Three-dimensional finite element analysis of current density andtemperature distributions during radio-frequency ablation

This study analyzed the influence of electrode geometry, tissue-electrode angle, and blood flow on current density and temperature distribution, lesion size, and power requirements during radio-frequency ablation. The authors used validated three-dimensional finite element models to perform these analyses. They found that the use of an electrically insulating layer over the junction between electrode and catheter body reduced the chances of charring and coagulation. The use of a thermistor at the tip of the ablation electrodes did not affect the current density distribution. For longer electrodes, the lateral current density decreased more slowly with distance from the electrode surface. The authors analyzed the effects of three tissue-electrode angles: 0, 45, and 90°. More power was needed to reach a maximal tissue temperature of 95°C after 120 s when the electrode-tissue angle was 45°. Consequently, the lesions were larger and deeper for a tissue-electrode angle of 45° than for 0 and 90°. The lesion depth, volume, and required power increased with blood flow rate regardless of the tissue-electrode angle. The significant changes in power with the tissue-electrode angle suggest that it is safer and more efficient to ablate using temperature-controlled RF generators. The maximal temperature was reached at locations within the tissue, a fraction of a millimeter away from the electrode surface. These locations did not always coincide with the local current density maxima. The locations of these hottest spots and the difference between their temperature and the temperature read by a sensor placed at the electrode tip changed with blood flow rate and tissue-electrode angle     

Low-threshold tensile-strained InGaAs-InGaAsP quantum-well laserswith single-step separate-confinement heterostructures

The authors studied tensile-strained InGaAs-InGaAsP quantum-well lasers with single-step separate-confinement heterostructures (SCH). They obtained threshold currents below 2 mA at 20°C and below 10 mA at 100°C with indium mole fractions of 0.3 and 0.35 in the active layers. They found that the poorer carrier confinement of the longer wavelength SCH layer lowered the characteristic temperature at high temperatures. A laser with two In_0.35Ga_0.65As wells and a 1.1-μm composition InGaAsP SCH layer produced a 1.6-mA CW threshold current at 20°C and lasing at 120°C. Using this laser, very short lasing delays under zero-bias current over a wide temperature range and 2 Gb/s modulation under zero-bias current at 70°C were achieved     

Improved high-temperature characteristics in a thickness-tapered1.3-μm beam-expander integrated ridge-waveguide laser

High-temperature performance of a beam-expander (BEX) integrated laser was dramatically improved by reducing the current leakage in both longitudinal and lateral directions. Proton implantation into the BEX region and a reverse-mesa structure were combined to improve the high-temperature characteristics. A threshold current of 23.1 mA at 85°C and a very high-characteristic temperature T₀ (25°C-85°C) of 74 K were achieved. Stable operation for over 3000 h under a 10-mW output power at 70°C were confirmed     

Temperature rise for the human head for cellular telephones and forpeak SARs prescribed in safety guidelines

The bioheat equation is solved for an anatomically based model of the human head with a resolution of 3 × 3 × 3 mm to study the thermal implications of exposure to electromagnetic (EM) fields typical of cellular telephones both at 835 and 1900 MHz. It is shown that similar to the measured data, up to 4.5°C temperature elevation may be caused for locations of the pinna by a cellular telephone warmed by electronic circuitry to temperatures as high as 39°C with temperature increases for the internal tissues such as the brain and eye that are no more than 0.1°C-0.2°C higher than the basal values. Similar to previous studies by other authors, additional temperature increases due to EM fields of cellular telephones are fairly small and typically less than 0.1°C. Another objective was to study the thermal implications of the SAR limits for the occupational exposures of 8 W/kg for any 1 g, or 10 W/kg for any 10 g of tissue suggested in the commonly used safety guidelines. Such specific absorption rates (SARs) would lead to temperature elevations for the electromagnetically exposed parts of the brain up to 0.5°C with 10 W/kg for any 10 g of tissue resulting in somewhat higher temperatures and for larger volumes. Similar temperature increases are also calculated by increasing the arterial blood temperature, except that the temperature increases due to the SAR are for the more limited volume rather than the entire brain     

Temperature dependence of the threshold current for InGaAlP visiblelaser diodes

The temperature dependence of the threshold current for InGaAlP visible-light laser diodes was investigated from the standpoint of gain-current characteristics. The dependence of the light output power versus the current characteristic on the cavity length was evaluated for a 40-μm-wide InGaP-InGaAlP broad-stripe laser in the temperature range between -70 and 90°C. The threshold-current density dependence on the cavity length shows that a linear-gain approximation is suitable for this system. A minimum threshold-current density of 860 A/cm² was achieved at room temperature with a cavity length of 1160 μm. The internal quantum efficiency decreased in the temperature range higher than -10°C, which affected the excess threshold-current increase and the decrease in the characteristic temperature at this temperature range     

A comparative study of human skin thermal response to sapphirecontact and cryogen spray cooling

Surface cooling, in conjunction with various thermally mediated therapeutic procedures, can provide a means to protect superficial tissues from injury while achieving destruction of deeper targeted structures. We have investigated the thermal response of in-vivo human skin to: (1) contact cooling with a sapphire window (6-12°C); and (2) spray cooling with a freon substitute cryogen [tetrafluoroethane; boiling point ≈-26°C at 1 atmospheric pressure (atm)]. Measurements utilizing infrared radiometry show surface temperature reductions from 30°C to 14-19°C are obtained within approximately is in response to sapphire contact cooling. Surface temperature reductions to values between 5°C and -9°C are obtained in response to 20-100-ms cryogen spurts. Computational results, based on fitting the measured radiometric surface temperature to estimate heat transfer parameters, show: (1) temperature reductions remain localized to approximately 200 μm of superficial tissue; and (2) values of heat flux and total energy removed per unit skin surface area at least doubled when using cryogen spray cooling     

Wavelength dependence of characteristics of 1.2-1.55 μmInGaAsP/InP p-substrate buried crescent laser diodes

Laser diodes with the p-substrate buried-crescent structure have been fabricated for the 1.2-1.55-μm wavelength region. The dependence of laser characteristics on wavelength has been measured. Up to 70°C, the increasing rates of the threshold current with temperature are similar, while, above 70°C, a shorter-wavelength laser shows a larger increasing rate. At the same full width at half maximum of the far-field pattern perpendicular to the junction plane, the external differential quantum efficiency of the 1.55-μm laser diode is only 10% smaller than that of the 1.3-μm laser. The absorption loss coefficients in the active layer of the 1.2-, 1.3-, and 1.55-μm laser are estimated to be 26, 34, and 73 cm^-1, respectively     

Highly uniform operation of high-performance 1.3-μm AlGaInAs-InPmonolithic laser arrays

We describe the fabrication of monolithically integrated 1×12 arrays of 1.3-μm strain-compensated multiquantum-well AlGaInAs-InP ridge lasers. The laser array shows highly uniform characteristics in threshold current, slope efficiency, and lasing wavelength with a standard deviation of 0.08 and 0.27 mA, 0.012 and 0.007 W/A, and 0.59 and 0.57 nm, respectively, at 20°C and 100°C. Besides, each laser on the array exhibits a low threshold current of 8 mA at 20°C and 21 mA at 100°C, a characteristic temperature of 92 K, and a slope efficiency drop of 0.7 db between 20°C and 80°C. A low thermal crosstalk of less than -4 dB can be obtained from one diode as the injected current of other elements is increased to 70 mA. Also, each laser on the array has a negligible degradation after a 24-hr burn-in test at 80 mA and 100°C. An expected lifetime of more than 20 years is estimated for the lasers when operating at 10 mW and 85°C. The lasers have a small-signal modulation bandwidth of about 9 GHz at 25°C and a low relative intensity noise of -155 dB/Hz without an isolator at 2.5 GHz. It can transmit a 2.5-GHz signal to 50 km through standard single-mode fiber and to 308 m through multimode fiber, with a clear eye opening in OC-48 data-rate tests     

激光冲击强化金属材料时的热传导

根据金属材料表面激光冲击强化的特点，建立了激光冲击的一维温度场数学模型，推导出了计算金属表面达到汽化温度所需的时间、金属表面的汽化速度及汽化层厚度这三个实用的公式，它们对实际的激光冲击强化处理具有理论上的指导意义。     

Inferring snow wetness using C-band data from SIR-C's polarimetricsynthetic aperture radar

In hydrological investigations, modeling and forecasting of snow melt runoff require timely information about spatial variability of snow properties, among them the liquid water content-snow wetness-in the top layer of a snow pack. The authors' polarimetric model shows that scattering mechanisms control the relationship between snow wetness and the copolarization signals in data from a multi-parameter synthetic aperture radar. Along with snow wetness, the surface roughness and local incidence angle also affect the copolarization signals, making them either larger or smaller depending on the snow parameters, surface roughness, and incidence angle. The authors base their algorithm for retrieving snow wetness from SIR-C/X-SAR on a first-order scattering model that includes both surface and volume scattering. It is applicable for incidence angles from 25°-70° and for surface roughness with rms height ⩽7 mm and correlation length ⩽25 cm. Comparison with ground measurements showed that the absolute error in snow wetness inferred from the imagery was within 2.5% at 95% confidence interval. Typically the free liquid water content of snow ranges from 0% to 15% by volume. The authors conclude that a C-band polarimetric SAR can provide useful estimates of the wetness of the top layers of seasonal snow packs     

A silicon probe with integrated microheaters for thermal markingand monitoring of neural tissue

This paper describes a microheater structure and its integration on a silicon microprobe. The 30-μm-diameter microstructure can be used to heat local areas of tissue or to measure local tissue temperature with an accuracy of <0.3°C. The polysilicon microheater is suspended on a dielectric membrane to reduce undesired heat conduction to the probe substrate. The heating efficiency is 4.4°C/mW in still water and 2.2°C/mW in guinea pig cortex. Six milliwatts applied for 2 min in cortex produces a temperature of 50°C, creating a well-defined 50-μm-wide lesion for determining probe position histologically. Fabrication of the heaters requires no additional masking or processing steps in addition to those normally used for recording or stimulating probes     

Temperature dependence of the properties of DBR mirrors used insurface normal optoelectronic devices

The variation in the center wavelength of distributed Bragg reflectors used in optoelectronic devices, such as surface emitting lasers and Fabry-Perot modulators, is measured as the temperature of the mirrors changes over the range 25°C to 105°C. An analytic expression for the shift in center wavelength with temperature is presented. The mirrors measured are made of InP/InGaAsP (λ_gap=1.15 μm), GaAs/AlAs, and Si/SiN_x. The linear shifts in center wavelength are 0.110±0.003 nm/°C, 0.087±0.003 nm/°C, and 0.067±0.007 nm/°C for the InP/InGaAsP, GaAs/AlAs, and Si/SiN mirrors, respectively. Based on these data, the change in penetration depth with temperature is calculated     

Effects of rapid thermal annealing on InAsP/InP strainedmultiquantum well laser diodes grown by metal organic chemical vapourdeposition

The authors report on the effect of rapid thermal annealing (RTA) on the performance of InAsP/InP strained multiquantum well (SMQW) laser diodes (LDs) grown by metal organic chemical vapour deposition. From the photoluminescence (PL) measurements, the optimal RTA temperature for the InAsP/InP strained single quantum well (SSQW) stack was found to be 700°C. The 700°C annealed SSQW stack was found to have a stronger PL peak intensity, no halfwidth broadening and small peak shift, indicating that the degree of interdiffusion of group-V elements can be much reduced. The threshold current and slope efficiency of the 700°C RTA SMQW LDs can be reduced significantly as compared to those of as-grown LDs     

A generalized split-window algorithm for retrieving land-surfacetemperature from space

Proposes a generalized split-window method for retrieving land-surface temperature (LST) from AVHRR and MODIS data. Accurate radiative transfer simulations show that the coefficients in the split-window algorithm for LST must vary with the viewing angle, if the authors are to achieve a LST accuracy of about 1 K for the whole scan swath range (±55° from nadir) and for the ranges of surface temperature and atmospheric conditions over land, which are much wider than those over oceans. The authors obtain these coefficients from regression analysis of radiative transfer simulations, and they analyze sensitivity and error over wide ranges of surface temperature and emissivity and atmospheric water vapor abundance and temperature. Simulations show that when atmospheric water vapor increases and viewing angle is larger than 45°, it is necessary to optimize the split-window method by separating the ranges of the atmospheric water vapor, lower boundary temperature, and the surface temperature into tractable subranges. The atmospheric lower boundary temperature and (vertical) column water vapor values retrieved from HIRS/2 or MODIS atmospheric sounding channels can be used to determine the range for the optimum coefficients of the split-window method. This new algorithm not only retrieves land-surface temperature more accurately, but is also less sensitive to uncertainty in emissivity and to instrument quantization error     

All MOCVD grown 850-nm-wavelength refractive-index-guidedsemiconductor-buried vertical-cavity surface-emitting lasers withp/n-InGaP current blocking layers

All metal-organic chemical vapor deposition (MOCVD) grown 850-nm-wavelength refractive-index-guided semiconductor-buried vertical-cavity surface-emitting laser is proposed and their performance is investigated. P/n-InGaP current-blocking region enables both selective regrowth and the formation of refractive-index-guided region which surrounds multiquantum-well active/core regions. We have achieved room temperature CW operation of the new types of vertical-cavity surface-emitting lasers. The minimum threshold current was 9.5 mA with 18 μm square mesa size at 30°C. The device lased at up to 70°C, and the maximum output power exceeds 1 mW at above 30°C. The near field pattern indicates the single-lobed output beam at low bias current     

Continuous-wave operation of single-transverse-mode 1310-nm VCSELsup to 115°C

Long-wavelength vertical cavity surface emitting lasers (VCSELs) have thus far not provided substantial continuous-wave (CW) output power above 70°C. We describe recent advances using a vertically integrated 850 nm optical pump with a 1310-nm VCSEL. Using this approach, the devices described demonstrate record high temperature performance. We show single-transverse mode CW operation from -40 to +115°C, 0.5 mw optical power up to +85°C, and excellent device uniformity     

High average power first-order distributed feedback quantum cascadelasers

We present distributed feedback quantum cascade lasers at 965 cm ^-1 with a high average optical output power at temperatures of up to 60°C. At a duty cycle of 3%, the averaged maximal output power of a 55-μm wide and 1.5-mm-long device at -30°C was 13.6 mW; at 60°C, the device emitted 2 mkV. Corresponding peak optical powers of 450 mW at -30°C and of 70 mW at 60°C have been observed. Due to the lateral current injection, we achieved single-mode behavior in a slightly distorted zero-order lateral mode across the whole range of investigated temperatures and output powers. At room temperature, the threshold current density was on the order of 6.7 kA/cm ²; the characteristic temperature T₀ was, due to tuning of the Bragg resonance into the gain curve, rather high, namely 310 K     

不同脉冲激光功率下生物组织温度场数值仿真研究

激光以其优异的性能广泛应用于医学和军事领域。为有效防护激光过度损伤,需研究激光与生物组织的热作用机理。本文分析了激光与生物组织作用的热传递数学模型,讨论了组织的边界条件,建立了皮肤生物组织的三层有限元网格模型,给出了采用ANSYS软件进行组织温度场求解的流程,数值仿真研究了不同功率脉冲激光在皮肤组织内部产生的温度场特性,得出了组织内部不同径向长度、轴向深度在不同时刻下的温度场变化趋势。结果表明,激光功率几何倍增时,组织内部的最大温升呈几何倍增趋势;条件一定时,组织温升区域不随激光功率变化而变化。随着激光功率增加,生物组织表层温度变化的剧烈程度增大,而内部温度变化的剧烈程度较小,且随着轴向深度增加,组织内部温度逐渐呈线性趋势。     

1.3 μm InAsyP1-y-InPstrained-layer quantum-well laser diodes grown by metalorganic chemicalvapor deposition

The authors have fabricated 1.3-μm InAsP-InP separate-confinement-heterostructure (SCH) strained-layer double-quantum-well (SL-DQW) laser diodes (LDs) by metalorganic chemical vapor deposition (MOCVD). A low threshold current density of 410 A/cm ² was obtained. The CW threshold current was as low as 1.8 mA at 20°C, and maximum CW operating temperature of 120°C was obtained. These characteristics are almost the same as those of well-designed GaInAsP-InP SL-QW LDs. Further improvement of the characteristics of InAsP-InP LDs is expected by optimizing the device structure     

FBG-type sensor for simultaneous measurement of force (ordisplacement) and temperature based on bilateral cantilever beam

An improved FBG-type sensor for simultaneous measurement of force (or displacement) and temperature based on the bilateral cantilever beam (BCB) is proposed and demonstrated. The two parts of the beam are subject to opposite forces (or displacements) leading to a red shift for the part of the FBG subject to stretch and to a blue shift for the other one. An FBG bonded to the surface of the middle of the BCB is experimentally demonstrated to have a force sensitivity of ~1.046 nm/N, a sensitivity of the displacement-based strain of ~0.317 nm/mm, and a temperature sensitivity of ~0.190 nm/°C between 0°C and 70°C, respectively