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The laser relay mirror technique has been under extensive research in recent years. The concept and the working process of the relay mirror system are analyzed in this paper. The model of the relay mirror system is established, the effect on 1km-altitude target with 500 m/s flying speed of the relay mirror system and the conventional ground-based laser system are calculated respectively. Obtains that the maximum coverage range of the ground-based laser system is 2.0 km and the maximum coverage range of the relay mirror system is 23.2 km. The relay mirror can largely open up the coverage range of the laser system and strengthen the attacking ability of the ground-based laser.

Experiments were performed in an entrained flow reactor to better understand the characteristics of biomass gasification. Rice husk was used in this study. Effects of the gasification temperature (700, 800, 900 and 1000 degrees C) and the equivalence ratio in the range of 0.22-0.34 on the biomass gasification and the axial gas distribution in the reactor were studied. The results showed that reactions of CnHm were less important in the gasification process except cracking reactions which occurred at higher temperature. In the oxidization zone, reactions between char and oxygen had a more prevailing role. The optimal gasification temperature of the rice husk could be above 900 degrees C, and the optimal value of ER was 0.25. The gasification process was finished in 1.42 s when the gasification temperature was above 800 degrees C. A first order kinetic model was developed for describing rice husk air gasification characteristics and the relevant kinetic parameters were determined.

The free-vortex aerodynamic windows (abbr. FADW) can take the place of the conventional solid windows for high energy lasers to solve the problems caused by the intrinsic fractional absorption of the laser energy. Usually the procedure in designing FADW includes two central processes. The first is to design the asymmetric supersonic laval nozzle using the method of characteristics and the method of simple wave under the ideal conditions, and the second is to design the diffuser. The method of designing the diffuser of FADW is based on the experimental method mostly, but the diffuser's properties influences the performance ofthe overall FADW system deadly, so an experimental prototype of FADW whose structure and layout is adjustable has been designed and manufactured to optimize the design of the diffuser for FADW system. This paper reports the design methods of the FADW system and discusses the experimental results. The results show that this prototype of the FADW has good running properties, and FADW whose structure and layout is adjustable can be used to optimize the FADW design perfectly.

The concept of the free-vortex aerodynamic windows (FADW) is one of the best effective methods taking the place of the conventional beam output crystal windows of high power laser. An experimental model of the supersonic free-vortex aerodynamic window has been designed and made in our latest study. This paper studies the aero-optical phenomena of the FADWs supersonic jet to realize the laser optical quality degradation caused by the free- vortex jet, and to find out the relation of output laser beam quality through the FADW to the structure of the FADWs shearing interferometry. At last the structure of FADWs jet has been studied by means of shearography.

The thermal and mechanical effects of shells with inner pressure that are exposed to CW laser are investigated in this paper. In the first step, we try to apply an analytical procedure to obtain temperature response from energy conservation equation and temperature field from the heat conduction equation, then thermal damage threshold in vacuum is obtained. When it comes to mechanical effects, numerical method is applied to study laser heating thermal stresses and analytic solution is applied for stress distribution induced by inner pressure. At last, the whole picture of damage due to combined effect is given and damage threshold is evaluated.

The He is usually used as diluent in combustion cw hydrogen/deuterium fluoride (HF/DF) chemical lasers. Sometimes, the N2 is also used as diluent in cw HF/DF chemical laser, because N2 is more cheaper than the He. It was thought that the efficiency of cw HF/DF laser with N2 diluent was lower than that of HF/DF laser with He diluent since the molecular weight of N2 is heavier than that of He. In this paper, the performance of cw DF chemical lasers with He and N2 diluent was investigated. The small signal gain, power spectral distributions, cavity pressure, power and efficiency of DF lasers with these two diluents have been calculated using a finite-difference technique for the numerical integration of the steady and unsteady Navier-Stokes equation with reactive flow (compressibility scaling method-CSM), which was developed in the chemical gas dynamic laboratory of the state institute of applied chemistry in Russia. The numerical results show that the efficiency of DF lasers with N2 diluent is not lower than that of the lasers with He diluent.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Different geometry nozzles used in CW hydrogen fluoride chemical laser are investigated. Four geometry parameters, including throat width; area ratio; axis length and base width are considered. The flow properties, laser outcoupling power and small signal gain (SSG) of a Fabry-Perot resonator are calculated. The results show that when throat width and area ratio increase, the power and SSG peak will decrease in varying degree; they also varied when axis length changed; larger base width is related to lower cavity pressure, and smaller base width is related higher cavity pressure.

Coherent beam combining of two fibre amplifier chains with a total power of 260 W in a compact system using the stochastic parallel gradient descent (SPGD) algorithm is demonstrated. A 150 MHz linewidth fibre laser is built and introduced for high-power amplification to mitigate stimulated Brillouin scattering (SBS). Compact high-power amplifier chains are built with low power all-fibre system and high-power bulk free-optics fibre amplifiers. When the total power is about 260 W, active phase-locking of two high-power amplifiers is demonstrated using the SPGD algorithm. In closed-loop, the power in the main lobe increases 1.68 times, the visibility is increased from 0 to 0.62, and the phase residual error is less than λ/10.

We present a new method for efficiently transforming a high-order mode beam into a nearly Gaussian beam with much higher beam quality. The method is based on modulation of phases of different lobes by stochastic parallel gradient descent algorithm and coherent addition after phase flattening. We demonstrate the method by transforming an LP11 mode into a nearly Gaussian beam. The experimental results reveal that the power in the diffraction-limited bucket in the far field is increased by more than a factor of 1.5.

We present a new approach for simultaneous spectral and coherent combining in a master oscillator power amplifier (MOPA) configuration with active phasing. Spectrally combined single-frequency seed lasers are employed as a master oscillator for the all-fiber power amplifier chain, which provides robust performance suppressing of the stimulated Brillouin scattering effect, while coherent combining of spectrally combined amplifiers with active phase control provides stable in-phase combining, despite the strong phase fluctuation. In experiments, two spectrally combined seed MOPA chains are coherently combined with a total output power of 390 W. The power of the main lobe in the closed loop is two times of that value in the open loop, and visibility of more than 75% of the long-exposure interference pattern at the receiving plane is obtained.

Coherent beam combination of a 1.08 kW fiber amplifier array has been demonstrated for the first time, to our knowledge. In the experiment, nine fiber amplifiers are tiled into a 3×3 array, and the output power of each amplifier is approximately 120 W. A single frequency dithering algorithm is used to compensate the phase noises between the elements, which runs on a signal processor based on field programmable gate array for phase control on the fiber amplifiers. When the phase control system goes into closed loop, the fringe contrast of the far-field intensity pattern is improved to more than 85%, and the residual phase error is less than λ/15.

Coherent beam combining of high-order-mode fiber lasers is an attractive choice for high-power lasers as high-order-mode fiber lasers have a higher power handling capability than fundamental mode lasers. As active phasing provides a robust way for in-phase mode coherent beam combining, coherent beam combining of high-order-mode fibers with active phase control is proposed and a proof-of-concept experiment is performed. In the experiment, LP11 mode lasers are generated by off-center launching of single-mode fiber laser beams into few-mode fibers and active phasing is realized using a stochastic parallel gradient descent algorithm. The results show that the long-exposure fringe contrast is increased from zero to 40% when the system evolves from open-loop to closed-loop. A scalable architecture for coherent beam combining of high-order-mode amplifiers with active phase control in a master oscillator power amplifier configuration (MOPA) is also proposed.

Multi-wavelength and non-single-frequency seed lasers can be used to suppress stimulated Brillouin scattering and improve the ultimate output power of a fiber laser amplifier. Coherent combining of non-single-frequency and/or multi-wavelength lasers/amplifiers is a promising way to obtain much higher total output power than from coherent combining of single-frequency lasers/amplifiers. Using a stochastic parallel gradient descent algorithm, we demonstrate coherent combining of four-channel multi-wavelength lasers in a master oscillator power amplifier (MOPA) configuration. Four lasers with different wavelengths, namely two non-single-frequency and two single-frequency lasers, are used. The mean power of the main lobe in the closed-loop case is three times that for the open-loop case, approaching 75% of its ideal value. The coherent combining of multi-wavelength and non-single-frequency lasers in a MOPA configuration is validated, and a feasible approach for scaling to high power coherent combining is provided.

We establish the model of a two-Cassegrain-telescope system that is commonly used in a relay mirror system. With this model, uplink transmission of the relay mirror system is theoretically analyzed. We determined that uplink transmission with turbulence completely corrected is not an optimal mode. We improve power coupling efficiency of the two-Cassegrain-telescope system by optimizing the optical phase at the launching telescope by use of the stochastic parallel gradient descent algorithm. For a 10 km vertical uplink transmission, power coupling efficiencies of the system are 63.10%, 87.82%, and 97.80% corresponding to an open-loop mode, a closed-loop mode, and a closed-loop with optimization mode, respectively. For a 30 km vertical uplink transmission, power coupling efficiencies of the system are 22.35%, 82.66%, and 91.91%, corresponding to an open-loop mode, a closed-loop mode, and a closed-loop with optimization mode, respectively. The results show that power coupling efficiency of the two-Cassegrain-telescope system is significantly improved.

The single frequency dithering technique for coherent beam combination with one single modulation frequency and without a reference beam is presented for the first time to our knowledge. Coherent beam combination of four fiber amplifiers is successfully demonstrated by using the single-dithering technique. When the phase control system is in the closed loop, the fringe contrast of far-field intensity pattern is improved by more than 85% from 8% in open loop, and the residual phase error is less than lambda/20. Experimental results reveal that the single-dithering technique has great potential in scaling to a large number of beamlets with a simple phase control system and low cost.

Background Cerebral ischemia-reperfusion injury may simultaneously result in functional variation of multiple genes/pathways. However, most prior time-sequence studies on its pathomechanism only focused on a single gene or pathway. Our study aimed to systematically analyze the time-dependent variation in the expression of multiple pathways and networks within 24 h after cerebral ischemia-reperfusion injury. Results By uploading 374 ischemia-related genes into the MetaCore software, the variation in the expression of multiple pathways and networks in 3 h, 12 h, and 24 h after cerebral ischemia-reperfusion injury had been analyzed. The conserved TNFR1-signaling pathway, among the top 10 pathways, was consistently enriched in 3 h, 12 h, and 24 h groups. Three overlapping pathways were found between 3 h and 12 h groups; 2 between 12 h and 24 h groups; and 1 between 3 h and 24 h groups. Five, 4, and 6 non-overlapping pathways were observed in 3 h, 12 h, and 24 h groups, respectively. Apart from pathways reported by earlier studies, we identified a novel pathway related to the time-dependent development of cerebral ischemia pathogenesis. The process of apoptosis stimulation by external signals, among the top 10 processes, was consistently enriched in 3 h, 12 h, and 24 h groups; 2, 1, and 2 processes overlapped between 3 h and 12 h groups, 12 h and 24 h groups, and 3 h and 24 h groups, respectively. Four, 5, and 5 non-overlapping processes were found in 3 h, 12 h and 24 h groups, respectively. The presence of apoptotic processes was observed in all the 3 groups; while anti-apoptotic processes only existed in 3 h and 12 h groups. Additionally, according to node degree, network comparison identified 1, 8,and 5 important genes or proteins (e.g. Pyk2, PKC, E2F1, and VEGF-A) in 3 h, 12 h, and 24 h groups, respectively. The Jaccard similarity index revealed a higher level of similarity between 12 h and 24 h groups than that between 3 h and 12 h groups. Conclusion Time-dependent treatment can be utilized to reduce apoptosis, which may activate anti-apoptotic pathways within 12 h after cerebral ischemia-reperfusion injury. Pathway and network analyses may help identify novel pathways and genes implicated in disease pathogenesis. Electronic supplementary material The online version of this article (doi:10.1186/s12918-015-0152-4) contains supplementary material, which is available to authorized users.