LEONOV Mikhail St.Petersburg National Research University of Information Technologies, Mechanics and Optics

Transient Pump–Probe Absorption Spectroscopy of Semiconductor Nnanotetrapods

Co-authors RUKHLENKO Ivan, NOSKOV Roman, BARANOV Alexander, GUN'KO Yurii, FEDOROV Anatoly

Semiconductor nanostructures of complex geometries are a topical subject of nanophotonics due to their variable optical properties. Nanotetrapods made of four quantum rods linked by a quantum dot are of particular interest from the practical viewpoint owing to their inherently strong optical anisotropy. Another reason of their practical significance is that the nanotetrapod's topology offers quite a few degrees of freedom (associated with the possibility to alter the sizes and shapes of the dots, the length and diameter of the rod, as well as the composition of both kinds of constituents) for flexible manipulation of its optical response. Despite these facts, the physical properties and electronic dynamics of nanotetrapods are poorly understood. A better understanding of these features may be achieved via the analysis of the nanotetrapod’s optical response measured using the time-resolved pump–probe spectroscopy. We develop a unified theory of transient pump–probe absorption spectroscopy of a semiconductor nanotetrapod. The physics underlying this spectroscopic method is treated within the frame of the density matrix formalism, while assuming absorption of the probe pulse to be induced by the pump pulse resonant to a certain interband transition of the nanotetrapod. We elucidate the physical conditions under which the dependence of the absorbed probe energy on the delay time between the pump and probe pulses is described by several exponential functions with exponents proportional to the energy relaxation rates of the nanotetrapod’s electronic states. Furthermore, we show that the transient absorption spectroscopy allows one to reliably determine the energy relaxation rates of the nanotetrapod’s electronic states. The derived analytical expressions for the absorbed energy of the probe’s pulse can be used for studying the dynamics of quantum transitions in semiconductor nanotetrapods.