ABSTRACT
In this work, a technique to generate aspherical liquid crystal lenses with positive and negative optical power is experimentally demonstrated. The main enabling element is a micro-metric electrode with variable spatial size. This produces a decreasing resistance towards the lens centre that generates the desired voltage/phase profiles. Then, the voltage is homogeneously distributed across the active area of the lens by micro-metric concentric electrodes. As it is demonstrated, the phase shift can be controlled with voltages from 0 to 4.5 VRMS. As a result, parabolic profiles are obtained both for negative and positive optical powers. Furthermore, this approach avoids some disadvantages of previous techniques; parabolic profiles can be obtained with only one lithographic step and one or two voltage sources. Other complex aspherical profiles could be fabricated using the same technique, such as elliptical or hyperbolic ones.
ABSTRACT
There is an increasing need to control light phase with tailored precision via simple means in both fundamental science and industry. One of the best candidates to achieve this goal are electro-optical materials. In this work, a novel technique to modulate the spatial phase profile of a propagating light beam by means of liquid crystals (LC), electro-optically addressed by indium-tin oxide (ITO) grating microstructures, is proposed and experimentally demonstrated. A planar LC cell is assembled between two perpendicularly placed ITO gratings based on microstructured electrodes. By properly selecting only four voltage sources, we modulate the LC-induced phase profile such that non-diffractive Bessel beams, laser stretching, beam steering, and 2D tunable diffraction gratings are generated. In such a way, the proposed LC-tunable component performs as an all-in-one device with unprecedented characteristics and multiple functionalities. The operation voltages are very low and the aperture is large. Moreover, the device operates with a very simple voltage control scheme and it is lightweight and compact. Apart from the demonstrated functionalities, the proposed technique could open further venues of research in optical phase spatial modulation formats based on electro-optical materials.
ABSTRACT
The study was carried out in 20 children aged 6-18 years receiving long-term corticosteroid treatment for nephrotic syndrome. In these children densitometric evaluation of bone by DEXA method (total body and spine) and ultrasound measurement of heel were performed. Moreover, basic parameters of calcium-phosphate metabolism were determined. Osteoporosis and osteopenia were diagnosed in 6/20 (30%) patients. Disturbances of bone mineralisation were accompanied by hyperhydroxyprolinuria, hypercalciuria, hypocalcemia and also by some clinical symptoms. The results of these pilot investigations point at necessity periodical assessment of bone mineralisation and calcium-phosphate metabolism in children with nephrotic syndrome receiving corticosteroid treatment.