Coherent control and dark pulses in second harmonic generation

We present the results of our study of the second harmonic generation (SHG) in a nonlinear crystal using phase modulated femtosecond laser pulses. We show experimentally that the SHG process is an analogue of two photon absorption (TPA), yet it provides a better way to study coherent control because it enables one easier control of some important parameters. We demonstrate that for a thick nonlinear crystal pure phase manipulation can result in nontrivial pulses maximizing the second harmonic conversion efficiency and in dark pulses which are not converted at all. With a π step phase modulation applied to the pulse we have measured conversion efficiency for a set of crystals with different thicknesses to explore the effect of a finite spectral width of the TPA transition.