CIPHR - ERA Chair for Computational Imaging and Processing in High Resolution

Permanent URI for this collectionhttps://hdl.handle.net/10062/91302

In the project, the Centre of Photonics and Computational Imaging is established at the UT. The combined application of photonics and computationally intensive data processing allows to enhance the image quality, resolution or add spatial dimension to the image beyond the physical or technical limits of the imaging system. By nature, the research is interdisciplinary and embraces the extensive competence of the University of Tartu in optics, spectroscopy, mathematics, computer science and their applications.

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Interferenceless incoherent digital holography with binary coded apertures optimized using direct binary search
(Elsevier B.V., 2022) Kumar, Manoj; Anand, Vijayakumar; Rosen, Joseph
Coded aperture correlation holography offers 3D imaging with improved lateral and axial resolutions. This study is an additional advancement in the line of imaging systems with a pseudorandom coded aperture. Starting with the coded aperture correlation holography system implemented on an incoherent on-axis interferometer, we proposed interferenceless and lensless versions of the system. In the present study, we propose replacing the multi-values phase aperture mask with a binary mask. Two binary masks synthesized iteratively are used in two camera shots. Each mask is obtained from an iterative optimization process known as direct binary search, where the optimized cost function is the peak-to-background ratio of a reconstructed point object. Overall, the system demonstrates a lower background noise compared to other methods, enabling 3D imaging capability with only two camera shots, a substantial improvement in comparison to the many shots in the original systems. Using binary masks might extend the usefulness of the coded aperture holography for new regions in the electromagnetic spectrum other than the visual band, as of X-ray and THz bands.
Three-Dimensional Incoherent Imaging Using Spiral Rotating Point Spread Functions Created by Double-Helix Beams [Invited]
(Springer Nature, 2022) Anand, V.; Khonina, S.; Kumar, R.; Dubey, N.; Reddy, A.N.K.; Rosen, J.; Juodkazis, S.
In recent years, there has been a significant transformation in the field of incoherent imaging with new possibilities of compressing three-dimensional (3D) information into a two-dimensional intensity distribution without two-beam interference (TBI). Most incoherent 3D imagers without TBI are based on scattering by a random phase mask exhibiting sharp autocorrelation and low cross-correlation along the depth axis. Consequently, during reconstruction, high lateral and axial resolutions are obtained. Scattering based-Imaging requires a wasteful photon budget and is therefore precluded in many power-sensitive applications. This study develops a proof-of-concept 3D incoherent imaging method using a rotating point spread function termed 3D Incoherent Imaging with Spiral Beams (3DI2SB). The rotation speed of the point spread function (PSF) with displacement and the orbital angular momentum has been theoretically analyzed. The imaging characteristics of 3DI2SB were compared with a direct imaging system using a diffractive lens, and the proposed system exhibited a higher focal depth than the direct imaging system. Different computational reconstruction methods such as the Lucy–Richardson algorithm (LRA), non-linear reconstruction (NLR), and the Lucy–Richardson–Rosen algorithm (LRRA) were compared. While LRRA performed better than both LRA and NLR for an ideal case, NLR performed better than both under real experimental conditions. Both single plane imaging, as well as synthetic 3D imaging, were demonstrated. We believe that the proposed approach might cause a paradigm shift in the current state-of-the-art incoherent imaging, fluorescence microscopy, and astronomical imaging.
Anisotropic 3D columnar micro-film coating for applications in infrared and visible spectral ranges
(Elsevier B.V., 2022) Hu, J.; Han, M.; Grineviciute, L.; Ng, S.H.; Anand, V.; Katkus, T.; Ryu, M.; Morikawa, J.; Tobin, M.J.; Vongsvivut, J.; Tolenis, T.
Polarisation analysis of thin (∼1 μm) SiO2 films deposited via evaporation at a glancing angle of 70◦ to the normal on resist pillar arrays was carried out using synchrotron-based Fourier transform infrared (s-FTIR) microspectroscopy in reflection mode. Changes in intensity of absorption bands were observed to follow the angular dependence of ∼ cos2 𝜃, consistent with the absorption anisotropy. The strongest absorption was found to be the sharp Si–O–Si stretching vibrational mode at 1040 ± 20 cm−1, which can be used for sensor applications, as well as radiative cooling in the atmospheric transparency window, within the range of 8-13 μm (i.e. 1250-769 cm−1). Anisotropy of IR absorbance is correlated with retardance/birefringence of the same patterns in the visible spectral range. Larger period patterns of 3D columnar SiO2 films of ∼1 μm in thickness deposited on polymer/resist pillar arrays provide the possibility to control anisotropy of the form-birefringent 3D columnar films.
Review of engineering techniques in chaotic coded aperture imagers
(Light: Advanced Manufacturing, 2022) Anand, V.; Rosen, J.; Juodkazis, S.
Coded aperture imaging (CAI) is a technique to image three-dimensional scenes with special controlled abilities. In this review, we survey several recently proposed techniques to control the parameters of CAI by engineering the aperture of the system. The prime architectures of these indirect methods of imaging are reviewed. For each design, we mention the relevant application of the CAI recorders and summarize this overview with a general perspective on this research topic.
Optical anisotropy of glancing angle deposited thin films on nano-patterned substrates
(Optica Publishing Group, 2022) Grineviciute, L.; Moein, T.; Han, M.; Ng, S.H.; Anand, V.; Katkus, T.; Ryu, M.; Morikawa, J.; Tobin, M.J; Vongsvivut, J.; Tolenis, T.
This study has demonstrated that 3D columnar micro-films/coatings can be deposited over pre-patterned surfaces with sub-micrometer periodic patterns. Four-angle polarisation analysis of thin (0.4 − 1~μm) Si and SiO2 films, evaporated via glancing angle deposition (GLAD) at 70° to the normal, was carried out in reflection mode using synchrotron infrared microspectroscopy at the Australian Synchrotron. The angular dependence of absorbance followed A(θ) ∝ cos 2θ, confirmed for Si substrates patterned by electron beam lithography and plasma etching, which were used to make checkerboard patterns of Λ = 0.4~μm period on Si. Retardance control by birefringence of a patterned SiO2 substrate coated by columnar SiO2 is promising for UV-visible applications due to the use of the same material to endow polarisation control.
Computational Imaging Using Deterministic Optical Fields and Non-linear Reconstruction
(Imaging and Applied Optics Congress 2022 (3D, AOA, COSI, ISA, pcAOP), 2022) Arockiaraj, Francis Gracy; Selva, Shakina Jothi; Inbanathan, Stephen Rajkumar; Kamalam, Manueldoss Beaula Ruby; Rajeswary, Aravind Simon John Francis; Anand, Vijayakumar; Rosen, Joseph
Computational imaging techniques are indirect ones consisting of two steps: optical recording and computational reconstruction. In this study, deterministic optical fields such as Bessel, Airy, Gaussian and Laguerre-Gaussian were studied in this indirect imaging framework.
Tuning Axial Resolution Independent of Lateral Resolution in a Computational Imaging System Using Bessel Speckles
(Licensee MDPI, 2022) Anand, Vijayakumar
Speckle patterns are formed by random interferences of mutually coherent beams. While speckles are often considered as unwanted noise in many areas, they also formed the foundation for the development of numerous speckle-based imaging, holography, and sensing technologies. In the recent years, artificial speckle patterns have been generated with spatially incoherent sources using static and dynamic optical modulators for advanced imaging applications. In this report, a basic study has been carried out with Bessel distribution as the fundamental building block of the speckle pattern (i.e., speckle patterns formed by randomly interfering Bessel beams). In general, Bessel beams have a long focal depth, which in this scenario is counteracted by the increase in randomness enabling tunability of the axial resolution. As a direct imaging method could not be applied when there is more than one Bessel beam, an indirect computational imaging framework has been applied to study the imaging characteristics. This computational imaging process consists of three steps. In the first step, the point spread function (PSF) is calculated, which is the speckle pattern formed by the random interferences of Bessel beams. In the next step, the intensity distribution for an object is obtained by a convolution between the PSF and object function. The object information is reconstructed by processing the PSF and the object intensity distribution using non-linear reconstruction. In the computational imaging framework, the lateral resolution remained a constant, while the axial resolution improved when the randomness in the system was increased. Three-dimensional computational imaging with statistical averaging for different cases of randomness has been synthetically demonstrated for two test objects located at two different distances. The presented study will lead to a new generation of incoherent imaging technologies.
Review of engineering techniques in chaotic coded aperture imagers
(2022) Anand, Vijayakumar; Rosen, Joseph; Juodkazis, Saulius
Coded aperture imaging (CAI) is a technique to image three-dimensional scenes with special controlled abilities. In this review, we survey several recently proposed techniques to control the parameters of CAI by engineering the aperture of the system. The prime architectures of these indirect methods of imaging are reviewed. For each design, we mention the relevant application of the CAI recorders and summarize this overview with a general perspective on this research topic.
Single Shot Multispectral Multidimensional Computational Imaging Using Quasi-Random Lenses
(Imaging and Applied Optics Congress 2022 (3D, AOA, COSI, ISA, pcAOP), 2022) Smith, Daniel; Gopinath, Shivasubramanian; Hock Ng, Soon; Katkus, Tomas; Renganathan, Dhanalakshmi; Navaneethakrishnan, Srinivasan; Juodkazis, Saulius; Anand, Vijayakumar
Quasi-random lenses (QRLs) were fabricated using electron beam lithography and conventional lens grinding to map every object point to a unique random intensity distribution. Multidimensional and multispectral computational imaging has been demonstrated using the QRLs.
White Light Correlation Holography Using a Random Lens for Astronomical Imaging Applications
(2022 Photonics & Electromagnetics Research Symposium (PIERS), 2022) Anand, V.; Ng, S. H.; Katkus, T.; Juodkazis, S.
Roadmap on chaos-inspired imaging technologies (CI2-Tech)
(Springer Nature, 2022) Rosen, Joseph; de Aguiar, H.B.; Anand, V.; Baek, Y.; Gigan, S.; Horisaki, R.; Hugonnet, H.; Juodkazis, S.; Lee, K.; Liang, H.; Liu, Y.
In recent years, rapid developments in imaging concepts and computational methods have given rise to a new generation of imaging technologies based on chaos. These chaos-inspired imaging technologies (CI2-Tech) consist of two directions: non-invasive and invasive. Non-invasive imaging, a much older research direction with a goal of imaging through scattering layers, has reached faster, smarter, and sharper imaging capabilities in recent years. The invasive imaging direction is based on exploiting the chaos to achieve imaging characteristics and increase dimensionalities beyond the limits of conventional imagers. In this roadmap, the current and future challenges in invasive and non-invasive imaging technologies are presented.
THz Filters Made by Laser Ablation of Stainless Steel and Kapton Film
(2022) Han, Molong; Smith, Daniel; Hock Ng, Soon; Vilagosh, Zoltan; Anand, Vijayakumar; Katkus, Tomas; Reklaitis, Ignas; Mu, Haoran; Ryu, Meguya; Morikawa, Junko; Vongsvivut, Jitraporn; Appadoo, Dominique; Juodkazis, Saulius
THz band-pass filters were fabricated by femtosecond-laser ablation of 25-μm-thick micro-foils of stainless steel and Kapton film, which were subsequently metal coated with a ∼70 nm film, closely matching the skin depth at the used THz spectral window. Their spectral performance was tested in transmission and reflection modes at the Australian Synchrotron’s THz beamline. A 25-μm-thick Kapton film performed as a Fabry–Pérot etalon with a free spectral range (FSR) of 119 cm−1, high finesse Fc≈17, and was tuneable over ∼10μm (at ∼5 THz band) with β=30∘ tilt. The structure of the THz beam focal region as extracted by the first mirror (slit) showed a complex dependence of polarisation, wavelength and position across the beam. This is important for polarisation-sensitive measurements (in both transmission and reflection) and requires normalisation at each orientation of linear polarisation.
Roadmap of incoherent digital holography
(Applied Physics B, 2022) Tahara, Tatsuki; Zhang, Yaping; Rosen, Joseph; Anand, Vijayakumar; Cao, Liangcai; Wu, Jiachen; Koujin, Takako; Matsuda, Atsushi; Ishii, Ayumi; Kozawa, Yuichi; Okamoto, Ryo; Oi, Ryutaro; Nobukawa, Teruyoshi; Choi, Kihong; Imbe, Masatoshi; Poon, Ting-Chung
This roadmap article focuses on spatially incoherent digital holography (IDH). Representative IDH methods such as optical scanning holography (OSH), Fresnel incoherent correlation holography (FINCH), coded aperture correlation holography (COACH), IDH with a Fresnel zone aperture, and IDH with an interferometer along with a state-of-the-art optical device are introduced as modern IDH methods. We describe these IDH techniques with applications of three-dimensional (3D) imagers, 3D thermography, and 3D microscopy.
Implementation of a Large-Area Diffractive Lens Using Multiple Sub-Aperture Diffractive Lenses and Computational Reconstruction
(Licensee MDPI, 2022) Gopinath, Shivasubramanian; Praveen, Periyasamy Angamuthu; Kahro, Tauno; Bleahu, Andrei-Ioan; Arockiaraj, Francis Gracy; Smith, Daniel; Ng, Soon Hock; Juodkazis, Saulius; Kukli, Kaupo; Tamm, Aile; Anand, Vijayakumar
Direct imaging systems that create an image of an object directly on the sensor in a single step are prone to many constraints, as a perfect image is required to be recorded within this step. In designing high resolution direct imaging systems with a diffractive lens, the outermost zone width either reaches the lithography limit or the diffraction limit itself, imposing challenges in fabrication. However, if the imaging mode is switched to an indirect one consisting of multiple steps to complete imaging, then different possibilities open. One such method is the widely used indirect imaging method with Golay configuration telescopes. In this study, a Golay-like configuration has been adapted to realize a large-area diffractive lens with three sub-aperture diffractive lenses. The sub-aperture diffractive lenses are not required to collect light and focus them to a single point as in a direct imaging system, but to focus independently on different points within the sensor area. This approach of a Large-Area Diffractive lens with Integrated Sub-Apertures (LADISA) relaxes the fabrication constraints and allows the sub-aperture diffractive elements to have a larger outermost zone width and a smaller area. The diffractive sub-apertures were manufactured using photolithography. The fabricated diffractive element was implemented in indirect imaging mode using non-linear reconstruction and the Lucy–Richardson–Rosen algorithm with synthesized point spread functions. The computational optical experiments revealed improved optical and computational imaging resolutions compared to previous studies.
Nonlinear Reconstruction of Images from Patterns Generated by Deterministic or Random Optical Masks—Concepts and Review of Research
(Journal of Imaging, 2022) Smith, Daniel; Gopinath, Shivasubramanian; Arockiaraj, Francis Gracy; Reddy, Andra Naresh Kumar; Balasubramani, Vinoth; Kumar, Ravi; Dubey, Nitin; Ng, Soon Hock; Katkus, Tomas; Selva, Shakina Jothi; Renganathan, Dhanalakshmi; Kamalam, Manueldoss Beaula Ruby; Rajeswary, Aravind Simon John Francis; Navaneethakrishnan, Srinivasan; Inbanathan, Stephen Rajkumar; Valdma, Sandhra-Mirella; Praveen, Periyasamy Angamuthu; Amudhavel, Jayavel; Kumar, Manoj; Ganeev, Rashid A.; Magistretti, Pierre J.; Depeursinge, Christian; Juodkazis, Saulius; Rosen, Joseph; Anand, Vijayakumar
Indirect-imaging methods involve at least two steps, namely optical recording and computational reconstruction. The optical-recording process uses an optical modulator that transforms the light from the object into a typical intensity distribution. This distribution is numerically processed to reconstruct the object’s image corresponding to different spatial and spectral dimensions. There have been numerous optical-modulation functions and reconstruction methods developed in the past few years for different applications. In most cases, a compatible pair of the optical-modulation function and reconstruction method gives optimal performance. A new reconstruction method, termed nonlinear reconstruction (NLR), was developed in 2017 to reconstruct the object image in the case of optical-scattering modulators. Over the years, it has been revealed that the NLR can reconstruct an object’s image modulated by an axicons, bifocal lenses and even exotic spiral diffractive elements, which generate deterministic optical fields. Apparently, NLR seems to be a universal reconstruction method for indirect imaging. In this review, the performance of NLR is investigated for many deterministic and stochastic optical fields. Simulation and experimental results for different cases are presented and discussed
Simultaneous Detection of Modal Composition and Wavelength of OAM Fields Using a Hexagonal Vortex Filter
(2022 Photonics & Electromagnetics Research Symposium (PIERS), 2022) Reddy, Andra Naresh Kumar; Anand, Vijayakumar; Podlipnov, Vladimir V.; Khonina, Svetlana Nikolaevna; Juodkazis, Saulius
Fresnel Incoherent Correlation Holography using Lucy-Richardson-Rosen Algorithm
(Digital Holography and 3-D Imaging 2022, 2022) Balasubramani, Vinoth; Anand, Vijayakumar; Reddy, Andra Naresh Kumar; Rajeswary, Aravind Simon John Francis; Magistretti, Pierre J.; Depeursinge, Christian; Juodkazis, Saulius
Fresnel incoherent correlation holography (FINCH) is a super-resolution imaging method which requires at least three camera shots to image an object. In this study, we have demonstrated single-shot FINCH using a recently developed Lucy-Richardson-Rosen algorithm.
Single Shot Lensless Interferenceless Phase Imaging of Biochemical Samples Using Synchrotron near Infrared Beam
(Licensee MDPI, 2022) Han, Molong; Smith, Daniel; Ng, Soon Hock; Katkus, Tomas; Rajeswary, Aravind Simon John Francis; Praveen, Periyasamy Angamuthu; Bambery, Keith R.; Tobin, Mark J.; Vongsvivut, Jitraporn; Juodkazis, Saulius; Anand, Vijayakumar
Phase imaging of biochemical samples has been demonstrated for the first time at the Infrared Microspectroscopy (IRM) beamline of the Australian Synchrotron using the usually discarded near-IR (NIR) region of the synchrotron-IR beam. The synchrotron-IR beam at the Australian Synchrotron IRM beamline has a unique fork shaped intensity distribution as a result of the gold coated extraction mirror shape, which includes a central slit for rejection of the intense X-ray beam. The resulting beam configuration makes any imaging task challenging. For intensity imaging, the fork shaped beam is usually tightly focused to a point on the sample plane followed by a pixel-by-pixel scanning approach to record the image. In this study, a pinhole was aligned with one of the lobes of the fork shaped beam and the Airy diffraction pattern was used to illuminate biochemical samples. The diffracted light from the samples was captured using a NIR sensitive lensless camera. A rapid phase-retrieval algorithm was applied to the recorded intensity distributions to reconstruct the phase information. The preliminary results are promising to develop multimodal imaging capabilities at the IRM beamline of the Australian Synchrotron.
Extraordinary Computational Imaging Technologies with Ordinary Optical Modulators (Invited)
(2022) Anand, Vijayakumar; Ng, Soon Hock; Maksimovic, Jovan; Katkus, Tomas; Han, Molong; Linklater, Denver P.; Klein, Annaleise; Bambery, Keith R.; Tobin, Mark J.; Ivanova, Elena P.; Vongsvivut, Jitraporn; Juodkazis, Saulius
Computational imaging technology (CIT) has revolutionized the field of imaging. CITs based on two genres namely random and deterministic optical fields generated by common optical modulators with extraordinary imaging capabilities are discussed.
Single-shot mid-infrared incoherent holography using Lucy-Richardson-Rosen algorithm
(Opto-Electronic Science, 2022) Vijayakumar, A.; Molong, H.; Jovan, M.; Hock, N.S.; Tomas, K.; Annaleise, K.; Keith, B.; Tobin Mark, J.; Jitraporn, V.; Saulius, J.
In recent years, there has been a significant transformation in the field of incoherent imaging with new possibilities of compressing three-dimensional (3D) information into a two-dimensional intensity distribution without two-beam interference (TBI). Most of the incoherent 3D imagers without TBI are based on scattering by a random phase mask exhibiting sharp autocorrelation and low cross-correlation along the depth. Consequently, during reconstruction, high lateral and axial resolutions are obtained. Imaging based on scattering requires an astronomical photon budget and is therefore precluded in many power-sensitive applications. In this study, a proof-of-concept 3D imaging method without TBI using deterministic fields has been demonstrated. A new reconstruction method called the Lucy-Richardson-Rosen algorithm has been developed for this imaging concept. We believe that the proposed approach will cause a paradigm-shift in the current state-of-the-art incoherent imaging, fluorescence microscopy, mid-infrared fingerprinting, astronomical imaging, and fast object recognition applications.

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