Broadband light source based on highly nonlinear non-circular core photonic crystal fiber for medical applications

We present a highly nonlinear non-circular core photonic crystal fiber (HNL-NCPCF) with all normal group velocity dispersion (GVD) to design a supercontinuum (SC) light source for optical coherence tomography (OCT) system. Nonlinear coefficient $\gamma$ is increased as large as 66 W^?1 km^?1 at $1.31\mathrm{\mu }\mathrm{m}$ by reducing the effective mode area and core is made non-circular to increase birefringence by putting the square lattice of air-holes inside the silica host. About 85 nm 10 dB spectral bandwidths for 2.5 ps input optical pulse and 140 nm 10 dB spectral bandwidths for 1.0 ps input optical pulse have been observed using the same fiber length of 200 m and input optical power of 15 W. Coherent lengths of the generated supercontinuum light sources are found $8.91\mathrm{\mu }\mathrm{m}$ for 2.5 ps input optical pulse and $5.41\mathrm{\mu }\mathrm{m}$ for 1.0 ps input optical pulse. Therefore, the highest longitudinal resolution for dental OCT at $1.31\mathrm{\mu }\mathrm{m}$ is found about $3.28\mathrm{\mu }\mathrm{m}$ for tooth enamel.     

Neutron induced alpha radiography

A radiography technique which makes use of $\alpha$-particles as penetrating radiation has been developed. The images were registered in the solid-state nuclear track detector CR-39 and the conditions to obtain the best radiography image were 2.2 h of irradiation and 25 min of etching in a KOH (30%) aqueous solution at $70{}^{\circ }\mathrm{C}$. For such conditions the resolution in the image was $23\mathrm{\mu }\mathrm{m}$. Some radiographs are shown and demonstrate the potential of the technique to inspect samples with thickness in the $\mathrm{\mu }\mathrm{m}$ range.     

First tests of the active shield for a gamma ray spectrometer

The operational problems of the gamma ray spectrometer shielded passively with 12 cm of lead and actively by five $0.5\mathrm{m}\times 0.5\mathrm{m}\times 0.05\mathrm{m}$ plastic veto shields are described. The active shielding effect from environmental gamma ray, cosmic muons, and neutrons was investigated. Wide range of scintillator pulses, corresponding to the energy range of 150 keV–75 MeV, was used for anticoincidence gating. With the optimal set up, the integral background of 0.31 c/s was achieved for the energy region of 50–3000 keV. The detector mass-related background was 0.345 c/kg s. The 511 keV annihilation line was reduced by factor of 7 by the anticoincidence gate. It is shown that the plastic shields increase the neutron capture gamma line intensities due to neutron termalization.     

YbNi2: A heavy fermion ferromagnet

Measurements of the magnetization and specific heat of YbNi₂ binary alloy are reported. The DC magnetic susceptibility displays a ferromagnetic behavior with a Curie temperature T_C=10.5 K, one of the highest found in Yb compounds. Moreover, the temperature dependence of the specific heat exhibits a lambda anomaly with a peak of 5.12 J/mol K at 9.4 K. The analysis also shows an additional magnetic contribution around 32 K stemming from the crystalline electric field of a quartet at ${\Delta }_1=72\mathrm{K}$ and a doublet at ${\Delta }_2=126\mathrm{K}$, according to the splitting of the Yb³⁺ ion in cubic symmetry. From the magnetic contribution to the specific heat, a relatively high Kondo temperature $T_K=27\mathrm{K}$ is estimated. Below the magnetic transition, the specific heat shows a huge value of the electronic coefficient ${\gamma }_{\mathit{LT}}=573\mathrm{mJ}/\mathrm{mol}\mathrm{K}$, which is a signature of a heavy fermion behavior. Therefore, this alloy is a fine example of enhanced ferromagnetism and heavy fermion behavior among Yb compounds.     

Principal and secondary luminescence lifetime components in annealed natural quartz

Time-resolved luminescence spectra from quartz can be separated into components with distinct principal and secondary lifetimes depending on certain combinations of annealing and measurement temperature. The influence of annealing on properties of the lifetimes related to irradiation dose and temperature of measurement has been investigated in sedimentary quartz annealed at various temperatures up to $900{}^{\circ }\mathrm{C}$. Time-resolved luminescence for use in the analysis was pulse stimulated from samples at 470 nm between 20 and $200{}^{\circ }\mathrm{C}$. Luminescence lifetimes decrease with measurement temperature due to increasing thermal effect on the associated luminescence with an activation energy of thermal quenching equal to $0.68\pm 0.01\mathrm{eV}$ for the secondary lifetime but only qualitatively so for the principal lifetime component. Concerning the influence of annealing temperature, luminescence lifetimes measured at $20{}^{\circ }\mathrm{C}$ are constant at about $33\mathrm{\mu }\mathrm{s}$ for annealing temperatures up to $600{}^{\circ }\mathrm{C}$ but decrease to about $29\mathrm{\mu }\mathrm{s}$ when the annealing temperature is increased to $900{}^{\circ }\mathrm{C}$. In addition, it was found that lifetime components in samples annealed at $800{}^{\circ }\mathrm{C}$ are independent of radiation dose in the range 85–1340 Gy investigated. The dependence of lifetimes on both the annealing temperature and magnitude of radiation dose is described as being due to the increasing importance of a particular recombination centre in the luminescence emission process as a result of dynamic hole transfer between non-radiative and radiative luminescence centres.     

Indentation measurements on the eardrum with automated projection moiré profilometry

Computer modeling of middle ear mechanics is an important tool to investigate its complex behavior, but correct mechanical and elastic parameters are needed to obtain realistic simulations. A possible way to determine eardrum elasticity in situ is the use of point indentation measurements. The eardrum is, however, a small fragile membrane, so a non-contacting high-resolution technique is needed to measure the shape change caused by point indentation. We have developed a projection moiré interferometer combined with an indentation actuator and a high-resolution force sensor. The apparatus applies deformations up to 1 mm with a resolution of $1\mathrm{\mu }\mathrm{m}$, while the indentation force is measured with a resolution better than 1 mN. The moiré setup delivers height data on $512\times 512$ points through phase-shifting, with a height resolution of $15\mathrm{\mu }\mathrm{m}$. Shape recordings are made on a rabbit eardrum at different indentation distances, and indentation force is recorded simultaneously.     

Experimental demonstration of a dual-band metamaterial absorber

We present the design, simulation and fabrication of a dual-band metamaterial absorber. The designed structure consists of periodic composite metallic holes array and dielectric layer. The availability of absorption enhancement is verified by our measured results. Cavity and electrical resonances lead to these two absorption peaks at ${\mathit{\lambda }}_1=1.8\mathrm{\mu }\mathrm{m}$ and ${\mathit{\lambda }}_2=4.3\mathrm{\mu }\mathrm{m}$. Effects of structural parameters on absorption and resonant wavelengths have been experimentally surveyed. The average absorption can be increased by optimizing the structural parameters of the designed metamaterial absorber.     

Analysis of the characteristics of the polarization splitter based on tellurite glass dual-core photonic crystal fiber

A novel kind of polarization splitter based on tellurite glass dual-core photonic crystal fiber is proposed. The characteristics of the polarization splitter have been studied by the finite element method. By adjusting the ellipticity of the dual-core PCF, a very high value of birefringence can be reached. The high birefringence can increase the D-value of coupling length in the two orthogonal polarization directions, then the polarization-independent splitter can be achieved. Comparing with the SF57 glass dual-core PCF, the tellurite glass dual-core PCF has higher extinction ratio, the extinction ratio can reach ?31 dB at the wavelength $\lambda =1.55\mathrm{\mu }\mathrm{m}$. The 0.36-mm-long splitter is proposed to achieve extinction ratio better than ?10 dB and a bandwidth of 20 nm.     

Po and Pb concentration of cigarettes traded in Hungary and their estimated dose contribution due to smoking

It is known that tobacco leaves may contain ²¹⁰Pb and ²¹⁰Po in significant concentrations. The cumulative alpha-radiation dose due to the radioactive content of inhaled cigarette smoke and the increasing number of lung cancer cases explain the importance of the investigation. The present study investigated the activity concentrations of these two radionuclides in 29 Hungarian cigarette samples. The relation between ²¹⁰Po/²¹⁰Pb activity and nicotine/tar content of these cigarettes was also examined. ²¹⁰Po was determined by alpha spectrometry using a PIPS detector after chemical leaching and spontaneous deposition of ²¹⁰Po on a high nickel-content (25%) stainless steel disk. The ²¹⁰Pb activity was calculated from the ²¹⁰Po originated from the decay of ²¹⁰Pb after a waiting period of eight months. The ²¹⁰Po activity concentrations of the measured types of cigarettes ranged from 10.0 to 33.5 mBq/cigarette, and the activity of ²¹⁰Pb varied from 9.6 to 32.5 mBq/cigarette. The average annual committed effective dose is estimated to be $185.6\pm 70.6\mathrm{\mu }\mathrm{Sv}/\mathrm{y}$ and $58.7\pm 22.7\mathrm{\mu }\mathrm{Sv}/\mathrm{y}$ due to cigarette smoking (20 cigarettes/day) for ²¹⁰Po and ²¹⁰Pb, respectively.