Defects in liquid crystals have been studied over decades to disclose information and knowledge on the structure of LC
phases. More recently, LC defects have been identified as a tool to implement new physical functions useful in optical
films for polarization conversion or mechanical actuators able to adopt novel exotic shapes. In the present paper we
describe a general methodology to engineer different defect patterns by combining the use of linear photopolymerizable
polymers and liquid crystals.
Holographic pulsed light induced recording in azobenzene polymers is being extensively studied due to its potential use
in optical storage applications. In this communication we show our studies in the formation of holographic grating
recording in different azobenzene side chain polymethacrylates irradiating with a single 4 ns light pulse at 532 nm.
Holographic gratings have been registered using intensity and polarization patterns. The time response and stability of
this diffraction efficiency have been studied as a function of the recording energy. Stable values of the diffraction
efficiency have been obtained in some of the polymers after one single pulse of several tenths of mJ/cm2. We have also
estimated the relevance of surface and phase contributions at different recording energy regimes. Polarization
holographic gratings with efficiencies of about 0.8% (measured at 632.8 nm) have been registered with no measurable
The measurement of complete polarimetric parameters for a broad spectrum of wavelengths is challenging because of the multi-dimensional nature of the data and the need to chromatically separate the light under test. As a result, current methods for spectropolarimetry and imaging polarimetry are limited because they tend to be complex and/or relatively slow. Here we experimentally demonstrate an approach to measure all four Stokes parameters using three polarization gratings and four simultaneous intensity measurements, with potential to dramatically impact the varied fields of air/space-borne remote sensing, target detection, biomedical imaging/diagnosis, and telecommunications. We have developed reactive mesogen polarization gratings using simple spin-casting and holography techniques, and used them to implement a potentially revolutionary detector capable of simultaneous measurement of full polarization information at many wavelengths with no moving or tunable elements. This polarimeter design not only enables measurements over a likely bandwidth of up to 70% of the center wavelength, it is also capable of measurements at relatively high speed (MHz or more) limited only by the choice of photo-detectors and processing power of the system. The polarization gratings themselves manifest nearly ideal behavior, including diffraction efficiencies of greater than 99%, strong polarization sensitivity of the first diffraction orders, very low incoherent scattering, and suitability for visible and infrared light. Due to its simple and compact design, simultaneous measurement process, and potential for preserving image registration, this spectropolarimeter should prove an attractive alternative to current polarization detection and imaging systems.
Polymeric relief structures are extensively used in display technology due to their ability to redirect light in a controlled way. Photo-embossing is a new photo-lithographic technique to generate surface relief structures using photopolymers. In the present paper we show a combinatorial methodology to explore this technique. We have prepared and evaluated (using automated atomic force microscopy) 2-dimensional libraries of photo-embossed gratings, each library with a gradient in period and a gradient in either exposure energy or development temperature or film thickness or photoinitiator concentration or monomer to binder ratio. We show how this combinatorial approach helps us to better understand the photo-embossing process. In addition, we show that this methodology is an effective tool to identify processing conditions resulting in optimum shape and height of the polymeric relief micro-structures to be used in specific applications.