Metamorphic InGaAs p-i-n Photodetectors with 1.75 mu m Cut-Off Wavelength Grown on GaAs

Top-illuminated metamorphic InGaAs p-i-n photodetectors (PDs) with 50% cut-off wavelength of 1.75 mu m at room temperature are fabricated on GaAs substrates. The PDs are grown by a solid-source molecular beam epitaxy system. The large lattice mismatch strain is accommodated by growth of a linearly graded buffer layer to create a high quality virtual InP substrate indium content in the metamorphic buffer layer linearly changes from 2% to 60%. The dark current densities are typically 5 x 10(-6) A/cm(2) at 0 V bias and 2.24 x 10(-4) A/cm(2) at a reverse bias of 5 V. At a wavelength of 1.55 mu m, the PDs have an optical responsivity of 0.48 A/W, a linear photoresponse up to 5 mW optical power at -4 V bias. The measured -3 dB bandwidth of a 32 mu m diameter device is 7 GHz. This work proves that InGaAs buffer layers grown by solid source MBE are promising candidates for GaAs-based long wavelength devices.

Visible blind p(+)-pi-n(-)-n(+) ultraviolet photodetectors based on 4H-SiC homoepilayers

p(+)-pi-n(-)-n(+) ultraviolet photodetectors based on 4H-SiC homoepilayers have been presented. The growth of the 4H-SiC homoepilayers was carried out in a LPCVD system. The size of the active area of the photodetectors was 300 x 300 mu m(2). The dark and illuminated I-V characteristics had been measured at reverse biases form 0 to 20 V at room temperature, and the illuminated current was at least two orders of magnitude than that of dark current below 13 V bias. The peak value zones of the photoresponse were located at 280-310 nm at different reverse biases, and the peak value located at 300 nm was 100 times greater than the cut-off response value in 380 nm at a bias of 10V, which showed the device had good visible blind performance. A small red-shift about 5 nm on the peak responsivity occurred when reverse bias increased from 5 to 15 V. (c) 2006 Elsevier Ltd. All rights reserved.

An analysis of subgrid-resolved scale interactions with use of results from direct numerical simulations

Subgrid nonlinear interaction and energy transfer are analyzed using direct numerical simulations of isotropic turbulence. Influences of cutoff wave number at different ranges of scale on the energetics and dynamics have been investigated. It is observed that subgrid-subgrid interaction dominates the turbulent dynamics when cut-off wave number locates in the energy-containing range while resolved-subgrid interaction dominates if it is in the dissipation range; By decomposing the subgrid energy transfer and nonlinear interaction into 'forward' and 'backward' groups according to the sign of triadic interaction, we find that individually each group has very large contribution, but the net of them is much smaller, implying that tremendous cancellation happens between these two groups.

InAs0.3Sb0.7 films grown on (100) GaSb substrates with a buffer layer by liquid-phase epitaxy

The growth of InAsxSb1-x films on (100) GaSb substrates by liquid-phase epitaxy (LPE) has been investigated and epitaxial InAs0.3Sb0.7 films with InAs0.9Sb0.09 buffer layers have been successfully obtained. The low X-ray rocking curve FHWM values of InAs0.3Sb0.7 layer shows the high quality of crystal-orientation structure. Hall measurements show that the highest electron mobility in the samples obtained is 2.9 x 10(4) cm(2) V-1 s(-1) and the carrier density is 2.78 x 10(16)cm(-3) at room temperature (RT). The In As0.3Sb0.7 films grown on (10 0) GaSb substrates exhibit excellent optical performance with a cut-off wavelength of 12 mu m. (c) 2007 Elsevier B.V. All rights reserved.

Elimination of loading reverberation in the split hopkinson torsional bar

The loading reverberation is a multiple wave effect on the specimen in the split Hopkinson torsional bar (SHTB). Its existence intensively destroys the microstructure pattern in the tested material and therefore, interferes with the study correlating the deformed microstructure to the macroscopic stress-strain response. This paper discusses the problem of the loading reverberation and its effects on the post-mortem observations in the SHTB experiment. The cause of the loading reverberation is illustrated by a stress wave analysis. The modification of the standard SHTB is introduced, which involves attaching two unloading bars at the two ends of the original main bar system and adopting a new loading head and a couple of specially designed clutches. The clutches are placed between the main bar system and the unloading bars in order to lead the secondary loading wave out of the main bar system and to cut off the connection in a timely manner. The loading head of the standard torsional bar was redesigned by using a tube-type loading device associated with a ratchet system to ensure the exclusion of the reflected wave. Thus, the secondary loading waves were wholly trapped in the two unloading bars. The wave recording results and the contrasting experiments for examining the post-mortem microstructure during shear banding both before and after the modification highly support the effectiveness of the modified version. The modified SHTB realizes a single wave pulse loading process and will become a useful tool for investigating the relation between the deformed microstructure and the macroscopic stress-strain response. It will play an important role especially in the study of the evolution of the microstructure during the shear banding process. (C) 1995 American Institute of Physics.

Detection of hepatitis B virus markers using a biosensor based on imaging ellipsometry

A biosensor based on imaging ellipsometry (BIE) has been developed and validated in 169 patients for detecting five markers of hepatitis B virus (HBV) infection. The methodology has been established to pave the way for clinical diagnosis, including ligand screening, determination of the sensitivity, set-up of cut-off values (CoVs) and comparison with other clinical methods. A matrix assay method was established for ligand screening. The CoVs of HBV markers were derived with the help of receiver operating characteristic curves. Enzyme-linked immunosorbent assay (ELISA) was the reference method. Ligands with high bioactivity were selected and sensitivities of 1 ng/mL and 1 IU/mL for hepatitis B surface antigen (HBsAg) and surface antibody (anti-HBs) were obtained respectively. The CoVs of HBsAg, anti-HBs, hepatitis B e antigen, hepatitis B e antibody and core antibody were as follows: 15%, 18%, 15%, 20% and 15%, respectively, which were the percentages over the values of corresponding ligand controls. BIE can simultaneously detect up to five markers within 1 h with results in acceptable agreement with ELISA, and thus shows a potential for diagnosing hepatitis B with high throughput.

Single attosecond pulse generation using two-color polarized time-gating technique

It is proposed that single attosecond pulses be generated via high-order harmonic generation by using a two-color pump pulse with time dependent ellipticity. The two-color pump pulse is created by the fundamental field and its second harmonic: the fundamental field is left-circularly polarized and the second harmonic is right-circularly polarized. Numerical simulations show that single attosecond pulses can be produced in the cut-off region by using the synthesis of 20 fs left-hand and right-hand circularly polarized pulses with a pulse delay of 20 fs. The attosecond pulses produced this way are much stronger than that produced by a few-cycle linear polarized pulse of comparable intensity. (c) 2005 Optical Society of America

A single-layer magnetic atom chip for trapping an array of Bose-Einstein condensate

We propose a simple single-layer magnetic microtrap configuration which can trap an array of magnetically-trapped Bose-Einstein condensate. The configuration consists of two series of parallel wires perpendicular to each other and all of the crossing points are cut off for maintaining the uniformity of the current. We analyse the trapping potential, the position of trapping centres and the uniformity of the array of the traps. The trapping depth and trapping frequency with different parameters are also calculated. Lastly, the effect of the cut-off crossing points, dissipate power, chip production are introduced concisely.

双包层光纤侧面耦合器

研究了一种侧面抽运双包层光纤的方法，从被剥除了外包层、端面为350μm×400μm的D型双包层光纤内包层上切下长度为3mm的一段柱体，并胶合在相同的双包层光纤内包层的侧面上，构成了柱体-光纤侧面耦合器。半导体激光器的抽运光从该柱体的一端入射并通过它耦合进入双包层光纤的内包层，实验测得耦合器最大耦合效率为85％。该方法适用于输出功率为数瓦的光纤激光器和放大器的侧面抽运。

Formation, thermal, optical and physical properties of GeS2-Ga2S3-AgCl novel chalcohalide glasses

Novel GeS2-Ga2S3-AgCl chalcohalide glasses had been prepared by melt-quenching technique, and the glass-forming region was determined by XRD, which indicated that the maximum of dissolvable AgCl was up to 65 mol%. Thermal and optical properties of the glasses were studied by differential scanning calorimetry (DSC) and Visible-IR transmission, which showed that most of GeS2-Ga2S3-AgCl glasses had strong glass-forming ability and broad region of transmission (about 0.45-12.5 mu m). With the addition of AgCl, the glass transition temperature, Tg decreases distinctly, and the short-wavelength cut-off edge (lambda(vis)) of the glasses also shifts to the long wavelength gradually. However, the glass-forming ability of the glass has a complicated evolutional trend depended on the compositional change. In addition, the values of the Vickers microhardness, H (v) , which decrease with the addition of AgCl, are high enough for the practical applications. These excellent properties of GeS2-Ga2S3-AgCl glasses make them potentially applied in the optoelectronic field, such as all-optical switch, etc.

Effect of bismuth oxide on the thermal stability and Judd-Ofelt parameters of Er 3(+)/Yb3(+) co-doped aluminophosphate glasses

The Er3+/Yb3+ co-doped glasses with compositions of xBi(2)O(3)-(65-x)P2O5-4Yb(2)O(3)-11Al(2)O(3)-5BaO-15Na(2)O (where x = 0, 2.5, 5, 7.5 and 10 mol%) were prepared using the normal melt quench technique. The optical absorption spectra of the glasses were recorded in the wavelength range 300-1700 nm. The effect of Bi2O3 content on the thermal stability and absorption spectra of glasses was investigated. In addition, the Judd-Ofelt parameters and oscillator strengths were calculated by employing Judd-Ofelt theory. It was observed that the positions of the fundamental absorption edge and cut-off wavelength shifted towards red as the content of Bi2O3 increased. However, there were no red shifts found both in the peak wavelength and in the center of mass wavelength of all absorption bands with Bi2O3 content increasing. The results of Judd-Ofelt theory analysis showed that Judd-Ofelt parameters Omega(t), (t = 2, 4, 6) changed sharply when Bi2O3 concentration exceeded 5 mol%. The variation trends of experimental oscillator strength were similar with those of Judd-Ofelt parameters as function of Bi2O3 concentrations. Moreover, differential scanning calorimetry experiments showed that the increases of Bi2O3 content weakened the network structure and then lowered the thermal stability of the glasses. The spontaneous emission probability A(rad), branching ratio beta and the radiative lifetime tau(rad) were also calculated and analyzed. The stimulated emission cross-section of Er3+ was calculated according to the McCumber theory. It was found that the stimulated emission cross-section of Er3+ was monotonically increases with Bi2O3 content increasing. (C) 2006 Elsevier B.V. All rights reserved.

TeO2-ZnCl2-BaO-NaF玻璃系统的结构及中红外透过特性的研究

制备了一种新型的氧卤碲酸盐玻璃：（80-x）TeO2—15ZnCl2-xBaO-5NaF（x=30、20、10、0mol％），对玻璃的机械强度、热稳定性、拉曼光谱、紫外吸收光谱、红外透过光谱等特性进行了研究．通过拉曼光谱分析研究了玻璃组分含量的变化对玻璃结构和红外透过性能的影响．结果表明，随着BaO含量的增加，玻璃在红外波段透过率显著增加，并且红外透过截止波长向长波方向移动，本文对这一实验结果进行了机理性的研究探讨．同时，通过在熔制过程中通入高纯O2，以及引入适量的卤化物有效地除去玻璃中的[OH]基团，使

Annealing effects on electron-beam evaporated Al2O3 films

The effects of post-deposited annealing on structure and optical properties of electron-beam evaporated Al2O3 single layers were investigated. The films were annealed in air for 1.5 h at different temperatures from 250 to 400 degrees C. The optical constants and cut-off wavelength were deduced. Microstructure of the samples was characterized by X-ray diffraction (XRD). Profile and surface roughness measurement instrument was used to determine the rms surface roughness. It was found that the cut-off wavelength shifted to short wavelength as the annealing temperature increased and the total optical loss decreased. The film structure remained amorphous even after annealing at 400 degrees C temperature and the samples annealed at higher temperature had the higher rms surface roughness. The decreasing total optical loss with annealing temperature was attributed to the reduction of absorption owing to oxidation of the film by annealing. Guidance to reduce the optical loss of excimer laser mirrors was given. (c) 2004 Elsevier B.V. All rights reserved.

沉积温度对LaF3薄膜性能的影响

abstract {LaF₃ single-layer coatings were prepared by thermal boat evaporation at the deposition temperatures of 189, 255, 277 and 321°C respectively. The crystal structures of the coatings were characterized by X-ray diffraction (XRD). A spectrophotometer was employed to measure its transmittance. Moreover, refractive index, extinction coefficient and cut-off wavelength were obtained from the measured transmittance spectral curve. The residual stress was evaluated by the Stoney's equation and optical interferometer. Laser induce damage threshold (LIDT) was performed by a tripled Nd:YAG laser system. The results show that the crystallization status becomes better with the deposition temperature increasing. Correspondingly, the grain size also gets larger. Meanwhile, the coatings become more compact and the refractive index increases. However, the absorption of coatings seriously rises and the cut-off wavelength drifts to the long wave. In addition, the residual stress also increases and the intrinsic stress plays a determinant role in the coating. The LIDT of the coating also enhances at high temperature.}