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Featured Application: Surface plasmon refractometry of conducting surfaces applied in terahertz plasmonic integrated circuits and communication lines. With the intensive development of data transmitting and processing devices in the terahertz (THz) frequency range, an important part of which are integrated plasmonic components and communication lines, it becomes necessary to measure correctly the optical constants of their conductive surfaces. In this paper, we describe a reliable method for determining the effective permittivity εm of a metal surface from the measured characteristics (refractive and absorption indices) of THz surface plasmon polaritons (SPPs). The novelty of the method is the conduction of measurements on a metal surface with a dielectric layer of subwavelength thickness, suppressing the radiative losses of SPPs, which are not taken into account by the SPP dispersion equation. The method is tested on a number of flat "gold sputtering–zinc sulfide layer–air" structures with the use of the THz radiation (λ0 = 141 μm) from the Novosibirsk free electron laser (NovoFEL). The SPP characteristics are determined from interferograms measured with a plasmon Michelson interferometer. It is found that the method allows a significant increase in the accuracy of the εm in comparison with measurements on the same metal surface without a dielectric layer. [ABSTRACT FROM AUTHOR]

The characteristics of high-power vortex Bessel beams in the terahertz range ( λ = 141 μm) obtained with the use of diffractive axicons (DAs) illuminated by a Gaussian beam of the Novosibirsk free-electron laser were studied. Two of the three possible types of DA recently described in our previous paper, namely, binary spiral silicon axicons (BAs), forming beams with a topological charge l equal to 0–4 and 9, and a diamond "holographic" axicon (HA), forming a beam with l = 9 , were used in the experiments. These axicons formed beams whose cross sections in the region of inner Bessel rings were close to those of ideal Bessel beams, but their intensities varied in azimuth with a frequency of l and 2 l for the BAs and HA, respectively. However, in the case of the BAs, the beams had a pronounced helical structure at the periphery, whereas for the HA, the beam was axisymmetric. By focusing these beams with a lens, we studied the structure of the so-called "perfect" beams (PBs). While an ideal Bessel beam exhibits a PB as a thin ring, in the case of the BAs, we observed a broadened ring structure consisting of 2 l short spirals, and for the HA, we observed a narrow ring with 2 l maxima in azimuth. A comparison of the numerical calculations and experiments showed that the observed azimuthal intensity variations can be attributed to inaccuracies in the preparation of the axicon relief and/or discrepancies between the calculated and actual wavelengths, within a few percent. The results of this work enable the establishment of quality requirements for axicon manufacture and the appropriate selection of the axicon type in accordance with the requirements for the beam. [ABSTRACT FROM AUTHOR]

The optical scheme and technical characteristics of terahertz planar Michelson interferometer based on surface plasmons are presented. A technique for determination of the complex index of refraction of surface plasmons () from interferograms is described. The paper presents the results of test measurements on flat surfaces with gold sputtering coated by ZnS layers 0 to 3 μm thick with application of the high-power coherent radiation from the Novosibirsk free electron laser at the wavelength λ0 = 141 μm. From the measurement results, the value of the effective permittivity of the sputtered gold surface was found, which turned out to be an order of magnitude lower than that of crystalline gold. Analysis of the energy losses in the plasmonic interferometer made it possible to estimate its dynamic range (106–108 in terms of radiation power) required for measurements on samples with different . Ways to increase the signal-to-noise ratio via optimization of the elements of the optical scheme and detector have also been proposed. [ABSTRACT FROM AUTHOR]

In this paper, an analytical theory for the diffraction of a Bessel beam of arbitrary order Jl(κr) on a 2D amplitude grating is presented. The diffraction pattern behind the grating turned out to be more complicated in comparison with the classical Talbot effect observed under illumination by a plane wave. In particular, the patterns in the main and fractional Talbot planes under certain conditions that are found in the article, are lattices of ring microbeams, the diameters of which depend on the period of the grating, the diameter of the illuminating beam, the number of the Talbot plane, and the topological charge l. For the rings near the optical axis, the latter reproduces l of the illuminating beam. The diffraction patterns observed in experiments on the Novosibirsk free electron laser behind gratings with periods of 1 to 6 mm, illuminated by zero- to second-order Bessel beams at a radiation wavelength λ = 141 µm, are in good agreement with both theoretical predictions and numerical calculations. We emphasize that an analytical theory based on the scalar theory of diffraction perfectly describes resulting diffraction patterns with hole diameters down to 0.25 mm, which are less than 2λ, when, formally speaking, the scalar theory becomes incorrect. Since the Laguerre–Gaussian beams can be represented as a superposition of Bessel beams, results of this paper can be applied to analysis of the Talbot effect with the Laguerre–Gaussian beams. A regular lattice of ring-like vortex microbeams, which can be formed in the Talbot planes, can be applied, for example, to creation of a lattice of optical traps, transmission of orbital angular momentum to elements of micromechanical devices, and to launching surface plasmon polaritons on an array of metal wires by 'the end-fire coupling technique'. [ABSTRACT FROM AUTHOR]

The development of efficient and reliable sensors operating at room temperature is essential to advance the application of terahertz (THz) science and technology. Pyroelectric THz detectors are among the best candidates, taking into account their variety, outstanding performance, ease of fabrication, and robustness. In this work, we compare the performance of six different detectors, based on either LaTiO3 crystal or different polymeric films, using monochromatic radiation of the Novosibirsk Free Electron Laser facility (NovoFEL) in the frequency range of 0.9–2.0 THz. The main characteristics, including noise equivalent power and frequency response, were determined for all of them. Possible reasons for the differences in the obtained characteristics are discussed on the basis of the main physicochemical characteristics and optical properties of the sensitive area. At least three detectors showed sufficient sensitivity to monitor the shape and duration of the THz macropulses utilizing only a small fraction of the THz radiation from the primary beam. This capability is crucial for accurate characterization of THz radiation during the main experiment at various specialized endstations at synchrotrons and free electron lasers. As an example of such characterization, the typical stability of the average NovoFEL radiation power at the beamline of the electron paramagnetic resonance endstation was investigated. [ABSTRACT FROM AUTHOR]