共查询到19条相似文献,搜索用时 375 毫秒
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磷光增感屏的内禀性质对磷光增感屏的成像性能影响很大.基于米氏(Mie)散射理论,计算得到磷光增感屏在不同颗粒尺寸和不同颗粒堆积密度情况下的散射系数和吸收系数.然后利用Monte Carlo(MC)方法模拟了可见光光子在磷光增感屏Gd2O2S:Tb(GOS)内的散射和吸收事件,得到磷光增感屏内不同位置处的可见光收集效率.利用MCNP程序模拟X射线束在磷光增感屏内的能量沉积分布,得到了金属-磷光增感屏总的点扩展函数(PSF).结果表明,在兆伏X射线成像系统中,使用小颗粒尺寸和高堆积密度的GOS磷光屏,可以改善增感屏系统的空间分辨率. 相似文献
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双模腔场中具有不同耦合常数的两原子多光子辐射谱 总被引:1,自引:0,他引:1
研究了与双模腔场具有不同耦合常数的两个二能级原子的多光子辐射谱,给出了双模多光子辐射谱的一般表达式.结果表明,当双模腔场分别处于不同数态时,虽然两原子与双模腔场之间具有不同的耦合常数,但对于任意的N1和N2(Ni(i=1,2,)为模i腔场被每个原子吸收或发射的光子数),辐射谱总是关于共振频率ω0对称分布;并且,当N1=N2时,对于任意的数态光子数n1和n2交换,辐射谱不变.上述特点用解析方法给予了解释.计算了非简并双光子情况下的辐射谱,并得到了一些新结果.双模腔场中单原子及具有相同耦合常数的两原子辐射谱可从本文结果分别做为特例而得到. 相似文献
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两原子非简并双光子Jaynes-Cummings模型的辐射谱 总被引:2,自引:2,他引:0
本文研究了两原子非简并双光子Jaynes-Cummings模型的辐射谱,结果表明,当双模腔场处于不同数态时,辐射谱呈现如下新特性:当一腔场处于真空态,另一腔场为强场时,辐射谱为对称六峰结构,任两对称峰的间距均与√2n2g成正比;当双模腔场均为强场时,辐射谱为对称四峰结构,两内峰的间距(4g)与数态光子数n1及n2无关;当一腔场处于真空态,另一腔场处于数态|n2>时,辐射谱一般为对称六峰结构,当n2=1时,谱变为对称四峰结构。 相似文献
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HD+离子在两个超短脉冲激光场作用下的解离几率分布 总被引:2,自引:2,他引:0
本文报告HD+离子在波长λ=306.7nm的三倍频超短脉冲弱光场E3和不同延时的二倍频超短脉冲强光场E2作用下解离几率分布的定量计算结果。E3和E2的脉冲宽度均为10fs.E3先行,E2延时取0、4、8、12、16、20、24、28fs.计算结果用三维图表出。图中看到,沿相对动量坐标有三个峰,分别位于动量2.1×10-18、4.4×10-18、5.8×10-18g·cm/s处,依次称为1号峰、2号峰、3号峰,位置各是λ=306.7nm的单光子能量、双光子能量、三光子能量消耗于解离能之后离子碎片具有相对动量。据分析,1号峰来源于E2场引起的受激发射作用。 相似文献
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光子晶体缺陷模的带宽与品质因子研究 总被引:22,自引:11,他引:11
利用光学传输矩阵法研究了结构参量对缺陷态光子晶体的缺陷模带宽和品质因子的影响.研究发现,当缺陷介质层厚度h0的值较小时,缺陷模的带宽很小且基本保持不变;当h0较大时,缺陷模的带宽随h0的增加而快速增加.另外发现,缺陷模的品质因子在某个h0处取最大值.但是总体上看,h0较小时的品质因子要远大于h0较大时的品质因子.此外,缺陷模的品质因子随光子晶体的周期数增加而急剧增加约4.788倍,而带宽则随周期数的增加而急剧减少约4.788倍.当周期数为13时就可以获得109以上的品质因子值和小于10-9的相对带宽值. 相似文献
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在一维铁磁性织构介观环的基础上, 计及电子-双声子相互作用, 介入了三项非经典效应抑制电子-单声子相互作用引起的量子涨落效应: 1) 跳步电子-单声子相干态关联效应;2) 由压缩相干态引起的声子压缩态-单声子相干态间过程关联效应;3) 声子位移-声子压缩态的表象关联效应.从结果来看, 电子-双声子相互作用明显加强了压缩效应(增大压缩参量), 而跳步电子-单声子相干态关联效应引起本征能量大幅度下降, 持续电流大幅度增加.特别是介入了声子压缩态-单声子相干态间过程关联效应后, 声子压缩参量远大于理想压缩态相应的压缩参量, 有效地抑制了Debye-Waller(D-W)效应.当声子压缩态-单声子相干态间过程关联与声子位移重整化效应结合在一起时, 声子场的压缩将更大幅度地增加, D-W效应(参量wph)将更大幅度地减小, wph << wph(0), 从而极大幅度地抑制了电子-单声子相互作用导致的量子涨落效应. 这样一来, 非经典态本征能量En极大幅度地下降, En << En(0), 与此同时, 本征持续电流振幅In 则极大幅度地增大, In >> In(0). 相似文献
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D. Cavouras I. Kandarakis D. Nikolopoulos I. Kalatzis G. Kagadis N. Kalivas A. Episkopakis D. Linardatos M. Roussou E. Nirgianaki D. Margetis I. Valais I. Sianoudis K. Kourkoutas N. Dimitropoulos A. Louizi C. Nomicos G. Panayiotakis 《Applied physics. B, Lasers and optics》2005,80(7):923-933
In this study Y3Al5O12: Ce powder scintillator was evaluated for use in X-ray imaging detectors. This phosphor, also known as YAG: Ce scintillator or P-46 phosphor, is a non-hygroscopic, emitting green light with very short decay time. These properties are very attractive for X-ray imaging. Y3Al5O12: Ce powder was used to prepare various test screens (33–166 mg/cm2). Absolute luminescence efficiency measurements were performed for various X-ray tube voltages (50–130 kVp). In addition parameters related to image quality such as the modulation transfer function and the detective quantum efficiency were examined. A theoretical model, describing radiation and light transfer, was employed to fit experimental data and to estimate values of optical parameters. Absolute efficiency was found to decrease with X-ray tube voltage. Highest efficiency was obtained for the 107 mg/cm2 screen. Light attenuation coefficients were close to those of green emitting rare earth scintillators. At low spatial frequencies the detective quantum efficiency was high for the 107–166 mg/cm2 screens. The light emission efficiency and imaging performance of Y3Al5O12: Ce was not better than currently employed scintillators. However due to its very fast response and high spectral compatibility to optical sensors it may be considered for use in digital imaging detectors. 相似文献
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C. Michail A. Toutountzis S. David N. Kalyvas I. Valais I. Kandarakis G. S. Panayiotakis 《Applied physics. B, Lasers and optics》2009,95(1):131-139
The aim of the present study was to measure the imaging transfer characteristics and the luminescence efficiency (XLE) of
a Lu2SiO5:Ce (LSO:Ce) powder scintillator for use in X-ray mammography detectors. An LSO:Ce powder scintillating screen, with a coating
thickness of 25 mg/cm2, was prepared in our laboratory. The imaging performance of the screen was assessed by experimental determination of the
modulation transfer function (MTF) and the detective quantum efficiency (DQE) as well as single index image quality parameters
such as noise equivalent pass band (Ne) and informational efficiency (n
I). A theoretical model, describing radiation and light transfer, was fitted to experimental MTF values in order to estimate
optical properties of the scintillator. Screen irradiation was performed under exposure conditions employed in mammographic
applications (27 kVp, 63 mAs). MTF was determined by the square wave response function (SWRF) method. Results showed that
LSO:Ce exhibits high MTF and DQE values, which are comparable to those of the commercially used Gd2O2S:Tb. Considering our image quality parameters and luminescence efficiency results as well as the fast response of the LSO:Ce
scintillator screen (40 ns), this material can be considered for use in X-ray mammographic detectors. 相似文献
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N. Kalyvas I. Valais S. David Ch. Michail G. Fountos P. Liaparinos I. Kandarakis 《Optics and Spectroscopy》2014,116(5):743-747
Single crystal scintilators are used in various radiation detectors applications. The efficiency of the crystal can be determined by the Detector Optical Gain (DOG) defined as the ratio of the emitted optical photon flux over the incident radiation photons flux. A parameter affecting DOG is the intrinsic conversion efficiency (n C ) giving the percentage of the X-ray photon power converted to optical photon power. n C is considered a constant value for X-ray energies in the order of keV although a non-proportional behavior has been reported. In this work an analytical model, has been utilized to single crystals scintillators GSO:Ce, LSO:Ce and LYSO:Ce to examine whether the intrinsic conversion efficiency shows non proportional behavior under X-ray excitation. DOG was theoretically calculated as a function of the incident X-ray spectrum, the X-ray absorption efficiency, the energy of the produced optical photons and the light transmission efficiency. The theoretical DOG values were compared with experimental data obtained by irradiating the crystals with X-rays at tube voltages from 50 to 140 kV and by measuring the light energy flux emitted from the irradiated screen. An initial value for n C (calculated from literature data) was assumed for the X-ray tube voltage of 50 kV. For higher X-ray tube voltages the optical photon propagation phenomena was assumed constant and any deviations between experimental and theoretical data were associated with changes in the intrinsic conversion efficiency. The experimental errors were below 7% for each experimental setup. The behavior of n C values for LSO:Ce and LYSO:Ce were found very similar, i.e., ranging with values from 0.089 at 50 kV to 0.015 at 140 kV, while for GSO:Ce, n C demonstrated a peak at 80 kV. 相似文献
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《Physics letters. A》2020,384(25):126601
We investigate the quantum thermodynamical properties of localised relativistic quantum fields, and how they can be used as quantum thermal machines. We study the efficiency and power of energy transfer between the classical gravitational degrees of freedom, such as the energy input due to the motion of boundaries or an impinging gravitational wave, and the excitations of a confined quantum field. We find that the efficiency of energy transfer depends dramatically on the input initial state of the system. Furthermore, we investigate the ability of the system to extract energy from a gravitational wave and store it in a battery. This process is inefficient in optical cavities but is significantly enhanced when employing trapped Bose Einstein condensates. We also employ standard fluctuation results to obtain the work probability distribution, which allows us to understand how the efficiency is related to the dissipation of work. Finally, we apply our techniques to a setup where an impinging gravitational wave excites the phononic modes of a Bose Einstein condensate. We find that, in this case, the percentage of energy transferred to the phonons approaches unity after a suitable amount of time. These results give a quantitative insight into the thermodynamic behaviour of relativistic quantum fields confined in cavities. 相似文献
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Near-infrared quantum cutting via resonant energy transfer from?Pr3+ to Yb3+ in LaF3 总被引:1,自引:0,他引:1
Experimental evidence of energy transfer from Pr3+ to Yb3+ were presented by the excitation spectra and emission spectra in LaF3:Pr3+,Yb3+. Temperature-dependent infrared emission and fluorescence decay curves have been measured to investigate the quantum cutting mechanism and energy transfer efficiency of the Pr3+?CYb3+ couple. Upon excitation of Pr3+ at 442?nm, Yb3+ emits two near-infrared photons around 1000?nm through two resonant energy transfer processes from Pr3+ to Yb3+ and the maximum total quantum efficiency reaches 161.6%. The excellent luminescence properties of the Pr3+?CYb3+ codoped LaF3 indicate its potential application in improving the energy conversion efficiency of the silicon based solar cells by converting one blue photon to two near-infrared ones. 相似文献
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半导体发光二极管发出的光谱能量分布曲线和视见函数可以近似地表示成适当参数的高斯函数。在测出LED总光通的情况下,我们可以积分算出LED的光视效能、功率效率和量子效率。对GaP,GaAs0.62P0.38和Ga0.68Al0.32As三种LED进行了计算,其结果与直接求面积法所得数据比较,表明两者符合较好。
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A rigorous theoretical model for In 0.53 Ga 0.47 As/InP single photon avalanche diode is utilized to investigate the dependences of single photon quantum efficiency and dark count probability on structure and operation condition.In the model,low field impact ionizations in charge and absorption layers are allowed,while avalanche breakdown can occur only in the multiplication layer.The origin of dark counts is discussed and the results indicate that the dominant mechanism that gives rise to dark counts depends on both device structure and operating condition.When the multiplication layer is thicker than a critical thickness or the temperature is higher than a critical value,generation-recombination in the absorption layer is the dominative mechanism;otherwise band-to-band tunneling in the multiplication layer dominates the dark counts.The thicknesses of charge and multiplication layers greatly affect the dark count and the peak single photon quantum efficiency and increasing the multiplication layer width may reduce the dark count probability and increase the peak single photon quantum efficiency.However,when the multiplication layer width exceeds 1 μm,the peak single photon quantum efficiency increases slowly and it is finally saturated at the quantum efficiency of the single photon avalanche diodes. 相似文献
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超二代像增强器多碱阴极光电发射特性研究 总被引:1,自引:1,他引:0
通过测量超二代像增强器多碱阴极的光谱反射率和透射率,根据能量守恒定律计算得到了多碱阴极的光谱吸收率.结果表明,只有当光子的能量大于1.333 eV以后,多碱阴极的吸收率才开始快速增大.这说明多碱阴极的光谱吸收存在一个1.333 eV的长波吸收限,入射光的光子能量如果小于该吸收限,多碱阴极将不吸收.在多碱阴极的表面电子亲合势进一步降低的情况下,多碱阴极光电发射的长波理论阈值由长波吸收限所决定.多碱阴极在吸收光子之后的电子跃迁过程中,跃迁电子的能量增加小于所吸收入射光子的能量,即存在一个"能量损失".光子的能量越高,所激发的跃迁电子所处的能级越高,能量损失越大.同时光子的能量越高,跃迁电子所处的能级越高,电子跃迁的几率越低.多碱阴极的量子效率由吸收率、跃迁几率和跃迁能级、扩散过程中的能量损失等因素共同决定,因此多碱阴极的量子效率存在长波阈的同时也存在短波阈.多碱阴极的量子效率在2.11 eV达到最大值之后,随着光子能量的增加而单调减小,在3.6 eV时,量子效率减小到零.多碱阴极在3.6 eV时的吸收系数仍然很高,但由于电子跃迁的几率低,同时电子扩散过程中的能量损失大,导致尽管多碱阴极对短波具有较高的吸收系数,但量子效率仍然较低.因此对多碱阴极所吸收的光子能量中,转换成为光电导、晶格热振动等其他非光电发射形式能量的比例而言,短波较长波高,对光电发射的贡献率而言,短波较长波低. 相似文献