טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentChene Tradonsky
SubjectTwo-Photon Time Resolved Optical Excitation of
Semiconductor Quantom Dots
DepartmentDepartment of Physics
Supervisor Full Professor Gershoni David
Full Thesis textFull thesis text - English Version


Abstract

In my work I report on experimental studies of optical excitations of semiconductor quantum dots using two resonant, temporally delayed, picosecond laser pulses. The experiments we performed included the preparation of a coherent superposition of a quantum-dot confined exciton eigenstates, and readout of the exciton state after an adjustable time delay. The preparation and readout were done using polarized laser-pulses tuned to the exciton and to the biexciton resonances, respectively. Since the photo-generated exciton state is a superposition of the two non-degenerate exciton eigenstates, their relative phase evolves with time. The time difference between the preparation and the readout pulses is used to follow this evolution. The absorption of the second, readout pulse generates two-excitons (biexciton) state. The absorption of the second pulse depends on the nature of the biexciton resonance and the time difference between the two pulses, which determine the relative spin polarization between the first exciton to the second one. The absorption into the biexciton resonance results eventually in photon emission from one of the quantum dot spectral lines. By monitoring this emission, one can measure the magnitude of the time dependent absorption into the biexciton resonance. We measured, this way, oscillations in the biexciton spectral lines as a function of the delay time between the pulses and thus determined the temporal evolution of the exciton's spin. At the same time we measured in addition, oscillations in the exciton spectral lines as well. These oscillations resulted from the effect of the probe pulse on the exciton part which was not converted into a biexciton. In my work I present and discuss the construction of the experimental setup and preliminary measurements which demonstrated these effects, for the first time.