Abstract-Terahertz time-domain spectroscopy of zone-folded acoustic phonons in 4H and 6H silicon carbide

Abebe T. Tarekegne, Binbin Zhou, Korbinian Kaltenecker, Krzysztof Iwaszczuk, Stewart Clark, and Peter Uhd Jepsen

Fig. 1 Experimental setup. BS – R/T 80/20 beamsplitter; SHG – second harmonic generation crystal; HWP – dual wavelength half-wave plate; Si – silicon plate; BD – beam dump; BPF – 400-nm band pass filter; APD – avalanche photodiode; L – focusing lenses. The setup is driven by 35-fs, 800 nm, 1.5 mJ laser pulses at 1 kHz repetition rate.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-3-3618

We investigate the dielectric properties of the 4H and 6H polytypes of silicon carbide in the 0.1-19 THz range, below the fundamental transverse-optical phonons. Folding of the Brillouin zone due to the specific superlattice structure of the two polytypes leads to activation of acoustic phonon modes. We use a combination of ultrabroadband terahertz time-domain spectroscopy and simulations based on density-functional perturbation theory to observe and characterize these modes, including band splitting due to the dissimilar carbon and silicon sublattices of the structures, and an indirect measurement of the anisotropic sound velocities in the two polytypes.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Amplification of resonant field enhancement by plasmonic lattice coupling in metallic slit arrays

Pernille Klarskov

, Abebe T. Tarekegne

, Krzysztof Iwaszczuk

, X.-C. Zhang

 & Peter Uhd Jepsen

http://www.nature.com/articles/srep37738

Nonlinear spectroscopic investigation in the terahertz (THz) range requires significant field strength of the light fields. It is still a challenge to obtain the required field strengths in free space from table-top laser systems at sufficiently high repetition rates to enable quantitative nonlinear spectroscopy. It is well known that local enhancement of the THz field can be obtained for instance in narrow apertures in metallic films. Here we show by simulation, analytical modelling and experiment that the achievable field enhancement in a two-dimensional array of slits with micrometer dimensions in a metallic film can be increased by at least 60% compared to the enhancement in an isolated slit. The additional enhancement is obtained by optimized plasmonic coupling between the lattice modes and the resonance of the individual slits. Our results indicate a viable route to sensitive schemes for THz spectroscopy with slit arrays manufactured by standard UV photolithography, with local field strengths in the multi-ten-MV/cm range at kHz repetition rates, and tens of kV/cm at oscillator repetition rates.