Interaction of laser beam with solids

Thesis

The present investigation is an extension of earlier work in this laboratory on the interaction of laser beams with metallic surfaces. It was conducted with a view to understanding the different processes involved in a laser surface interaction. Initial experiments (Chapter Five) were performed with low laser intensity, so that the Richardson effect was not prominent. The results were interpreted in terms of a double-photon photoeffect. The idea of such a double-photon photoeffect was also supported by the nonlinear optical absorption and double-photon photo- conductivity in a CdS crystal (Chapter Eight).

The effect of linear absorption (single-photon absorption) process was investigated for metal surfaces and the results were interpreted in terms of a temperature rise of the target surface. When high intensity laser pulses were incident onto metal surfaces, the generation of a cloud of ionized particles was observed. The cloud was found to move away from the target in a plasma state. The various properties of this plasma and the mechanism of the generation of current signals by the directed motion of the different species of the charges in an applied electric field has been investigated in Chapter Six. In the same chapter, experiments on the reverse photoelectric effect (photo- electric emission from the surrounding metal parts by the high energy photons generated from the metal plasma) showed a positive contribution to the shape of the current signals by such electrons.

Finally, the controversial chenomena of 'rear-side electron emission' was further investigated in Chapter Seven. It was concluded that the observed current recorded at a collector placed at the rear side of the target when the front surface was irradiated with a focussed Q-switched laser beam could be explained in terms of a capacitance effect. The electrostatic coupling between a collector and any neighbouring metal part, because of the stray capacitance between them, will be of considerable importance when a rapid voltage change of the collector is concerned.

The results of all the experiments were summed up and a general conclusion of the work was presented in Chapter Nine.

Authors: Ahmad, R

• DOI: 10.5287/ora-1rn5jeeqr
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford