Development of a laser differential confocal–atomic force sensor for inertial confinement fusion target profile measurement

The high-resolution, non-destructive measurements of the outer and inner profiles of inertial confinement fusion (ICF) targets are crucial and still a critical challenge. To address this challenge, we developed a laser differential confocal–atomic force sensor (LDC–AFS). This sensor combines the laser differential confocal (LDC) method with atomic force probe (AFP) technology by installing an AFP at the focal point of the objective. It utilizes an LDC linear segment to detect the deflection of the AFP microcantilever and uses the nanoscale tip of the AFP to break through the optical diffraction limit and improve the resolution of the sensor. By utilizing the tomographic characteristics of the LDC method, the nanoscale non-destructive focusing of the inner profile of the target was achieved. High-resolution, non-destructive measurements of the outer and inner profiles of the target along the same trace were realized by in-situ switching between the two measurement modes. Preliminary experiments and theoretical analyses indicated that the axial resolution of the AFP mode was 0.5 nm with a lateral resolution of 1.3 nm, and the axial resolution of the LDC mode was 2 nm with a lateral resolution of 350 nm. The measurements of the outer and inner profiles of the target by LDC–AFS can better predict the effect of the target's shape accuracy on the fusion ignition. This sensor lays the foundation for the development of ICF target profilometers.