Filtering of Elastic Waves by Opal-Based Hypersonic Crystal

Abstract

We report experiments in which high quality silica opal films are used as three-dimensional hypersonic crystals in the 10 GHz range. Controlled sintering of these structures leads to well-defined elastic bonding between the submicrometer-sized silica spheres, due to which a band structure for elastic waves is formed. The sonic crystal properties are studied by injection of a broadband elastic wave packet with a femtosecond laser. Depending on the elastic bonding strength, the band structure separates long-living surface acoustic waves with frequencies in the complete band gap from bulk waves with band frequencies that propagate into the crystal leading to a fast decay.

Damping of coherent acoustic vibrations by nanosized pores in colloidal hypersonic crystals

“…When the frequencies of the phonon modes lie within the phononic band gap, the phonon propagation through the bulk sample is prohibited, resulting in the localization of such phonons in the near surface layers. 6,[29][30][31][32] In fact, as suggested by previous theoretical work by Akimov et al, the first band gap along the crossplane (C-L) direction of a close-packed SiO 2 crystal with a diameter of 302 nm is predicted to be centered at 8.7 GHz, which is very close to our experimentally observed frequency (8.5 GHz). 6,29 Compared to the bulk mode, the surface mode has much longer lifetime and is still observable even at long time delay.…”

Probing Dynamics in Colloidal Crystals with Pump-Probe Experiments at LCLS: Methodology and Analysis

“…The Fourier spectrum of the simulated data (see Figure 9a), as well as its 3σ level are shown in Figure 9b. It can be seen that the contribution of the vibrational mode in the Fourier spectrum is higher than the criterion stipulated by Equation (6). Therefore, the algorithm detected the presence of the 4.97 GHz frequency signal.…”

High-frequency acousto-optic effects in Bragg reflectors

“…With careful design, such structures may confine both optical and acoustic waves simultaneously, leading to a significant enhancement of the interactions between photons and phonons [15,25]. In practice, however, this situation is hard to achieve as producing structures which possess both complete photonic and phononic stop bands is a technically complex task [26]. Theoretical works in this area are mostly limited to calculations of dispersion relations for photonicphononic crystals [27].…”