Mark A. Hughes

Fabrication and characterization of femtosecond laser written waveguides in chalcogenide glass

The authors describe the fabrication of buried waveguides in a highly nonlinear chalcogenide glass, gallium lanthanum sulfide, using focused femtosecond laser pulses. Through optical characterization of the waveguides, they have proposed a formation mechanism and provide comparisons to previous work. Tunneling has been identified as the dominant nonlinear absorption mechanism in the formation of the waveguides. Single mode guidance at 633nm has been demonstrated. The writing parameters for the minimum propagation loss of 1.47dB∕cm are 0.36μJ pulse energy and 50μm∕s scanning speed.

Ultrabroad emission from a bismuth doped chalcogenide glass

We report emission from a bismuth doped chalcogenide glass which is flattened, has a full width at half maximum (FWHM) of 600 nm, peaks at 1300 nm and covers the entire telecommunications window. At cryogenic temperatures the FWHM reaches 850 nm. The quantum efficiency and lifetime were as high as 32% and 175 mus, respectively. We also report two new bismuth emission bands at 2000 and 2600 nm. Absorption bands at 680, 850, 1020 and 1180 nm were observed. The 1180 nm absorption band was previously unobserved. We suggest that the origin of the emission in Bi:GLS is Bi22- dimers.

Advanced bismuth-doped lead-germanate glass for broadband optical gain devices

We fabricated a series of glasses with the composition 94.7-χGeO2-5Al2O3-0.3Bi2O3-χPbO (χ=0-24mol.%). Characteristic absorption bands of bismuth centered at 500, 700, 800, and 1000 nm were observed. Adding PbO was found to decrease the strength of bismuth absorption. The addition of 3%-4% PbO resulted in a 50% increase in lifetime, a 20-fold increase in quantum efficiency, and a 28-fold increase in the product of emission cross section and lifetime on the 0% PbO composition. We propose that the 800 nm absorption band relates a different bismuth center than the other absorption bands.

Spectroscopy of vanadium (III) doped gallium lanthanum sulphide chalcogenide glass

Vanadium doped gallium lanthanum sulphide glass (V:GLS) displays three absorption bands at 580, 730, and 1155nm identified by photoluminescence excitation measurements. Broad photoluminescence, with a full width at half maximum of ∼500nm, is observed peaking at 1500nm when exciting at 514, 808, and 1064nm. The fluorescence lifetime and quantum efficiency at 300K were measured to be 33.4μs and 4%, respectively. From the available spectroscopic data, the authors propose the vanadium ions’ valence to be 3+ and be in tetrahedral coordination. The results indicate a potential for the development of a laser or optical amplifier based on V:GLS.

On the analogy between photoluminescence and carrier-type reversal in Bi- and Pb-doped glasses

Reaction order in Bi-doped oxide glasses depends on the optical basicity of the glass host. Red and NIR photoluminescence (PL) bands result from Bi(2+) and Bin clusters, respectively. Very similar centers are present in Bi- and Pb-doped oxide and chalcogenide glasses. Bi-implanted and Bi melt-doped chalcogenide glasses display new PL bands, indicating that new Bi centers are formed. Bi-related PL bands have been observed in glasses with very similar compositions to those in which carrier-type reversal has been observed, indicating that these phenomena are related to the same Bi centers, which we suggest are interstitial Bi(2+) and Bi clusters.

Evaluating upconversion materials developed to improve the efficiency of solar cells: comment

The upconversion efficiency depends on the pump power density. Materials exhibiting a high upconversion efficiency under high pump power density do not necessarily have a reasonable upconversion efficiency under the pump power density around that of the concentrated sunlight. Also, materials which have an upconversion efficiency not so high under high pump power density do not necessarily have no practical upconversion efficiency under the pump power density of concentrated sunlight. To avoid the inconveniences in measuring the upconversion efficiency under the pump power density of concentrated sunlight which is very weak, a method which can evaluate the significance of upconversion materials for solar cells is proposed.

An ultra-low leakage current single carbon nanotube diode with split-gate and asymmetric contact geometry

A single carbon nanotube diode is reported, with Ti and Pd contacts, and split gates. Without gate bias the device displays strong rectification, with a leakage current (I0) of 6 × 10−16 A, and an ideality factor (η) of 1.38. When the gate above the Ti contact is biased negatively the diode inverts. When positive bias is then applied to the gate above the Pd contact minority carrier injection is suppressed. Configured such I0 and η were 2 × 10−14 A and 2.01, respectively. Electrical characterization indicates that the Schottky barrier height for electrons is lower for the Pd contact than the Ti contact.

Excitation wavelength dependence of quantum efficiencies of Nd-doped glasses for solar pumped fiber lasers

The quantum efficiencies of the emission from the 4F3/2(R) level of Nd doped in tellurite glass were measured with an integrating sphere using natural sunlight(ηns), simulated sunlight (ηns), and 808 nm laser light (η808), respectively. The radiative quantum efficiency (ηr) was estimated from the fluorescence lifetime (τf) and the radiative lifetime calculated by Judd-Ofelt analysis (τr). ηr was almost 100 % for χ ≤ 0.5 mol.%. η808 was 86 % for χ=0.05 mol.% and decreased monotonically with increasing in χ. ηns had a peak at χ=0.5 mol.% and the maximum was 33 %. It is thought absorption of the excitation light by the host glass limits the quantum efficiency of the tellurite glass under sunlight excitation. Therefore, it is important to reduce absorption of the tellurite glass host in order to realize efficient solar-pumped tellurite fiber lasers.

Crystal field analysis of Dy and Tm implanted silicon for photonic and quantum technologies

We report the lattice site and symmetry of optically active Dy3+ and Tm3+ implanted Si. Local symmetry was determined by fitting crystal field parameters (CFPs), corresponding to various common symmetries, to the ground state splitting determined by photoluminescence measurements. These CFP values were then used to calculate the splitting of every J manifold. We find that both Dy and Tm ions are in a Si substitution site with local tetragonal symmetry. Knowledge of rare-earth ion symmetry is important in maximising the number of optically active centres and for quantum technology applications where local symmetry can be used to control decoherence.

Transition metal doped chalcogenide glasses for broadband near-infrared sources

In this paper we report the spectroscopic data for samples of 0.031% iron, 0.017% nickel, 0.01% chromium and 0.017% cobalt (molar) doped gallium lanthanum sulphide (GLS) glass. Photoluminescence (PL) with a full width half maximum (FWHM) of around 500 nm and peaking between 1120 nm and 1460 nm is observed when excited using wavelengths of 850 nm and 1064 nm. The emission lifetime for nickel-doped GLS at 300 K was measured to be 40 μs. Photoluminescence excitation (PLE) peaks for chromium-doped GLS at 700 nm and 1020 nm have been observed. By comparisons of our spectroscopic data to that of transition metals doped into other hosts we determine the oxidation states of the transition metal ions and propose transitions for the observed spectroscopic peaks.