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Optical Nanolithography
Published in Bruce W. Smith, Kazuaki Suzuki, Microlithography, 2020
Using off-axis illumination, source shaping such as dipole, quadrupole, annular, and more customized variations can lead to improvements in the printing of photoresist features. Although incoherent illumination leads to the limits of resolution for an optical system (and a k1 = 0.25), the image quality at these limits will generally be poor. This is especially true as defocus and other image degradation mechanisms (e.g. aberrations) are considered. For projection optical lithography, incoherent illumination should be thought of as a starting point, where improvements in image quality can be achieved through the removal of select portions of a full σ = 1 illuminator. This approach leads to an understanding of how off-axis illumination and more customized illumination are an integral part of leading edge optical lithography.
A new approach to non-mydriatic portable fundus imaging
Published in Expert Review of Medical Devices, 2022
Faizal Hafiz, Renoh Johnson Chalakkal, Sheng Chiong Hong, Glenn Linde, Roger Hu, Ben O’Keeffe, Yim Boobin
Figure 3 shows illumination, buffer and imaging regions in the retina following the conventional ring illumination, off-axis illumination and the proposed approach. Note that, with the proposed approach (Figure 3c), the retina is irradiated at two vertically symmetric spots as the illumination sources are positioned 180 degrees apart and around the optical axis. This approach overcomes the issue of optical axis mismatch in the off-axis illumination while keeping the illumination system relatively simpler compared to the ring illumination. The nun IR camera can be used for a minimum pupil size of 3.5 mm. Accordingly, the imaging region at the pupil or the (crystal) lens is limited to 3 mm. The size of the retinal illumination spots is limited to 1 mm to create a buffer region between the illumination and imaging regions. The buffer region plays a key role in minimizing the corneal and the lens back-reflections.