Volume 7, Issue 4 - Optical Materials Part 1 / Guest Editors: Younès Messaddeq, Tigran Galstian and Réal Vallée

Flexible optical sheets are thin large-area polymer light guide structures that can be used to create innovative passive light-harvesting and illumination systems. The optically transparent micro-patterned polymer sheet is designed to be draped over arbitrary surfaces or hung like a curtain. The light guidance sheet is fabricated by bonding two or more micro-patterned layers with different indices of optical refraction. By imprinting micro-optical elements on the constituent layers, it is possible to have portions of the optical sheet act as a light concentrator, near ‘lossless’ transmitter, or diffuser. However, the performance and efficiency of the flexible optical sheet depends on the overall curvature ( κ ) of the optical sheet and the relative orientation of incident light source. To illustrate this concept, the impact of key design parameters on the controlled guidance of light through a two-layer polydimethylsiloxane (PDMS) concentrator-transmitter-diffuser optical sheet is investigated using ray tracing simulation software. The analysis initially considers a flat ( κ =0) PDMS optical sheet exposed to a collimated light source. The impact of sheet curvature ( κ >0) on both system efficiency and illumination uniformity is then briefly explored. Critical design guidelines for creating multifunctional monolithic optical sheets are also summarized.

Materials with high deep-ultraviolet (DUV; λ<300 nm) transmission are important for many industrial applications. Fluoride single crystals and various glasses, pure SiO 2 , fluoride, phosphate, multicomponent silicates, and organic materials (PMMA), were investigated. The role of intrinsic absorption (UV edge) due to electron transitions between the main components, and extrinsic absorption due to trace impurities, effect of polyvalent ions, redox behavior, and radiation-induced transmission loss were considered. The optical basicity and optical properties were used to order the materials.

Conducting polymer films acting as both electrodes and alignment layers are very promising for the development of flexible and wearable tunable liquid crystal devices. The majority of existing publications report on the electro-optical properties of polymer-dispersed liquid crystals and twisted nematic liquid crystals sandwiched between highly conducting polymers. In contrary, in this paper, electro-optics of nematic liquid crystals placed between rubbed weakly conducting polymers is studied. The combination of weakly conducting polymers and nematics enables a frequency-dependent tuning of the effective threshold voltage of the studied liquid crystal cells. This unusual electro-optics of liquid crystal cells utilizing nematics and weakly conducting polymers can be understood by considering equivalent electric circuits and material parameters of the cell. An elementary model of the observed electro-optical phenomenon is also presented.

Controlled translational displacement between a large-surface photosensitive planar substrate and a wide and short 1D grating phase-mask enables the printing of large-width, spatially highly coherent gratings of principally unlimited length, using a limited number of opto-mechanical control parameters. The phase-mask is illuminated by a temporally modulated exposure light sheet controlled by a displacement sensor. The proposed method is compared with existing techniques, and its functional elements and their combination are analyzed.

Ultrashort laser pulses are widely used for the precise structuring of semiconductors like silicon (Si). We present here, for the first time, a comparative study of experimentally obtained and numerically simulated two-dimensional ablation profiles based on parameters of commercially relevant and widely used near-infrared and diode pumped femtosecond lasers. Single pulse laser ablation was studied at a center wavelength of 1040 nm and pulse duration of 380 fs (FWHM) in an irradiating fluence regime from 1 J/cm 2 to 10 J/cm 2 . Process thresholds for material transport and removal were determined. Three regimes, scaling with the fluence, could be identified: low and middle fluence regimes and a hydrodynamic motion regime. By comparing the simulated and experimental ablation profiles, two conclusions can be drawn: At 2 J/cm 2 , the isothermal profile of 3800 K is in excellent agreement with the observed two-dimensional ablation. Thus exceeding a temperature of 3800 K can be accepted as a simplified ablation condition at that fluence. Furthermore, we observed a distinct deviation of the experimental from the simulated ablation profiles for irradiated fluences above 4 J/cm 2 . This points to hydrodynamic motion as an important contributing mechanism for laser ablation at higher fluences.