Uddin Nezam, Sheng Qiwen, Mitul Abu Farzan, Lee Seungsup, Reinke Matthew L, Donovan David, Shafer Morgan, Han Ming
Department of Electrical and Computer Engineering, Michigan State University, East Lansing, Michigan 48824, USA.
Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA.
Rev Sci Instrum. 2021 Feb 1;92(2):023515. doi: 10.1063/5.0038763.
Fiber-optic bolometers (FOBs) intended for plasma radiation measurement in magnetically confined fusion have been previously developed using a silicon pillar that functions as both a Fabry-Perot interferometer (FPI) for temperature measurement and an absorber for the radiation. We report an FOB design that can significantly improve the detection sensitivity over earlier designs by engineering the absorber of the FOB. Our design uses the fact that, compared with a silicon pillar, a gold film with the same x-ray absorption thickness will show a much higher temperature rise from a given power density of the radiation. Therefore, the responsivity of an FOB can be improved by attaching a large gold disk to the silicon FPI as the absorber. We have developed a fabrication method for FOBs of such design and obtained an FOB with a 4-µm-thick, 0.6-mm-diameter gold disk attached to a 200-µm-diameter, 100-µm-thick silicon FPI. We have characterized the noise, responsivity, response time, and noise-equivalent power density (NEPD) and compared these with the earlier design where the absorber is mainly the silicon FPI itself. The experimental result suggests that the FOB with the gold disk achieves a responsivity of ∼2.8 mK/(W/m) and a noise-equivalent-power-density of 0.13 W/m, which are, respectively, more than nine times larger and six times smaller compared to the FOB using a previous design. Improved NEPD and good absorption over a broad frequency range will make the FOB more attractive for applications in magnetic-confinement fusion devices.
用于磁约束聚变中测量等离子体辐射的光纤测辐射热计（FOB），此前已通过使用硅柱进行开发，该硅柱既作为用于温度测量的法布里 - 珀罗干涉仪（FPI），又作为辐射的吸收体。我们报告了一种FOB设计，通过对FOB的吸收体进行工程设计，可显著提高其检测灵敏度。我们的设计利用了这样一个事实，即与硅柱相比，具有相同X射线吸收厚度的金膜在给定辐射功率密度下会表现出更高的温度上升。因此，通过在硅FPI上连接一个大金盘作为吸收体，可以提高FOB的响应度。我们已经开发出了这种设计的FOB制造方法，并获得了一个FOB，它将一个4μm厚、直径0.6mm的金盘连接到一个直径200μm、厚度100μm的硅FPI上。我们对噪声、响应度、响应时间和噪声等效功率密度（NEPD）进行了表征，并将这些与早期设计（其吸收体主要是硅FPI本身）进行了比较。实验结果表明，带有金盘的FOB实现了约2.8 mK/(W/m)的响应度和0.13 W/m的噪声等效功率密度，与使用先前设计的FOB相比，分别大了九倍多和小了六倍。改进的NEPD以及在宽频率范围内的良好吸收将使FOB在磁约束聚变装置中的应用更具吸引力。
