Towards µm-Sized Laser Spots in a TEM

Utilizing both photons and electrons to characterize a material is emerging as a field, for example when dealing with nanoscale transport properties, or simply to record gain and loss electron spectroscopy signals for higher energy resolution. In both examples, having a very tightly focused spot on the specimen surface is desirable. Tighly focusing a laser beam on a TEM specimen is a challenge, because the sample lies in a tight space between the top and bottom part of the objective lens of the microscope.<br/>Ongoing efforts at Attolight AG are directed at reaching the smallest spot sizes on a TEM sample using the Mönch® add-on mirror, which is inserted between the part of the objective lens closest to the electron source and the sample. While it was initially used for light collection, it is seeing increasing interest for injection.<br/>This contribution will describe the dedicated apparatus and experimental procedure developed to characterize and optimize the light injection spot on a TEM sample surface. This apparatus is based on an Allalin® SEM platform, rigged with a Mönch light collection/injection add-on. This allows the use of the Allalin collection optics to be used in conjunction with the Mönch mirror, both as a reference and collection apparatus for defocused beam conditions.<br/>The advantages and limitations of the Mönch as an injection method will be discussed. In particular, sensitivity to defocus and misalignment will be discussed, both on-axis and off-axis.