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Wide-angle optics

Panomorph stereoscopic system for 3D reconstruction of objects in a scene
Student: Anne-Sophie Poulin-Girard

Recent developments in lens design have lead to the creation of new panoramic lenses with special characteristics. Panomorph lenses are panoramic anamorphic lenses that exhibit a variation of the magnification over the field of view. High distortion is often seen as an inconvenient but is used to create this effect. Variable magnification generates enhanced resolution areas, a feature that can be taken advantage of computer vision. The suggested stereoscopic system will be made of two cameras and Panomorph lenses and will present interesting qualities. Objects located in common enhanced resolution areas (ROI) of the field of view of the system will undergo a better 3D reconstruction while keeping a large total common field of view, a characteristic that would be impossible to achieve with fisheye lenses for example. Since enhanced resolution areas are located on both side of the optical axis, canonical, convergent and divergent configurations could be used depending on the application and the position and number of region of interest needed. Even if the calibration of the suggested system is a challenge, non-uniform distortion lenses will give computer vision system designers a new degree of freedom to better answer the needs of specific applications.

Papers size
A.-S. Poulin-Girard, S. Thibault et D. Laurendeau, "Passive stereoscopic panomorph system", Proceedings of SPIE Vol. 8650, 86500S (2013) 573 KB Download
A.-S. Poulin-Girard, X. Dallaire, A. Veillette, et al., "Study of camera calibration process with ray tracing", Proceedings of SPIE Vol. 9192, 91920B (2014) 809 KB Download
A.-S. Poulin-Girard, X. Dallaire, S. Thibault, and D. Laurendeau, "Virtual camera calibration using optical design software", Applied Optics, Vol. 53, Issue 13, pp. 2822-2827 (2014) 582 KB Download
Miniaturization of wide-angle lenses
Student: Xavier Dallaire

Among optical systems, wide-angle lenses (panomorph and fisheye) are extremely difficult to miniaturize, principally because of the high amount of optical surfaces, their shape and their complexity (free-form surface). Right now, the techniques used to manufacture miniature cellphones are not well suited to the needs of a miniature wide-angle lens. Therefore, there is a need to explore different avenues if we are to see the integration of wide-angle lens into modern technological applications.

The goal of the project is to use the most advanced methods to miniaturize complex optical systems. More precisely:

• Develop design strategies to create small wide angle-lens.
• Compare those strategies via simulations.
• Develop and assemble the most promising prototype.
• • Evaluate the prototype.

In order to succeed, it is important to begin by examining the existing miniaturization and simplification techniques and to filter which one could be of use. Here we are talking about micro lens array, discrete field of view, image reconstruction, sampling techniques, folded designs, etc. Moreover, certain recent developments in optics will be investigated (nanowires and transformation optics). Once this phase is complete, a group of criteria will be chosen to ensure an adequate comparison between each technique. After, numerical simulation will ensure the validity of the different solution before a prototype is constructed and tested.

Papers Size

Metrology and wavefront control

Panomorph stereoscopic system for 3D reconstruction of objects in a scene
Student: Anne-Sophie Poulin-Girard

Recent developments in lens design have lead to the creation of new panoramic lenses with special characteristics. Panomorph lenses are panoramic anamorphic lenses that exhibit a variation of the magnification over the field of view. High distortion is often seen as an inconvenient but is used to create this effect. Variable magnification generates enhanced resolution areas, a feature that can be taken advantage of computer vision. The suggested stereoscopic system will be made of two cameras and Panomorph lenses and will present interesting qualities. Objects located in common enhanced resolution areas (ROI) of the field of view of the system will undergo a better 3D reconstruction while keeping a large total common field of view, a characteristic that would be impossible to achieve with fisheye lenses for example. Since enhanced resolution areas are located on both side of the optical axis, canonical, convergent and divergent configurations could be used depending on the application and the position and number of region of interest needed. Even if the calibration of the suggested system is a challenge, non-uniform distortion lenses will give computer vision system designers a new degree of freedom to better answer the needs of specific applications.

Papers size
A.-S. Poulin-Girard, S. Thibault et D. Laurendeau, "Passive stereoscopic panomorph system", Proceedings of SPIE Vol. 8650, 86500S (2013) 573 KB Download
A.-S. Poulin-Girard, X. Dallaire, A. Veillette, et al., "Study of camera calibration process with ray tracing", Proceedings of SPIE Vol. 9192, 91920B (2014) 809 KB Download
A.-S. Poulin-Girard, X. Dallaire, S. Thibault, and D. Laurendeau, "Virtual camera calibration using optical design software", Applied Optics, Vol. 53, Issue 13, pp. 2822-2827 (2014) 582 KB Download
Adaptive optics test bench for the Mont Mégantic observatory
Student: William Deschênes

The current construction & design of next generation telescopes such as the TMT and E-ELT requires the creation and validation of numerous new technologies to get the most out of them. Adaptive Optics (AO) is one of those technologies, allowing us to reach the diffraction limit of these telescopes despite the distorting effects of the atmosphere. Many new AO devices in development, such as new wavefront sensors and deformable mirrors lack the technological readiness level (TRL) to be used in such expensive system. To demonstrate their reliability, they need to be tested in a real telescope observing the sky. However, most laboratories lack access to a telescope, much less a technological platform, to test their devices.

The current project involves the creation of an AO test bench for the Mont Mégantic observatory (Observatoire du Mont Mégantic or OMM) to test AO devices currently being developed in Canada. The test bench is based on a system already in use in our laboratories, which allows new devices to be compared alongside well-known AO standards, such as a Shack-Hartmann wavefront sensor and a Voice-Coil deformable mirror. This gives us instantaneous information on the performance of the new devices.

The test bench is currently in its assembly phase. First light is expected in March 2015, where we will also test a Pyramid wavefront sensor at development at the Institut National d’Optique.

Papers Size
Magnetic nanoparticles-filled elastomeric membranes for the development of novel deformable mirrors
Student: Renaud Lussier

This project is taking place in a chemistry master degree focusing on the functional materials field. The aim of the project is the conception and production of deformable materials for application in adaptive optics. We aim for materials consisting of an elastomeric membrane filled with magnetic ferrous oxide nanoparticles responding to the application of magnetic field applied from an actuators system. The spin coating method is used to obtain thin and smooth membranes. Applications in optics require a surface on wich the roughness has a very low amplitude of the order of the nanometer. The polydimethylsiloxane (PDMS) of which the membrane is made is heated to induce reticulation giving it its elastomeric texture. These devices will differ from ferrofluid based liquid mirrors by the elimination of the liquid part thus facilitating their implementation. We are interested in the response that will be shown by the membranes under the influence of an external magnetic field and we consider the possibility of orienting the nanoparticles before the curing of the polymer. Different characterization techniques will be used on the membranes to study their surface (profilometry) and the distribution of the nanoparticles inside the polymer matrix (scanning electron microscopy). The addition of a thin reflecting aluminum layer at the surface of such membranes would produce a deformable mirror. Thus, if the amplitude of deformation and the lateral resolution are adequate, usable deformable mirrors without liquid component will be obtained.

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Extreme focusing by non-paraxial optical elements
Student: Denis Panneton

This project aims the modelization and the development of analytical tools for non-paraxial focaliza- tion. Exact vectorial electromagnetic solutions are developed according to an extension of the Richards- Wolf formalism to systems without single-point focus. Introducing a combined method, based on ray tracing and diffraction integrals, the model enhances the classical treatment of wave-focusing in three different ways. First, it is a viable method for non-paraxial, high-aperture focusing since it consid- ers a vectorial diffraction analysis. Second, spread-focus systems can be analytically and rigorously described, as opposed to the usual aberration treatment, which induces approximated correcting phase- terms. Finally, the analytic elegance gives a general physical insight on interference phenomenas near the focus of complex systems, while encouraging the development of inverse methods leading to a non-iterative backtracking of physical conditions for beam manipulation. Ultimately, these analytical tools would help researchers and developers in hyper-resolution microscopy, mainly, but also in data storage, optical trapping and even in particle acceleration.
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Non-imaging photonics

Optical and opto-mechanical design of detection channels using avalanche photodiodes for diffuse optical tomography
Student: Charles Pichette

Diffuse optical tomography (DOT) is a 3D non-invasive imaging technique used to detect the spatial distribution of the absorption and diffusion coefficient of a small animal. This technique is also used to localize fluorescence inclusion inside the volume and is therefore very useful in pharmacology and oncology where it is used to follow the progression of pathologies or to detect cancerous cells.

The method used to gather these results is based around time-correlated single photon counting (TCSPC) techniques. The detectors used in this kind of setup are usually photomultiplier tubes (PMT). These are particularly useful because of their good sensitivity and fast response time. However, PMTs are expensive and vulnerable to ambient light. Therefore, it could be interesting to consider avalanche photodiodes (APD) to replace PMTs due to their low cost and resistance to ambient light. They are also smaller than PMTs which allows us to increase the number of detectors and reduce the acquisition time while still maintaining a good sensitivity. However, APDs have very small detection zone compared to PMTs which makes efficient focusing of light on the detector, a challenge.

The goal of this project is to do the optical and opto-mechanical design of these new detection channels. These will include the avalanche photodiodes and should reduce the acquisition time while still maintaining a good count rate. The project will end with the integration of the channels in the laboratory of Professor Yves Bérubé-Lauzière at the University of Sherbrooke.

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Three-dimensional dose measurements of megavoltage photon beams with a light-field imager and plastic scintillator
Student: Madison Rilling

Dosimetry systems play an essential role in medical physics for clinical quality assurance: the use of such detectors increases delivery accuracy to a targeted tumor, minimizes exposure of organs at risk and thus greatly improves treatment outcomes.

This master’s project consists of developing a three-dimensional (3D) radiation dose detector system using a plastic scintillator volume and a light-field imager for medical physics applications. In particular, the goal is to improve its temporal and spatial resolution to make it a usable quality assurance tool for external beam radiation treatments.

The proposed 3D detector device is the only medical physics tool potentially capable of measuring complete three-dimensional radiation doses in near real-time. This dosimetry system uses a uniform plastic scintillator volume as a target for verifying radiation treatments: when irradiated, this material emits a fluorescent light, which is proportional to the dose locally absorbed by the medium. During the delivery, images are acquired using a light-field imager, which has an array of microlenses in front of its actives sensor. With this additional optical component, the camera thus records spatial as well as directional information of light in its field of view. Hence, each image consists of a multi-focal plane measurement, containing information on the intensity of emitted light through the whole depth of the scintillator. Pixel-by-pixel tomographic algorithms are applied to images acquired during a treatment delivery to reconstruct the delivered 3D dose distribution, which can then be compared to the planned treatment.

Papers Size
M. Goulet, M. Rilling, L. Gingras, S. Beddar, L. Beaulieu and L. Archambault, “Novel, full 3D scintillation dosimetry using a static plenoptic camera,” Med. Phys. 41, 082101 (2014). 1.92MB Download