Two-photon polymerization (TPP) is capable of fabricating 3D structures with dimensions from sub-µm to a few hundred µm. As a direct laser writing (DLW) process, fabrication time of 3D TPP structures ...scale with the third order, limiting its use in large volume fabrication. Here, we report on a scalable fabrication method that cuts fabrication time to a fraction. A parallelized 9 multi-beamlets DLW process, created by a fixed diffraction optical element (DOE) and subsequent stitching are used to fabricate large periodic high aspect ratio 3D microstructured arrays with sub-micron features spanning several hundred of µm
. The wall structure in the array is designed with a minimum of traced lines and is created by a low numerical aperture (NA) microscope objective, leading to self-supporting lines omitting the need for line-hatching. The fabricated periodic arrays are applied in a cell - 3D microstructure interaction study using living HeLa cells. First indications of increased cell proliferation in the presence of 3D microstructures compared to planar surfaces are obtained. Furthermore, the cells adopt an elongated morphology when attached to the 3D microstructured surfaces. Both results constitute promising findings rendering the 3D microstructures a suited tool for cell interaction experiments, e.g. for cell migration, separation or even tissue engineering studies.
In this paper we present an infrared laser pointer, consisting of a vertical-cavity surface-emitting laser (VCSEL) and a diffractive optical element (DOE), encapsulated into a scleral contact lens ...(SCL). The VCSEL is powered remotely by inductive coupling from a primary antenna embedded into an eyewear frame. The DOE is used either to collimate the laser beam or to project a pattern image at a chosen distance in front of the eye. We detail the different SCL constitutive blocks, how they are manufactured and assembled. We particularly emphasize the various technological challenges related to their encapsulation in the reduced volume of the SCL, while keeping the pupil free. Finally, we describe how the laser pointer operates, what are its performances (e.g. collimation, image formation) and how it can be used efficiently in various application fields such as visual assistance and augmented reality.
The use of high-speed cameras permits to visualize, analyze or study physical phenomena at both their time and spatial scales. Mixing high-speed imaging with coherent imaging allows recording and ...retrieving the optical path difference and this opens the way for investigating a broad variety of scientific challenges in biology, medicine, material science, physics and mechanics. At high frame rate, simultaneously obtaining suitable performance and level of accuracy is not straightforward. In the field of mechanics, this prevents high-speed imaging to be applied to full-field vibrometry. In this paper, we demonstrate a coherent imaging approach that can yield full-field structural vibration measurements with state-of-the-art performances in case of high spatial and temporal density measurements points of holographic measurement. The method is based on high-speed on-line digital holography and recording a short time sequence. Validation of the proposed approach is carried out by comparison with a scanning laser Doppler vibrometer and by realistic simulations. Several error criteria demonstrate measurement capability of yielding amplitude and phase of structural deformations.
Holography is often considered as the most promising immersive technology because it provides all the depth cues of the human visual system. Some limitations still need to be overcome such as the ...huge computational load of high-definition holograms and the noise introduced in the reconstructed scene during the quantization process. In this paper, we propose what we believe is a novel view-specific layer-based stereogram approach combined with a view-dependent error diffusion algorithm that aims to solve those limitations. This method selects the light waves of the 3D scene that reach a specific viewing area and leverages this particular configuration to apply an error diffusion algorithm. Two additional quality enhancement features are observed: the reduction of the conjugate order perceptibility and the increased brightness of the reconstructed scene. Numerical and optical experiments demonstrate the time savings and quality enhancements of our approach.
An approach for the optimization and fabrication of a phase-only faceted Fresnel type diffractive optical element (FDOE) creating 3D virtual object is proposed. The FDOE is a transmissive Fresnel ...type DOE array, which produces the perception of a customized floating 3D virtual object behind the FDOE when illuminated with a divergent monochromatic Light Emitter Diode (LED) source. Each DOE unit of the FDOE is optimized by a modified iterative Fourier transform algorithm (M-IFTA). Every unit of the FDOE locally deflects the incident light to the same position to form a designated view in the target plane. The FDOE is fabricated using our home-built parallel writing photo-lithography machine. Numerical simulations and optical experiments are performed to verify the proposed design method. This work may find important applications in the advanced design of optical security hologram and anti-counterfeiting component.
This paper presents a method for wide-field vibrometry based on high-speed digital holographic interferometry. We demonstrate the possibility of measuring transient vibrations of structures at ...100 kHz frame rate when providing 46600 quantitative data on 380 cm2 rectangular spot at the object surface. Investigation of travelling acoustic waves propagating in alloy plate equipped with a two-dimensional acoustic black hole (ABH) is considered. Such a structure leads to localized vibrations of high amplitude and constitutes a good candidate for methodology testing. The wave front is generated by a short shock with duration about 50 μs? The time sequence of the vibration field obtained after the shock is depicted and exhibits the propagation of the wave front in the plate and inside the ABH. It follows that the observation of the modification of the wave propagation can be observed at very short time scale. The modification of the wave front due to the gradient in elastic properties related to the ABH area is also highlighted.
While additive manufacturing based on multiphoton polymerization is currently considered to be a very promising technique for the fabrication of 3D micro‐ and nanostructures, long fabrication times ...are a major limitation of this approach. Parallelization of the fabrication process is an important technique to overcome this issue. The fabrication process is parallelized by imaging a 1920 × 1080 pixel spatial light modulator into an ultrasensitive triplet–triplet annihilation resist. However, proximity effects between close pixels generate uncontrolled polymerization and make the controlled fabrication of 3D structures difficult. This work models light propagation and chemical interactions in the system to predict fabricated structures with a view to precompensating plot data and improving 3D resolution by performing optical and chemical proximity correction. A simple model gives reasonable predictions of fabricated structures helping us fabricate fully 3D structures in parallel.
While multiphoton polymerization allows the fabrication of 3D nanostructures, long fabrication times are a major limitation of this approach. Imaging a spatial light modulator overcomes this issue. However, proximity effects between close pixels make the controlled fabrication of 3D structures difficult. This work aims to predict fabricated structures with a view to precompensating plot data and improving resolution.
This paper shows how a phase only spatial light modulator (SLM) can be used to implement compact, wide field of view (FOV) projection systems, using a foveal imaging approach. The SLM is tested in ...two different configurations. First, as a wavefront corrector to locally compensate aberrations in wide angle projection, when illuminated by a white (RGB) light source. Second, as re-configurable diffractive optical element (DOE) to display phase computer generated holograms (CGHs) of wide angle images, that include aberration corrections for peripheral regions of interest (ROI) of the output image, when illuminated by a coherent source. Finally, the foveal projection system is coupled with a commercial combiner to project 11° ×4° virtual images at 2~m and assess the foveal correction method on different ROIs in the FOV.
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