Abstract
In this paper, we investigate the femtosecond-optical-pulse-induced strain dynamics in relatively thin (100 nm) and thick (10 000 nm) silicon plates based on finite-element simulations. In the thin sample, almost spatially homogeneous excitation by the optical pulse predominantly generates a standing wave of the lowest-order acoustic resonance mode along the out-of-plane direction. At the same time, laterally propagating plate waves are emitted at the sample edge through the open edge deformation. Fourier transformation analysis reveals that the plate waves in the thin sample are mainly composed of two symmetric Lamb waves, reflecting the spatially uniform photoexcitation. In the thick sample, on the other hand, only the near surface region is photo-excited and thus a strain pulse that propagates along the out-of-plane direction is generated, accompanying the laterally propagating pulse-like strain dynamics through the edge deformation. These lateral strain pulses consist of multiple Lamb waves, including asymmetric and higher-order symmetric modes. Our simulations quantitatively demonstrate the out-of-plane and in-plane photoinduced strain dynamics in realistic silicon plates, ranging from the plate wave form to pulse trains, depending on material parameters such as sample thickness, optical penetration depth, and sound velocity.
Highlights
Ultrafast light-induced strain dynamics in solid materials have attracted significant attention since the development of femtosecond laser sources
In this paper, we investigate the femtosecond-optical-pulse-induced strain dynamics in relatively thin (100 nm) and thick (10 000 nm) silicon plates based on finite-element simulations
We investigated the ultrafast carrier-strain dynamics of silicon thin (d 1⁄4 100 nm) and thick (d 1⁄4 10 000 nm) plates using the finiteelement method
Summary
Ultrafast light-induced strain dynamics in solid materials have attracted significant attention since the development of femtosecond laser sources. In thick samples that satisfy d ) a, on the other hand, carriers are only excited near the surface region [Fig. 1(c)] It induces the strain dynamics significantly different from those in thin samples. Due to the localized stress, a strain pulse is generated at the surface and begins to propagate along the out-of-plane direction [Fig. 1(d)]. For the thin sample (d 1⁄4 100 nm), it was determined that the sample was approximately homogeneously excited and that the out-of-plane standing waves were dominated by the lowestorder acoustic resonance mode because the optical penetration depth a (’1000 nm) was much greater than d. The laterally propagating plate waves generated at the edge of the sample via the out-of-plane standing waves were mainly composed of two symmetric Lamb waves at the lowest-order acoustic resonance frequency. The laterally propagating strains in the thick sample exhibited various branches and frequencies, including both asymmetric and symmetric Lamb waves
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call