Bringing out-of-focus into the picture
2010 R&D 100 Winner
Common practice in optical analysis is to utilize optical information from a single in-focus or near-focus plane on the assumption that out-of-focus planes can’t be salvaged.
Researchers at the National Institute of Standards and Technology, Gaithersburg, Md., gathered useful data from this discarded imagery and developed Through-focus scanning optical microscopy (TSOM), a measurement and analysis method that transforms ubiquitous conventional optical microscopes into 3D metrology tools with nanometer scale lateral and vertical sensitivity and a wide scope of applicability.
As in confocal microscopy, optical images are acquired as the target is scanned along the focus direction. The TSOM method preserves all optical data, using dimensional changes from image to image to build an overall picture of the sample. The method increases lateral and vertical measurement resolutions over optical microscopy by more than 100 and 1,000 times, respectively, matching atomic force microscopy and scanning electron microscopy. But neither SEM nor AFM are capable of analyzing buried targets under a transparent layer.
Through-focus scanning optical microscope
Through-focus scanning optical microscopy (TSOM) Development Team from NIST: