Henighan, T,Trigo, M,Chollet, M,Clark, JN,Fahy, S,Glownia, JM,Jiang, MP,Kozina, M,Liu, H,Song, S,Zhu, D,Reis, DA

2016

July

Physical Review B

Control of two-phonon correlations and the mechanism of high-wavevector phonon generation by ultrafast light pulses

Validated

Altmetric: 1 ()

X-RAY-SCATTERING STATES

94

Impulsive optical excitation can generate both coherent and squeezed phonons through first-and second-order Raman-like processes. The expectation value of the phonon displacement < u(q)> oscillates at the phonon mode frequency for the coherent state but remains zero for a pure squeezed state. In contrast, both show oscillations in at twice the phonon mode frequency. Therefore it can be difficult to distinguish them in a second-order measurement of the displacements as is typical in x-ray diffuse scattering. Here we demonstrate a simple method to distinguish the generation mechanism by measurement of the diffuse scattering following double-impulsive excitation. We find in the case of Ge and GaAs that the generation of large wavevector phonons spanning the Brillouin zone is dominated by a second-order process.

10.1103/PhysRevB.94.020302