QUALITY ASSESSMENT OF BINARY OBJECT IMAGES RECONSTRUCTED BY COMPUTER-GENERATED HOLOGRAMS

Subject of Research. The paper considers the issues of objective quality assessment of computer-generated Fresnel holograms and reconstructed binary object images. Method. The work is performed by the method of projection holographic photolithography based on computer-generated Fresnel holograms. The synthesis of holograms was carried out by mathematical modeling of the physical processes of hologram recording and reconstruction in the original software package using the following parameters: the binary object characteristic size of 80 × 80 nm, laser wavelength of 13.5 nm, hologram pixel size of 20 × 20 nm, the distance between an object and hologram planes equal to 20.4 μm, reference wave incidence angle of 14°42′. The hologram synthesis for each object under research was carried out for the case of two different synthesis setup parameters. The reconstructed images of these objects were compared by three methods: the peak signal-to-noise ratio calculation method, the structural similarity index calculation method, and the method of image quality assessment based on the calculation of the number of levels at the threshold image processing, which is an imitation of photoresist response to actinic radiation exposure. Main Results. Diffraction-based criterion, traditionally applied in optics, is proven to be the most relevant for the quality evaluation of projection photolithographic systems, including systems based on computer-generated holograms. It is established that the methods based on the calculation of the structural similarity index and on estimation of the number of levels at the threshold image processing are the most suitable methods for assessing the reconstructed image quality in the field of projection holographic photolithography. Moreover, the second method does not require any additional calculations. Practical Relevance. Application of an adequate quality assessment method makes it possible to compare quickly and objectively the reconstructed images of the same objects obtained for various parameters of the synthesis setup and select the object representation form and the hologram synthesis setup that is the most suitable for a particular task.