An optical method for direct determination of the radiometric aperture area at high accuracy

A. Lassila, P. Toivanen, E. Ikonen

Research output: Contribution to journalArticleScientificpeer-review

37 Citations (Scopus)


An optical method for calibration of the aperture area is described and studied both theoretically and experimentally. A spatially uniform, known irradiance is formed over the aperture by overlapping identical, parallel laser beams centred at constant spacing in an orthogonal lattice. The ratio of the throughput power and irradiance gives the area of the aperture. The method has several advantages compared with previous methods: it measures the area of the aperture directly, the shape of the aperture is not limited to a circle, it is relatively inexpensive to establish, it does not damage the edges of the aperture and the calibration set-up is similar to that for the actual use of the aperture. It is estimated that the relative standard uncertainty is 1.6 × 10-4 in calibration of a circular 3 mm diameter aperture. The results that the present method gave for one aperture have been compared with the result of a mechanical calibration at the National Physical Laboratory (UK). The relative difference between the results was 2.4 × 10-4, with a combined standard uncertainty of 2.5 × 10-4.

Original languageEnglish
Pages (from-to)973-977
Number of pages5
JournalMeasurement Science and Technology
Issue number9
Publication statusPublished - 1 Jan 1997
MoE publication typeA1 Journal article-refereed


Dive into the research topics of 'An optical method for direct determination of the radiometric aperture area at high accuracy'. Together they form a unique fingerprint.

Cite this