Controlling material transformation and phonon oscillation with trains of femtosecond laser pulses

Laser transformation of materials is a highly complex process involving multiple steps and time scales. We explored the laser-solid interaction on sub-ps and ps time scales using single and multiple pulses in the high intensity regime. The mechanism of ablation and plasma photon emission for various materials was studied using two 50 fs pulses with variable delay up to 110 ps. A study of the plasma polarization gave rise to a novel spectroscopic technique called polarization resolved laser induced breakdown spectroscopy (PRLIBS).;In a second set of experiments, coherent control of phonon oscillation in GaAs was performed using trains of three pulses with separations 165 fs-1.5 ps. The fluorescence signal generated from the sample showed oscillations with the characteristic phonon period of the crystal. The effect of various laser parameters on the phonon oscillation was studied to reveal the mechanism. A study of the surface morphology was also performed to observe the effect of electron phonon coupling on nanoparticle generation.