Laser ablation

In response to Linda Thomas' request for information on laser
ablation:

Laser ablation is the removal of material from a surface as a result
of absorption of laser radiation.  Laser ablation is now routinely
used in a number of conservation studios across Europe as an
extremely selective method of removing a range of unwanted surface
layers (pollution crusts, previous treatments, certain corrosion
layers etc.) from a wide range of materials. In this instance,
provided the technique is carried out appropriately, by a trained
conservator, the underlying surface of the artwork is preserved.  In
Liverpool we have successfully cleaned dinosaur fossils using a
laser.

It is also possible to analyse the surface using the same type of
laser, (most probably a Nd:YAG laser emitting energy at a wavelength
of 1064 nm (near infrared) in pulses of approximately 20 ns
duration). Analytical techniques such as LIBS (Laser Induced
Breakdown Spectroscopy) work by increasing the power delivered to
the surface so that a small amount of material is removed (ablated)
from the surface to be analysed. A plasma is created as the ejected
particles emit light which is characteristic of the elements in the
surface. By analysing the spectrum of the light it is possible to
determine which elements were present in the volume which has just
been sampled. The technique is therefore qualitative. The amount of
material which has to be removed is very small (too small to be
detected by the naked eye) but the actual amount will depend on the
experimental set-up--in reality a volume with the diameter of the
laser spot and a depth of 10s-100s microns will be removed by each
pulse.

I hope you find this useful. Regards,

Martin Cooper
Research Scientist
Laser Technology
National Museums and Galleries on Merseyside
Conservation Centre
Whitechapel
Liverpool L1 6HZ
+44 151 478 4904
Fax: +44 151 478 4990


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                  Conservation DistList Instance 13:52
                  Distributed: Friday, April 21, 2000
                       Message Id: cdl-13-52-001
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