Theoretical model of the helium pinhole microscope
Theoretical model of the helium pinhole microscope
复制标题
氦针孔显微镜的理论模型
DOI：
--
复制
发表时间：
2016
期刊：
影响因子：
--
通讯作者：
B. Holst
中科院分区：
文献类型：
--
作者：
A. S. Palau;G. Bracco;B. Holst
近年来，中性氦显微镜的发展得到了越来越多的关注。氦原子的低能量、电荷中性和惰性使得氦显微镜成为一系列样品成像的有吸引力的候选者。最简单的中性氦显微镜就是所谓的针孔显微镜。它由两个连续的孔径（撇渣器和针孔）准直的超音速膨胀氦束组成，它们共同决定了束斑尺寸，从而决定了在给定的工作距离上到样品的分辨率。由于中性氦原子的高电离势，很难建立高效的氦探测器。因此，优化显微镜设计以在给定分辨率和工作距离下最大化强度至关重要。在这里，我们提出了一个氦针孔显微镜系统的优化模型。我们表明，对于给定的分辨率和工作距离，存在单个强度最大值。此外，我们表明，与目前的国家的最先进的检测器技术（电离效率1 ifmmode 伊梅塞尔 exttimesfi{}{10}^{ensuremath{-}3}$），在3 mm的工作距离处的600 nm量级的分辨率是可能的。为了进行这种量化，我们假设了朗伯反射表面，并根据现有设计计算了光束光斑尺寸，该光束光斑尺寸在$0.02ensuremath{pi}$ sr的立体角内提供100 cts/s的信号。将工作距离减小到微米范围导致分辨率提高到约40 nm。
In recent years, the development of neutral helium microscopes has gained increasing interest. The low energy, charge neutrality, and inertness of the helium atoms makes helium microscopy an attractive candidate for the imaging of a range of samples. The simplest neutral helium microscope is the so-called pinhole microscope. It consists of a supersonic expansion helium beam collimated by two consecutive apertures (skimmer and pinhole), which together determine the beam spot size and hence the resolution at a given working distance to the sample. Due to the high ionization potential of neutral helium atoms, it is difficult to build efficient helium detectors. Therefore, it is crucial to optimize the microscope design to maximize the intensity for a given resolution and working distance. Here we present an optimization model for the helium pinhole microscope system. We show that for a given resolution and working distance, there is a single intensity maximum. Further we show that with present-day state-of-the-art detector technology (ionization efficiency $1ifmmode imeselse exttimesfi{}{10}^{ensuremath{-}3}$), a resolution of the order of 600 nm at a working distance of 3 mm is possible. In order to make this quantification, we have assumed a Lambertian reflecting surface and calculated the beam spot size that gives a signal 100 cts/s within a solid angle of $0.02ensuremath{pi}$ sr, following an existing design. Reducing the working distance to the micron range leads to an improved resolution of around 40 nm.