Study of the laser-induced forward transfer of liquids for laser bioprinting

Laser-induced forward transfer (LIFT) is a direct-writing technique that allows printing patterns of diverse materials with a high degree of spatial resolution. In conventional LIFT a small fraction of a solid thin film is vaporized by means of a laser pulse focused on the film through its transparent holder, and the resulting material recondenses on the receptor substrate. It has been recently shown that LIFT can also be used to transfer materials from liquid films. This widened its field of application to biosensors manufacturing, where small amounts of biomolecules-containing solutions have to be deposited with high precision on the sensing elements. However, there is still little knowledge on the physical processes and parameters determining the characteristics of the transfers.In this work, different parameters and their effects upon the transferred material were studied. It was found that the deposited material corresponds to liquid droplets which volume depends linearly on the laser pulse energy, and that a minimum threshold energy has to be overcome for transfer to occur. The liquid film thickness was varied and droplets as small as 10 μm in diameter were obtained. Finally, the effects of the variation of the film to substrate distance were also studied and it was found that there exists a wide range of distances where the morphology of the transferred droplets is independent of this parameter, what provides LIFT with a high degree of flexibility.     

Two-dimensional materials for ultrafast lasers

As the fundamental optical properties and novel photophysics of graphene and related two-dimensional(2D) crystals are being extensively investigated and revealed, a range of potential applications in optical and optoelectronic devices have been proposed and demonstrated. Of the many possibilities, the use of 2D materials as broadband, cost-effective and versatile ultrafast optical switches(or saturable absorbers) for short-pulsed lasers constitutes a rapidly developing field with not only a good number of publications, but also a promising prospect for commercial exploitation. This review primarily focuses on the recent development of pulsed lasers based on several representative 2D materials. The comparative advantages of these materials are discussed, and challenges to practical exploitation, which represent good future directions of research, are laid out.     

飞秒激光器中超宽带色散补偿啁啾镜对的设计

根据设计目标和制备要求, 以双啁啾作为啁啾镜膜系初始结构设计方法, 详细分析了双啁啾调制系数以及双啁啾层数对啁啾镜反射特性和色散特性的影响, 确立了两者之间的最佳取值组合. 利用分析结果设计了单个啁啾镜, 并实现了啁啾镜的配对设计, 获得了600–1050 nm范围内反射率大于99.5%, 平均群延迟色散-40 fs², 振荡小于± 20 fs²的啁啾镜对, 满足了钛宝石飞秒激光系统的色散补偿要求. 关键词： 超快激光 色散补偿薄膜 双啁啾镜 啁啾镜对     

Control of gain and thermal carrier loss profiles for mode optimization in 980-nm broad-area vertical-cavity surface-emitting lasers

Optical gain and thermal carrier loss distributions regarding current diffusion and various electric contact areas are investigated to improve the near-field modes from the ring-shape to a Gaussian-like configuration for extra-broad-area and oxide-confined vertical-cavity surface-emitting lasers. In this work an equivalent circuit network model is used. The resistance of the continuously-graded distributed Bragg reflectors （DBRs）, the current diffusion and the temperature effect due to different electric-contact areas are calculated and analyzed at first, as these parameters affect one another and are the key factors in determining the gain and thermal carrier loss. Finally, the gain and thermal carrier loss distributions are calculated and discussed.     

Influence of statistical distribution properties on ultrafast random-number generation using chaotic semiconductor lasers

We study the influence of statistical distribution properties on ultrafast random-number generators (RNGs) using chaotic laser system consisting of a semiconductor laser subject to dual-chaotic optical injections. Two completely different distributions are considered in this paper: one is a long-tailed distribution, and the other is a well-fitted Gaussian distribution. The numerical results show that, using minimum post-processing, symmetric distribution allows for the extraction of 4 least significant bits (LSBs) per sample; while for the asymmetric distribution the produced sequence based on the last LSB still exhibits certain bias. In other words, the important role of symmetric distribution in fast generation of random bits using multi-bit extraction scheme is demonstrated in numerical simulations.     

Attosecond spectroscopy for filming the ultrafast movies of atoms,molecules and solids

Three decades ago, a highly nonlinear nonpertubative phenomenon, now well-known as the high harmonic generation (HHG), was discovered when intense laser irradiates gaseous atoms. As the HHG produces broadband coherent radiation, it becomes the most promising source to obtain attosecond pulses. The door to the attosecond science was opened ever since. In this review, we will revisit the incredible adventure to the attoworld. Firstly, the progress of attosecond pulse generation is outlined. Then, we introduce the efforts on imaging the structures or filming the ultrafast dynamics of nuclei and electrons with unprecedented attosecond temporal and Angstrom spatial resolutions, utilizing the obtained attosecond pulses as well as the high harmonic spectrum itself.     

810-nm InGaA1As/A1GaAs double quantum well semiconductor lasers with asymmetric waveguide structures

The 810-nm InGaA1As/A1GaAs double quantum well (QW) semiconductor lasers with asymmetric waveguide structures, grown by molecular beam epitaxy, show high quantum efficiency and high-power conversion efficiency at continuous-wave (CW) power output. The threshold current density and slope efficiency of the device are 180 A/cm2 and 1.3 W/A, respectively. The internal loss and the internal quantum efficiency are 1.7 cm-1 and 93%, respectively. The 70% maximum power conversion efficiency is achieved with narrow far-field patterns.     

高功率固体激光驱动器的优化设计

扼要介绍了高功率固体激光系统物理设计中的一些基本概念 ,并阐述了系统优化设计的主要方法。针对神光 原型装置的物理设计 ,提出了其能流分布设计优化的判据和设计的限制条件 ,给出了原型装置主放大级的初步优化设计结果。     

Parameters optimization of laser brazing in crimping butt using Taguchi and BPNN-GA

The laser brazing (LB) is widely used in the automotive industry due to the advantages of high speed, small heat affected zone, high quality of welding seam, and low heat input. Welding parameters play a significant role in determining the bead geometry and hence quality of the weld joint. This paper addresses the optimization of the seam shape in LB process with welding crimping butt of 0.8 mm thickness using back propagation neural network (BPNN) and genetic algorithm (GA). A 3-factor, 5-level welding experiment is conducted by Taguchi L₂₅ orthogonal array through the statistical design method. Then, the input parameters are considered here including welding speed, wire speed rate, and gap with 5 levels. The output results are efficient connection length of left side and right side, top width (WT) and bottom width (WB) of the weld bead. The experiment results are embed into the BPNN network to establish relationship between the input and output variables. The predicted results of the BPNN are fed to GA algorithm that optimizes the process parameters subjected to the objectives. Then, the effects of welding speed (WS), wire feed rate (WF), and gap (GAP) on the sum values of bead geometry is discussed. Eventually, the confirmation experiments are carried out to demonstrate the optimal values were effective and reliable. On the whole, the proposed hybrid method, BPNN-GA, can be used to guide the actual work and improve the efficiency and stability of LB process.     

Parametric optimization of a narrow-band 13.5-nm emission from a Li-based liquid-jet target using dual nano-second laser pulses

We demonstrate the applicability of a Li-based liquid jet as a regenerative source of narrow-band extreme-ultraviolet (EUV) emission at 13.5 nm. It was found that a conventionally used single laser pulse did not produce optimum plasma conditions for a low-Z target, like Li. It was shown that deployment of dual nano-second laser pulses enhanced the in-band EUV conversion efficiency (CE) at 13.5 nm in 2 sr by three times its value using a single laser pulse. Dependence of the emission spectra and EUV CE on the delay time between dual laser pulses revealed that the emission at 13.5 nm from Li ions was preferably enhanced at a lower plasma temperature compared to that at 13.0 nm from oxygen ions.     

Optical gain and threshold properties of strained InGaAlAs/AlGaAs quantum wells for 850-nm vertical-cavity surface-emitting lasers

The valence subband structures, optical gain spectra, transparency carrier densities, and transparency radiative current densities of different compressively strained InGaAlAs quantum wells with Al_0.3Ga_0.7As barriers are systematically investigated using a 6 × 6 k · p Hamiltonian including the heavy hole, light hole, and spin-orbit splitting bands. The results of numerical calculations show that the maximum optical gain, transparency carrier densities, transparency radiative current densities, and differential gain of InGaAlAs quantum wells can be enhanced by introducing more compressive strain in quantum wells. However, further improvement of the optical properties of InGaAlAs quantum wells becomes minimal when the compressive strain is higher than approximately 1.5%. The simulation results suggest that the compressively strained InGaAlAs quantum wells are of advantages for application in high-speed 850-nm vertical-cavity surface-emitting lasers.     

Micro via and line patterning for PCB using imprint technique

Today’s electronic devices such as mobile phones, PDA, computers, etc. have more functions in a smaller size. Thus conducting lines and via holes of PCB (printed circuit board) which has a role of land for all kinds of electronic components are getting finer. In this study, the conducting lines and via holes are produced using thermal imprint technique rather than the conventional photo-lithography process. Imprint technique is a press process that transfers patterns of stamp to resins. Imprint technique is used to produce micro size trench lines and via holes in epoxy resins.Resins used in this work are silica (SiO₂) reinforced epoxy. Resins were imprinted using 10 * 10 mm size Ni or polymer stamp. Line/space of pattern is 10/10 μm while diameter of via hole is 30 μm. The depths of lines and via holes are 15 and 30 μm, respectively. The anti-sticking treated stamp and epoxy resins were pressed at 100 °C for 30 min in vacuum. The stamp was released after resins were cured for 1 h at 130 °C. All patterns of stamp were successfully transferred with high fidelity and any noticeable defect was not observed within imprinted area. Imprinted resins were de-smeared to remove the residue at the bottom of via holes and to enhance the adhesion of resins with Cu. Electro/less copper plating was followed to fill in the imprinted patterns. Since the excess Cu layer was formed on the resins during Cu plating, the planarization process was introduced to obtain isolated lines and via holes.     

On the equilibrium equation for a generalized biological membrane energy by using a shape optimization approach

A mechanical equilibrium equation of a vesicle membrane under a generalized elastic bending energy is obtained in this paper. Moreover, the derivation of this equilibrium equation is based on some shape optimization tools. This approach is new and more concise than the tensorial tools used previously for this problem.     

Improved thermal property of strained InGaAlAs/AlGaAs quantum wells for 808-nm vertical cavity surface emitting lasers

The 808-nm vertical cavity surface emitting laser (VCSEL) with strained In_0.13Ga_0.75Al_0.12As/Al_0.3Ga_0.7As quantum wells is designed and fabricated. Compared with the VCSELs with Al_0.05Ga_0.95As/Al_0.3Ga_0.7As quantum wells, the VCSEL with strained In_0.13Ga_0.75Al_0.12As/Al_0.3Ga_0.7As quantum wells is demonstrated to possess higher power conversion efficiency (PCE) and better temperature stability. The maximum PCE of 43.8% for 10-μm VCSEL is achieved at an ambient temperature of 30 ℃. The size-dependent thermal characteristics are also analyzed by characterizing the spectral power and output power. It demonstrates that small oxide-aperture VCSELs are advantageous for temperature-stable performance.     

Eikonal approximation for single-electron capture from hydrogen molecules by proton impact

A four-body eikonal approximation is developed to study the single-electron capture process in collision of the fast protons with the hydrogen molecular targets. For a fixed orientation of the molecular axis, the double-differential cross sections are evaluated for electron capture. Interference patterns originated from the two atomic centres are obtained for different orientations of the molecular target. Equal-weighted average of the differential capture cross sections over all the possible orientations of the molecular target is calculated for various impact energies. Angular distributions of the differential cross sections for single charge transfer at various impact energies as a function of the angle between the axis of the molecule and the incident beam direction are calculated and compared with their corresponding experimental values as well as the results obtained from other theories. Integrated cross sections are calculated and compared with available experimental data and other theoretical calculations.     

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介绍了EAST超导托卡马克偏滤器的最新冷却模块结构。利用FLUENT有限元软件对不同参数下的模型进行了稳态热分析,定量研究了冷却模块换热能力随各参数的变化规律。针对EAST装置给出了初步优化的参数范围,为水冷钨铜偏滤器的设计制造提供了参考。这对于托卡马克装置及聚变堆偏滤器研究具有十分重要的意义。     

Parameters optimization of high efficiency discrete Raman fiber amplifier by using the coupled steady-state equations

By using the coupled steady-state equations, we have numerically studied the characteristics optimization of Raman fiber amplifier (RFA) in a signal/pump double-passes-the-gain-medium scheme. The simulation results are in very good agreement with those of experimental data. Given a constant pumping power, the length of dispersion compensation fiber (DCF) in a RFA could be determined. The optimum design shows that the best length of the DCF is at around 3.8 ± 0.2 km in our study. This could provide both the highest signal output power and the lowest noise figure among all conditions we choose.     

Optical velocimeters for moving surfaces using gas and semiconductor lasers

A differential arrangement using a laser for the measurement of the velocity of moving surfaces is discussed. Configurations of optical velocimeters with diffraction beam-splitters are shown not to be critical on the wavelength stability of a semiconductor laser. Laser meters measuring the velocity and length of rolled stock have been built on the basis of the devices considered.     

Application of femtosecond‐pulsed lasers for direct optical manipulation of biological functions

Absorption of photon energy by cells or tissue can evoke photothermal, photomechanical, and photochemical effects, depending on the density of the deposited energy. Photochemical effects require a low energy density and can be used for reversible modulation of biological functions. Ultrashort‐pulsed lasers have a high intensity due to the short pulse duration, despite its low average energy. Through nonlinear absorption, these lasers can deliver very high peak energy into the submicrometer focus area without causing collateral damage. Absorbed energy delivered by ultrashort‐pulsed laser irradiation induces free electrons, which can be readily converted to reactive oxygen species (ROS) and related free radicals in the localized region. Free radicals are best known to induce irreversible biological effects via oxidative modification; however, they have also been proposed to modulate biological functions by releasing calcium ions from intracellular organelles. Calcium can evoke variable biological effects in both excitable and nonexcitable cell types. Controlled stimulation by ultrashort laser pulses generate intracellular calcium waves that can modulate many biological functions, such as cardiomyocyte beat rate, muscle contractility, and blood–brain barrier (BBB) permeability. This article presents optical methods that are useful therapeutic and research tools in the biomedical field and discuss the possible mechanisms responsible for biological modulation by ultrashort‐pulsed lasers, especially femtosecond‐pulsed lasers.