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Partially coherent beam generation with metasurfaces

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Photonics Research 2023年第9期11卷 1535-1541页

作者： ROMAN CALPE ATRI HALDER MEILAN LUO MATIAS KOIVUROVA jari turunen Center for Photonics Sciences University of Eastern FinlandFI-80101 JoensuuFinland Department of Physics and Synergetic Innovation Center for Quantum Effects and Applications Hunan Normal UniversityChangsha 410081China Tampere Institute for Advanced Study Tampere University33100 TampereFinland Faculty of Engineering and Natural Sciences Tampere UniversityFI-33720 TampereFinland

An optical system for the generation of partially coherent beams with genuine cross-spectral density functions from spatially modulated globally incoherent sources is *** spatial intensity modulation of the incoherent source is achieved by quasi-planar metasurfaces based on spatial-frequency modulation of binary Bragg surface-relief diffraction *** types of beams are demonstrated experimentally:(i)azimuthally periodic,radially quasi-periodic beams and(ii)rotationally symmetric Bessel-correlated beams with annular far-zone radiation patterns.

关键词： coherent periodic quasi

Coherence of bulk-generated supercontinuum

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Photonics Research 2019年第11期7卷 1345-1353页

作者： Atri Halder Vytautas Jukna Matias Koivurova Audrius Dubietis jari turunen Department of Physics and Mathematics University of Eastern FinlandFl-80101 JoensuuFinland Laser Research Center Vilnius UniversityLT-10223 VilniusLithuania Photonics Laboratory Physics UnitTampere UniversityFl-33101 TampereFinland

We have developed a numerical framework that allows estimation of coherence in spatiotemporal and spatiospectral domains. Correlation properties of supercontinuum(SC) pulses generated in a bulk medium are investigated by means of second-order coherence theory of non-stationary fields. The analysis is based on simulations of individual space–time and space–frequency realizations of pulses emerging from a 5 mm thick sapphire plate,in the regimes of normal, zero, and anomalous group velocity dispersion. The temporal and spectral coherence properties are analyzed in the near field(as a function of spatial position at the exit plane of the nonlinear medium) and as a function of propagation direction(spatial frequency) in the far field. Unlike in fiber-generated SC, the bulk case features spectacularly high degrees of temporal and spectral coherence in both the spatial and spatial-frequency domains, with increasing degrees of coherence at higher pump energies. When operating near the SC generation threshold, the overall degrees of temporal and spectral coherence exhibit an axial dip in the spatial domain, whereas in the far field, the degree of coherence is highest around the optical axis.

关键词： pump sapphire fiber

Spectral measurement of coherence Stokes parameters of random broadband light beams

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Photonics Research 2019年第6期7卷 669-677页

作者： HENRI PARTANEN ARI T.FRIBERG TERO SET?L? jari turunen Institute of Photonics University of Eastern Finland

We introduce a spectrally resolved Young’s interferometer based on a digital micromirror device, a grating spectrometer, and a set of polarization-modulation elements to measure the spectral coherence(two-point) Stokes parameters of random light beams. An experimental demonstration is provided with a spatially partially coherent superluminescent diode amounting to a complex structure of spatio-spectral coherence induced by a quartzwedge depolarizer. We also show that the polarization and spatial coherence of light can vary with wavelength on a subnanometer scale. The technique is simple and robust and applies to light beams with any spectral bandwidth.

关键词： Spectral measurement light beams

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多光束分光光栅的优化设计(英文)

光学学报 1988年第10期8卷 946-953页

作者： jari turunen,卞新高,金国藩清华大学精密仪器系清华大学精密仪器系清华大学精密仪器系

本文描述了一种设计计算二元光栅结构参数的数值方法,这种方法可以把光栅衍射谱的分布误差控制在1%以内.作为实验验证,本文给出了一个二元光栅谱分布的测试结果,该光栅将入射平面波转换成在中央11×11级次内均匀分布的衍射波.

关键词：多光束光栅分光优化设计

Optimization of the Mean Radius Flow Path of a Multi-Stage Steam Turbine with Evolution Algorithms

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Journal of Thermal Science 2011年第4期20卷 318-323页

作者： Jukka Huttunen Jaakko Larjola Teemu turunen-Saaresti jari Backman Savonia Power ljytie 678710 VarkausFinlandjukka Lappeenranta University of Technology P.O.Box 2053851 LappeenrantaFinland

A prototype model of the mean radius flow path of a four-stage,high speed 1 MWe axial steam turbine was optimized by using evolution algorithms,DE(differential evolution) algorithm in this *** the cost-benefits of the optimization were *** optimization was successfully performed but the accuracy of the optimization was slightly less than hoped when compared to the control modeling executed with the CFD(computational fluid dynamics).The mentioned inaccuracy could have been hardly avoided because of problems with an initial presumption involving semi-empiric calculations and of the uncertainty concerning the absolute areas of qualification of the *** kind of algebraic modeling was essential for the success of the optimization because ***-calculation could not have been done on each step of the *** the optimization some problems occurred with the adequacy of the computer capacity and with finding a suitable solution that would keep the algorithms within mathematically allowable boundaries but would not restrict the progress of the optimization too *** rest of the problems were due to the novelty of the application and problems with preciseness when handling the areas of qualification of the *** the accuracy of the optimization results was not exactly in accordance with the objective,they did have a favorable effect on the designing of the *** optimization executed with the help of the DE-algorithm got at least about 3.5 % more power out of the turbine which means about 150 000 € cost-benefit per turbine in the form of additional electricity capacity.

关键词：演化算法平均半径汽轮机优化通流部分差分进化算法计算流体力学多级

Numerical Modelling of a Supersonic Axial Turbine Stator

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Journal of Thermal Science 2010年第3期19卷 211-217页

作者： Aki Grnman Teemu turunen-Saaresti Ahti Jaatinen jari Backman LUT Energy Lappeenranta University of TechnologyP.O.Box 20FI-53851 LappeenrantaFinland

In order to improve the turbocharging process,a supersonic axial turbine stator was modelled numerically with a pulsatile inlet mass *** main objectives of the study were to find out how pulsation affects the flow field and the performance of the *** the beginning of the study,a supersonic turbine stator was modelled using three different techniques:quasi-steady,time-accurate with constant boundary conditions and time-accurate with a pulsatile inlet mass *** time-averaged and quasi-steady flow fields and performance were compared,and the flow field and stator performance with a pulsatile inlet mass flow was studied in detail at different time-steps.A hysteresis-like behaviour was captured when the total-to-static pressure ratio and efficiency were plotted as a function of the inlet mass flow over one pulse *** total-to-static pressure ratio and efficiency followed the sinusoidal shape of the inlet flow as a function of *** was also concluded that the stator efficiency decreases downstream from the stator trailing edge and the amplitude of the pulsating mass flow is decreased at the stator throat.

关键词：轴流式水轮机数值模拟超音速定子时间平均稳态流场正弦函数流量脉动

Effect of high negative incidence on the performance of a centrifugal compressor stage with conventional vaned diffusers

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Journal of Thermal Science 2011年第2期20卷 97-105页

作者： Ahti Jaatinen Aki Grnman Teemu turunen-Saaresti jari Backman Lappeenranta University of Technology

Three vaned diffusers, designed to have high negative incidence (-8°) at the design operating point, are studied experimentally. The overall performance (efficiency and pressure ratio) are measured at three rotational speeds, and flow angles before and after the diffuser are measured at the design rotational speed and with three mass flow rates. The results are compared to corresponding results of the original vaneless diffuser design. Attention is paid to the performance at lower mass flows than the design mass flow. The results show that it is possible to improve the performance at mass flows lower than the design mass flow with a vaned diffuser designed with high negative incidence. However, with the vaned diffusers, the compressor still stalls at higher mass flow rates than with the vaneless one. The flow angle distributions after the diffuser are more uniform with the vaned diffusers.

关键词：离心压缩机扩散器级性能发病率设计工作叶片扩压器旋转速度质量流量