Abstract

A non-axial-scanning confocal microscope employing a monochromatic light source has been developed. The system controls the defocus of an objective into three to five optimized states by using a membrane-adaptive mirror, and determines the axial height of an object according to the confocal output value with each defocus. A genetic algorithm is employed to optimize the adaptive mirror shape, with the information entropy of the spectrum of the lateral confocal spot profile used as a cost function in the genetic algorithm. Our experimental system successfully determined axial object height within 50 µm range with 0.64 % of error.

© 2002 Optical Society of America

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References

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Appl. Opt.

J. Mod. Opt.

Tiziani H. J. and Ach i R. and Kr¨amer R. N., �??Chromatic confocal microscopy with microlenses,�?? J. Mod. Opt. 43, 155�??163, (1996).
[CrossRef]

Measurement Sci. Technol.

Jordan M. and Wegner M. and Tiziani H. J., �??Highly accurate non-contact characterization of engineering surfaces using confocal microscoy,�?? Measurement Sci. Technol. 9, 1142�??1151 (1998).
[CrossRef]

Opt. Laser Tech.

Tiziani H. J. and Ach iR. and Kramer R. N. and Hessler T. and Gale M. T. and Rossi M. and Kunz R. E., �??Microlens arrays for confocal microscopy,�?? Opt. Laser Tech. 29, 85�??91 (1997).
[CrossRef]

Opt. Lett.

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Figures (4)

Fig. 1.
Fig. 1.

The scheme of the developed confocal microscope. Pol. and QWP represent the polarizer and quarter wavelength plate, Pin. is the pinhole, BS and PBS are a beam splitter and a polarization beam splitter, Ls and Obj. are lenses and a microscope-objective, respectively. The scanning stage is a piezo-stage, which is driven only during initial calibration.

Fig. 2.
Fig. 2.

Reference axial responses of each channel. Each channel is optimized with a different height of the reference mirror.

Fig. 3.
Fig. 3.

Projection-plots of reference channel outputs. Each channel output is projected onto the surface of the unit sphere surface in the channel space, where each axis represents each channel.

Fig. 4.
Fig. 4.

Measured height of the object. The horizontal axial represents actual object height and the vertical axis represents measured height. Plots (1) and (2), respectively, are calculated from 3 and 5 channel-outputs. The solid lines represent theoretical lines.

Equations (4)

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P μ ν = f ̂ μ ν μ , ν f ̂ μ ν .
= μ , ν P μ ν log P μ ν .
r = R R
θ = arccos ( r · m )

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