Of the two factors here I hope the reader sees that the degree of absorption is the more difficult to assess, and achieve. Unfortunately lowering absorption is often the factor that determines the success of cleaning. Surprisingly, this is a facility not even the largest of laser manufacturers have. Below is a typical heating and cooling curve of a mirror irradiated with a low power CO2 laser, the rate of heating and cooling allows calculation of the absorption of an optic. In the next few months we will be measuring used optics to assess just what level of absorption can be suggested as cut off point, and to identify contaminants that are particularly strongly absorbing.
Early results show that the physical state of the contaminant is a major factor.
For example a finely divided powder has very different absorption compared to a thin film of the same material. To give an idea of results that will be obtained, the following heating and cooling curve is of the same laser and mirror as above. During the measurement however some vinegar was dripped on the mirror. It could be easy to see this happening in real life perhaps by some fluid trapped on the side of the optic, or in the mount. When after 60 seconds a drop of vinegar was placed onto the mirror, the kink in the curve shows the gain in the rate of heating.