Ultrafast modification of oxide glass surface hardness

Locker, Sean, and S. K. Sundaram. "Ultrafast modification of oxide glass surface hardness." Applied Physics B 125, no. 12 (2019): 225.

Abstract

Application of femtosecond lasers is widely utilized in micromachining transparent materials. We have successfully altered the surface hardness of various commercial silicate glasses using a high-intensity femtosecond pulse laser. The femtosecond laser generates pulse energy of 500 nJ with a central wavelength of 800 nm. Using a peak power of 2.2 W and a repetition rate of 5.1 MHz, we observed an 18–20% increase surface hardness in glasses with low-modifier content and 16.6% decrease in glasses with high-modifier content. All laser exposed glasses show no detectable induced-crystallization or surface ablation. X-ray photoelectron spectroscopy results of our samples confirmed that the laser irradiation had no detectable effect on surface chemistry. X-ray reflectometry data showed the change in hardness was attributed to a thin layer with modified density. Experimental results suggest the strengthening mechanism derives from local structural transformation of interatomic bond distances and angles.

for full paper see https://link.springer.com/article/10.1007/s00340-019-7334-5

"Soda-lime silicate (SLS), Borofoat (BF), and aluminoborosilicate (ABS) refractive indices were characterized using terahertz time domain spectroscopy (THz-TDS, TPS Spectra 3000, Teraview, UK). Terahertz radiation is produced by a mode-locked Ti:Sapphire laser with central wavelength of 800 nm, 80 MHz repetition rate and pulse width of 100 fs. The pulse is separated into a pump and probe beam; pump beam generates THz radiation and probe beam detects THz pulses using GaAs semiconductors. Samples were mounted on a holder with an optical aperture of 4.55 mm. Reference measurements were made with the empty sample holder in air. Broadband THz pulses are converted to a frequency regime through Fourier transformation. Measurements were performed by averaging 3000 scans with a resolution of 1.200 cm−1 and scan frequency of 30 Hz."

Terahertz shielding properties of aero-GaN

Braniste, Tudor, Sergey Zhukov, Mircea Dragoman, Liudmila Alyabyeva, Vladimir Ciobanu, Martino Aldrigo, Daniela Dragoman et al. "Terahertz shielding properties of aero-GaN." Semiconductor Science and Technology 34, no. 12 (2019): 12LT02.

Abstract 

The electrodynamic properties of the first aero-material based on compound semiconductor, namely of Aero-GaN, in the terahertz frequency region are experimentally investigated. Spectra of complex dielectric permittivity, refractive index, surface impedance are measured at frequencies 4–100 cm−1 and in the temperature interval 4–300 K. The shielding properties are found based on experimental data. The aero-material shows excellent shielding effectiveness in the frequency range from 0.1 to 1.3 THz, exceeding 40 dB in a huge frequency bandwidth, which is of high interest for industrial applications. These results place the aero-GaN among the best THz shielding materials known today. 

Keywords: aero-GaN, complex dielectric permittivity, THz shielding

for full paper see https://iopscience.iop.org/article/10.1088/1361-6641/ab4e58/pdf

domain spectrometer TeraViewTPS 3000. The measurements were realized in the range ν = 4 cm -1 – 100 cm-1 and temperature interval T from 4 K to 300 K. The spectra of real and imaginary … 

Impact of additives and processing on microstructure and dielectric properties of willemite ceramics for LTCC terahertz applications

Synkiewicz-Musialska, B., D. Szwagierczak, J. Kulawik, N. Pałka, and P. R. Bajurko. "Impact of additives and processing on microstructure and dielectric properties of willemite ceramics for LTCC terahertz applications." Journal of the European Ceramic Society 40, no. 2 (2020): 362-370.

Abstract

The paper presents the fabrication procedure, microstructure and dielectric properties of the low temperature cofired ceramics (LTCC) based on Zn2SiO4 doped with AlF3, CaB4O7, Li2TiO3 and MgTiO3. The heating microscope studies and differential thermal analysis were used for characterization of the behavior of the green tapes and ceramic samples during heating up to high temperatures. The microstructure and composition were analyzed by scanning electron microscopy, X-ray energy dispersive spectroscopy and XRD method. The dielectric properties were investigated in three frequency regions: 100 Hz–2 MHz, 90–140 GHz and 0.15–3 THz. The developed materials are promising candidates for the LTCC submillimeter wave applications due to a low sintering temperature of 900–980 °C, good compatibility with silver pastes and good dielectric properties – a low dielectric permittivity of 6–6.8, a relatively low dissipation factor of 0.005–0.008 at 1 THz, and a weak temperature dependence of dielectric permittivity.

for full paper see https://www.sciencedirect.com/science/article/abs/pii/S0955221919306764

… The applied setup (TeraView), which comprises an advanced optoelectronic system with a femtosecond laser, photoconductive antennas and a delay line, enabled the generation and accurate detection of a 0.5 ps …

NDE characterization and inspection techniques of trailing edges in wind turbine blades using terahertz waves

Im, Kwang-Hee, Sun-Kyu Kim, Jong-An Jung, Young-Tae Cho, Yong-Deuck Wood, and Chien-Ping Chiou. "NDE characterization and inspection techniques of trailing edges in wind turbine blades using terahertz waves." Journal of Mechanical Science and Technology 33, no. 10 (2019): 4745-4753.

Abstract

Terahertz waves (T-ray) were extensively studied for the nondestructive evaluation of the characterization of trailing edges composed with composite materials. The NDE system consisted of both continuous wave (CW) and time domain spectroscopy (TDS). The FRP composites were utilized for both trailing edges of wind energy (non-conducting polymeric composites) and carbon fiber composites with conducting properties. The signals of T-ray in the TDS mode almost resembles that of ultrasound waves; however, a terahertz pulse could not penetrate a material with conductivity, unlike ultrasound. The refractive index (n) was utilized as one of the material properties, so a method was suggested to obtain the “n” in the materials. The data of refractive index (n) were utilized due to obtained data for the trailing edges. The trailing edges were scanned for charactering and inspecting. C-scan and B-scan images were obtained and the optimal NDE techniques were suggested for complicated geometry samples by terahertz radiation. In particular, the penetrating time-of-flight (TOF) of T-ray corresponded with the calculated TOF for the trailing edges with greater thickness (about 70 mm).

for full paper see https://link.springer.com/article/10.1007/s12206-019-0915-8

… is an NDE equipment. This equipment is intended to obtain the material properties and property values of the sandwich test specimen. This experiment used a terahertz system manu- factured by TeraView (UK). This equipment …

Broad-Band Spectroscopy of Nanoconfined Water Molecules

Belyanchikov, M. A., M. Savinov, Z. V. Bedran, P. Bednyakov, P. Proschek, J. Prokleska, V. I. Torgashev et al. "Broad-Band Spectroscopy of Nanoconfined Water Molecules." In International Conference on Nanotechnologies and Biomedical Engineering, pp. 7-11. Springer, Cham, 2019.

Abstract

We have performed broad-band spectroscopic investigations of vibrational and relaxational excitations of water molecules confined to nanocages within artificial beryl and mineral cordierite crystals. Signatures of quantum critical phenomena within the H2O molecular network are registered in beryl. In cordierite, a density functional analysis is applied to reconstruct the potential energy landscape experienced by H2O molecules, revealing a pronounced anisotropy with a potential well of about 10 meV for the molecular dipole moment aligned along the b-axis. This anisotropy leads to a strongly temperature dependent and anisotropic relaxational response of the dipoles at radiofrequencies with the activation energies corresponding to the barriers of the rotational potential. At T ≈ 3 K, we identify signatures of a transition into a glassy state composed by clusters of H2O dipoles. Rich set of anisotropic and temperature-dependent excitations are observed in the terahertz frequency range which we associate with rotational/translational vibrations.

for full paper see https://link.springer.com/chapter/10.1007/978-3-030-31866-6_2

… For terahertz measurements, a commercial time-domain TeraView 3000 spectrometer
was used........................