Photostimulated control of laser transmission through photoresponsive cholesteric liquid crystals.

Cholesteric liquid crystals (CLCs) are selectively reflective optical materials, the color of which can be tuned via electrical, thermal, mechanical, or optical stimuli. In this work, we show that self-regulation of the transmission of a circularly polarized incident beam can occur upon phototuning of the selective reflection peak of a photosensitive CLC mixture towards the pump wavelength. The autonomous behavior occurs as the red-shifting selective reflection peak approaches the wavelength of the incident laser light. Once the red-edge of the CLC bandgap and incident laser wavelength overlap, the rate of tuning dramatically slows. The dwell time (i.e., duration of the overlap of stimulus wavelength with CLC bandgap) is shown to depend on the radiation wavelength, polarization, and intensity. Necessary conditions for substantial dwell time of the CLC reflection peak at the pump beam wavelength include irradiation with low intensity light (~1mW/cm²) and the utilization of circularly polarized light of the same handedness as the helical structure within the CLC. Monitoring the optical properties in both reflection and transmission geometries elucidates differences associated with attenuation of the light through the thickness of the CLC film.

Folding flexible co-extruded all-polymer multilayer distributed feedback films to control lasing.

We report on improved gain and spectral control in co-extruded all-polymer multilayer distributed feedback (DFB) lasers achieved by folding and deliberate modification of the center "defect" layer. Because DFB laser gain is greater at spectral defects inside the reflection band than at the band edges, manipulation of structural defects can be used to alter spectral defects and thereby tune the output wavelength and improve laser efficiency. By experimentally terracing the layer that becomes the center of the fold, we tuned the lasing wavelength across the reflection stop-band (∼25 nm) in controllable, discrete steps. The increased density of states associated with the defect resulted in a lower lasing threshold and, typically, a 3- to 6-fold increase in lasing efficiency over non-folded samples.

Synthesis and evaluation of benzoxazole derivatives as 5-lipoxygenase inhibitors.

5-Lipoxygenase (5-LOX) is important enzyme in the biosynthesis of leukotrienes, and is a potential target in the treatment of asthma and allergy. We designed and synthesized a series of benzoxazoles and benzothiazoles as 5-LOX inhibitors. Fourteen compounds prepared showed the inhibition of LTC4 formation with IC(50) value of 0.12-23.88 µM. Also two compounds 2d and 2g showed improved airway hypersensitiveness.

Mode delocalization in 1D photonic crystal lasers.

We have investigated the formation of in-bandgap delocalized modes due to random lattice disorder as determined from the longitudinal mode spacing in a distributed Bragg laser. We were able to measure the penetration depth, and from transfer matrix simulations, determine how the localization length is altered for disordered lattices. Transfer matrix simulations and studies of the ensemble average were able to connect the gap delocalized modes to localized modes outside of the gap as expected from consideration of Anderson localization, as well as identify the controlling parameters.

Melt-processed all-polymer distributed Bragg reflector laser.

We have assembled and studied melt-processed all-polymer lasers comprising distributed Bragg reflectors that were fabricated in large sheets using a co-extrusion process and define the cavities for dye-doped compression-molded polymer gain core sheets. Distributed Bragg reflector (DBR) resonators consisting of 128 alternating poly(styrene) (PS) and poly(methyl methacrylate) (PMMA) layers were produced by multilayer co-extrusion. Gain media were fabricated by compression-molding thermoplastic host poly notmers doped with organic laser dyes. Both processing methods can be used in high-throughput roll-to-roll manufacturing. Optically pumped DBR lasers assembled from these components display single and multimode lasing in the reflection band of the resonators, with a slope efficiency of nearly 19% and lasing thresholds as low as 90microJ/cm(2). The lasing wavelength can be controlled via the layer thickness of the DBR resonator films, and variation of the laser dye. Studies of threshold and efficiency are in agreement with models for end-pumped lasers.