Time-resolved investigation of exciton-polariton dephasing in CuCl

Abstract

The intrinsic dephasing time of an exciton polariton is investigated in the time domain by use of a time-resolved coherent two-photon excitation and probe technique. This method allows discrimination of the elementary interaction processes of the exciton polariton in semiconductors. The results obtained in CuCI show the role of the different phonons in the exciton-polariton dephasing.PACS numbers: 78.47.+p, 42.65.Re, 71.36,+c Propagation and redistribution of electromagnetic energy near the band gap of polar semiconductors is expected to proceed through the exciton polariton. It is thus of fundamental interest to have information on the underlying dynamics of these quasiparticles and, in particular, on the processes that condition their coherence and lifetime. These aspects up to now have been investigated using indirect techniques lacking selectivity for the discrimination of the exciton-polariton relaxation channels.Thus, in the time domain, the incoherent time-resolved techniques, 1 " 3 such as time-resolved luminescence or induced absorption, only provide global information on the energy content and loss in the crystal, subsequent to a few scattering events averaging out the elementary scattering mechanisms. Furthermore, extraction of this information is complicated because of the inherent polariton propagation and transmission at the crystal surfaces which may substantially alter the bulk polariton features. 4 The exciton-polariton dephasing has also been addressed in the time domain using a time-resolved four-wave-mixing technique. This technique proceeds via strong linear polariton excitation within the absorption layer, close to the crystal surface, and, hence, only gives access to the high-excitation regime where the polariton dephasing is dominated by polariton-polariton interactions. 5 ' 6 In the frequency domain, the dispersion of the polariton damping has been indirectly studied 7 but with a limited selectivity.Here we show that the intrinsic dephasing of an upper-branch exciton polariton can be precisely and directly measured along its dispersion curve in a noncentrosymmetric semiconductor by a time-resolved twophoton coherent nonlinear technique. The demonstration of this new method, which allows the first direct determination of an exciton-polariton dephasing time, is performed on the Z3 exciton polariton in cuprous chloride (CuCI) whose characteristics have been extensively investigated. 8 The technique consists of pico-second coherent two-photon excitation and detection of an exciton-polariton wave packet. Coherent excitation of an exciton polariton of frequency w en and wave vector k en (o) eK ) is realized in the bulk of the crystal by twophoton absorption of two synchronized picosecond pulses with frequencies co\ and a>2 and wave vectors ki and k2 such that G) e " = co\ + 002 and k en = k\+\L2. These conditions can only be satisfied for the upper-branch polariton, restricting the applicability of the technique to this mode. 9 The exciton polariton is an admixture of a material excitation a...

Bipolariton coupling in biexciton optical decay: Degenerate and nondegenerate polariton emissions in CuCl

“…Their estimated values are larger than previously observed 47 because the UBP energy is much higher than before. Detailed analysis about the width will be given separately.…”

Nonlinear Optical Response of the GaAs Exciton Polariton

“…1(b), the leading term in the nonlinear response under these conditions is excitation-induced dephasing, as expected from earlier experiments. Following the approach in [2,27,28] we take the linewidth g to depend on the excitation density: g g 0 1 jN, where g 0 is the dephasing rate at temperature T at zero exciton density, and jN is the additional dephasing due to exciton-exciton interactions at exciton density N. In the polariton picture, we note that exciton-exciton scattering refers to the exciton component of the polariton [6,[29][30][31]. Inserting this g into the above expression for the complex index of refraction and solving for the absorption coefficient (recognizing that the density N is itself determined by the optical intensity and the absorption coefficient) we numerically determine the DT response as a function of laser intensity following the assumptions given in [18] for treatment of the two dispersion branches.…”

Ultranarrow homogeneous broadening of confined excitons in quantum dots: Effect of the surrounding matrix

“…However, quantum dots-they are often referred to as artificial atoms-to our knowledge, have never been studied in this direction. In this paper, the homogeneous linewidth is measured experimentally by using CuCl quantum dots as a sample where the linewidth in the bulk material is well studied, [5][6][7] and its broadening mechanism is discussed by paying attention to the influence of the matrix.…”

“…The value is narrower than the homogeneous width of excitonic polaritons in the bulk crystal by an order of magnitude. 6,7 This extreme narrowing of the homogeneous width of confined excitons in quantum dots is considered to come from the spatial confinement of the exciton wave function and that of the acoustic phonons in quantum dots.…”