Hiromi Ezaki

Excitonic n-string in linear chains

Abstract The bound states of n Frenkel excitons ( n = 2,3,…), which are called excitonic n-strings, are theoretically shown to exist in contrast with a system of Wannier excitons. The electronic structure and nonlinear optical responses of these excitonic n-strings are clarified. The first evidence for the excitonic 2- and 3-strings is provided from comparison of the calculated and observed differential transmission spectrum of an Anthracene-PMDA crystal pumped by femtosecond laser pulses.

Mesoscopic enhancement of third-order-optical susceptibility due to excitons in semiconductor microcrystallites

Abstract Spectrum of third-order optical susceptibility χ(3)(ω;−ω,ω,−ω) due to excitons in semiconductor microcrystallites is calculated for a little wider frequency region in which mesoscopic enhancement of χ(3) is expected. The peaks and singularities of χ(3) appear not only around ω = ω0 but also at ω = ω0 + ωint and ω = ω0 + 2ωint, where ω is frequency of incident radiation field, ω0 one of the lowest exciton and ωint the exciton-exciton interaction frequency.

Stochastic theory of a quasiparticle propagating in a dynamically fluctuating medium

Abstract A stochastic theory describing properties of a quasiparticle propagating in a dynamically fluctuating medium is developed on the basis of the single-site dynamical coherent potential approximation and the time-convolution equation formalism involving the partial cumulant expansion. The optical absorption spectra I(ω), the density of states N(ω) and the diffusion constant D are calculated for the quasiparticle suffering site-energy (diagonal) fluctuations consisting of an arbitrary number of two-state-jump Markoff processes with an asymmetric probability distribution of the stochastic variable. With these fluctuations, we have interpolated a two-state-jump Markoff process and a Gaussian Markoff process, and described the behavior of I(ω), N(ω) and D related to the intermediate processes. Effects of the asymmetric distribution, which may be ascribed to the temperature of the fluctuating medium, on I(ω), N(ω) and D have also been clarified, including a tendency for D to increase with increasing asymmetry.

Photon number squeezing enhanced by two-photon process in excitonic systems

We demonstrate quenching of pump noise by two-photon resonant absorption in a cavity under competition with the one-photon process. This quenching leads to strong squeezing of photon number fluctuation, thus converting a largely super-Poissonian field into a sub-Poissonian one. A strong candidate as an appropriate medium in the microcavity is Anthracene-PMDA or CuCl. These crystals exhibit giant two-photon absorption due to the formation of excitonic 2-strings or biexcitons. We also present results for the spectral content of the cavity field which confirm the complementary nature of the amplitude and phase fluctuations.

Photon Number Squeezing due to Two-Photon Absorption in Internal and External Fields of a Microcavity

The amplitude and phase noise spectra of the internal and external field of a microcavity are calculated using the quantum mechanical Langevin equations. We assume that two-photon absorber works inside a cavity, which brings photon-number squeezing in the internal field as well as the external field. The individual frequency components of the output field have strong squeezing at cavity resonance due to the interference between the input and the cavity field, which is similar to the quadrature squeezing in a parametric oscillator and the photon number squeezing in a saturated laser oscillator. However, the degree of the squeezing is not perfect becuase the material fluctuation remains.

PHOTON STATISTICS IN THE EXTENDED JAYNES-CUMMINGS MODEL

Abstract The photon statistics of the extended Jaynes-Cummings model including cavity damping and pumping in an atomic system, and the exciton effect are investigated by numerically solving the density matrix equation. It is found that stationary photon-number squeezing is possible under incoherent pumping with the photon decay from the microcavity, and that the exciton effect enhances squeezing under both stationary and transient pumping.

Photon Number Squeezing Enhanced by Multi-Photon Absorption in Microcavity

We demonstrate that m -photon resonant absorption ( m =2, 3, …) in a microcavity produce strong photon number squeezing. The dependence of the Fano factor and the mean photon number on the pumping rate, linear damping rate and m -photon decay rate is investigated analytically and numerically. We show the existence of a lower limit equaling 50% of the Fano factor for the radiation field within the cavity in both transient and steady-state cases. This photon-number squeezing is robust against pumping and one-photon dissipation processes.

The effects of quasiperiodic grating on surface-plasmon polariton

A quasiperiodic grating induces new surface plasmon modes and peculiar light emission. The energy spectrum of the plasmon mode is equivalent to that of a quasiperiodic electronic system with long range electron transfer. The angle-resolved emission spectra from tunnel junction show sharp peaks according to the quasiperiodicity.

Optical absorption of molecular chains with conformational disorder

Abstract Conformational disorder in a molecular chain leads to randomness of orientation of transition dipole moments which simultaneously induces randomness of exciton transfer. The optical absorption spectrum is sensitive to both of randomness and represents their correlation effect. The drastic change of the spectral profile near the critical point of helix-coil phase transition is also demonstrated.

Optical Absorption of Molecular Chains with Conformational Disorder

In Frenkel exciton systems, conformational disorder in a molecular chain leads to randomness of orientation of transition dipole moments which simultaneously induces randomness of exciton transfer. The optical absorption spectrum is sensitive to both of randomness and represents their correlation effect. The drastic change of the spectral profile near the critical point of helix-coil phase transition is also demonstrated.