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Proceedings Paper

Monitoring of overmodulation effect in high efficient generally slanted transmission gratings produced in photopolymers
Author(s): Petr Vojtíšek; Milan Kvĕtoň; Ivan Richter
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Paper Abstract

In our laboratory, we use for fabrication of volume phase diffraction gratings a photopolymer recording material Bayfol HX. It is an extremely effective recording material; a high value of the refractive index modulation is obtained already during a holographic exposure. The value of this refractive index modulation influences the diffraction properties (e.g. efficiency) of the recorded gratings and, in the case of transmission gratings, the growth of this modulation beyond the optimal value leads to an effect of so called overmodulation. This effect is, in the most cases, unwanted as it causes the decrease of the diffraction efficiency from its maximum value (practically close to 100%). The analysis whether the grating is over- or under- modulated is relatively difficult as the value of the refractive index modulation can’t be measured directly and it is evaluated from the measurement of the diffraction efficiency. However, the obtained value can be often incorrect due to the overmodulation effect. In this contribution, we would like to extend (to include any arbitrary slanted transmission gratings) and discuss a simple measurement method for the determination of the correct value of the refractive index modulation based on a multiple/two-wavelength measurement of a diffraction efficiency of transmission gratings. The theoretical idea of this method and also experimental results obtained on photopolymer Bayfol HX will be presented. From practical point of view, this approach help us mainly for correct adjustment of exposure parameters to reach efficient gratings.

Paper Details

Date Published: 11 November 2016
PDF: 10 pages
Proc. SPIE 10151, Optics and Measurement International Conference 2016, 1015115 (11 November 2016); doi: 10.1117/12.2256488
Show Author Affiliations
Petr Vojtíšek, Institute of Plasma Physics of the ASCR, v.v.i. (Czech Republic)
Czech Technical Univ. in Prague (Czech Republic)
Milan Kvĕtoň, Holoplus s.r.o. (Czech Republic)
Ivan Richter, Czech Technical Univ. in Prague (Czech Republic)


Published in SPIE Proceedings Vol. 10151:
Optics and Measurement International Conference 2016
Jana Kovacicinova, Editor(s)

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