ABSTRACT
Pulse shaping was in the minds of scientists well before femtosecond lasers were demonstrated. Initial research involved simple pulse compression. During those early days, nonlinear optical processes, such as second harmonic generation, were being studied for fundamental curiosity and also because they could be considered for optical switching. Therefore, scientists were exploring how pulse shaping affected second harmonic generation. One of the interesting findings was that a highly dispersed pulse could be made to generate much higher second harmonic signal by blocking some portions of the spectrum using a pulse shaper. The use of shaped laser pulses for controlling molecules and their chemical reactions was proposed in the 1990s and inspired a number of chemists and physicists. Some spectroscopic methods known as multidimensional spectroscopy, coherent spectroscopy, and four-wave mixing depend on three or more pulses with well-defined phase between them to excite a molecular system, and sometimes a fourth pulse is mixed with the output signal.
