Enhancement of coherent charge oscillations in coupled quantum wells by femtosecond pulse shaping

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Abstract
The effect of femtosecond pulse shaping on the amplitude of optically excited coherent charge oscillations in degenerate coupled quantum wells is analyzed. In the absence of dephasing, the final oscillating polarization after the end of the shaped pulse depends only on the optical power spectrum; pulse shaping cannot enhance the final coherent polarization. However, appropriately shaped ultrashort pulses can lead to strong peaks in the oscillating dipole during the laser pulse. I present a method for designing waveforms capable of producing strong peaks in the coherent polarization and illustrate this approach by giving several examples. The computed results indicate the possibility of enhancing the peak oscillating dipole (and hence the resulting terahertz emission) by at least a factor of 4.