RESUMEN
A transmissive adaptable optical setup to generate a range of perfect vortex beams (PVBs) carrying different topological charges (TC) without using moving parts is presented. The setup is composed of an ad hoc transparent reconfigurable liquid crystal (LC) spiral phase plate (SPP), a refractive axicon and a convergent refractive lens. The LC SPP electrodes are manufactured ablating indium-tin oxide (ITO) glass substrates using direct laser writing (DLW) resulting in a very high fill factor device. In-house tailored electronics drive the 72 LC SPP electrodes giving rise to 72 different configurations with orbital angular momentum. In this work, the generation of PVBs with 36 positive or 36 negative TCs using this optical setup is accomplished.
RESUMEN
The manufacturing and characterization of a large-size 72-electrode liquid crystal-based reconfigurable spiral phase plate (SPP) is presented. The SPP is addressed by a custom-made driver with 72 independent channels, which allows for the generation of any arbitrary integer or fractional optical vortex beam with topological charges ranging from -24 to +24. The 25 mm diameter device is fabricated using direct laser writing, leading to a fill factor over 99%. The device performance and flexibility exceed previous transparent reconfigurable SPP in terms of size, tuning range, and fill factor. The device and the light path have been simulated using the angular spectrum propagation method, showing excellent correspondence.
RESUMEN
Polymer based photonic devices offer the possibility cost effective roll-to-roll manufacture of photonic devices. The incorporation of luminescent dopants within a solid polymer waveguide allows for the generation of light within the device avoiding tedious mechanical light coupling. However, when a dopant is embedded in a solid matrix, depending on its concentration and the nature of materials involved, the emitted light may be quenched due to aggregation effects. In this work, thin films and ridge waveguides processed by UV-photolithography have been successfully obtained from a selection of standard photopolymerizable organic monomers, SU8, EpoCore and OrmoStamp doped with a selection of standard dyes like Rhodamine-B, Coumarin-540A and Pyrromethene-580. All structures were manufactured on glass substrates. An analysis of the solubility and optical properties including band gap energy, absorption coefficient ([Formula: see text]) and fluorescence of the doped photoresists at different concentrations has been performed. Photoresists doped with Rhodamine-B shows a higher energy of indirect allowed band gap transition (2.04-2.09 eV) compared to previously reported pure Rhodamine-B thin films (1.95-1.98 eV). Fabrication protocols of dye doped photoresists covering the entire visible spectrum is established.
RESUMEN
Lyotropic liquid crystals play an important role in many biological environments, such as micelles, liposomes, and phospholipid bilayers of cell membranes. In this work, we explore the performance of lyotropic liquid crystals as biosensors for macromolecules, proteins and whole microorganisms in hydrophilic media, i.e., the natural media where these specimens exist. The aim is to detect specific targets employing simple, unpowered sensors that can be used in the field, with minimum additional equipment. A number of different structures have been explored. The novelty in this work is the inclusion of a new optical effect, flow enhanced amplification, that allows for the semiquantitative detection of microscopic targets in lyotropic liquid crystal cells using the naked eye only.
RESUMEN
The design and characterisation of a reconfigurable multi-level spiral phase plate is shown. The device is based on a pie-shape liquid-crystal structure with 24 slices driven by custom electronics that allow independent excitation control of each electrode. The electrooptical cell was manufactured using maskless laser ablation lithography and has shown an unprecedented high fill factor. The topological charge can be dynamically changed between 1, 2, 3, 4, 6, 8 and 12. The device has been calibrated and characterised at 632.8 nm but can be employed at any wavelength in the visible and near infrared spectrum, just modifying the driving parameters of the electrodes. The experimental results have been compared to predictions derived from simulations. An excellent correspondence between theoretical and experimental result has been found in all cases.
RESUMEN
We have studied the formation of topological defects in liquid crystal (LC) matrices induced by multiwalled carbon nanotubes (MWCNTs) and external electric fields. The defects are ascribable to a distortion of the LC molecular director in proximity of the MWCNT surface. The system is analyzed macroscopically using spectroscopic variable angle ellipsometry. Concurrently, confocal micro-Raman spectroscopy is used to study the system state at the microscale. This allows to acquire a three-dimensional, spatially-resolved map of the topological defect, determining scale length variations and orientation topography of the LC molecules around the MWCNT.
RESUMEN
In this paper, the detection of crystalline elements in protein crystallization droplets containing precipitate is illustrated using the rotating-polarizer microscope technique. The sensitivity of this automated birefringence technique enables the detection of microcrystals in a precipitate that appears to be amorphous using traditional methods of inspection. The technique is illustrated with lysozyme and glucose isomerase. Glucose isomerase microcrystals were used successfully for seeding experiments and the conditions of both of the systems were refined to produce crystals suitable for X-ray analysis. The results are relevant to the field of high-throughput crystallography as an automated crystal-detection method as well as being a useful tool for detailed precipitate analysis.
