1,720,994 research outputs found
Digital holographic-volumetric bio-printing using binary-phase HoloTile on a DMD
No full textWe present the option to use the patented [1, 2] Computer Generated Holography (CGH) modality, HoloTile, as a better alternative light delivery system for volumetric additive manufacturing (VAM). Holographic light delivery promises many of the qualities sought after in VAM, including higher photon efficiency, inherent wavefront shaping, full point spread function control, and lower mechanical complexity. These qualities, along with the unique control that is gained with HoloTile, may allow for the use of low-power light sources at low print times with real-time aberration and scattering compensation
Femtosecond laser inscribed advanced calibration phantom for optical coherence tomography (OCT)
Get PDFOptical coherence tomography (OCT) has developed rapidly and is widely used in different fields such as biomedicine and optometry. The characterization and calibration of OCT systems is essential when testing the system and during normal use to ensure that there is no misalignment or distortion that could affect clinical decisions. Imaging distortion is a significant challenge for OCT systems when viewing through non-planar surfaces. Here we present a new multi-purpose plano-convex OCT phantom which is designed to be used for OCT characterization and calibration as well as to validate the post-processing algorithm for the imaging distortion of the OCT systems. A femtosecond laser direct writing technique is used to fabricate this phantom which consists of a landmark layer with radial lines at a 45-degree angular spacing inscribed at 50μm in apparent depth (AD) underneath the planar surface. Below that there are a further 8 layers of a spherical inscription pattern which has a 150μm (in AD) separation between each layer. The first spherical layer is located at 150μm (in AD) underneath the planar surface. Due to the laser power loss when travelling through the deeper layer, an increased power is applied to the deeper layers. The spherical pattern overcomes orientation issues seen with existing calibration phantoms. The landmark layer is applied so that it can easily tell the exact location when scanning which will also benefit the image distortion correction process
Holo Tile:a novel digital holographic light sculpting modality for volumetric 3D printing (Invited Paper)
No full textHoloTile is our novel and recently patent-filed approach [1,2] to obtain very fastreconfigurable and strongly speckle-reduced digital holography. Using HoloTile we haveexperimentally demonstrated more than 90 % photon-efficient phase-only projecteddynamic and static far field diffraction both with and without a lens. A key aim forinventing and innovating HoloTile has been to effectively solve the challenge of rapidand speckle-free coherent or semi-coherent light sculpting without the need for timeaveragingtechniques - a challenge that exists in several fields of optics and photonics. Inparticular, HoloTile provides four new unique key features as CGH-modality for highresolutionspatial light modulators, reconfigurable DOEs or new meta-surface MOEs: •A 100x speed improvement over standard CGH-modalities • Substantial specklereduction by matched tiling and PSF-shaping • Real-time dynamic and output 'pixel'discretized digital holograms • Lens-free scaling or zoom by software adapted HoloTilephase-encodin
Novel fabrication method for highly conformable THz metasurfaces
No full textThe continuously increasing interest in flexible and integrated photonics requires new strategies for device manufacturing on arbitrary complex surfaces and with lowest possible size, respectively. Terahertz (THz) technology can particularly benefit from this approach to implement compact systems for generation, detection and on-demand manipulation of THz radiation. Here we present a novel fabrication method to realize conformable metasurfaces. The flexible and versatile character of polymeric nanomembranes is combined with direct laser writing via two-photon polymerization and metal deposition to develop freestanding ultra-thin quasi-perfect plasmonic absorbers with an unprecedentedly high level of conformability. Moreover, revealing new flexible dielectric materials presenting low absorption and permittivity in the THz range, this work paves the way for the realization of ultra-thin, conformable hybrid or all-dielectric devices enhancing the application of THz technologies, and flexible/integrated photonics in general.</p
Temperature compensated strain sensor in fused silica by femtosecond laser inscription
No full textMeasuring strain without parasitic thermal influence is vital. A temperature compensated strain sensor is fabricated in fused silica using femtosecond laser micromachining. Utilizing femtosecond laser direct writing and femtosecond irradiation followed by chemical etching, two Bragg gratings are fabricated in the bulk of a fused silica substrate. By suspending one of the Bragg gratings in a cantilever, it is mechanically isolated from the rest of the substrate. Thermal and tensile characterization showed that both Bragg gratings are sensitive to thermal changes with a sensitivity around 10.5 pm/°C, while only the non-isolated Brag grating is sensitive to strain with a sensitivity of 1.1 pm/µϵ. Hence, it is proven that the parasitic thermal influence on the strain sensor can be compensated by taking into account the response of the isolated Bragg grating
Large-Area Scatterometry for Nanoscale Metrology
Get PDFMany applications across photonics and semiconductor industries require the fabrication of nanostructures with non-trivial geometries with a precision and reproducibility down to the nanometer scale. Slanted gratings and metamaterials are examples of such designs that have vast applications in Augmented Reality and LiDAR. State-of-the-art lithography techniques, such as nanoimprint lithography or UV lithography, can provide such levels of fabrication precision for high-volume production. However, a rapid in-line quality inspection method for such complex patterns is required to monitor the fabrication process, verify the sample quality, and to ensure reproducibility. Here, we demonstrate a novel technique that allows us to inspect the quality of the samples in a non-destructive and fast manner, and to extract geometrical parameters of the nanostructures over large areas, generating spatial variations maps across wafers.</p
High-efficiency fill factor recovery using refractive microlens arrays imprinted on 0.5–256 kpixel front-side illuminated SPAD imagers
No full textSilicon-based single-photon avalanche diodes (SPADs) implemented in front-side illuminated arrays and imagers have often suffered from fill factor limitations. The corresponding reduced sensitivity can be sometimes traded off with longer acquisition times thanks to SPAD’s noiseless read-out. The use of SPADs can however be critically affected in many applications, especially when photon-starved, or when several photons need to be detected in coincidence. The fill factor loss can be recovered by employing microlens arrays, which are difficult to build with relatively large pitch (> 10 μm) and low native SPAD fill factor (as low as 10%). To address these challenges, we have developed several generations of refractive microlenses by photoresist reflow used to fabricate molds. These structures were used to imprint UV-curable hybrid polymer microlenses on SPAD arrays. Replications were successfully carried out on large SPAD arrays with very thin residual layers (~10 μm), as required for higher numerical aperture (NA > 0.25). Replications were also carried out for the first time in a multi-chip operation regime at the wafer reticle level. By optimizing the lens sag and residual layer thickness, concentration factors (CFs) within 15-20% of the theoretical maxima were obtained for the smaller arrays (32×32 and 512×1). The spectral response was flat above 400 nm. CF values up to 4.2 with good uniformity were measured on large 512×512 arrays with 16 μm pixel pitch and a native fill factor of 10.5%. This result was confirmed by simulations when using the actual measured lens shape. We thus demonstrated good spectral and spatial uniformity and high CF, while moving to higher NAs and larger sensor sizes with respect to previous work.AQU
Holographic beam shaping for volumetric 3D printing
No full textLight-based technologies for 3D printing have recently been developed and are leading the field thanks to their unmatched performance. However, these techniques are still limited to using incoherent light patterning for printing. Here, we present a novel approach that allows us to print using coherent patterns by combining light-beam shaping and tomographic projections. We demonstrate this concept with a volumetric printer based on reverse tomography using a Digital Micromirror Device (DMD) in a holographic configuration. The Lee holograms method allowed us to use the DMD as a fast phase modulator and the HoloTile approach to achieve fast and speckle-reduced holograms
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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