Study of Coherent and Incoherent Plasma Emissions: Role of Plasma Wave Excitation and Breaking

Here we experimentally map the dynamics of electron plasma waves in laser solid interaction. We do time resolved measurements of second harmonic and hard X-ray generation from interaction of intense ($10^{16} W cm^{-2}$, 100 fs, 800nm) laser with a pre-plasma generated on a solid surface. The parameter space explored in this time resolved study includes variation of scale length, laser polarization and laser intensity in conjunction. These measurements done together brings novel features of strongly driven electron plasma wave behavior, which have not been explored experimentally so far. We model the results in terms of Resonance Absorption and Wave-Breaking mechanisms. The Harmonic and X-ray emission show contrasting behaviour, which indicates pitfalls in trying to increase harmonic efficiencies by brute force. However by simple adjustments, we observe that hard X-rays can be enhanced or controlled upto two orders of magnitude and second harmonic upto one order of magnitude under optimum conditions. These results should help us understand the governing mechanisms for short wavelength generation and fast particle generation to develop more efficient sources for application purposes.