We present a novel all optical technology for precision nanoscale pattern inspection. The approach utilizes imaging system with the high value of axial chromatic aberration and a low-cost light source tunable in the ~30 nm wavelength bandwidth. Such combination allows us to capture defocused images in highly stable conditions without mechanical scanning of either tested sample or image sensor. Further processing of the diffraction images in the defocused planes gives one an ability to compare inspected objects and, using a library of preliminary measured data, define their geometrical parameters with nanoscale accuracy. The proposed method was tested with calibrated lines (height 50 nm, length 100 μm, width range 40-150 nm with 10 nm step) on top of monocrystalline silicon substrate. Measurement accuracy of the optical technology was estimated as ~1 nm.
The possibilities of the development of the 1-D tomographic fiber-optical measuring system based upon the set of the
loop-shaped fiber-optical measuring lines with different lengths were investigated. Single fiber multimode
interferometers were proposed as measuring lines. The system's signals processing algorithm was developed. The
scheme of the arrangement of the single fiber multimode interferometers in the 1-D multichannel tomographic system
was offered. The reconstruction of the lateral deformation pattern in the object (structural beam) under study was shown.
Possibilities of obtaining quantitative information about the deformation influence on the SFMI with a small number of
excited modes by using a correlation method are investigated. It was shown that usage of diffusive scatterer allows us to
transform the radiation of SFMI to a speckle field which can easily be processed. The value of the measurement error of
SFMI elongation is ±10 &mgr;m. The working range of the SFMI deformation measurements is 0 - 160 &mgr;m.
KEYWORDS: Charge-coupled devices, Signal processing, Speckle pattern, Interferometers, CCD cameras, Refractive index, Multimode fibers, Signal detection, Temperature metrology, Digital signal processing
The correlation method for processing signals from a single-fibre multimode
interferometer by using a digital charge-coupled device is studied experimentally and
theoretically. Optimal conditions are determined for recording multimode interference
patterns with charge-coupled devices. It is found that the nonlinearity of characteristics of
such devices affects the results of correlation measurements. The method for eliminating
this influence is proposed. The correlation method considered in the paper allows one to measure a linear deformation of the interferometer within 0-80 &mgr;m
with an accuracy of ~
±3&mgr;m for typical single-mode fibres with the core diameter 50 &mgr;m.
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