Evaluation of the optical efficiency
of diffractive grids
Student: Martin Halicek
Supervisors: Ing. Vladimir Kolarik, PhD.
Mgr. Frantisek Matejka
This Diploma work is focused on the estimation of the optical efficiency of synthetic diffractive grids created by means of electron lithography. A diffractive grid is a periodical structure of parallel lines with given line width, period and angle. Theoretically, the analysis is based on a transmittance concept of diffraction on grids, which results from a solution of the 1st Rayleigh-Sommerfeld diffractive problem. A MatLab program called "VYPOCET" was written to the assessment of diffractive grids efficiency. From the analyses of diffractive grids may be concluded that some of the grids have the same position of the main maximum, although they were designed as different grids as period and angle are concerned. Furthermore, some grids presents one or more of the following aspects: an important neighbouring maximum, a high efficiency of zero diffractive order, a mismatch between the real and the designed period or angle.
Based on analysis results, some grids were eliminated from the library and some grids were recommended for the modification. The results of the analysis were confirmed by measuring the optical efficiency of chosen grids. Profiles of some grids were measured by atomic force microscope - AFM. Analysis results show that 25 x 25 mm grids included in the library generate only some diffractive orders of the all the possible. Thus, further grids can be designed to complete the library.
Figures: A measured grid profile - (top), the measurement workbench (bottom).
