Medición del índice de refracción de láminas planas en un interferómetro de división de frente de onda en configuración confocal

Two proposals were studied for measuring the refractive index of flat plates in a wavefront-splitting interferometer in confocal configuration by the identification of the best focused interferogram in two configurations: when the light passing through the plate is measured (transmission method), an...

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Autores:: Rueda Parra, Santiago

Tipo de recurso:: Work document

Fecha de publicación:: 2020

Institución:: Universidad Nacional de Colombia

Repositorio:: Universidad Nacional de Colombia

Idioma:: spa

Description
Summary:	Two proposals were studied for measuring the refractive index of flat plates in a wavefront-splitting interferometer in confocal configuration by the identification of the best focused interferogram in two configurations: when the light passing through the plate is measured (transmission method), and when the light reflecting on the surfaces of the plate is measured (reflection method). The interference pattern in defocused planes were analyzed numerically by solving the Rayleigh–Sommerfeld diffraction integral and by performing a ray tracing of the system using the exact form of Snell's law, and analytically by using the Fresnel approximations for point sources. Also, an analytical description of the Spherical Aberration influence on the Axial Irradiance was done. Using the transmission method, two significant figures for the refractive index were measured. The percentage uncertainties found using the transmission method were about 1.11 % and 4.19 %; the percentage differences between the reference value (N-BK7) and measured values, were about 1.41 % and 3.21 %. Using the reflection method, there was found an experimental error in the refractive index in the second significant figure and the percentage uncertainties were about 1.04 % and 3.58 %, and the percentage differences related with the expected value were about 1.40 % and 7.04 %. The experimental factors that limit the precision of the methods were analyzed. In the transmission method different positions in the plate are correlated. Because of that, the refractive index measurement is highly affected by variations in the thickness of the plate. By the other hand, the reflection method is a local measurement in a single position of the plate. For that reason, the refractive index measurement is highly affected by the local thickness of the plate. Because the origin of the experimental errors in both methods are different, it is not possible to use both methods simultaneously to improve the measurement. Our main conclusion is that our proposal is not well suited as high precision metrology for refractive index measurement of plates with a given thickness. Instead of that, it is possible to use the transmission method to measure differences in thickness, and the reflection method to measure local thickness, with sensitivities in the order of the nanometers. It is recommended to keep researching in that direction.

Medición del índice de refracción de láminas planas en un interferómetro de división de frente de onda en configuración confocal

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