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Proceedings Paper

Automatic unit for measuring refractive index of air based on Ciddor equation and its verification using direct interferometric measurement method
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Paper Abstract

In scanning probe microscopy laser interferometers are usually used for measuring the position of the probe tip with a metrological traceability. As the most of the AFM setups are designed to work under standard atmospheric conditions the changes of the refractive index of air have an influence to measured values of the length with 1.0exp(-4) relatively. In order to achieve better accuracies the refractive index of air has to be monitored continuously and its instantaneous value has to be used for compensating the lengths measured by all of the interferometric axes. In the presented work we developed a new concept of an electronic unit which is able to monitor the refractive index of air on basis of measurement of ambient atmospheric conditions: temperature, humidity, pressure of the air and the CO2 concentration. The data processing is based on Ciddor equation for calculating the refractive index of air. The important advantage of the unit is a very low power consumption of the electronics so the unit causes only negligible temperature effects to the measured environment. The accuracy of the indirect measuring method employed by the unit was verified. We tested the accuracy in comparison with a direct method of measuring refractive index of air based on an evacuatable cell placed at the measuring arm of a laser interferometer. An experimental setup used for verification is presented together with a set of measurements describing the performance. The resulting accuracy of the electronic unit falls to the 4.1 exp(-7) relatively.

Paper Details

Date Published: 13 May 2013
PDF: 9 pages
Proc. SPIE 8788, Optical Measurement Systems for Industrial Inspection VIII, 878837 (13 May 2013); doi: 10.1117/12.2020756
Show Author Affiliations
V. Hucl, Institute of Scientific Instruments of the ASCR, v.v.i. (Czech Republic)
M. Čížek, Institute of Scientific Instruments of the ASCR, v.v.i. (Czech Republic)
J. Hrabina, Institute of Scientific Instruments of the ASCR, v.v.i. (Czech Republic)
B. Mikel, Institute of Scientific Instruments of the ASCR, v.v.i. (Czech Republic)
Š. Řeřucha, Institute of Scientific Instruments of the ASCR, v.v.i. (Czech Republic)
Z. Buchta, Institute of Scientific Instruments of the ASCR, v.v.i. (Czech Republic)
P. Jedlička, Institute of Scientific Instruments of the ASCR, v.v.i. (Czech Republic)
A. Lešundák, Institute of Scientific Instruments of the ASCR, v.v.i. (Czech Republic)
J. Oulehla, Institute of Scientific Instruments of the ASCR, v.v.i. (Czech Republic)
L. Mrňa, Institute of Scientific Instruments of the ASCR, v.v.i. (Czech Republic)
M. Šarbort, Institute of Scientific Instruments of the ASCR, v.v.i. (Czech Republic)
R. Šmíd, Institute of Scientific Instruments of the ASCR, v.v.i. (Czech Republic)
J. Lazar, Institute of Scientific Instruments of the ASCR, v.v.i. (Czech Republic)
O. Číp, Institute of Scientific Instruments of the ASCR, v.v.i. (Czech Republic)


Published in SPIE Proceedings Vol. 8788:
Optical Measurement Systems for Industrial Inspection VIII
Peter H. Lehmann; Wolfgang Osten; Armando Albertazzi, Editor(s)

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