Y. Kagotani

Superfluorescent pulsed emission from biexcitons in an ensemble of semiconductor quantum dots

Picosecond time-resolved photoluminescence from biexcitons in CuCl quantum dots (QDs) embedded in a NaCl matrix has been measured using an optical Kerr gate method. Ultrafast pulsed emission from the biexciton states was observed for the first time, only under resonant two-photon excitation of biexcitons. This implies that complete population inversion between the biexciton and exciton states is necessary in order to trigger the pulsed emission. In addition, the nature of the dependence of the time profiles of the pulsed emission on the excitation intensity reveals that the peak intensity is directly proportional to the square of the number of excited QDs. We conclude that this phenomenon is caused by superfluorescence, that is, the cooperative spontaneous radiative decay of many isolated excited states coupled by a resonant electromagnetic wave. Such a phenomenon has been observed for the first time in an ensemble of semiconductor QDs in this study. The results presented in this paper show that it is possible to control the microscopic coherent dynamics of electronic excited states in a QD ensemble.

Transition from amplified spontaneous emission to superfluorescence from biexcitons in semiconductor quantum dots

A transition from amplified spontaneous emission to superfluorescnece from biexcitons in semiconductor quantum dots was observed with increasing the excitation density under resonant two-photon excitation of the biexcitons.

Superfluorescence of biexcitons in CuCl quantum dots under two-photon resonant excitation

Time-resolved photoluminescence of biexcitons in CuCl quantum dots has been performed by optical Kerr-gate method. Pulse-shaped luminescence like superfluorescence has been observed under resonant two-photon excitation of the biexcitons.

Highly efficient biexcitonic lasing of semiconductor quantum dots under resonant two-photon excitation

Highly efficient biexcitonic lasing of CuCl quantum dots has been observed under resonant two-photon excitation. We discuss the mechanism of the lasing in view point of the dynamics of biexciton confined in the quantum

Excited-state absorption of excitons and biexcitons confined in CuCl quantum dots

This study reports the first observation of the temporal evolution of the infrared transient absorption (IRTA) of CuCl quantum dots by means of tunable ultrafast pump-probe spectroscopy technique based on two optical parametric amplifiers (pulse width: 2 ps, repetition rate: 1 kHz). Results show that the IRTA originates not only from the excitons but also from the biexcitons confined in the quantum dots under high excitation intensities.