arXiv subjects

Hideki Gotoh

Publications and source records attributed to Hideki Gotoh.

5 recordsLinked to original sources

arXiv2026

Enhanced Third-Harmonic Generation in Diamond Photonic Crystal Slabs via Doubly Resonant Quasi-Bound States in the Continuum

We propose and numerically demonstrate doubly resonant third-harmonic generation (THG) in a diamond photonic crystal (PhC) slab, in which the fundamental harmonic (FH) and the third harmonic (TH) modes are simultaneously resonant within the same membrane. A hexagonal-lattice slab with triangular air holes is designed so that a K-point band-edge FH mode and a $\Gamma$-point quasi-bound-state-in-the-continuum (quasi-BIC) TH mode satisfy the frequency-tripling condition $3\omega_1\approx\omega_3$. Modifying the hole shape from circular to equilateral triangular breaks the in-plane symmetry that otherwise forces the nonlinear coupling to vanish, thereby converting a TH mode with negligible overlap into one with finite while simultaneously reducing the required slab thickness. Guided by a closed-form expression for THG efficiency derived from coupled-mode theory, we design the unit cell and a PhC heterostructure cavity. Three-dimensional simulations of the designed cavity yield a normalized THG efficiency $\eta=2.7\times10^{-7}~\mathrm{W}^{-2}$ under moderate quality factors, which is projected to reach ~$0.034~\mathrm{W}^{-2}$ at the fabrication-limited quality factor (Q = 200,000). Because the operating wavelength is set by the lattice constant, this design, combined with the ultra-wide transparency window of diamond, can map a single geometry across various fabricable wavelengths, spanning from telecommunication bands to color-center-resonant visible and deep-UV outputs. These results establish a robust route toward efficient, monolithic on-chip frequency conversion in an all-diamond platform for quantum and nonlinear photonics.

physics.optics↗

arXiv2019

Strain-induced exciton decomposition and anisotropic lifetime modulation in a GaAs micromechanical resonator

We demonstrate mechanical modulations of the exciton lifetime by using vibrational strain of a gallium arsenide (GaAs) resonator. The strain-induced modulations have anisotropic dependences on the crystal orientation, which reveals the origin of these modulations to be the piezoelectric effect. Numerical analyses based on the tunneling model clarify that the mechanical strain modulates the internal electric field and spatially separates the electrons and holes, leading to non-radiative exciton decomposition. This carrier separation also generates an optomechanical back-action force from the photon to the resonator. Therefore, these results indicate that the mechanical motion can be self-modulated by exciton decays, which enables one to control the thermal noise of the resonators and provides a photon-exciton-phonon interaction in solid-state systems.

physics.optics↗

arXiv2017

Coherent coupling of dark and bright excitons with vibrational strain

In many physical systems, there are specific electronic states called dark state that are protected from the rapid radiative decay imposed by the system symmetry. Although their long-lived nature indicates their potential for quantum information and spintronic applications, their high stability comes at the expense of optical accessibility. Breaking the symmetry by using magnetic and electric fields has been employed to hybridize dark and bright states thus making them optically active, but high-frequency and on-chip operation remains to be developed. Here we demonstrate the strain-induced coherent coupling of dark and bright exciton states in a GaAs mechanical resonator. The in-plane uniaxial strain breaks the rotational symmetry of the crystal, allowing the dark states to be optically accessible without any external fields. Such dark-bright coupling is tailored by the local strain distribution, which enables the coherent spin operation in the gigahertz regime and opens the way to on-chip excitonic quantum memories and circuits.

cond-mat.mes-hall↗

arXiv2014

Valley-antisymmetric potential in graphene under dynamical deformation

When graphene is deformed in a dynamical manner, a time-dependent potential is induced for the electrons. The potential is antisymmetric with respect to valleys, and some straightforward applications are found for Raman spectroscopy. We show that a valley-antisymmetric potential broadens Raman $D$ band but does not affect $2D$ band, which is already observed by recent experiments. The space derivative of the valley antisymmetric potential gives a force field that accelerates intervalley phonons, while it corresponds to the longitudinal component of the previously discussed pseudoelectric field acting on the electrons. Effects of a pseudoelectric field on the electron is quite difficult to observe due to the valley-antisymmetric coupling constant, on the other hand, such obstacle is absent for intervalley phonons with $A_{1g}$ symmetry that constitute the $D$ and $2D$ bands.

cond-mat.mes-hall↗

arXiv2013

Topological Raman Band in Carbon Nanohorn

Raman spectroscopy has been used in chemistry and physics to investigate the fundamental process involving light and phonons (quantum of lattice vibration). The carbon nanohorn introduces a new subject to Raman spectroscopy, namely topology. We show theoretically that a photo-excited carrier with a non-zero winding number activates a topological $D$ Raman band through the Aharonov-Bohm effect. The topology-induced $D$ Raman band can be distinguished from the ordinary $D$ Raman band for a graphene edge by its peak position.

cond-mat.mes-hall↗