ABSTRACT
While progress has been considerable in instrumentation using
scanning interferometry for the measurement of microscopic sur-
face roughness and buried structures in transparent and biological
layers, achieving real-time measurement, while maintaining high
image quality remains a challenge. The main reasons for this are the
requirements of a high bandwidth for the data acquisition by the
detector, the transfer of data to the processor, and the processing
itself. One solution is to use continuous fringe scanning over the
depth of the sample together with a high-speed camera and cabled
logic for the processing. We present here a summary of the 4D
microscopy system we have developed for inline measurement of
3D surface roughness using a high-speed CMOS camera and parallel
processing with an FPGA that enables data processing rates of up to
1.28 Gb/s. Details of the system are presented together with the two
fringe detection algorithms that have been implemented based on
the detection of the maximum fringe intensity and on the maximum
of the fringe modulation function. The practical performance is
demonstrated on the measurement of changing samples, with 3D
image rates of up to 22 i/s being achieved for an image size of 256
× 320 pixels, and 3 i/s for an image size of 640 × 1024 pixels over a depth of 5 μm. Depths of up to 20 μm can be measured. While
online 4D microscopy opens up new applications for characterizing
soft and surfaces moving in a nonperiodic way, a discussion is
then presented of how such a system could be adapted to the
measurement of volumic images for tomography.