Laser mirror evaluation
The low absorption basis of colinear mirage effect
spectroscopy can be used in extreme metrological environments. To
evaluate the quality of exceptional multilayer laser mirrors (R>99,99%)
of Ta2O5SiO2 on SiO2 which will be used as optics for the
Franco-Italian project Virgo, a colinear mirage based experiment
was developed. In this case the absorption is within the coating of the
mirror to be tested, defects giving rise to localized heating even in
interferometer cavity with the highest finesse that can be attained with
present technology. Typical absorption values can be on the order of 0.5
parts per million. This heating then in turn may be probed in the same
manner as described above and the deflection of the probe beam indicates the
local absorption factor. An Nd-Yag laser is used as the pump beam, and a
HeNe laser is used as the probe. This technique has the important advantage
of being non-contact and can thus be used for nondestructive evaluation of
these sometimes unique optical components. In addition, independent layers
may be analyzed for defects by this technique.