CO2 laser interaction with germanium
thesisposted on 17.11.2015 by Lionel J. Willis
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
A study of the design and development of transversely excited atmospheric pressure carbon dioxide lasers has been carried out. Three lasers were constructed with output energies ranging from a few millijoules to several joules. Damage in transmitting output mirrors is one of the limiting factors in the development of high energy density carbon dioxide lasers. One form of damage in uncoated germanium components is characterised by regular patterns. A detailed examination of these damage patterns on several mirrors has been carried out using both optical and electron microscopy. A semi-quantitative physical model describing the damage structure formation is proposed, and good agreement with experimental observation is found. The thesis goes on to examine in depth particular aspects of the model with the object of making the analysis fully quantitative. The thesis concludes by preparing the necessary data base for quantitative computer modelling. A full description is prepared of the behaviour of all the relevant physical parameters characterising germanium from room temperature to melting point temperature (300K - 1210K). The technique adopted is to use a theoretical (or sometimes empirical) framew6rk within which to extrapolate from available published data into parameter ranges not hitherto available. For germanium, numerical values have been assigned to all relevant physical parameters (thermal, electrical and optical) over the full temperature range. The way is now open for computer simulation of. the interaction between laser radiation and germanium under a wide variety of circumstances. A significant refinement of the model describing damage structure has already occurred. When the magnitudes and temperature variation of Є' and Є" for germanium were established, the particular model behaviour of germanium suggested a generalised view of the behaviour of other materials. At the time of writing, the model is being adapted to account for the observations of other workers on a wide variety of other materials.