Remote measurement of oxide thickness and steel composition using laser techniques

This paper is based upon experience gained with an instrument which has been developed at Marchwood Engineering Laboratories for measuring the thickness of magnetite layers on mild steel surfaces in hostile (hot and highly radioactive) environments. It is thought that the understanding of the interaction of powerful pulses of laser light with magnetite which has been gained in this work could have applications to a much wider field.A model of the production of the laser hole has been developed which is simple to understand, easy to apply, and sufficiently accurate for most practical purposes. The model differs substantially from the generally accepted form and has led to the development of an alternative explanation for the occurence of molten droplets which are spattered in all directions when the laser is fired. A technique for measuring the sulphur content of steels using mass spectrometry is also described.