Three-beam scanning laser radar microprofilometer

Vasyl V. Molebny; Gary W. Kamerman; Eugene M. Smirnov; Leonid M. Ilchenko; Sergiy O. Kolenov; Vadym O. Goncharov

doi:10.1117/12.327200

8 September 1998 Three-beam scanning laser radar microprofilometer

Vasyl V. Molebny, Gary W. Kamerman, Eugene M. Smirnov, Leonid M. Ilchenko, Sergiy O. Kolenov, Vadym O. Goncharov

Proceedings Volume 3380, Laser Radar Technology and Applications III; (1998) https://doi.org/10.1117/12.327200
Event: Aerospace/Defense Sensing and Controls, 1998, Orlando, FL, United States

Abstract

In many scientific and technologic applications, for example, in ophthalmology, microelectronics, etc, the problem exists of profile investigation with nanometer accuracy. Double-frequency phase-difference interferometric technique is known, that uses phase difference measurement between two beams propagation to the investigated surface and back at two different carrier frequencies. These measurements give profile's derivative along the line of scanning, that can be reconstructed into the profile using mathematical operation of integration. To get high accuracy, integration error must be excluded or compensated. It can be easily done, if special specimen plate is used with reference plane. Live objects, like human cornea, have no reference planes or points. We report here on the technique using measurement of two partial derivatives, thus enabling correct reconstruction of a 3D surface. Three laser beams are configured in acousto-optical system of modulators and scanners, in which partial derivatives are measured in each point for orthogonal X and Y directions. For this purpose, two modulators are positioned in series, producing alternatively neighboring beam pairs oriented along X or Y axis and having the same frequency difference for both directions. For image format 512 X 512, corresponding to investigated area 7 X 7 mm, with chosen geometry and frequency difference (f₁ - f₂) equals 1 MHz, time of measurement in each point is about 1 microsecond, resulting in total time less than 0.3 sec. per frame. The instrument is sensitive to profile variations less than 4 nm.

Citation Download Citation

Vasyl V. Molebny, Gary W. Kamerman, Eugene M. Smirnov, Leonid M. Ilchenko, Sergiy O. Kolenov, and Vadym O. Goncharov "Three-beam scanning laser radar microprofilometer", Proc. SPIE 3380, Laser Radar Technology and Applications III, (8 September 1998); https://doi.org/10.1117/12.327200

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