Selctive detection of phonon-plasmon coupled oscillation in indium phosphide using a coherent control technique

Summary form only given. Coherent oscillations of phonons are excited by irradiation of a femtosecond laser pulse which duration is much shorter than those vibrational periods. Transient reflectivity shows modulation due to these coherent oscillations and gives dynamic information of phonons, known as time-domain spectroscopy (TDS). Furthermore, using a pair of femtoseconds laser pulses for excitation, amplitude of the coherent oscillations can be controlled by changing separation time between the pulses (coherent control technique) [1,2]. In polar semiconductors, coherent oscillations of phonon-plasmon coupled mode are also excited when the plasma frequency and the phonon frequency are similar. Dynamics of longitudinal optical (LO) phonons and LO-phonon-plasmon coupled (LOPC) oscillations have been studied using TDS [3]. However, the intensity of LOPC is too small and hidden under the LO-phonon oscillations. Then dynamical information of LOPC has not been obtained. In this paper, we detected the LOPC coherent oscillations in InP by suppressing the strong LO-phonon oscillations using the coherent control technique.We measured transient reflectivity using a femtosecond time-resolved pump and probe technique [1] at room temperatures. The laser used was a mode-locked Ti:sapphire laser with a wavelength centered at 800 nm, providing approximately 40 fs. The sample used was a single crystal of Zn-doped n-type InP (100) with a carrier density of 1.1x1018 cm-3. The pump beam was split into two beams by using a Michelson-type interferometer to produce a double-pulse pump beam with a separation time of Δt, which was varied by moving the mirror on an arm in the interferometer.