The development of lasers and of femtosecond laser pulses provides many examples, how science and technology mutually reinforce each other. A brief historical overview is presented of this synergy between curiosity-driven and goal-oriented research in this field of optics, which supports the current activity in pulsed laser-materials interactions.
Breakdown of air by a focused pulse from a Q-switched ruby laser was first observed in 1962. This marked the beginning of studies on laser-generated plasmas and of laser-induced breakdown in solids, liquids and gases. A historical overview will be presented of major developments in the basic physical processes involved, including multiphoton ionization and avalanche breakdown. Recent experiments on plasma creation and damage induced by femtosecond pluses have thrown new light on this subject, which continues to be of great technical interest.
Transient energy transfer or two-beam coupling is demonstrated in CS2 and other transparent Kerr liquids using frequency chirped, 17 picosecond (HW1/eM) 532 nm pulses with several polarization combinations. As the temporal delay between pulses in a standard pump-probe geometry is varied within the coherence time, the first pulse always loses energy while the second pulse gains this energy. Scattering from phase gratings can lead to coherent energy coupling only if the nonlinearity has a finite relaxation time. This two-beam coupling in Kerr media such as CS2 is associated with stimulated Rayleigh-wing scattering (SRWS). The frequency difference needed for beam coupling can be achieved with chirped pulses or with short pulses in nonlinear materials if irradiance dependent phase shifts are being developed during the laser pulse due to self and cross-phase modulation. Here we consider the interaction between linearly chirped pulses obtained from our modelocked, Q-switched Nd:YAG laser. This leads to an energy transfer linearly proportional to irradiance, so that the signal can be observed at irradiances lower than those needed for induced phased modulation. The measurements are performed on CS2 but the results are valid for any Kerr liquid that has a nonlinear index of refraction with a relaxation time on the order of the laser pulse width. We demonstrate that the interaction follows the polarization dependence of SRWS. The only parameters needed for the theoretical fittings are the nonlinear index n2, its relaxation time and the linear chirp of the laser pulse. The first two are well known for CS2 and the laser chirp is independently measured using first and second order autocorrelations.