Using frequency-domain manipulation of stretched femtosecond laser pulses to create fast rise and fall times on picosecond pulses

We show how femtosecond laser pulses that are stretched to many picoseconds duration can be manipulated to create useful picosecond pulses. The picosecond pulse shape is manipulated by masking in the frequency domain. Rise and fall times of 1.5 ps are possible using direct masking. Sub-picosecond fall times are theoretically possible if the phase is also controlled. It is shown how these novel picosecond pulse shapes are used to control the spatial alignment of gas-phase molecules.