| A study of harmonic generation in Laser produced plasmas is presented. Experiments were performed on Royal Holloway College's carbon-dioxide laser system and on the Rutherford Appleton Laboratory's neodymium-glass laser facility. Various targets were irradiated. The backscattered radiation was spectrally analysed in the vicinity of the incident(w0) and twice incident frequency(2w0). Optical and x-ray diagnostics were also undertaken. Theoretical models for harmonic generation in laser produced plasmas by Cairns, Erokhin, Silin and others are reviewed and compared to the experimental results. It is shown that theories due to Cairns and Silin give reasonable estimates of plasma temperature, from the experimental shift of the second harmonic (2w), though the former requires the plasma density scale-length to be known to a greater accuracy. However, Cairns explains satisfactorily the observed structure of the second harmonic spectra. Other theories account well for the observed dependence of the intensity of the second harmonic to that incident. Finally, an attempt is made to explain features of the 2w spectrum in terms of plasma motion, resonance absorption, density profile modification and ponderomotive forces. |
