The interaction of infra-red laser radiation with solid targets
The pulsed HF chemical laser was discovered in 1966 by Deutsch. Early lasers had very low power outputs; it is only more recently that high power pulsed HF/DF lasers have emerged. This thesis is concerned with the development of a 10J HF laser in 1976 and subsequent interaction experiments. The high power HF/DF laser is a potentially valuable new device in view of its large gain coefficient and output intermediate in wavelength to the Nd:glass and CO2 laser. Information on interactions at this wavelength has been lacking and the solid target interactions presented here help to remedy this deficiency. In addition, certain investigations were carried out using the CO2 laser. These experiments aided direct comparison of the interaction data at the two infra-red wavelengths.In the first chapter basic laser-plasma interaction theory is discussed. A vacuum environment is firstly considered, and emphasis is given to those models relevant to target irradiances available in our laboratories. Anomalous heating is only superficially treated as these studies were carried out below the non-linear thresholds. The theoretical variation of plasma parameters with laser wavelength is presented next, followed by a consideration of the gaseous environment. A brief review of pulsed HF laser design is gIven In chapter 2 followed by an account of our own design studies in the next chapter. Chapters 4 and 5 are devoted to laser-target interaction studies employing vacuum and gaseous environments respectively. The first published comprehensive vacuum interaction study, using the HF laser, is presented in chapter 4. The Z dependence of ion-velocity scaling, ion-number scaling, and reflection variation is recorded, together with the first x-ray temperature measurements at this wavelength. The gaseous environment is considered in the following chapter, where thermal coupling and laser supported detonation wave observations are given. Chapter 6 deals with vacuum interaction studies carried out at the CO2 wavelength. The final chapters deal with the comparison of experimental results with theory, together with a general review of other published interaction investigations.