Abstract-High-resolution THz gain measurements in optically pumped ammonia

Martin Mičica, Sophie Eliet, Mathias Vanwolleghem, Roman Motiyenko, Anastasia Pienkina, Laurent Margulès, Kamil Postava, Jaromír Pištora, and Jean-François Lampin

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-16-21242

This study is aimed at the evaluation of THz gain properties in an optically pumped NH3 gas. NH3 molecules undergo rotational-vibrational excitation by mid-infrared (MIR) optical pumping provided by a MIR quantum cascade laser (QCL) which enables precise tuning to the NH3infrared transition around 10.3 μm. Pure inversion transitions, (J = 3, K = 3) at 1.073 THz and (J = 4, K = 4) at 1.083 THz were selected. The THz measurements were performed using a THz frequency multiplier chain. The results show line profiles with and without optical pumping at different NH3 pressures, and with different MIR tuning. The highest gain at room temperature under the best conditions obtained during single pass on the (3,3) line was 10.1 dB×m−1 at 26 μbar with a pumping power of 40 mW. The (4,4) line showed lower gain of 6.4 dB×m−1 at 34 μbar with a pumping power of 62 mW. To our knowledge these THz gains are the highest measured in a continuous-wave MIR pumped gas.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Experimental Gouy phase shift compensation in Terahertz time-domain spectroscopy

Pierre Koleják, Kamil Postava,  Martin Mičica , Petr Kužel, Filip Kadlec, Jaromír Pištora,

https://www.sciencedirect.com/science/article/pii/S1569441017303048

Terahertz time-domain spectroscopy experiments are usually carried out with focused beams. In this case the Gouy phase shift modifies the retrieved dielectric spectra of thick samples [Opt. Express 18, 15338 (2010)]. We show that a significant influence of the Gouy shift occurs also in commercial THz spectrometers where the focusing conditions may be a priori unknown. A method of experimental compensation of the Gouy shift influence is described and demonstrated.

Abstract- Free-Space Characterization of Magneto-Optical Hexaferrites in the Submillimeter-Wave Range

 Tomáš Horák,  Guillaume Ducournau,  Martin Mičica,   Kamil Postava, Jamal Ben Youssef,  Jean-François Lampin,  Mathias Vanwolleghem

http://ieeexplore.ieee.org/document/8014472/

We present the quasi-optical free-space characterization of magneto-optical hexagonal ferrites—crystalline BaFe12O19 and both ceramic and crystalline SrFe12O19—in the range between 325 and 500 GHz using a vector network analyzer. This method provides us the full complex spectrum of the 2 × 2 S-matrix element of the sample. Transmission through free air and reflection of a perfect mirror have been used as references. We determined the complex optical indices, permittivities, and permeabilities of all samples by fitting a calculated model to the measured data. The perturbing effects of multiple reflections between setup components were filtered out by inverse fast Fourier transform of the measured signal and subsequent time gating in the obtained time-domain signal. The results presented in this paper show that this processing method reliably deals with all perturbing effects in free-space measurement and therefore can be applied for characterization of various types of magneto-optical samples with different sizes and significant surface roughness as well. Furthermore, it provides convincing indications regarding the usefulness of the different types of hexaferrites for nonreciprocal devices (such as isolators) for submillimeter applications.