Propagation Beats of Quadrupole Polaritons in Cu₂O

Abstract

Abstract Time‐resolved measurements of transmission in resonance with the 1 S quadrupole polariton in Cu 2 O reveal a long‐lasting signal which is modulated by pronounced oscillations with time‐dependent period. These oscillations are interpreted as “propagation beats”, which are caused by superposition of excited states of both polariton branches which propagate coherently through the crystal. At higher excitation intensities the decay becomes faster and the beats disappear. Magneto‐quantum beats are also influenced significantly by propagation effects in transmission measurements.