Vitaly V. Krasnov

The results of a soft X-ray chemically sensitive ptychographic imaging of non-planar nanoscale 3D objects - atom probe tomography tips, with resolution down to 12 nm at 800 eV using scanning X-ray microscope at the electron storage ring BESSY II are presented. We validate that this approach can be used to determine the tip (emitter) shape, and to resolve inner nano-scale structures as relevant for semiconductor applications and even for quantitative chemical composition analysis. Imaging of buried interfaces with below 30 nm resolution is demonstrated. This work might pave the way for contactless, ptychographic in-situ characterization of APT tips with tabletop coherent EUV sources.

Optical encryption methods attract a lot of attention owing to their high encryption speed and bandwidth. Recently, neural networks (NNs) have been used for cryptanalysis of optical encryption techniques. In this paper, we for the first time to our knowledge applied a NN for ciphertext only attack on an optical encryption system with spatially incoherent illumination. A NN was used to extract encryption keys from ciphertexts, which can be used to decrypt the plaintext QR codes. Additionally, an optically encrypted QR code was successfully decoded after using the key extracted by the trained NN, that has been processed to account for discrepancies between the numerical model and the optical setup. The results show the vulnerability of the existing optical encryption system with incoherent light to attacks of this type, which indicates the need for improved optical encryption security.

Голографическое кодирование цветного видеопотока формата 4K с помощью фазовых жидкокристаллических модуляторов света

Fast reconstruction of holographic and diffractive optical elements (DOE) can be implemented by binary digital micromirror devices (DMD). Since micromirrors of the DMD have two positions, the synthesized DOEs must be binary. This work studies the possibility of improving the method of synthesis of amplitude binary inline Fresnel holograms in divergent beams. The method consists of the modified Gerchberg–Saxton algorithm, Otsu binarization and direct search with random trajectory technique. To achieve a better quality of reconstruction, various binarization methods were compared. We performed numerical and optical experiments using the DMD. Holograms of halftone image with size up to 1024 × 1024 pixels were synthesized. It was determined that local and several global threshold methods provide the best quality. Compared to the Otsu binarization used in the original method of the synthesis, the reconstruction quality (MSE and SSIM values) is improved by 46% and the diffraction efficiency is increased by 27%.

Digital holography is widely used for the fast and accurate reconstruction of objects and three-dimensional (3D)-scene characteristics, such as intensity, depth locations, density, temperature, refractive index, etc. There are various types of noise in digital holography, including speckle noise, zero order and twin image, camera shot noise, and fixed-pattern noise. Therefore, additional hologram processing is required to obtain a high-quality reconstructed image. This paper proposes an optical-digital method of noise suppression in digital holography. First, a set of uncorrelated holograms is registered. The reconstructed images are treated as a 3D array, to which a 3D filter is then applied. A 3D median filter is used in this study; however, other 3D filters based on weighted averages can also be utilized. The proposed method is verified using computer-generated and optically registered digital Fresnel holograms. Even with a small number of images, the method significantly improves the quality: the normalized standard deviation was decreased by up to 3–10 times and the speckle contrast was reduced by more than six times. Registration of only ten holograms is sufficient to obtain a quality close to the maximum. The flexibility of the proposed method allows the ratio of the reconstruction quality to be varied according to the processing time.

High-speed optical reconstruction of 3D-scenes can be achieved using digital holography with binary digital micromirror devices (DMD) or a ferroelectric spatial light modulator (fSLM). There are many algorithms for binarizing digital holograms. The most common are methods based on global and local thresholding and error diffusion techniques. In addition, hologram binarization is used in optical encryption, data compression, beam shaping, 3D-displays, nanofabrication, materials characterization, etc. This paper proposes an adaptive binarization method based on a combination of local threshold processing, hologram division into blocks, and error diffusion procedure (the LDE method). The method is applied for binarization of optically recorded and computer-generated digital holograms of flat objects and three-dimensional scenes. The quality of reconstructed images was compared with different methods of error diffusion and thresholding. Image reconstruction quality was up to 22% higher by various metrics than that one for standard binarization methods. The optical hologram reconstruction using DMD confirms the results of the numerical simulations.

The necessity of the correction of errors emerging during the optical encryption process led to the extensive use of data containers such as QR codes. However, due to specifics of optical encryption, QR codes are not very well suited for the task, which results in low error correction capabilities in optical experiments mainly due to easily breakable QR code’s service elements and byte data structure. In this paper, we present optical implementation of information optical encryption system utilizing new multilevel customizable digital data containers with high data density. The results of optical experiments demonstrate efficient error correction capabilities of the new data container.