This article investigates the dichroic properties of aligned γ-Al2O3 nanofibers coated with graphene in the terahertz (THz) regime, revealing significant variance in absorption based on the orientation of the electric field in relation to the nanofibers, arising from the anisotropic nature of the material. Samples are prepared in a hot-wall chemical vapor deposition reactor with varying growth times, resulting in 5 samples with increasing graphene content. Compositional characterization is carried out using scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The samples are characterized electromagnetically using two distinct measurement techniques. First, a novel waveguide measurement setup is deployed, wherein square waveguide cassettes are used to capture the anisotropic behavior of the material and equally measure both polarization states in 67–500 GHz. Then, the samples are characterized using terahertz time-domain spectroscopy up to 4 THz. Both techniques highlight absorption enhancement when the electric field is parallel to the fibers, opening new possibilities for THz devices using polarization filtering.

A dielectric disk resonator employing whispering gallery modes is one of promising sensors for millimeter-wave and sub-terahertz frequency bands due to its small size, high quality factor and ability to operate with one-side access to the object under investigation. However, the whispering-gallery-mode resonator operating on the fundamental mode is not well suited for testing bulky dielectric materials. The reason is that the resonance is crucially suppressed by stray fields arising in the tested material near the disk edge, and thus the high quality factor of the resonator cannot be realized. In this work, it is shown that the higher-order whispering gallery modes are preferable in such applications. Though the unloaded quality factor of the resonator sensor is not as high as in the case of the fundamental mode, it nevertheless suffices to detect small levels of moisture content in the dielectric materials. A dielectric disk resonator with the diameter of 20 mm and thickness 3 mm made of a high-purity alumina was used as a moisture sensor operating in the frequency band near 63 GHz. The performance of the dielectric disk resonator sensors was demonstrated experimentally in the evaluation of moisture content in thick sheets of ABS plastic and gasoline-water mixtures, when the water fraction in the material amounted to 200-1000 ppm.

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A modified method of approximate analytical description of the guided waves of a rectangular dielectric waveguide (RDW) is proposed. The presented formulation is valid, with no modification, for both TE- and TM-like fundamental waveguide modes and thus allows one to evaluate characteristics of propagating waves in a wide range of the waveguide parameters. In this work, this method was used to find optimal dimensions of RDW in the sense of the best confinement of the propagating wave. The spatial resolution in the near-field measurements apparently depends on the degree of confinement. Some experimental examples of the millimeter-wave near-field imaging with subwavelength resolution are presented.

We demonstrate that polymer composites with a low loading of graphene, below 1.2 wt. %, are efficient as electromagnetic absorbers in the THz frequency range. The epoxy-based graphene composites were tested at frequencies from 0.25 THz to 4 THz, revealing total shielding effectiveness of 85 dB (1 mm thickness) with graphene loading of 1.2 wt. % at the frequency f=1.6 THz. The THz radiation is mostly blocked by absorption rather than reflection. The efficiency of the THz radiation shielding by the lightweight, electrically insulating composites, increases with increasing frequency. Our results suggest that even the thin-film or spray coatings of graphene composites with thickness in the few-hundred-micrometer range can be sufficient for blocking THz radiation in many practical applications.

We present the study of the influence of different thin silver nanowire layers on electrical and optical properties in the Terahertz (THz) frequency range. We demonstrate that the absorbance, transmittance and reflectance of the metal nanowire layers in the frequency range of 0.2~THz to 1.2~THz is non-monotonic and depends on the nanowire dimensions and density. We present and validate also a theoretical approach describing well the experimental results and allowing to model the THz response as function the nanowire layer structure. Our results pave the way toward the application of silver nanowires as a perspective material for transparent and conductive coatings, and printable antennas operating in the terahertz range – significant for future wireless communication devices.

Thin layers of silver nanowires are commonly studied for transparent electronics. However, reports of their terahertz (THz) properties are scarce. Here, we present the electrical and optical properties of thin silver nanowire layers with increasing densities at THz frequencies. We demonstrate that the absorbance, transmittance and reflectance of the metal nanowire layers in the frequency range of 0.2 THz to 1.3 THz is non-monotonic and depends on the nanowire dimensions and filling factor. We also present and validate a theoretical approach describing well the experimental results and allowing the fitting of the THz response of the nanowire layers by a Drude–Smith model of conductivity. Our results pave the way toward the application of silver nanowires as a prospective material for transparent and conductive coatings, and printable antennas operating in the terahertz range—significant for future wireless communication devices.

The change of electrical conductivity in chalcopyrite (i.e., Cu(Inx, Ga1−x)Se2 or CIGSe) solar cells induced by nanosecond laser pulses is investigated as a function of the elemental composition and its spatial distribution. The underlying laser induced phase transformation process, which results in a decomposition of the CIGSe semiconductor and a modification of its elemental composition, is utilized to form the monolithic series interconnection between front and back contact in CIGSe based thin film solar cells. The results show a dependence of the composition of the CIGSe layer and the resulting series resistance on the applied laser fluence. Lower series resistance is primarily related to an enhanced fraction of copper, gallium and zinc in the laser transformed zone resulting from selective vaporization of absorber elements. For intermediate laser fluences (~0.36J/cm2) a patterning process is established that allows reliable and high-quality series interconnection. Both, lower and higher laser fluences result in high series resistances due to incomplete phase transformation or damages of the back contact, respectively.

Laser filaments interacting with cirrus like ice crystals not only fragment the particles in smaller ones but also produce a large number of small secondary ice particles by re-condensation of the released water vapor. This new phenomenon drastically modifies the radiative forcing properties of these ice clouds.

We present a study of the degradation of thin-film CIGS material in the vicinity of P2 phase-transformation type of laser scribes. They comprised optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, photoluminescence and Raman spectroscopy. While the optical and electron microscopy measurements have shown a clear change of the morphological properties of CIGS including removal, melting and dislocation of material from the area scribed by the laser, the X-ray analysis revealed an accumulation of O, Zn, Ga, and Cu elements in the melted phase and an evaporation of more volatile In atoms from the region of visually changed CIGS. At the same time Raman and photoluminescence measurements have shown substantial alteration of semiconductor material properties, i.e. of the crystallinity and the bandgap energy even far beyond of this region. More precisely, the amplitudes of the A1 and B2,E Raman peaks were found to increase continuously with increasing distance from the P2 scribes, reaching the distances of approximately three times the 3 diameter of the beam. A similar tendency was also observed for photoluminescence signals, that additionally revealed a systematic shift of the bandgap energy in CIGS as estimated from the maximum of the emission spectrum. Our results indicate that the phase-transformation scribing generates changes in thin-film CIGS material far beyond the heat affected zone. As such they can help to decide on optimal spacing between P1-P3 scribes and thus reduce a "dead area" of thin-film CIGS solar cells.

Using the aerosol and cloud simulation chamber AIDA, we investigated the laser filament induced particle formation in ambient air, humid synthetic air, humid nitrogen, argon–oxygen mixture, and pure argon in order to simulate the particle formation under realistic atmospheric conditions as well as to investigate the influence of typical gasphase atmospheric constituents on the particle formation. Terawatt laser plasma filaments generated new particles in the size range 3 to 130 nm with particle production rates ranging from 1× 107 to 5× 109 cm−3 plasma s −1 for the given experimental conditions. In all cases the particle formation rates increased exponentially with the water content of the gas mixture. Furthermore, the presence of a few ppb of trace gases like SO 2 andα-pinene clearly enhanced the particle yield by number, the latter also by mass. Our findings suggest that new particle formation is efficiently supported by oxidized species like acids generated by the photoionization of both major and minor components of the air, including N2, NH3, SO2 and organics.

Potential impacts of lightning-induced plasma on cloud ice formation and precipitation have been a subject of debate for decades. Here, we report on the interaction of laser-generated plasma channels with water and ice clouds observed in a large cloud simulation chamber. Under the conditions of a typical storm cloud, in which ice and supercooled water coexist, no direct influence of the plasma channels on ice formation or precipitation processes could be detected. Under conditions typical for thin cirrus ice clouds, however, the plasma channels induced a surprisingly strong effect of ice multiplication. Within a few minutes, the laser action led to a strong enhancement of the total ice particle number density in the chamber by up to a factor of 100, even though only a 10−9 fraction of the chamber volume was exposed to the plasma channels. The newly formed ice particles quickly reduced the water vapor pressure to ice saturation, thereby increasing the cloud optical thickness by up to three orders of magnitude. A model relying on the complete vaporization of ice particles in the laser filament and the condensation of the resulting water vapor on plasma ions reproduces our experimental findings. This surprising effect might open new perspectives for remote sensing of water vapor and ice in the upper troposphere.

At relative humidities above 70%, femtosecond laser filaments generate aerosol particles and water droplets in the atmosphere. The water vapour condensation and droplet stabilization are assured by soluble species produced in the laser plasma.

In this work we present results of different strategies of how CIGSe solar cells can be laser scribed focusing on P2 and P3. Therefore a laser source with a wavelength of 532 nm and pulse duration of 13 ns, as well as a laser, with pulse durations of 10 ps for both wavelengths of 532 nm and 1064 nm are used. The ablation mechanisms and the results ablation process (behaviors) due to different wavelengths and pulse durations are studied. Different parameters like process speed, scribe quality and solar cell performance are discussed. Successful laser patterning of all layers is demonstrated on a minimodule reaching 10% efficiency which is slightly better than the needle scribed reference.

The ring-down decay inside a high optical bandwidth cavity was excited by using the white light supercontinuum emitted from a photonic fiber to determine absorption properties of atmospheric air between 610-730 nm by means of the CRD-Spectrography.

A single crystal sapphire fiber pumped with ultrashort laser pulses was used to generate supercontinuum light. Its emission was next compared with this of the PCF based source in terms of the applicability to Multiwavelength-CRD-Spectrography.