When vision is provided through thermal-imaging systems field-of-view is reduced, effectively the soldier must operate with severe tunnel vision and so there is a requirement for a system which provides automated warning and immersive imaging. We present a computational multi-aperture thermal infrared (MA-TIR) imaging system with single-photon range imaging to provide enhanced video-rate detection of obscured biological signatures in clutter. Our multi-camera computational imaging system creates a 360° panoramic image, and we employ synthetic baseline integral imaging (SBII) for the construction of three-dimensional thermal scenes, including detection of occluded objects. We further fuse thermal imaging with covert time-correlated single-photon counting (TCSPC) LIDAR to provide the complementary capability of video-rate ranging with the ability to detect and classify targets through clutter, particularly based on movement signatures. Finally, we demonstrate the ability to discriminate between biological scene components and static clutter based on temporal modulations of picosecond resolution TCSPC returns.
We describe how the use of multiple-camera imaging systems provides an interesting alternative imaging modality to conventional single-aperture imaging, but with a different challenge: to computationally integrate diverse images while demonstrating an overall system benefit. We report the use of super-resolution with arrays of nominally identical longwave infrared cameras to yield high-resolution imaging with reduced track length, while various architectures enable foveal imaging, 4π and 3D imaging through the exploitation of integral imaging techniques. Strikingly, multi-camera spectral imaging using a camera array can uniquely demonstrate video-rate imaging, high performance and low cost.
While the performance of optical imaging systems is fundamentally limited by diffraction, the design and manufacture of practical systems is intricately associated with the control of optical aberrations. The fundamental Shannon limit for the number of resolvable pixels by an optical aperture is generally therefore not achieved due to the presence of off-axis aberrations or large detector pixels. We report how co-called computational-imaging (CI) techniques can enable an increase in imaging performance using more compact optical systems than are achievable with traditional optical design. We report how discontinuous lens elements, either near the pupil or close to the detector, yield complex and spatially variant PSFs that nevertheless provide enhanced transmission of information via the detector to enable imaging systems that are many times shorter and lighter than equivalent traditional imaging systems. Computational imaging has been made possible and attractive with the trend for advanced manufacturing of aspheric, asymmetric lens shapes at lower cost and by the exploitation of low-cost, high-performance digital computation. The continuation of these trends will continue to increase the importance of computational imaging.
Imaging samples with a depth in excess of the depth of field of the objective poses a serious challenge in microscopy. The available techniques such as focus-stacking accomplish the task; however, besides necessitating complicated optical and mechanical arrangements, these techniques often exhibit very long acquisition times. As a result, their applicability is limited to static samples. We describe a simple and practical hybrid 3D imaging technique which permits the acquisition of 3D images in a single snapshot. Additionally, the proposed method solves the post-recovery artefact formation problem which plagues hybrid imaging systems; thus, enabling high-quality, artefact-free images to be obtained. Experimental results indicate that this method can yield an image quality comparable to that given by a focus-stack (which can require up to a few hundred snapshots) from a single snapshot.
A new phase mask typology for wavefront-coding is proposed, the meshed phase mask (MPM). It is intended
to be a flexible form in order to be easily adaptable. The use of an evaluating criterion to measure the
performance of the MPM is used to optimize its shape. The MPM is uniquely defined by the fixed phase in
a number of control points equally spaced in the pupil area. These control points define a regular mesh, and
the continuous MPM phase surface is obtained from cubic spline interpolation. A global search algorithm is
used to optimize the values at the control points, thus optimizing the MPM. The preliminary results show
an improvement over the conventional cubic phase mask, especially in reducing the undesired artefacts in
the final restored images.
We present the results of the utilization of a Spatial Light Modulator Liquid Crystal Display for the implementation of
wavefront codification procedures in an imaging system. The light modulator works in transmission mode at the pupil of the instrument. The main disadvantage is that the procedure implies a calibration of the device as well as an inherent image processing. The more interesting feature we can obtain is the versatility related to the use of an electronic device at the pupil, as compared with conventional (fixed) manufactured ones.
Wave-front coding techniques are being used nowadays in vision systems to obtain invariance to aberrations and,
especially, extended depth of focus capabilities. Besides using a phase mask for coding, one of the basic steps of the
method is the digital processing of the images captured by means of a pixelated sensor (for example a CCD device).
This capture process can become crucial for the overall performance of the procedures, since the effects due to the
averaging within a pixel and to the related noise inherent to the detection can be indeed the most determinant ones.
This work presents a simulation tool for fully assessing the role of a pixelated sensor in a vision system working by
wave-front coding techniques, including diffractive effects, the averaging in detection, the modeling of the noise that
might be added and the influence in the restoration algorithm. The numerical tool computes (in order): diffraction
during image formation, averaging at the pixels and digital image processing. Similarly, noise could be added to the
detection as well as other effects influencing the final image quality.
The influence of these topics in the design of the phase masks is analyzed for several cases. Our results show that the
pixelated character of the detector can not be considered a final refinement only and can not be obviated in the design
stage of phase plates for wave-front coding.
A study of the non-linear optical properties of Si-nc embedded in SiO2 has been performed by using the z-scan method in the nanosecond and femtosecond ranges. Substoichiometric SiOx films were grown by plasma-enhanced chemical-vapor deposition (PECVD) on silica substrates for Si excesses up to 24 at. %. An annealing at 1250 °C for 1 hour was performed in order to precipitate Si-nc, as shown by EFTEM images. Z-scan results have shown that, by using 5-ns pulses, the non-linear process is ruled by thermal effects and only a negative contribution can be observed in the non-linear refractive index, with typical values around -10-10 cm2/W. On the other hand, femtosecond excitation has revealed a pure electronic contribution to the nonlinear refractive index, obtaining values in the order of 10-12 cm2/W. Simulations of heat propagation have shown that the onset of the temperature rise is delayed more than half pulse-width respect to the starting edge of the excitation. A maximum temperature increase of ΔT = 123.1 °C has been found after 3.5 ns of the laser pulse maximum. In order to minimize the thermal contribution to the z-scan transmittance and extract the electronic part, the sample response has been analyzed during the first few nanoseconds. By this method we found a reduction of 20 % in the thermal effects. So that, shorter pulses have to be used to obtain just pure electronic non-linearities.