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Ultrafast Phenomena and Nanophotonics

Thermal free ultrafast luminescence due to nonlocal light-matter interaction (Conference Presentation)

Masayoshi Ichimiya, Takuya Matsuda, Hajime Ishihara, Masaaki Ashida

Published Mar 10, 2020• 0 citations
Publisher

Abstract

We demonstrate ultrafast superradiance showing 10-fs decay due to the nonlocal interaction between light waves and exciton waves in CuCl mesoscopic thin films. This time constant is comparable with the thermal dephasing even at room temperature. Actually, we observed photoluminescence signal from one confined mode of translational motion of the exciton surviving at room temperature. In addition, temperature dependence of the photoluminescence spectra with multiple peaks was reproduced well by theoretical calculation. This finding opens a new avenue of “thermal free photonics”, where the exciton coherence is utilized at higher temperature.

DOI
10.1117/12.2544760

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We demonstrate ultrafast superradiance showing 10-fs decay due to the nonlocal interaction between light waves and exciton waves in CuCl mesoscopic thin films. This time constant is comparable with the thermal dephasing even at room temperature. Actually, we observed photoluminescence signal from one confined mode of translational motion of the exciton surviving at room temperature. In addition, temperature dependence of the photoluminescence spectra with multiple peaks was reproduced well by theoretical calculation. This finding opens a new avenue of “thermal free photonics”, where the exciton coherence is utilized at higher temperature.
We report the observation of a remarkably strong coupling between light and a multinode-type exciton. The observed radiative decay time reaches the order of 100 fs, which is much faster than the dephasing process of nonradiative scattering. In this high-speed superradiance, the light wave and the excitonic wave in a high-quality thin film form a harmonized wave-wave coupling over a range of multiple wavelengths. This mechanism contradicts the conventional physical description of light-matter interaction based on the long-wavelength approximation.
The coherent volume of single quantum states of matter is typically smaller than that of photons by several orders of magnitude, and hence, interactions between photons and single quantum states are normally very weak. This limits the speed of radiative decay of matter states in free space. Recent efforts to speed-up radiative processes have been focused on creating a small mode volume of photons using cavity systems, or on realizing spontaneous synchronization among quantum emitters to create a dipole at the macroscopic scale, which accelerates photon emission up to a couple of hundred femtoseconds. Here, we demonstrate the 10-fs class of photoluminescence (PL) of a single quantum state in solid thin films without the use of a photo-cavity system or the spontaneous synchronization effect. Significantly, this speed can beat thermal dephasing of relevant excited states at room temperature, which is typically a couple of tens of femtoseconds. The process occurs due to the giant interaction volume between light waves and the multipole excitonic waves. This result indicates the possibility to realize photoemission processes that complete before the thermal dephasing process activates, which opens up the hidden potential of ubiquitous solids as thermal-free or extremely low-energy-loss photonic materials.
Summary form only given. Excitons confined in nanocrystals or quantum dots attract much attention because they have a very long phase relaxation time that opens the way to the artificial coherent control of the excitons. CuCl quantum dot is a typical material in which the translational motion of the exciton is confined. In this paper, we report on the high resolution measurement of the resonant luminescence of CuCl quantum dots embedded in glass and NaCl matrices under weak excitation condition, and show that the zero-phonon line of the resonant luminescence has a narrow homogeneous linewidth reflecting the long phase relaxation time.