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根据透射材料对入射激光散射特性与衰减特性分析,为提高探测器阵列靶测量系统的抗激光损伤能力,选用可以承受激光功率密度10 kW/cm2的石英毛玻璃作为第一取样面。毛玻璃散射特性与其表面颗粒分布及粒径大小等因素相关,透射散射光一般呈高斯状分布,如图2(a)所示,可见,仅使用毛玻璃对入射激光取样的匀化散射作用有限,在毛玻璃后加上工程漫射体,其散射光分布在±20°范围内有一定起伏的类平顶区域,如图2(b)所示,但是工程漫射体由于其材料属性,抗激光损伤能力有限。
Figure 2. Distribution characteristics of transmission and scattering angle. (a) Ground glass; (b) Engineering diffuser
基于上述对取样材料属性的分析,设计了毛玻璃与工程漫射体组合的散射取样衰减单元,结构设计如图3所示,由毛玻璃、工程漫射体、消光通道、探测单元组成,消光通道用于吸收大角度散射光,防止阵列通道间相互串扰。毛玻璃与工程漫射体具有透射材料的光学特性,组合结构在可见光至中红外较宽光谱范围内都能适用。在常用的近红外测量波段1000~1100 nm,透过率基本不变。
采用实验室高功率激光器进行取样衰减材料抗激光损伤测试,出射光功率940 W,聚焦发射,到材料表面功率密度可达2 000 W/cm2。测试单片毛玻璃、工程漫射体材料以及两种材料组合时不同间距的激光损伤情况,实验结果如表1所示,组合间距为d。结果显示:工程漫射体放至毛玻璃后表面1.5 mm处,辐照时长20 s未有实验元件损坏,实际应用中,为了提高集成度,以1.5 mm为设计间隔。
Materials Power density/W·cm−2 Irradiation time/s Damaged condition Ground glass 2 000 20 Undamaged Engineering diffuser 2 000 1 damaged Ground glass + engineering diffuser (d=0.5 mm) 2 000 8 Damaged Ground glass + engineering diffuser (d=1 mm) 2 000 12 Damaged Ground glass + engineering diffuser (d=1.5 mm) 2 000 20 Undamaged Ground glass + engineering diffuser (d=2 mm) 2 000 20 Undamaged Ground glass + engineering diffuser (d=2.5 mm) 2 000 20 Undamaged Table 1. Laser damage test of sampling attenuation materials
Design of scattering sampling attenuation unit for detector array target
doi: 10.3788/IRLA20210150
- Received Date: 2021-03-10
- Rev Recd Date: 2021-06-01
- Available Online: 2022-01-06
- Publish Date: 2021-12-31
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Key words:
- detector array target /
- power density /
- sampling attenuation /
- bidirectional transmission distribution function
Abstract: The detector array target is a common equipment for measuring the spatial and temporal distribution of laser intensity. In order to achieve high-precision measurement of target laser parameters, the sampling attenuation method is its key point. Aiming at scattering sampling attenuation technology for detector array target, based on the bidirectional transmission distribution function, the transmission and scattering characteristics of ground glass and other materials were studied. And the calculation formula of the laser intensity attenuation magnification which was scattered to the photosensitive surface of the detector was deduced. The scattering sampling attenuation unit combined with ground glass and engineering diffuser was designed. Combined with the ABg scattering model, the simulation model of scattering sampling attenuation materials were established by TracePro software. The results show that the designed sampling attenuation structure is able to withstand the power density of 2 000 W/cm2 laser irradiation for 20 s; within the scattering emission angle of ±5.44°, the sampling unevenness of the detection surface is about 3.34%; the attenuation magnification simulation design result and experimental measurement error is about 0.805%. The scattering sampling attenuation method has the advantages of strong resistance to laser damage, better spot homogenization effect, quantitative attenuation of laser intensity and broad spectral response. This manner has a good application prospect.