3-D Tomography and Ultrafast Laser-Material Interactions
The development of high fidelity material property models often requires three-dimensional information on the distribution of phases, grains or extrinsic defects. Concurrently, information on orientation and spatial distribution of elements may also be essential. Acquisition of this information in appropriate representative volume elements is a major challenge. We have developed femtosecond lasers for rapid layer-by-layer ablation provides new capabilities in terms of the volume of material that can be sampled as well as new opportunities for multimodal analysis.
The high pulse frequency (1 kHz) of ultra-short (150 fs) laser pulses can induce material ablation with virtually no thermal damage to the surrounding area. This technique has been demonstrated ex-situ with optical imaging and an example of a 3-D dataset where the distribution of micron-scale nitrides within mm3-scale volumes of a steel have been characterized is shown.
More recently, we have developed an in-situ “TriBeam” approach that combines the femtosecond laser within a focused ion beam platform to permit high resolution imaging, as well as crystallographic and elemental analysis, without intermediate surface preparation or removal of the sample from the chamber. The TriBeam system, shown schematically below, combines the high resolution and broad detector capabilities of the FEI Versa 3D microscope with the high material removal rates of the femtosecond laser, allowing 3D datasets to be acquired at rates 4 to 6 orders of magnitude faster than 3D FIB datasets. The TriBeam platform couples the laser and electron optics systems and employs a positioning of a stage that can quickly and automatically be located to the multiple analysis positions. This system also allows for acquisition of “multimodal” datasets wherein structural information as well as chemical information (EDS) and crystallographic information (EBSD) can be quickly acquired for each material slice.
This system is capable of generating 3D mesoscale (mm-scale) datasets for a broad array of materials systems; examples of datasets generated to date are shown in the image gallery.