Chiroptical properties in azobenzene molecule-doped side-chain polymeric films

Thin, intrinsically achiral films of a side-chain polymeric liquid crystal system doped with photochromic azobenzene molecules exhibited dynamic chiroptical properties when irradiated with circularly polarized light (CPL). Photoinduced circular anisotropy was observed in these films with increasing CPL irradiation time. Reversible chiroptical switching was also realized by alternating irradiation with right- and left-CPL. We also monitored photoinduced chirality as a function of excitation wavelength.     

Optical second harmonic generation in a low-bandgap polymer

Recently, much research has been performed on developing low-bandgap polymers for e.g. harvesting solar energy. In the quest to improve these properties, little attention has been paid to their nonlinear optical properties, despite their interesting linear optical spectra and structural similarities to certain nonlinear optically active compounds. We characterized the optical second harmonic generation of corona poled films of poly(cyclopenta[2,1-b;3,4-b′] dithiophen-4-ylidenedioctylmalonate). The unexpectedly large nonlinear optical susceptibilities and the thermal and temporal stability of the material compare favorably to other novel nonlinear optical materials despite the lack of a donor-acceptor dye. Additionally, the polymer displays a very low absorption in the relevant wavelength region. These results demonstrate the promise of these materials for nonlinear optical devices.     

Nonlinear optical and optical limiting properties of phthalocyanines in solution and thin films of PMMA at 633 nm studied using a cw laser

We present our results on nonlinear optical (NLO) and optical limiting properties of Tetra tert-butyl phthalocyanine and Zinc tetra tert-butyl phthalocyanine studied at 633 nm using a continuous wave laser. We have evaluated the sign and magnitude of the third-order nonlinearity from the closed aperture Z-scan data while the nonlinear absorption properties were assessed using the open aperture data. We have observed low power optical limiting, with low limiting thresholds, based on nonlinear refraction in both the samples. We also present results on the NLO properties of the same dyes doped in Polymethylmethacrylate (PMMA). These studies indicate that both the phthalocyanines are potential candidates for low power optical limiting applications.     

Luminescent and thermal properties of a novel red-emitting silicon fluoride acrylate-Eu(III) copolymer for white LEDs

A red-emitting silicon fluoride acrylate (SFA)-Eu(III) copolymer was prepared based on water-in-oil emulsion polymerization method. Its photoluminescence including the temporal decay was studied in addition to the thermal properties. Of the emissions due to the ⁵D₀ → ⁷F_J (J = 0–4) transitions of Eu³⁺ ions, an intense red emission due to ⁵D₀ → ⁷F₂ transition was observed at 618 nm under the 395 nm excitation, together with a weak ⁵D₀ → ⁷F₀ emission at 580 nm. Compared with some commercial phosphor, the SFA-Eu(III) copolymer also have a higher QE value. From the optical properties it was suggested that Eu³⁺ ions were located at the disordered non-inversion Eu³⁺ sites in the copolymer. The glass transition temperature (T_g) was estimated about −51.5 °C from a differential scanning calorimetric curve, while chemical decomposition was estimated to start from 385 °C from a thermogravimetry analysis curve. Taking into account the thermal stability in a wide temperature range from −51.5 °C to 385 °C, the SFA-Eu(III) copolymer is expected to act as a potential red component for near-UV excited white LEDs.     

Confined growth of Ag2S semiconductor nanocrystals in the presence of PDMAEMA-co-AA polyampholyte co-polymer

Silver sulfide (Ag₂S) nanoparticles were synthesized in the presence of poly(2-(dimethylamino)ethyl methacrylate-co-acrylic acid) co-polymer. It was shown that this polyampholyte can stabilize the growth of the Ag₂S in solution which resulted in formation of nanoparticles with relatively narrow size distribution. The obtained nanoparticles were characterized with structural and optical methods. The results showed that their average size depended on the number of acrylic acid units along the polymer chains.     

Energy dependent saturable and reverse saturable absorption in cube-like polyaniline/polymethyl methacrylate film

Solid films of cube-like polyaniline synthesized by inverse microemulsion polymerization method have been fabricated in a transparent PMMA host by an in situ free radical polymerization technique, and are characterized by spectroscopic and microscopic techniques. The nonlinear optical properties are studied by open aperture Z-scan technique employing 5 ns (532 nm) and 100 fs (800 nm) laser pulses. At the relatively lower laser pulse energy of 5 μJ, the film shows saturable absorption both in the nanosecond and femtosecond excitation domains. An interesting switchover from saturable absorption to reverse saturable absorption is observed at 532 nm when the energy of the nanosecond laser pulses is increased. The nonlinear absorption coefficient increases with increase in polyaniline concentration, with low optical limiting threshold, as required for a good optical limiter.     

Formation of Ag nanoparticles within the thermosensitive hairy hybrid particles

Herein we report on the production of composite core-shell particles, which are actually self-assembly of poly (N-isopropylacrylamide)-based amphiphilic block copolymers as a template for metal-block copolymer nanocomposites formation. Organic-inorganic composites were prepared with Ag nanoparticles embedded within colloidal particles of an amphiphilic, thermally responsive polymer. To promote the incorporation of unaggregated Ag nanoparticles, temperature responsive microspheres of poly (N-isopropylacrylamide) (NIPAM) block with polystyrene were synthesized. Polyethyleneimine (PEI) could act as the linker between Ag ions (Ag nanoparticles) and poly (styrene-b-N-isopropylacrylamide) (PS-b-PNIPAM) colloids and the reducing agent in the formation of Ag nanoparticles. Transmission electron microscopy (TEM) measurements confirmed the nanostructures, ¹HNMR and FTIR characterized the components of the resulting nanoobjects. These stimuli-responsive hybrid microspheres will have potential applications in biomedical areas, such as tissue engineering and drug delivery.     

Nonvolatile Electrically Reconfigurable Integrated Photonic Switch Enabled by a Silicon PIN Diode Heater

Reconfigurability of photonic integrated circuits (PICs) has become increasingly important due to the growing demands for electronic–photonic systems on a chip driven by emerging applications, including neuromorphic computing, quantum information, and microwave photonics. Success in these fields usually requires highly scalable photonic switching units as essential building blocks. Current photonic switches, however, mainly rely on materials with weak, volatile thermo-optic or electro-optic modulation effects, resulting in large footprints and high energy consumption. As a promising alternative, chalcogenide phase-change materials (PCMs) exhibit strong optical modulation in a static, self-holding fashion, but the scalability of present PCM-integrated photonic applications is still limited by the poor optical or electrical actuation approaches. Here, with phase transitions actuated by in situ silicon PIN diode heaters, scalable nonvolatile electrically reconfigurable photonic switches using PCM-clad silicon waveguides and microring resonators are demonstrated. As a result, intrinsically compact and energy-efficient switching units operated with low driving voltages, near-zero additional loss, and reversible switching with high endurance are obtained in a complementary metal-oxide-semiconductor (CMOS)-compatible process. This work can potentially enable very large-scale CMOS-integrated programmable electronic–photonic systems such as optical neural networks and general-purpose integrated photonic processors.