Photonic Cavity-Mediated Tunable Ultrafast Absorption Dynamics in BaTiO₃-Based One-Dimensional Photonic Crystal

Abstract

The ultrafast absorption dynamics of photonic modes and enhanced features of electronic states have been demonstrated in a barium titanate (BaTiO 3 , BTO)-embedded onedimensional photonic crystal. The photonic structure has been realized as an optical microcavity, where a BTO central layer is sandwiched between two SiO 2 /TiO 2 -distributed Bragg reflectors. Angle-dependent transient absorption behavior reveals the excitedstate absorption dynamics of cavity-tuned BTO defect energies. Furthermore, the dynamic evolution of photonic minibands of both sides of the photonic cavity mode demonstrates the enormous cavity field confinement effect. The temporal evolution of nonlinear absorption dynamics is specific to cavity angle tuning and is evidenced by seven orders of two-photon absorption enhancement in BTO mid-bandgap energies. Overall, the results highlight the impact of strong optical field confinement within the BTO central layer. The simulations of spatial and angledependent localized optical field and energy deposition within the photonic structure further support the experimental findings. The enhanced features of ultrafast absorption dynamics and strong optical nonlinearities of the BTO-based active photonic structure offer a better understanding of electron−photon interaction, which paves the way for many novel nonlinear, hybrid optoelectronic, and photonic device applications.

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“…The detailed experimental setup can be found elsewhere. 108,109 In this experiment, the pump energy has been kept constant at 1 μJ for all of the samples of porphyrins. Both the pump and probe beams have been temporally and spatially overlapped on the sample surface to record the absorption dynamics at different intervals of ultrashort (ps) time scales.…”

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“…The normalized transmittance for OA and CA Z -scan traces can be well expressed by the following equations: 61,64,65 where Δ ϕ denotes the nonlinear phase shift, which provides information about the nonlinear refractive index ( n 2 ) as at an excitation wavelength λ , x is ( z / z r ) and is the Rayleigh length, and the beam waist is denoted as ω 0 . L eff is the effective sample length, expressed as .…”

“…To monitor the pump-induced modifications and excited-state absorption dynamics, a broadband femtosecond supercontinuum (350–1000 nm) weak probe beam is temporally and spatially overlapped with the pump beam at the sample surface. The transient difference absorption Δ A ( τ , λ ) is defined as follows: 65 where ( I Probe λ / I ref λ ) exc is the ratio of probe and reference signal after pump excitation and ( I Probe λ / I ref λ ) corresponds to the unexcited sample. The temporal evolution is monitored at each delay time between pump and probe beam.…”

“…To monitor the pump-induced modifications and excited-state absorption dynamics, a broadband femtosecond supercontinuum (350-1000 nm) weak probe beam is temporally and spatially overlapped with the pump beam at the sample surface. The transient difference absorption ΔA(τ, λ) is defined as follows: 65 ΔAðτ; λÞ ¼ À log The temporal evolution is monitored at each delay time between pump and probe beam. The detailed experimental setups can be found elsewhere.…”

“…The detailed experimental setups can be found elsewhere. 65 The TAS measurement for all the samples was performed at 4 µJ pump energy under ambient conditions. Fig.…”