Prototype of time digitizing system for BESⅢ endcap TOF upgrade

The prototype of a time digitizing system for the BESⅢ endcap TOF (ETOF) upgrade is introduced in this paper. The ETOF readout electronics has a distributed architecture. Hit signals from the multi-gap resistive plate chamber (MRPC) are signaled as LVDS by front-end electronics (FEE) and are then sent to the back-end time digitizing system via long shield differential twisted pair cables. The ETOF digitizing system consists of two VME crates, each of which contains modules for time digitization, clock, trigger, fast control, etc. The time digitizing module (TDIG) of this prototype can support up to 72 electrical channels for hit information measurement. The fast control (FCTL) module can operate in barrel or endcap mode. The barrel FCTL fans out fast control signals from the trigger system to the endcap FCTLs, merges data from the endcaps and then transfers to the trigger system. Without modifying the barrel TOF (BTOF) structure, this time digitizing architecture benefits from improved ETOF performance without degrading the BTOF performance. Lab experiments show that the time resolution of this digitizing system can be lower than 20 ps, and the data throughput to the DAQ can be about 92 Mbps. Beam experiments show that the total time resolution can be lower than 45 ps.     

Scanning interferometric method for measuring group delay of dispersive mirrors

A scanning white-light interferometer is built for precisely measuring phase properties of dispersive multi- layer thin film structure with the aid of the commercial spectrometer. Combining seeking optimal function for interferogram maximas with wavelet denoising algorithm, a novel time-domain algorithm is presented which enables the direct extraction of group delay and thus obtains a remarkable decrease of noise level in group delay and group delay dispersion. The apparatus shows reasonable potential for multilayer mea- surement, material characterization, displacement measurement as well as profilometry.     

原子层沉积制备Ta_2O_5薄膜的光学特性研究

以乙醇钽[Ta(OC2H5)5]和水蒸气为前驱体,采用原子层沉积(ALD)方法分别在基板温度为250℃和300℃的K9和石英衬底上制备了Ta2O5光学薄膜。采用分光光度计、X射线光电子能谱(XPS)、X射线衍射(XRD)、扫描电子显微镜(SEM)和原子力显微镜(AFM)等手段对薄膜的光学特性、微结构和表面形貌进行了研究。结果表明,用ALD方法制备的Ta2O5薄膜在刚沉积和350℃退火后均为无定形结构,而250℃温度下沉积的薄膜其表面粗糙度低,聚集密度很高,光学均匀性优,在中紫外到近红外均表现出很好的光学特性,可以作为高折射率材料很好地应用于光学薄膜中。     

基于白光干涉测量色散补偿薄膜的群延迟色散

为精确测量超快激光色散补偿薄膜的群延迟色散,提出了一种基于窗口傅里叶变换和样条插值去噪算法的新型白光干涉测量方案。计算机模拟表明此方法测试精度可达0.58fs2。分析了高斯噪声和光强平均效应对测试精度的影响,并使用此方法对实验制备的Gires-Tournois干涉反射镜和啁啾镜进行了测试,在宽光谱范围内测试误差小于10fs2。该方法相比其他算法可以更快速、更精确地实现薄膜相位信息的提取,具有更高的测试精度和实用性。     

Anti-reflection coating at 550 nm fabricated by atomic layer deposition

Trimethylamine （TMA）, TIC14, and water are applied as the precursors to deposit Al2O3 and TiO2. With different substrate temperatures, the optical properties and surface morphologies of the two oxides TiO2 and SiO2 are studied, respectively. With substrate temperature of 120 ℃, amorphous TiO2 can be obtained, and the surface roughness （RMS） is only 0.928 nm. Applying Al2O3 and TiO2 deposited in 120 ℃ as low and high refractive index materials, anti-reflection （AR） coating at single point （550 nm） is designed. Furthermore, with the calibrated growth rates, this AR coating is fabricated, and its ultimate reflectance for the AR coating at 550 nm is less than 0.2%, which can meet the requirement for most applications.