Image Drift Under High-Power Laser Irradiation in a Side-Entry Fiber-Optic TEM Holder

In situ laser irradiation in a transmission electron microscope (TEM) enables direct observation of laser-induced microstructural evolution. A side-entry TEM holder with an optical fiber has been fabricated for 808 nm continuous-wave near-infrared irradiation, and the apparent image-drift behavior under high-power laser exposure has been investigated. Support-free Au, Cu, Ni, and stainless steel (SS) grids were first examined using a 30 s laser-on/30 s laser-off protocol. The image-drift magnitude followed the order SS > Ni > Cu ≈ Au, with rapid switching displacement followed by a continued drift at a progressively decreasing rate. To investigate the effect of support materials on the image drift, Au and Cu grids with lacey carbon and continuous carbon films were also evaluated. For both metals, image drift consistently increased in the order: support-free < lacey carbon < continuous carbon film, reflecting the combined effects of optical absorption, thermal transport, and mechanical constraint. Infrared thermography under vacuum further confirmed material-dependent heating, consistent with the thermoelastic interpretation of the measured drift. The Cu grid showed no visible damage under irradiation of ≤3 W, whereas higher-power irradiation led to grid degradation. These results provide practical guidelines for selecting TEM grids and support materials for stable, high-power laser-assisted TEM observations.