Coherent phonon oscillations excited by second-order Raman scattering in CdZnTe multiple quantum wells and cubic ZnTe

Abstract

We report observation of strong phonon-pair oscillations in CdZnTe multiple quantum wells and cubic ZnTe͑001͒. Using femtosecond laser pulses with photon energies far below the bandgap, the coherent phononpair oscillations are generated via the impulsive stimulated Raman scattering of the second order. Polarizationand phase-sensitive measurements allow us to resolve both relative Raman polarizabilities of various symmetry modes and their initial phases, simultaneously.

Indication of Te segregation in laser-irradiated ZnTe observed by in situ coherent-phonon spectroscopy

“…[15][16][17] The 3.6-THz resonance was also observed in coherent-phonon spectroscopy, 18-20 but its origin is still a matter of debate. [16][17][18][19][20] Note that ZnTe has a relatively large cross section for twophoton absorption (TPA), 21,22 which limits its efficiency for THz wave generation. 23 This drawback, however, might turn into a benefit in terms of material modification using femtosecond laser pulses.…”

“…19,25,26 However, the other, h1 10i-polarized TO mode is excited, yet by setting the probe polarization to an angle of 45 with respect to the pump polarization, the probe will experience a fully isotropic response, resulting in a vanishing ellipticity signal. 18,19,26 Figure 1(a) displays as-recorded ultrafast pump-induced changes in the sample anisotropy after pump exposure times of 0, 7, and 30 min. Signals S(s) are seen to consist of a slowly varying background, a (negative) peak around zero delay and an oscillatory part [ Fig.…”

Measuring phonon dephasing with ultrafast pulses using Raman spectral interference

“…The reflectivity ͑or transmittivity͒ of a subsequent probe pulse displays a time dependence that follows the vibrational frequency and population of excited phonons. This method was used to study the phonon decay in various solids, 8 their symmetry modes, 9 and their interaction with charge carriers 10 and with other phonons. 11 In these experiments, impulsive stimulated Raman scattering has been established as the coherent phonon generation mechanism.…”

Resonantly excited coherent optical phonons in wide-gap semiconductor ZnTe

“…Regardless of E c , the coherent oscillation frequency was obtained 6.3070.04 THz, which corresponds to the LO phonon mode of ZnTe. Higher order modes like overtone or deference modes were not observed [9]. The pulse energy was too weak to couple to the electronic charge oscillations with the LO phonon motion even with the resonant excitation.…”