Tauno Kahro

Coded aperture imaging (CAI) is a powerful imaging technology that has rapidly developed during the past decade. CAI technology and its integration with incoherent holography have led to the development of several cutting-edge imaging tools, devices, and techniques with widespread interdisciplinary applications, such as in astronomy, biomedical sciences, and computational imaging. In this review, we provide a comprehensive overview of the recently developed CAI techniques in the framework of incoherent digital holography. The review starts with an overview of the milestones in modern CAI technology, such as interferenceless coded aperture correlation holography, followed by a detailed survey of recently developed CAI techniques and system designs in subsequent sections. Each section provides a general description, principles, potential applications, and associated challenges. We believe that this review will act as a reference point for further advancements in CAI technologies.

Coded aperture imaging (CAI) is a powerful imaging technology that has rapidly developed during the past decade. CAI technology and its integration with incoherent holography have led to the development of several cutting-edge imaging tools, devices, and techniques with widespread interdisciplinary applications, such as in astronomy, biomedical sciences, and computational imaging. In this review, we provide a comprehensive overview of the recently developed CAI techniques in the framework of incoherent digital holography. The review starts with an overview of the milestones in modern CAI technology, such as interferenceless coded aperture correlation holography, followed by a detailed survey of recently developed CAI techniques and system designs in subsequent sections. Each section provides a general description, principles, potential applications, and associated challenges. We believe that this review will act as a reference point for further advancements in CAI technologies.

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.

As an atomically thin electric conductor with a low density of highly mobile charge carriers, graphene is a suitable transducer for molecular adsorption. In this study, we demonstrate that the adsorption properties can be significantly enhanced with a laser-deposited TiO₂ nanolayer on top of single-layer CVD graphene, whereas the effective charge transfer between the TiO₂-adsorbed gas molecules and graphene is retained through the interface. The formation of such a heterostructure with optimally a monolayer thick oxide combined with ultraviolet irradiation (wavelength 365 nm, intensity 2 years) in ambient air. The results pave the way for an emerging class of gas sensor structures based on stacked 2D materials incorporating highly charge-sensitive transducer and selective receptor layers.

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.

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 barium fluoride substrate close to the sample. Preliminary results of imaging thick and sparse silk fibers showed an improved focal depth with a slight decrease in lateral resolution and increase in background noise.

Chemiresistive gas sensors were produced by functionalizing graphene with a ~3 nm layer of mixed oxide xCu₂O⸱yMnO using pulsed laser deposition (PLD) from a hopcalite CuMn₂O₄ target. Sensor response time traces were recorded for strongly oxidizing (NO₂, O₃) and reducing (NH₃, H₂S) poisonous gases at ppb and ppm levels, respectively. The morphology of the MOX layer was modified by growth temperature during PLD, resulting in the optimization of the sensor response. Differences in decomposition or oxidation rates on catalytically active metal oxide (MOX) were utilized to achieve partial selectivity for pairs of gases that have similar adsorption and redox properties. The predominant selectivity towards ozone in most samples at different measuring conditions remained difficult to suppress. A distinct selectivity for H₂S emerged at higher measurement temperatures (100–150 °C), which was assigned to catalytic oxidation with O₂. Several gas–MOX interaction mechanisms were advanced to tentatively explain the sensor behavior, including reversible electron transfer in the simplest case of NO₂, decomposition via ionic transients for O₃, and complex catalytic oxidative transformations for NH₃ and H₂S.

Manufacturing large area diffractive lenses (DLs) is a challenging task, as in many cases, the outermost zone width surpasses the photolithography limit and even the wavelength limit. In this study, a computational imaging method is proposed which allows realizing a single large area strong DL with multiple sub-aperture weak DLs. The sub-aperture DLs collect light and focus it into multiple points within the area of the image sensor instead of a single point which increases the width of the zones of the DL. A computational reconstruction method was applied to reconstruct a high-resolution image from the multiple low-resolution images.