Monitoring of overmodulation effect in high efficient generally slanted transmission gratings produced in photopolymers

0469352 - ÚFP 2017 RIV US eng C - Conference Paper (international conference)
Vojtíšek, Petr - Květoň, M. - Richter, I.
Monitoring of overmodulation effect in high efficient generally slanted transmission gratings produced in photopolymers.
Proceedings of SPIE 10151, Optics and Measurement International Conference 2016. Vol. 10151. Bellingham: SPIE, Society of Photo-Optical Instrumentation Engineers, 2016 - (Kovačičinová, J.), č. článku 1015115. SPIE. ISBN 978-1-5106-0753-8. ISSN 0277-786X.
[OAM 2016, Optics and Measurement International Conference 2016. Liberec (CZ), 11.10.2016-14.10.2016]
R&D Projects: GA MŠMT(CZ) LO1206
Institutional support: RVO:61389021
Keywords : photopolymer * overmodulation * two-wavelength measurement * multiple-wavelength measurement
Subject RIV: JI - Composite Materials
http://dx.doi.org/10.1117/12.2256488

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
Permanent Link: http://hdl.handle.net/11104/0267153