Delayed formation of coherent LO phonon-plasmon coupled modes in n-type   and p-type GaAs measured using a femtosecond coherent control technique
  Coherent control experiments using a pair of collinear femtosecond laser pulses have been carried out to manipulate longitudinal optical (LO) phonon-plasmon coupled (LOPC) modes in both p- and n-type GaAs. By tuning the interpulse separation, remarkably distinct responses have been observed in the two samples. To understand the results obtained a phenomenological model taking the delayed formation of coherent LOPC modes into account is proposed. The model suggests that the lifetime of coherent LOPC modes plays a key role and the interference of the coherent LO phonons excited successively by two pump pulses strongly affects the manipulation of coherent LOPC modes. 
Jianbo Hu, Oleg V. Misochko, Arihiro Goto, Kazutaka G. Nakamura
cond-mat.mtrl-sci cond-mat.str-el