Sirvi Autor "Kasikov, Aarne" järgi

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Coded Aperture Imaging using Non-Linear Lucy-Richardson Algorithm
(2025) Xavier, Agnes Pristy Ignatius; Kahro, Tauno; Gopinath, Shivasubramanian; Tiwari, Vipin; Smith, Daniel; Kasikov, Aarne; Piirsoo, Helle-Mai; Ng, Soon Hock; Rajeswary, Aravind Simon John Francis; Vongsvivut, Jitraporn; Tamm, Aile; Kukli, Kaupo; Juodkazis, Saulius; Rosen, Joseph; Anand, Vijayakumar
Imaging involves the process of recording and reproducing images as close to reality as possible, encompassing both direct and indirect approaches. In direct imaging, the object is directly recorded. Coded aperture imaging (CAI) is an example of indirect imaging, that utilizes optical recording and computational reconstruction to obtain information about an object. Computational reconstruction can be achieved using different linear, non-linear, iterative, and deep learning algorithms. In this study, we proposed and demonstrated two computational reconstruction algorithms based on the non-linear Lucy-Richardson algorithm (NL-LRA), one for limited support images and another for full-view images based on entropy reduction. The efficacy of these algorithms has been validated through simulations and optical experiments carried out in visible and infrared (IR) light with different coded phase masks. The methods were also tested on a commercial IR microscope with internal Globar™ and synchrotron sources. The results obtained from the two algorithms were compared with those from their parent methods, and a notable improvement in both entropy and the convergence rate was observed. We believe the developed algorithms will drastically improve image reconstruction in incoherent imaging applications
Extending the Depth of Focus of Infrared Microscope Using a Binary Axicon Fabricated on Barium Fluoride
(2024) Han, Molong; Smith, Daniel; Kahro, Tauno; Stonytė, Dominyka; Kasikov, Aarne; Gailevičius, Darius; Tiwari, Vipin; Xavier, Agnes Pristy Ignatius; Gopinath, Shivasubramanian; Ng, Soon Hock; Rajeswary, Aravind Simon John Francis; Tamm, Aile; Kukli, Kaupo
Axial resolution is one of the most important characteristics of a microscope. In all microscopes, a high axial resolution is desired in order to discriminate information efficiently along the longitudinal direction. However, when studying thick samples that do not contain laterally overlapping information, a low axial resolution is desirable, as information from multiple planes can be recorded simultaneously from a single camera shot instead of plane-by-plane mechanical refocusing. In this study, we increased the focal depth of an infrared microscope non-invasively by introducing a binary axicon fabricated on a barium fluoride substrate close to the sample. Preliminary results of imaging the thick and sparse silk fibers showed an improved focal depth with a slight decrease in lateral resolution and an increase in background noise.
Interferenceless coded aperture correlation holography for five-dimensional imaging of 3D space, spectrum and polarization
(2025) Joshi, Narmada; Tiwari, Vipin; Kahro, Tauno; Xavier, Agnes Pristy Ignatius; Tahara, Tatsuki; Kasikov, Aarne; Kukli, Kaupo; Juodkazis, Saulius; Tamm, Aile; Rosen, Joseph; Anand, Vijayakumar
Interferenceless coded aperture correlation holography (I-COACH) is a robust imaging technique for recovering three-dimensional object information using incoherent holography without two-beam interference. In this study, five-dimensional (5D) imaging along 3D space, spectrum and polarization in I-COACH is proposed and experimentally demonstrated for the first time. The proposed technique exploits the polarization-dependent light modulation characteristics of spatial light modulators to record polarization-dependent intensity distributions, which are distinguished by significant blurring between orthogonal polarization states. 5D I-COACH is implemented by inter-connecting all five dimensions in a single frame, and image recovery is attempted from different configurations of recorded point spread intensity distributions and response-to-object intensity distributions along 5D using recently developed deconvolution techniques. The simulation and experimental results confirm the 5D imaging capabilities of I-COACH. The proposed technique can be a useful tool for birefringence microscopy, and functional and structural imaging applications.
Optical characterization of inhomogeneous thin films
(2010-06-01T12:58:36Z) Kasikov, Aarne
Töö tegeleb õhukeste väheneelavate kilede optiliste parameetrite määramisega olukorras, kus kile murdumisnäitajat läbi materjali ei saa lugeda konstantseks. Näidatakse, et mõõdetud läbilaskvusspektri alusel on võimalik määrata murdumisnäitaja struktuuri, kirjeldades kilet Lorentzi dispersioonsõltuvusega, kasutades kahest alakihist koosnevat struktuuri ja mitmeparameetrilist globaalset optimeerimist. Seejuures peab ühe alakihi paksus olema väiksem, kui optiline veerandlaine kasutatavas mõõtepiirkonnas. Demonstreeritakse, et sel viisil arvutuslikult saadud struktuurid on korduvad, kui aurustustingimused pole muutunud. Veel parem lähendus saadakse, kui arvesse on võetud ka sujuv üleminek alakihtide vahel, kuid sel juhul pole kindel, et tulemus kirjeldab kihi struktuuri, aga mitte mõõtmisega kaasnevat müra. Vaakumaurustatud kilede jaoks (MgF2, Y2O3 jt.) annab modelleerimine tulemuseks negatiivse mittehomogeensusega struktuuri, mille korral ülemisel, õhuga kokkupuutes oleval alakihil, on väiksem murdumisnäitaja, kui alumisel, alusega kokkupuutuval alakihil. Kumbal pool paikneb õhuke alakiht, pole võimalik määrata spektrist, kuid neid kaht paigutust ja lineaarse mittehomogeensuse juhtu on võimalik eristada, kui võtta juurde kihi füüsilise paksuse mõõtmise tulemus. Aatomkihtsadestatud kilede jaoks on näidatud, et neil on protsessitingimustest sõltuvalt võimalik nii positiivne kui ka negatiivne mittehomogeensus. TiO2 kilede jaoks on tõestatud, et modelleerimisega on võimalik kihi struktuurist informatsiooni saada ka juhul, kui kile paksusest ei piisa interferentsiekstreemumide tekkeks. Kasvuaegse minimaalse kandegaasi voo korral kujuneb TiO2 kihi korral õhuke, väiksema murdumisnäitajaga, alakiht kontaktis sulakvartsist alusega. Läbilaskvusspektri kasutamine annab võimaluse uurida kile struktuuri lihtsamaid vahendeid kasutades. Reaalsete kilede kirjeldamine murdumisnäitaja mittehomogeensust arvestavas lähenduses lubab ka paremini aru saada mitmekihiliste katete käitumisest ja loodetavasti parandada nende omadusi.
Spatio spectral correlations in interferenceless coded aperture correlation holography with vortex speckles
(2025) Vilardell, Eulàlia Puig; Gopinath, Shivasubramanian; Tiwari, Vipin; Kahro, Tauno; Kasikov, Aarne; Kõiv, Markus; Reddy, Andra Naresh Kumar; Rosen, Joseph; Kukli, Kaupo; Gailevičius, Darius; Juodkazis, Saulius; Anand, Vijayakumar
Interferenceless coded aperture correlation holography (I-COACH) is a computational imaging method that enables three-dimensional information of an object to be obtained without the need for two-beam interference. For the first time, in this study, we propose and demonstrate I-COACH with vortex speckles (I-COACH-VS). The vortex speckle distribution is generated by designing a unique coded mask by combining several spiral phases with different topological charges and linear phases using the transport of the amplitude into the phase based on the Gerchberg-Saxton algorithm (TAP-GSA). The spiral phase generates multiple beams carrying different orbital angular momentum, and the linear phase is used to map the beams at different locations within the image sensor to achieve a random vortex speckle distribution. The recently developed Lucy-Richardson-Rosen algorithm (LRRA) is used for image reconstruction. The theory, simulation studies, design of a coded mask by TAP-GSA, fabrication of coded masks by photolithography, and experimental demonstration of I-COACH-VS are presented. We believe that the developed method will be impactful in fields such as incoherent digital holography and computational imaging.