用半球形分析器扩展角分辨光电发射系统的动量视场
Expanding the momentum field of view in angle-resolved photoemission systems with hemispherical analyzers
摘要：
在光电子能谱学中，测量的电子动量范围与激发光子能量有内在的关系。低光子能量$<10$ eV通常在基于激光的光电发射中遇到，并且导致小于大多数材料的布里渊区的动量范围。这可能成为一个限制因素时，研究凝聚态物质与激光为基础的光电发射。一个额外的限制是引入了广泛使用的半球形分析仪，只记录电子光发射的立体角设置的孔径大小在分析仪入口。在这里，我们提出了一个升级，以增加有效的立体角，是用半球分析仪测量。我们通过利用样品上的偏置电压产生的电场将光电子加速到分析仪来实现这一点。我们的实验几何形状是一个平行板电容器，因此，我们近似的电场是均匀的沿光电子轨迹。在这个假设下，我们建立了一个分析的，无参数的模型，该模型将测量的角度与固体中的电子动量联系起来，并通过与电荷密度波材料TbTe $_3$的实验结果进行比较来验证其有效性。通过在动量空间中提供更大的视场，我们使用偏置电势的方法大大扩展了基于激光的光电发射装置的灵活性。
英文摘要：
In photoelectron spectroscopy, the measured electron momentum range is intrinsically related to the excitation photon energy. Low photon energies $<10$ eV are commonly encountered in laser-based photoemission and lead to a momentum range that is smaller than the Brillouin zones of most materials. This can become a limiting factor when studying condensed matter with laser-based photoemission. An additional restriction is introduced by widely used hemispherical analyzers that record only electrons photoemitted in a solid angle set by the aperture size at the analyzer entrance. Here, we present an upgrade to increase the effective solid angle that is measured with a hemispherical analyzer. We achieve this by accelerating the photoelectrons towards the analyzer with an electric field that is generated by a bias voltage on the sample. Our experimental geometry is comparable to a parallel plate capacitor and, therefore, we approximate the electric field to be uniform along the photoelectron trajectory. With this assumption, we developed an analytic, parameter-free model that relates the measured angles to the electron momenta in the solid and verify its validity by comparing with experimental results on the charge density wave material TbTe$_3$. By providing a larger field of view in momentum space, our approach using a bias potential considerably expands the flexibility of laser-based photoemission setups.
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