Multimodal Stigmatic Laser Ion Imaging Mass Spectrometry

Statement of the Problem: Forensic analysis of particles of special nuclear materials found in the environment is used to gain crucial information about compliance of nations with processing of nuclear materials. Multiple analytical techniques are needed to reach high certainty conclusions in a short timeframe but means of combining these techniques has heretofore been disjointed. This project seeks to develop a unified characterization approach of high sensitivity and rapidity that incorporates multiple analytical modalities for enhanced certitude of the outcome. How this problem is being addressed: A new tool for multi-modal elemental and isotopic microanalysis of solids, Stigmatic Laser Ion Microscope (SLIM), has been proposed. The SLIM combines stigmatically imaging mass spectrometry (MS) with in-situ optical microscopy. It will enable parallel and instantaneous detection of ions laser-ablated from large ~100µm×100µm fields of view with high lateral (~200 nm) and depth (~1 nm) resolutions. This approach will enable rapid (<1 hour) acquisition of high resolution 2-D isotopic maps over 1 cm2 areas with exact registry with a sub-micron-resolving collinear light microscope. What was done in Phase I: In Phase I, the optical front-end of the SLIM was designed. It combines achromatic light optics with ion extraction and projection optics. Light optics were fabricated, passed extensive testing, demonstrated submicron lateral resolution, and delivered a flat-top laser probe on the sample. This work retired most important engineering risks and successfully demonstrated a proof of concept. What is planned for the Phase II project: We propose to design, build, and demonstrate an alpha prototype of the SLIM. It will function as a stigmatically imaging linear time-of-flight (TOF) MS with ion source based on a deep-ultraviolet femtosecond laser probe. The probe will feature a square flat-top beam profile for homogeneous irradiation of large spots. Ion optics will be manufactured and integrated with the existing light optics to form the front-end of the laser ionization MS with pulsed ion extraction. The alpha SLIM will be then demonstrated in operation with test samples. Commercial Applications and Other Benefits: Usually, MS is the technique with the highest analytical sensitivity available. Yet, commercially available imaging MS instruments perform analyses in raster-scanned microprobe mode at low speed and with moderate sensitivity. The SLIM will make major improvements on both fronts. This combination of properties is expected to foster adoption in fields such as nuclear forensics, geological and environmental sciences, materials science, and life sciences.