Dosimetric characteristics of Gd-doped silica glass subjected to neutron and gamma irradiations

The dosimetric characteristics of newly developed gadolinium (Gd) glass dosimeter produced via sol-gel method are reported. Irradiation were made using a 750 kW neutron flux thermal power and 1.25 MeV ⁶⁰Co gamma rays with entrance doses from 2 to 10 Gy. Investigation has been done on various Gd dopant concentrations, ranging from 1 to 10 mol%. The Gd-doped silica glass have been characterised for thermoluminescence (TL) dose response, sensitivity, linearity index, glow curve and kinetic parameter analysis. For particular dopant concentration obtained in 6 mol% Gd, the least squares fit shows the change in TL yield, correlation coefficient (r²) of better than 0.980 (at 95% confidence level), with neutron and gamma exposure to be 8 and 4 times greater than that of 1 mol% Gd, respectively. Broad peaks in the absence of any sharp peak observed in the glow curve confirms the amorphous nature of the prepared glass. A glow curve of Gd-doped SiO₂ sample is observed with a single prominent peak (T_m) within 200-250 °C (peak shifting appears with respect to the increment of dopant concentration) and 350 °C (for all respective Gd dopants) for neutron and gamma irradiations, respectively. Deconvolution shows the glow curves of the Gd-doped SiO₂ glass to be formed of seven and five overlapping peaks, with figures of merit below 2% (FOM) of between 1.38-1.79 and 1.30-1.97 for the particular neutron and gamma irradiations, respectively. Through use of Glowfit deconvolution software, the key trapping parameters of activation energy, E and frequency factor, s^-1 were calculated for the Gd-doped SiO₂ glass. The mechanism of TL yield with the gradual increase in Gd concentrations and doses is explained upon the incorporation of Gd and radiation damage that change the structure of the electron traps in the glass matrix. These early results indicate that selectively screened Gd-SiO₂ glass can be developed into a promising TL system towards dosimetric applications.

Pump distribution effect in dual-wavelength Raman-erbium random distributed feedback fiber laser

This work demonstrates a simple dual-wavelength random distributed feedback fiber laser via excitation of the Raman-erbium hybrid gain by a single pump source. Lasing wavelengths at 1568 nm and 1595 nm with 48.48 dBm maximum OSNR were generated without the need for physical reflectors. Enhancements were performed using pump power distribution and a seeded feedback to reduce the peak disparity to only 0.16 dB. The long cavity hybrid random laser with its balanced and broadly spaced dual-wavelength output offers immense potential for long distance dual laser applications.

Photoluminescence and thermoluminescence properties of Li₂O-Na₂O-B₂O₃ glass

Influence of Nd(3+) concentration on the optical and thermoluminescence (TL) properties of melt-annealed synthesized 10 Na2O: 20 Li2O: (70-x) B2O3 : xNd2O3, where 0.1≤ x ≤0.7 (LNB) glasses are determined. The absence of sharp peaks in X-ray diffraction patterns confirms the amorphous nature of the prepared glasses. The photoluminescence spectra under 800 nm laser excitations at room temperature exhibit three prominent peaks centred at 538, 603 and 675 nm corresponding to the transitions of (4)G(7/2) → (4)I(9/2), [(4)G(7/2) → (4)I(11/2), (4)G(5/2) → (4)I(9/2)] and [(4)G(7/2) → (4)I(13/2), (4)G(5/2) → (4)I(11/2)], respectively. The TL glow curve exhibits a prominent peak (T(m)) at 180°C. The best performance of the prepared glass was found at 0.5 mol% of Nd2O3. We achieved a good linearity of TL response against dose between 0.5 to 4.0 Gy. The calculated value of the effective atomic number, Z(eff), is 7.55 which is nearly tissue equivalent (Z(eff) = 7.42). These promising features demonstrate the capability of the aforementioned glass to be used as a radiation dosimeter.

HIGHLIGHTS

The thermoluminescence and optical properties of new compositions of lithium sodium borate glasses doped with Nd(3+) ions were reported. Attractive features were obtained from the TL, PL and UV-Vis light analysis. Three upconversion luminescences permitting green, orange and red emissions were observed.

The thermoluminescence glow curve and the deconvoluted glow peak characteristics of erbium doped silica fiber exposed to 70-130 kVp x-rays

In regard to thermoluminescence (TL) applied to dosimetry, in recent times a number of researchers have explored the role of optical fibers for radiation detection and measurement. Many of the studies have focused on the specific dopant concentration, the type of dopant and the fiber core diameter, all key dependencies in producing significant increase in the sensitivity of such fibers. At doses of less than 1 Gy none of these investigations have addressed the relationship between dose response and TL glow peak behavior of erbium (Er)-doped silica cylindrical fibers (CF). For x-rays obtained at accelerating potentials from 70 to 130 kVp, delivering doses of between 0.1 and 0.7 Gy, present study explores the issue of dose response, special attention being paid to determination of the kinetic parameters and dosimetric peak properties of Er-doped CF. The effect of dose response on the kinetic parameters of the glow peak has been compared against other fiber types, revealing previously misunderstood connections between kinetic parameters and radiation dose. Within the investigated dose range there was an absence of supralinearity of response of the Er-doped silica CF, instead sub-linear response being observed. Detailed examination of glow peak response and kinetic parameters has thus been shown to shed new light of the rarely acknowledged issue of the limitation of TL kinetic model and sub-linear dose response of Er-doped silica CF.

Numerical investigation on cascaded 1 × 3 photonic crystal power splitter based on asymmetric and symmetric 1 × 2 photonic crystal splitters designed with flexible structural defects

We propose a photonic crystal slab-based 1 × 3 power splitter with high output transmission and equal power distribution. It is designed by cascading an asymmetric 1 × 2 power splitter and a symmetric 1 × 2 power splitter. Desired equal power splitting is achieved by introducing and optimizing the splitting region of the 1 × 2 power splitters with flexible structural defects. Simulations were carried out by using 3-D Finite Difference Time Domain method showing equal normalized power distributions of 29.6%, 28.9% and 30.5% at 1550 nm optical wavelength. In addition, equal power splitting also takes place at 1561 nm.

Extended nonlinear parametric process in anomalously pumped linear cavity oscillator

We demonstrate a linear cavity fiber optical parametric oscillator with extended pump-signal separation of 14.3 THz (116 nm). The signal laser is provided by a pair of 1675nm fiber Bragg gratings and a tunable idler from 1456.12 nm to 1462.48 nm is generated by detuning the pump wavelength in the anomalous dispersion regime of a highly nonlinear fiber. At such large pump-signal separation, we are still able to record a parametric conversion efficiency of more than -35 dB and idler optical signal-to-noise-ratio of 50 dB on average. The stability of the lasing signal and idler is examined and result shows both signal and idler peak power fluctuation is less than 1 dB over a period of 30 minutes.