed laser (New Wave Research Inc). This laser allows the generation of infrared pulses (1064 nm) and, including non-linear active filter, it can be also obtained the second (532 nm) , third (355 nm) and fourth harmonic (266 nm), the two latter in the UV range. The active crystals are a KTP for second harmonic generation and two BBO to generate the third and fourth harmonic. Note that the inclusion of a Haas diode at the laser output allows us to know the exact area where the pulses will come into contact with the surface. The Polaris III pulsed laser stands out due to its flexibility, portability and high performance.

Pulsed laser applications: I.R. radiation

IR Radiation has been successfully applied since the mid-seventies (Asmus, 1973) in order to clean stone materials. In general we can say that this type of radiation is strongly absorbed by the dirt layers while largely reflected by the stone material. Thus, the IR pulses are absorbed by the outer layers and produce the photoablation of these layers by thermal effect. When the IR pulses arrives to the stone material to preserve then they are reflected without causing any damage to the original artwork. This is a highly self-limiting process. Controlling parameters such as energy or repetition rate of the pulses a very high control of the thermal photoablation process can be reached.

Another application of IR pulsed radiation is the elimination of repaints obviously made after the original painting. Varying the energy and the number of pulses one can make a controlled photoablation process, layer by layer, that allows to stop this process when the original pigment is exposed.

 

Pulsed laser applications: U.V. radiation

Although the applications of UV pulsed radiation on artworks are more recent that the use of IR pulsed radiation, numerous advantages are opening a wide range of possibilities. The UV pulsed radiation is been mainly used on cleaning of polychrome, stained glass and textiles materials.

The effect which produces the interaction between this type of radiation and matter is different than the effect produced by IR pulsed radiation. In this case, there is a non-thermal photoablation based on photochemical effect. One of its most important applications is the controlled removal of varnish layers, which due to its aging and discoloration should be eliminated. From an analytical point of view, it is useful to "microeliminate" the varnish in order to detect more easily (ie without the fluorescence contribution of this varnish) the pigments of an artwork.