Investigation of Q-switched InP-based 1550 nm semiconductor lasers

High energy picosecond pulse generation from a two contact tapered 5 quantum well (QW) InGaAlAs/InP diode laser (1550 nm) is investigated using a passive Q-switching technique. Single peak pulses with pulse energies as high as 500 pJ and durations of typically hundreds of picoseconds are obtained from the device by applying reverse bias voltages in the range of 0 V to ?18 V to the absorber section of the device. It is also demonstrated that more symmetrical Q-switched pulses are obtained by reducing the duration of electrical pulses applied to the gain section of the laser. Such an improvement is attributed to the reduced time of the population inversion in the gain section due to shorter electrical pulse. We also show comparatively the dependence of optical spectra on the reverse bias voltage for diode lasers emitting at 1550 nm and 1350 nm, and demonstrate that better spectral output is obtained from AlGaInAs lasers emitting at a wavelength of 1550 nm.     

Degradation of nitrobenzene in aqueous solution by dual-pulse ultrasound enhanced electrochemical process

The present work reports a novel dual-pulse ultrasound enhanced electrochemical degradation (US-ECD) process that synchronizes alternatively ultrasound pulses and potential pulses to degrade nitrobenzene in aqueous solution with a high percentage degradation and low energy consumption. In comparison to the test results generated from the conventional US-ECD and original electrochemical degradation (ECD) process, the dual-pulse US-ECD process increased degradation percentages to nitrobenzene by 2% and 17%, respectively, while energy used in the pulse process was only about 46.5% of that was used in the conventional US-ECD process. Test results demonstrated a superior performance of the dual-pulse US-ECD process over those of other conventional ones. Impacts of pulse mode, initial pH value, cell voltage, supporting electrolyte concentration and ultrasonic power on the process performances were investigated. With operation conditions optimized in the study at pH = 3.0, cell voltage = 10 V, ultrasonic power = 48.84 W, electrolyte concentration = 0.1 M and an experiment running time of 30 min, the percentage degradation of nitrobenzene could reach 80% (US pulse time = 50 ms and ECD pulse time = 50 ms). This process provided a reliable and effective technical approach to degrade nitrobenzene in aqueous solution and significantly reduced energy consumption in comparison to the conventional US-ECD or original ECD treatment.     

Efficient high voltage pulser for piezoelectric air coupled transducer

The design of high voltage pulser for air coupled ultrasound imaging is presented. It is dedicated for air-coupled ultrasound applications when piezoelectric transducer design is used. Two identical N-channel MOSFETs are used together with 1200 V high and low side driver IC. Simple driving pulses’ delay and skew circuit is used to reduce the cross-conduction. Analysis of switch peak current and channel resistance relation to maximum operation frequency and load capacitance is given. PSPICE simulation was used to analyze the gate driver resistance, gate pulse skew, pulse amplitude influence on energy consumption when loaded by capacitive load. Experimental investigation was verified against simulation and theoretical predictions. For 500 pF capacitance, which is most common for piezoelectric air coupled transducers, pulser consumes 650 μJ at 1 kV pulse and 4 μJ at 50 V. Pulser is capable to produce up to 1 MHz pulse trains with positive 50 V–1 kV pulses with up to 10 A peak output current. When loaded by 200 kHz transducer at 1 kV pulse amplitude rise time is 40 ns and fall time is 32 ns which fully satisfies desired 1 MHz bandwidth.     

Thermal imaging during infrared final cooking of semi-processed cylindrical meat product

The temperature measurements during the infrared cooking of the semi-cooked cylindrical minced beef product (koefte) were taken by both contact (thermocouples) and non-contact (thermal imaging) techniques. The meat product was semi-cooked till its core temperature reached up to 75 °C by ohmic heating applied at 15.26 V/cm voltage gradient. Then, infrared cooking was applied as a final cooking method at different combinations of heat fluxes (3.7, 5.7 and 8.5 kW/m²), applied distances (10.5, 13.5 and 16.5 cm) and applied durations (4, 8 and 12 min). The average surface temperature increased as the heat flux and the applied duration increased but the applied distance decreased. The temperature distribution of the surface during infrared cooking was determined successfully by non-contact measurements. The temperature homogeneity varied between 0.77 and 0.86. The process condition of 8.5 kW/m² for 8 min resulted in core temperature greater than 75 °C, which was essential for safe production of ready-to-eat (RTE) meat products. Thermal imaging was much more convenient method for minimizing the point measurement mistakes and determining temperature distribution images more clear and visual.     

Control by osmolarity and electric field strength of electro-induced gene transfer and protein release in fission yeast cells

A high electric pulse was applied to the uptake of DNA into cells, the sterilization of cells, and the release of protein from cells. These applications to fission yeast showed a strong dependence on both the osmolarity of pulsing sorbitol solution and the intensity of the electric pulse. In electroporation, high transformation efficiency was obtained with a wide range of sorbitol (0.6–1.6 M) at 10.0 kV/cm for about 5 ms. Furthermore, the highest efficiency was achieved in 1.5 M sorbitol at a higher strength, 12.5 kV/cm, although the cell survival rate dropped. The release of protein generally increased with increasing electric field strength, due mainly to leakage from dead cells under hypotonic conditions. However, protein was released significantly in 1.5 M sorbitol at a lower strength, 7.5 kV/cm, although a high survival rate was maintained. Thus, the application of the high electric pulse to fission yeast under hypertonic conditions increased the uptake and release of macromolecules controlled by the electric field strength.     

The growth and field evaporation of Er and deuterated Er films

The morphological structure of clean and deuterated Er films deposited on W substrates and their removal by field evaporation have been investigated as part of a program directed toward the development of deuterium ion sources for neutron generators. Annealed Er films up to ~ 20 monolayers in thickness deposited on W < 110 > substrates appear pseudomorphic. Thicker annealed films form a hexagonal close-packed < 0001 > orientated over-layer with the Pitsch–Schrader orientation relation. The pseudomorphic and hexagonal close-packed character of the films is retained up to the last atomic layer that forms the film-substrate interface. Deuterated Er films appear polycrystalline. At 77 K in Ar, annealed Er films field evaporate at 2.5 V/Å primarily as Er^2 + and deuterated Er films evaporate at ~ 2.4 V/Å primarily as ErD_x^2 +. Field evaporation of both clean and deuterated Er films shows signs of space charge induced field lowering when film thicknesses exceeding ~ 10 layers were field evaporated using 20 ns duration voltage pulses.     

Effect of dc bias on the compositional ratio of WNX thin films prepared by rf-dc coupled magnetron sputtering

The effect of the dc bias on the compositional ratio, resistivity, and deposition rate for tungsten nitride (WN_X) films prepared by rf-dc coupled magnetron sputtering have been investigated in detail. The value of the film compositional ratio (N/W) is significantly decreased from 0.8 to 0.2 with increasing the target dc bias voltage. The increase of the target dc bias voltage from −100 to −500 V results in a dramatical decrease in the resistivity of WN_X films. It is shown that the N/W ratio and the resistivity of WN_X thin films deposited at the target dc bias voltage of −200 V are about 0.5 and 370 μΩ cm, respectively.     

Near-white emitting QD-LED based on hydrophilic CdS nanocrystals

In this work we report fabrication of a nanocrystal (NC)-based hybrid organic–inorganic LED with structure of ITO/PEDOT:PSS/PVK/CdS-NCs/(Al or Mg:Ag). The hydrophilic CdS NCs were synthesized using a novel aqueous thermochemical method at 80 °C and sizes (around 2 nm) were controlled by thioglycolic acid (TGA) as the capping agent. The favorite feature of these NCs is their relatively high emission intensity and broad, near-white emission. The hydrophilic CdS NCs were successfully spin coated using Triton X-100 as the wetting agent. The fabricated LEDs demonstrated a turn on voltage about 7 V for Al metallic contact. The electroluminescence was a broad spectrum at 540 and 170 nm width, which was about 50 nm red shifted compared to photoluminescence spectra. The CIE color coordinates of the LED at (0.33, 0.43) demonstrated a near white light LED with an emission on green–yellow boundary of white. Annealing of the device up to 190 °C had a positive effect on the performance, possibly due to better contacts between layers. Replacing Al contacts with Mg:Ag reduced the turn-on voltage to 6 V and changed CIE color coordinate to (0.32, 0.41). The EL peak was also shifted to 525 nm, with a brightness of 15 Cd/m² at working voltage of 15 V. The current efficiency and external quantum efficiency of device were 0.08 Cd/A and 0.03% at current densities higher than 10 mA/cm².     

Synthesis and characterization of PPV-based light-emitting copolymer with alkylsilylphenyloxy pendant group for light-emitting diode applications

A novel light-emitting copolymer with high brightness and luminance efficiency was synthesized using the Gilch polymerization method, and its electro-optical properties were investigated. A polymer light-emitting diode (PLED) was fabricated in ITO/PEDOT/light-emitting copolymer/Ca/Al configuration. The turn-on voltage of the PLED was about 5.0 V with maximum brightness and luminance efficiency up to 1420 cd/m² at 16.2 V and 0.5 cd/A at 6.8 V, respectively.     

On the meniscus deformation when the pulsed voltage is applied

Effect of the pulsed voltage on the meniscus deformation was investigated. Results show that both the pulsed voltage and its width as well as the bias voltage affected the behaviour of spraying. There appeared three spraying modes, e.g. dripping, pulsating jet and cone-jet. Cone-jet has been created by applying a pulsed voltage of 1.5 kV to a bias voltage of 5.0 kV for 300 ms.     

Comparison of BOLD,diffusion-weighted fMRI and ADC-fMRI for stimulation of the primary visual system with a block paradigm

The blood oxygen level-dependent (BOLD) effect is extensively used for functional MRI (fMRI) but presents some limitations. Diffusion-weighted fMRI (DfMRI) has been proposed as a method more tightly linked to neuronal activity. This work proposes a protocol of DfMRI acquired for several b-values and diffusion directions that is compared to gradient-echo BOLD (GE-BOLD) and to repeated spin-echo BOLD (SE-BOLD, acquisitions performed with b = 0 s/mm²), which was also used to ensure the reproducibility of the response.A block stimulation paradigm of the primary visual system (V1) was performed in 12 healthy subjects with checkerboard alternations (2 Hz frequency). DfMRI was performed at 3 T with 5 b-values (b = 1500, 1000, 500, 250, 0 s/mm²) with TR/TE = 1004/93 ms, Δ/δ = 45.4 ms/30 ms, and 6 spatial directions for diffusion measures. GE-BOLD was performed with a similar block stimulation design timing. Apparent Diffusion Coefficient (ADC)-fMRI was computed with all b-values used. An identical Z-score level was used for all fMRI modalities for the comparison of volumes of activation. ADC-fMRI and SE-BOLD fMRI activation locations were compared in a voxel-based analysis to a cytoarchitectural probability map of V1.SE-BOLD activation volumes represented only 55% of the GE-BOLD activation volumes (P < 0.0001). DfMRI activation volumes averaged for all b-values acquired represented only 12% of GE-BOLD (P < 0.0001) and only 22% of SE-BOLD activation volumes (P < 0.005). Compared to SE-BOLD-fMRI, ADC-fMRI activations showed fewer pixels outside of V1 and a higher average probability of belonging to V1.DfMRI and ADC-fMRI acquisition at 3 T could be easily post-processed with common neuro-imaging software. DfMRI and ADC-fMRI activation volumes were significantly smaller than those obtained with SE-BOLD. ADC-fMRI activations were more precisely localized in V1 than those of SE-BOLD-fMRI. This validated the increased capability of ADC-fMRI compared to BOLD to enhance the precision of localizing an fMRI activation in the cyto-architectural zone V1, thereby justifying the use of ADC-fMRI for neuro-scientific studies.     

Alternate pulses of ultrasound and electricity enhanced electrochemical process for p-nitrophenol degradation

A novel alternated ultrasonic and electric pulse enhanced electrochemical process was developed and used for investigating its effectiveness on the degradation of p-nitrophenol (PNP) in an aqueous solution. The impacts of pulse mode, pH, cell voltage, supporting electrolyte concentration, ultrasonic power and the initial concentration of PNP on the performance of PNP degradation were evaluated. Possible pathway of PNP degradation in this system was proposed based on the intermediates identified by GC–MS. Experimental results showed that 94.1% of PNP could be removed at 2 h in the dual-pulse ultrasound enhanced electrochemical (dual-pulse US-EC) process at mild operating conditions (i.e., pulse mode of electrochemical pulse time (T_EC) = 50 ms and ultrasonic pulse time (T_US) = 100 ms, initial pH of 3.0, cell voltage of 10 V, Na₂SO₄ concentration of 0.05 M, ultrasonic powder of 48.8 W and initial concentration of PNP of 100 mg/L), compared with 89.0%, 58.9%, 2.4% in simultaneous ultrasound enhanced electrochemical (US-EC) process, pulsed electrochemical (EC) process and pulsed ultrasound (US), respectively. Moreover, energy used in the dual-pulse US-EC process was reduced by 50.4% as compared to the US-EC process. The degradation of PNP in the pulsed EC process, US-EC process and dual-pulse process followed pseudo-first-order kinetics. Therefore, the dual-pulse US-EC process was found to be a more effective technique for the degradation of PNP and would have a promising application in wastewater treatment.     

An infrared pyroelectric detector improved by cool isostatic pressing with cup-shaped PZT thick film on silicon substrate

In this paper, we presented a new pyroelectric detector with back to back silicon cups and micro-bridge structure. The PZT thick film shaped in the front cup was directly deposited with designed pattern by electrophoresis deposition (EPD). Pt/Ti Metal film, which was fabricated by standard photolithography and lift-off technology, was sputtered to connect the top electrode and the bonding pad. The cold isostatic press (CIP) treatment could be applied to improve the pyroelectric properties of PZT thick film. The infrared (IR) properties the CIP-optimized detector were measured. The voltage responsivity (R_V) was 4.5 × 10² V/W at 5.3 Hz, the specific detectivity (D^*) was greater than 6.34 × 10⁸ cm Hz^1/2 W⁻¹ (frequency > 110 Hz), and the thermal time constant was 51 ms, respectively.     

Dynamic temperature rise of shielded MR sensors during simulated electrostatic discharge pulses of variable pulse width

The temperature rise from electrical over-stress (EOS) and electrostatic discharge (ESD) of shielded AMR sensors used for magnetic tape storage devices is studied using square wave voltage pulses with widths from 35 ns to 2 ms. A phenomenological model has been developed to describe the dynamic stripe temperature versus pulse width and power for the time range studied as well as for a wide range in sensor geometries. The temperature required to melt the stripes was determined to be $1437\pm 69{}^{\circ }\mathrm{C}$. The activation energy required to achieve a 2% increase in stripe resistance for pulses between 100 ns and 1 ms was determined to be 2.8 eV and is associated with interdiffusion of the stripe metals.     

Effects of thickness of β-barium borate and angle of non-collinearity on the fs pulse generation by optical parametric amplification

Non-collinear optical parametric amplifiers (NOPAs) are used for the generation of tunable femtosecond pulses. The spectra of the uncompressed output from a lab-built NOPA in the 470–650 nm range have been recorded. Theoretical simulations for the effect of the length of the β-barium borate (BBO) crystal as well as the non-collinear angles between the pump and seed wavelengths have been carried out. For these we have obtained the initial experimental data from a 2 mm-thick BBO crystal when pumped with the second harmonic of the Ti:sapphire laser pulses of 100 fs duration. The pulse splitting length (PSL) and the group velocity mismatch (GVM) have been considered in simulations of the output. It was found that the crystal length of 1.3 mm and the crystal tilt of approximately 3.7° are optimal for the generation of pulses of ～11 fs at 600 nm.     

Wide-band fanned-out supercontinuum source covering O-, E-, S-, C-, L- and U-bands

A wide-band supercontinuum source generated by mode-locked pulses injected into a Highly Non-Linear Fiber (HNLF) is proposed and demonstrated. A 49 cm long Bismuth–Erbium Doped Fiber (Bi–EDF) pumped by two 1480 nm laser diodes acts as the active gain medium for a ring fiber laser, from which mode-locked pulses are obtained using the Non-Polarization Rotation (NPR) technique. The mode-locked pulses are then injected into a 100 m long HLNF with a dispersion of 0.15 ps/nm km at 1550 nm to generate a supercontinuum spectrum spanning from 1340 nm to more than 1680 nm with a pulse width of 0.08 ps and an average power of ?17 dBm. The supercontinuum spectrum is sliced using a 24 channel Arrayed Waveguide Grating (AWG) with a channel spacing of 100 GHz to obtain a fanned-out laser output covering the O-, E-, S-, C-, L- and U-bands. The lasing wavelengths obtained have an average pulse width of 9 ps with only minor fluctuations and a mode-locked repetition rate of 40 MHz, and is sufficiently stable to be used in a variety of sensing and communication applications, most notably as cost-effective sources for Fiber-to-the-Home (FTTH) networks.     

Structural and electrochemical properties of layered lithium nitridocuprates Li3 − xCuxN

We report a systematic study of the layered lithium nitridocuprates Li_3 ? xCu_xN with 0.1 ≤ x ≤ 0.39. The structural data obtained from experimental XRD patterns, Rietveld refinements and unit cell parameters calculation vs x, indicate that copper (I) substitute interlayer lithium ions in the parent nitride Li₃N to form the Li_3 ? xCu_xN compound without any Li vacancy in the Li₂N^? layer. Electrochemical results report Li insertion into the corresponding layered structures cannot take place in the 1.2/0.02 V voltage range as in the case of lithium into nitridonickelates and nitridocobaltates. However, in the initial charge process of Li_3 ? xCu_xN at 1.4 V leading to a specific capacity higher than 1000 mA h/g, the oxidation of copper and nitride ions is probably involved inducing a strong structural disordering process. As a consequence a new rechargeable electrochemical system characterized by discharge–charge potential of ≈ 0.3 V/1.2 V appears from the second cycle. Cycling experiments 0.02 V voltage/0.02 V range induce a complete destruction of the layered host lattice and the presence of Cu₃N in the charge state suggests a conversion reaction. The capacity recovered in the 1.4/0.02 V range practically stabilizes around 500 mA h/g after 20 cycles.     

Fabrication and characteristics of photodiode based on ZnO nanowire arrays and spray-coated regioregular P3HT layers

A photodiode based on well-aligned ZnO nanowire arrays (ZNAs) and spray-coated regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) layers hybrid hetero junctions was fabricated, and its electrical characteristics in dark and under illumination with a solar simulator were investigated. Current–voltage (I–V) data of ITO/ZNAs/P3HT/Ag device in dark and under illumination showed typical diode characteristics. A rectification ratio (RR) of 22.7 at 1.7 V and a low turn-on voltage of 0.4 V in dark were obtained. Also, the photodiode with high photo-response in the order of 0.31 A/W at -2 V using 80 mW/cm² illumination power was observed. Upon increasing illumination power from 40 to 100 mW/cm², the RR value for the photodiode continuously was improved with a highest value of 12.5.     

On the step-graded doped-channel (SGDC) field-effect transistor

An i-InGaP/n-In_xGa_1 − xAs/i- GaAs step-graded doped-channel field-effect transistor (SGDCFET) has been fabricated and studied. Due to the existence of a V-shaped energy band formed by the step-graded structure, a large output current density, a large gate voltage swing with high average transconductance, and a high breakdown voltage can be expected. In this study, first, a theoretical model and a transfer matrix technique are employed to analyze the energy states and wavefunctions in the step-graded quantum wells. Experimentally, for a 1  ×  80 μm²gate dimension device, a maximum drain saturation current density of 830 mAmm ^− 1, a maximum transconductance of 188mSmm ^− 1 , a high gate breakdown voltage of 34 V, and a large gate voltage swing 3.3 V with transconductance larger than 150 mSmm ^− 1are achieved. These performances show that the device studied has a good potentiality for high-speed, high-power, and large input signal circuit applications.     

Synthesis and properties of a new class of fluorine-containing dilithium salts for lithium-ion batteries

A facile synthetic route for the development of a new class of dilithium salts is described. Because of the presence of two lithium ions per molecule, these salts require lower concentrations than commonly used salts to achieve comparable ionic conductivities at ambient temperatures. An ionic conductivity of 3.55 × 10^− 3 S/cm at 30 °C was obtained using 0.5 M salt solution in 1:1 wt/wt ethylene carbonate:dimethyl carbonate. The salts exhibit excellent thermal stabilities to at least 350 °C and are electrochemically stable below 4.2 V versus lithium metal. The best salt was tested with a polymer electrolyte system. Incorporation of a polyethylene glycol-based borate ester plasticizer improved the ionic conductivity of the solid polymer electrolyte film up to 1.36 × 10^− 5 S/cm at 30 °C, which is 10 times higher than that of un-plasticized electrolyte films.