We report observation of oscillations in the dynamics of a microcavity polariton condensate formed under pulsed nonresonant excitation. While oscillations in a condensate have always been attributed to Josephson mechanisms due to a chemical potential unbalance, here we show that under some localization conditions of the condensate, they may arise from relaxation oscillations, a pervasive classical dynamics that repeatedly provokes the sudden decay of a reservoir, shutting off relaxation as the reservoir is replenished. Using nonresonant excitation, it is thus possible to obtain condensate injection pulses with a record frequency of 0.1 THz.

From: Milena De Giorgi, Dario Ballarini, Paolo Cazzato, George Deligeorgis, Simos I. Tsintzos, Zacharias Hatzopoulos, Pavlos G. Savvidis, Giuseppe Gigli,
Fabrice P. Laussy, and Daniele Sanvitto. “Relaxation Oscillations in the Formation of a Polariton Condensate” Phys. Rev. Lett.,
112, 113602 (2014).