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.