A New Method for Tungsten Oxide Nanopowder Deposition on Carbon-Fiber-Reinforced Polymer Composites for X-ray Attenuation.

A new method for the synthesis and deposition of tungsten oxide nanopowders directly on the surface of a carbon-fiber-reinforced polymer composite (CFRP) is presented. The CFRP was chosen because this material has very good thermal and mechanical properties and chemical resistance. Also, CFRPs have low melting points and are transparent under ionized radiation. The synthesis is based on the direct interaction between high-power-density microwaves and metallic wires to generate a high-temperature plasma in an oxygen-containing atmosphere, which afterward condenses as metallic oxide nanoparticles on the CFRP. During microwave discharge, the value of the electronic temperature of the plasma, estimated from Boltzmann plots, reached up to 4 eV, and tungsten oxide crystals with a size between 5 nm and 100 nm were obtained. Transmission electron microscopy (TEM) analysis of the tungsten oxide nanoparticles showed they were single crystals without any extended defects. Scanning electron microscopy (SEM) analysis showed that the surface of the CFRP sample does not degrade during microwave plasma deposition. The X-ray attenuation of CFRP samples covered with tungsten oxide nanopowder layers of 2 µm and 21 µm thickness was measured. The X-ray attenuation analysis indicated that the thin film with 2 µm thickness attenuated 10% of the photon flux with 20 to 29 KeV of energy, while the sample with 21 µm thickness attenuated 60% of the photon flux.

Impact of 3MeV Energy Proton Particles on Mid-IR QCLs.

This paper reports the results obtained for a distributed-feedback quantum cascade laser (DFB-QCL) exposed to different fluences of proton particles: 1014, 1015 and 1016 p/cm2. Dedicated laboratory setups were developed to assess the irradiation-induced changes in this device. Multiple parameters defining the QCL performances were investigated prior to and following each irradiation step: (i) voltage-driving current; (ii) emitted optical power-driving current; (iii) central emitting wavelength-driving current; (iv) emitted spectrum-driving current; (v) transversal mode structure-driving current, maintaining the system operating temperature at 20 °C. The QCL system presented, before irradiation, two emission peaks: a central emission peak and a side peak. After proton irradiation, the QCL presented a spectral shift, and the ratio between the two peaks also changed. Even though, after irradiation, the tunning spectral range was reduced, at the end of the tests, the system was still functional.

GHz-THz Dielectric Properties of Flexible Matrix-Embedded BTO Nanoparticles.

BaTiO3 (BTO) nanoparticles produced by wet chemistry methods were embedded in several types of flexible materials in order to fabricate flexible electronic devices. Starting from the produced nanoparticle dielectric properties, flexible material dielectric properties were tested for high electromagnetic frequencies (30 GHz-2 THz) using time domain spectroscopy. Dielectric performances of the different materials obtained with variable nanoparticle concentrations up to 40 wt.%, embedded in, gelatin, epoxy, and styrene-butadiene were compared at several working temperatures between 0 °C and 120 °C. Beside the general trend of ε' decrease with temperature and loses increase with the operating frequency, we were able to identify few matrix dependent optimal nanoparticle concentrations. The best composite performances were achieved by the BTO-SBS matrix, with filler concentration of 2 wt.%, where the losses have been of 1.5%, followed by BTO-gelatin matrix, with filler concentration of 40 wt.%, with higher losses percent of almost 10% for THz frequencies.

Response of Various Yb3+-Doped Oxide Glasses to Different Radiation Treatments.

The radiation effects of electrons and protons on the spectroscopic and optical properties of oxide glasses doped with Yb3+ in various glass systems were investigated to understand the impact of the glass composition on the glass photo-response. Changes in the optical and emission properties were seen after the radiation treatment, and the magnitude of the changes depended on the irradiation source and dose. For all the investigated materials, the absorption coefficients in the 200-550 nm range increase post-irradiation, revealing the formation of defects in the glasses during the irradiation. While the spectroscopic properties of the tellurite glass remain unchanged, a small reduction in the Yb3+ emission intensity was seen after irradiating the phosphate, borosilicate, and germanate glasses, indicating that a reduction of Yb3+ to Yb2+ might occur in these glasses during the radiation treatment. The changes in the optical and spectroscopic properties after proton irradiation are small as they are localized at the surface of the glasses due to the shallow penetration depth of the proton in the glass. Even though the doses are small, the electron irradiation produces larger changes in the optical and spectroscopic properties since the electrons penetrate the entire volume of the glasses. All the changes in the optical and spectroscopic properties of the glasses were successfully reversed after a short heat treatment revealing the reversible nature of the photo-response of the investigated glasses.

Selective Mid-IR Metamaterial-Based Gas Sensor System: Proof of Concept and Performances Tests.

In this paper, we propose a highly selective and efficient gas detection system based on a narrow-band IR metasurface emitter integrated with a resistive heater. In order to develop the sensor for the detection of specific gases, both the microheater and metasurface structures have been optimized in terms of geometry and materials. Devices with different metamaterial structures and geometries for the heater have been tested. Our prototype showed that the modification of the spectral response of metasurface-based structures is easily achieved by adapting the geometrical parameters of the plasmonic micro-/nanostructures in the metasurface. The advantage of this system is the on-chip integration of a thermal source with broad IR radiation with the metasurface structure, obtaining a compact selective radiation source. From the experimental data, narrow emission peaks (FWHM as low as 0.15 µm), corresponding to the CO2, CH4, and CO absorption bands, with a radiant power of a few mW were obtained. It has been shown that, by changing the bias voltage, a shift of a few tens of nm around the central emission wavelength can be obtained, allowing fine optimization for gas detection applications.

Optical and THz investigations of mid-IR materials exposed to alpha particle irradiation.

The paper is the first comprehensive study on alpha particle irradiation effects on four mid-IR materials: CaF2, BaF2, Al2O3 (sapphire) and ZnSe. The measurements of the optical spectral transmittance, spectral diffuse reflectance, radioluminescent emission, terahertz (THz) spectral response, transmittance, absorbance, refractive index, real and imaginary parts of the dielectric constant and THz imaging are used as complementary investigations to evaluate these effects. The simulations were run to estimate: (i) the penetration depth, (ii) the scattering of alpha particle beam, (iii) the amount of material affected by this interaction, and (iv) the number of vacancies produced by the radiation exposure for each type of material. The simulation results are compared to the off-line measurement outcomes. The delay and spectral composition change of the reflected THz signal highlight the modification induced in the tested materials by the irradiation process.

Low-Loss Coupling of Quantum Cascade Lasers into Hollow-Core Waveguides with Single-Mode Output in the 3.7-7.6 µm Spectral Range.

We demonstrated low-loss and single-mode laser beam delivery through hollow-core waveguides (HCWs) operating in the 3.7-7.6 µm spectral range. The employed HCWs have a circular cross section with a bore diameter of 200 µm and metallic/dielectric internal coatings deposited inside a glass capillary tube. The internal coatings have been produced to enhance the spectral response of the HCWs in the range 3.5-12 µm. We demonstrated Gaussian-like outputs throughout the 4.5-7.6 µm spectral range. A quasi single-mode output beam with only small beam distortions was achieved when the wavelength was reduced to 3.7 µm. With a 15-cm-long HCW and optimized coupling conditions, we measured coupling efficiencies of >88% and transmission losses of <1 dB in the investigated infrared spectral range.

Characterization of scintillating X-ray optical fiber sensors.

The paper presents a set of tests carried out in order to evaluate the design characteristics and the operating performance of a set of six X-ray extrinsic optical fiber sensors. The extrinsic sensor we developed is intended to be used as a low energy X-ray detector for monitoring radiation levels in radiotherapy, industrial applications and for personnel dosimetry. The reproducibility of the manufacturing process and the characteristics of the sensors were assessed. The sensors dynamic range, linearity, sensitivity, and reproducibility are evaluated through radioluminescence measurements, X-ray fluorescence and X-ray imaging investigations. Their response to the operating conditions of the excitation source was estimated. The effect of the sensors design and implementation, on the collecting efficiency of the radioluminescence signal was measured. The study indicated that the sensors are efficient only in the first 5 mm of the tip, and that a reflective coating can improve their response. Additional tests were done to investigate the concentricity of the sensors tip against the core of the optical fiber guiding the optical signal. The influence of the active material concentration on the sensor response to X-ray was studied. The tests were carried out by measuring the radioluminescence signal with an optical fiber spectrometer and with a Multi-Pixel Photon Counter.

Investigation of UV optical fibers under synchrotron irradiation.

The focus of the present paper deals, for the first time, with commercial UV optical fibers, characterizing their behaviour as they are subjected to very high flux wiggler generated synchrotron radiation. Five distinct types of UV optical fibers, produced by three manufactures, were exposed to total doses between 5 Gy and 2000 Gy. The exposure to synchrotron radiation was performed in two campaigns. The tests were run off-line and considered the dependence of the radiation induced attenuation (RIA) as function of the total dose. The recovery of the radiation induced colour centres was studied at room temperature and after heating the samples up to 560 K. As a première, we also investigated through THz imaging and spectroscopy the irradiated optical fiber samples. Under these conditions, three of the optical fibers proved to be radiation resistant. The two optical fibers sensitive to synchrotron radiation exhibited a linear variation of the optical absorption at the wavelengths of λ = 229 nm, λ = 248 nm, and λ = 265 nm, for total doses between 60 Gy and 2000 Gy. These two samples showed also an increase of the optical absorption in the UV spectral range when heated to 560 K. The optical fibers sensitive to synchrotron radiation can potentially be used for on-line radiation dosimetry.