Abstract-Shaping the spectrum of terahertz photoconductive antenna by frequency-dependent impedance modulation

Denis Vladimirovich Lavrukhin, Alexander Eduardovich Yachmenev, Alexander Pavlov, Rustam Anvarovich Khabibullin, Yurii Goncharov, Igor Spektor, Gennady Komandin, Stanislav O Yurchenko, Nikita V Chernomyrdin, Kirill I Zaytsev

http://iopscience.iop.org/article/10.1088/1361-6641/aaff31/pdf

In this paper, we report on an approach for shaping the spectra of THz pulse generation in photoconductive antennas (PCAs) by frequency-dependent impedance modulation. We introduce a theoretical model describing the THz pulse generation in PCAs, and accounting for impedances of the photoconductor and of the antenna. Additionally we account a detector response for com-
 parative analysis with experimental data. In order to showcase an impact of frequency-dependent impedance modulation on the spectra of THz pulse generation, we applied this model to simulating broadband PCAs with log-spiral topology. Finally, we fabricated two dierent log-spiral PCAs and characterized them experimentally using the THz pulsed spectroscopy. The observed results demon-
 strate agreement between the theoretical model and experiment, justifying a potential of shaping the spectra of THz pulse generation in PCA by modulation of frequency-dependent impedances. This approach makes possible optimizing the PCA performance and thus accommodating the needs of THz pulsed spectroscopy and imaging in fundamental and applied branches of THz science and
 technologies.

Abstract-The optical characteristics of the nonlinear optical single crystal CdSiP2 in the terahertz and infrared ranges

Gennady Komandin, Sergey Chuchupal, Yurii Goncharov, Oleg Porodinkov, Igor Spektor, Kewin Zawilski, Peter Schunemann

http://iopscience.iop.org/article/10.1088/2053-1591/aaeec6

Experimental study of mechanisms forming absorption of Terahertz (THz) radiation in the advanced nonlinear-optical crystal CdSiP2 has been performed by backward-wave oscillator, time-domain and infrared spectroscopy. The classical oscillator model and Lyddane–Sachs–Teller relation were used to determine the dispersion parameters of phonon modes. The spectra of complex permittivity and absorption coefficient have been determined based on calculated dispersion parameters. The application of the Fresnel formulas for the absorption analysis in the THz region together with the results of the fit of the phonon modes made it possible to obtain quantitative data on the magnitude of the additional radiation losses in the THz range. Additional loss mechanisms give rise to increase the total absorption by at least an order of magnitude compared to the phonon contribution. The increase of the polariton absorption in the low-frequency dispersion branch is typical for crystals with ionic and ion-covalent bond and is composed of extrinsic losses and difference multi-particle processes. The level of total losses in the THz region in the CdSiP2 single crystal is comparable to the values in other nonlinear-optical crystals, which makes this material promising for nonlinear-optical conversion of the infrared radiation into the THz region.