Wednesday, July 26, 2017

Abstract-Terahertz Frequency Metrology for Spectroscopic Applications: a Review

We provide an overview on terahertz (THz) frequency metrology, starting from the nowadays available continuous wave THz sources, discussing their main features such as tunability, spectral purity, and frequency referencing to the primary frequency standards. A comparison on the achieved results in high-precision molecular spectroscopy is given and discussed, and finally, a special emphasis poses on the future developments of this upcoming field.

Abstract-Effective Terahertz Wave Parametric Generation Depending on the Pump Pulse Width Using a LiNbO 3 Crystal

 Kouji Nawata ;  Shin'ichiro Hayashi ;  Hideki Ishizuki ;  Kousuke Murate , Kazuki Imayama,  Yuma Takida,   Vincent Yahia,  Takunori Taira,  Kodo Kawase,  Hiroaki Minamide

Injection-seeded terahertz (THz)-wave parametric generation pumped by subnanosecond pulses was demonstrated as an exploration of the effective pump pulse width. In experiments, pump sources with different pump widths of 35–850 ps were used. The relationship between the undesirable effect of stimulated Brillouin scattering (SBS) and the THz-wave output in LiNbO 3 was analyzed. The transient effect on SBS was not actualized around the acoustic phonon lifetime of LiNbO 3 . Pump widths below 420 ps were found to provide THz-wave generation with an energy conversion efficiency of 10−4. With a pump width of 700 ps, which is around five phonon lifetimes, the conversion efficiency was decreased about one order of magnitude from that of the pump width of 420 ps. Additionally, the peak power of the THz-wave output was maintained at about 15 kW with an actual range of 10–20 kW below 200 ps. A continuous change in the THz-wave pulse energy was obtained for six-fold energy scaling from 100 to 600 nJ.

Abstract-Temperature tunability of surface plasmon enhanced Smith-Purcell terahertz radiation for semiconductor-based grating

In this work, the terahertz (THz) Smith-Purcell radiations (SPRs) for the relativistic electron bunch passing over an indium antimonide (InSb)-based substrate with a subwavelength grating under various temperatures of substrate are investigated by FDTD simulations and theoretical analyses. The explored SPR is locked and enhanced at a certain emission wavelength with the emission angle still following the wavelength-angle relation of the traditional SPR. This wavelength agrees with the (vacuum) wavelength of surface plasmons (SPs) at the air-InSb interface excited by the electron bunch. The enhancement of SPR at this wavelength is attributed to the energy from electron concentrated in the excited SPs and then transformed into radiation via the SPR mechanism. When the temperature of InSb increases, the emission wavelength of the enhanced SPR decreases along with the emission angles increasing gradually. This work demonstrates that the emission wavelength and angle of the enhanced SPR from the InSb grating can be manipulated by the temperature of InSb. The temperature tunability of SP-enhanced SPR has potential applications in the fields of optical beam steering and metamaterial light source.

Abstract-Anharmonic Coupling between Intermolecular Motions of Water Revealed by Terahertz Kerr Effect

Formation of local molecular structures in liquid water is believed to have marked effect on the bulk properties of water, however, resolving such structural motives in an experiment is challenging. This challenge might be handled if the relevant low-frequency structural motion of the liquid is directly driven with an intense electromagnetic pulse. Here, we resonantly excite diffusive reorientational motions in water with intense terahertz pulses and measure the resulting transient optical birefringence. The observed response is shown to arise from a particular configuration, namely the restricted trans-lational motion of water molecules whose motions are predominantly orthogonal to the dipole moment of the excited neighboring water molecules. Accordingly, we estimate the strength of the anharmonic coupling between the rotational and the restricted translational degrees of freedom of water.

Tuesday, July 25, 2017

Abstract-Doubly dressed bosons: Exciton-polaritons in a strong terahertz field

B. Piętka, N. Bobrovska, D. Stephan, M. Teich, M. Król, S. Winnerl, A. Pashkin, R. Mirek, K. Lekenta, F. Morier-Genoud, H. Schneider, B. Deveaud, M. Helm, M. Matuszewski, and J. Szczytko

We demonstrate the existence of a novel quasiparticle: an exciton in a semiconductor doubly dressed with two photons of different wavelengths: near infrared cavity photon and terahertz (THz) photon, with the THz coupling strength approaching the ultra-strong coupling regime. This quasiparticle is composed of three different bosons, being a mixture of a matter-light quasiparticle. Our observations are confirmed by a detailed theoretical analysis, treating quantum mechanically all three bosonic fields. The doubly dressed quasiparticles retain the bosonic nature of their constituents, but their internal quantum structure strongly depends on the intensity of the applied terahertz field.