Single crystals of semiorganic nonlinear optical material Triglycine Sodium Halides(TGSH) have been grown from aqueous solution by slow evaporation technique at constant temperature. The powder X-ray diffraction of the grown crystals is recorded and indexed. Functional groups present in the samples are identified by FTIR spectral analysis. The optical absorption studies shows that the UV cut off wavelength is around 300nm and has a wide transparency window. The powder second harmonic generation efficiency of the crystals is measured by Kurtz and Perry powder technique using Nd:YAG laser and it is 1.5 times for Triglycine Sodium Chloride, 1.2 times for Triglycine Sodium Bromide and 1.4 times for Triglycine potassium Iodide crystals that of the standard KDP crystals. Triglycine Sodium halide crystals show very good stability under laser irradiation with no signs of decomposition. Laser damage threshold energy density of Triglycine Sodium Iodide is found to be 857 MW/cm2 and 540MW/cm2 for Triglycine Sodium Chloride crystals.

Defect structures in Rubidium Titanyl Phosphate (RTP) crystals (non-doped and doped) grown by the Top Seeded Solution Growth (TSSG) method were characterized using Synchrotron White Beam X-ray Topography. Main defects observed in non-doped crystals are growth sector boundaries while both growth sector boundaries and growth striations are observed in the Nb single doped and (Nb,Yb)-codoped crystals with relatively few linear defects such as dislocations. Results show that the overall crystalline quality is lowered as more doping elements are incorporated. Details of defect distributions are correlated with the growth process to facilitate high quality growth of doped RTP.

Two methods for the fabrication of flexible and stretchable photonic crystal slabs are demonstrated and compared. In both cases a periodically nanostructured polydimethylsiloxane (PDMS) membrane is used as substrate. The first method is based on oblique-angle vapor deposition of SiO as a high refractive index material onto the nanostructured membrane. The deposition is made at an angle of 45° to the surface. The grooves of the nanostructure are aligned such that shading effects cause an inhomogeneous layer thickness distribution on the surface. This supports controlled, periodic cracking of the high index layer upon stretching. In the second approach ZnO nanoparticles are spin-coated on the nanostructured PDMS membrane. Here, the membrane can be stretched and serves as a photonic crystal slab without the need of any further treatment. For both types of flexible photonic crystal slabs a shift of the guided mode resonances to longer wavelengths is observed upon stretching. For a 20% strain perpendicular to the grating grooves a resonance shift of more than 50 nm is obtained.

Organic semiconductor technology paves the way to low cost lightweight, flexible, printable electronics circuits and sensors. A novel lateral multilayer organic semiconductor photosensor is fabricated using small molecule organic semiconductor. A specialized interface layer is introduced between the metal electrodes and the organic semiconductor layer. The interface layer material is a large band gap and low electronic conductivity material. The use of interface layer limits the charge injection from the electrodes to the organic semiconductor and overall improves the photosensor dark current performance with an additional advantage to apply high voltage for improved collection. This design has low dark current with high photo-to-dark current ratio and can be set to high bias mode of operation.

Lateral interdigitated photodetector, with bottom contact Metal Semiconductor Metal (MSM) is fabricated consisting of interface layer and organic semiconductor bilayer. Small molecule organic semiconductor 3,4,9,10 perylenetetracarboxylic bisbenzimidazole (PTCBI) and Copper-Phthalocyanine (CuPc) are used as the active bilayer, where as polyamide forms the interface layer. Current through the sensor is measured in both dark and in light (wavelength 400nm). The dark current density in a 1mm2 photosensor area with 5μm lateral electrode spacing at 10V/μm measured equal to 10-5mA/cm2 and a photocurrent density of 10-3 mA/cm2 under 0.3mW/cm2 incident optical power. The photo to dark current ratio is measured to be equal to ∼103.

This photosensor has an application in large area imaging for example portable lightweight detectors. Other applications of this sensor include indirect medial imaging and as a biosensor in UV Spectroscopy study of bacteria cultures.

We have investigated the photon-energy dependence of nonlinear optical absorption in graphene in the near infrared (NIR) and visible range (1.13 – 3.1 eV). Two nonlinear processes, namely one-photon interband absorption saturation and two-photon absorption (2PA), have been unambiguously determined in high-quality, CVD-grown, multilayer graphene films with using femtosecond Z-scan technique. The absorption saturation is found to have a square dependence on the photon energy. The 2PA spectrum is measured to be close to the theoretical prediction of ω-4 dependence at NIR wavelengths. In the visible range, however, the photon-energy dependence of 2PA is dominated by the excitonic Fano resonance.

It is well known that exposure to ultraviolet (UV) light can result in various physical and psychological diseases. Therefore, there is a strong demand for a reliable sensor to monitor UV exposure levels in the physiologically relevant intensity ranges of mW/cm2. Here, we demonstrate a UV sensor based on a silica whispering gallery mode microresonator. This UV sensor works over physiologically relevant intensity ranges with linear performance both in the forward and backward operating directions, with very high signal-to-noise ratio that can be utilized in monitoring the UV exposure for various applications.

To prepare cholesteric liquid crystalline nonlinear optical materials with ability to be vitrified on cooling and form long time stability cholesteric glasses at room temperature, a series of platinum acetylide complexes modified with cholesterol has been synthesized. The materials synthesized have the formula trans-Pt(PR3)(cholesterol (3 or 4)-ethynyl benzoate)(1-ethynyl-4-X-benzene), where R = Et, Bu or Oct and X = H, F, OCH3 and CN. A cholesteric liquid crystal phase was observed in the complexes R = Et, and X = F, OCH3 and CN but not in any of the other complexes. When X = CN, a cholesteric glass was observed at room temperature which remained stable up to 130 °C, then converted to a mixed crystalline/cholesteric phase and completely melted to an isotropic phase at 230 °C. When X = F or OCH3 the complexes were crystalline at room temperature with conversion to the cholesteric phase upon heating to 190 and 230 °C, respectively. In the series X = CN, OCH3 and F, the cholesteric pitch was determined to be 1.7, 3.4 and 9.0 µ, respectively.

We have been studying a number of nanosystems that either have potential applications in bioimaging and/or light-activated therapies, or are bioderived. The standard Z-scan technique was routinely used for most of the measurements which were carried out in a wide wavelength range, typically from ∼550 nm to 1.6 μm. The range of nanoparticles studied has included colloidal semiconductor nanoparticles (e.g. CdS, CdSe), plasmonic nanoparticles, metal clusters, lanthanide-doped fluoride and oxide nanocrystals as well as core-shell systems. Among the bioderived systems studied especially interesting one is that of protein amyloid fibers.

Many of these materials exhibit nonlinear absorption features due not only to the typical two-photon absorption processes, but also due to multiple-photon absorption taking place, especially at longer wavelengths (e.g. three- four- and five-photon processes). On the other hand, absorption saturation processes may prevail or compete with multi-photon absorption in certain wavelength ranges in some of these materials, especially those characterized by broadband absorption due to surface plasmon excitation.

We investigated theoretically the transmission spectra in one-dimensional photonic quasicrystals (1DPQ) made up from dielectric materials organized in accordance to a discrete varying electric permittivity profile that obeys an analogous of the quasiperiodic potential in the so-called Audry-André (AA) model, in order to modulate the refraction index. Our results show that due to the incommensurate dielectric distribution, the spectrum splits into a fractal set of pass- and forbidden-band structure. By studying the transmission spectra as a function of the modulation phase ϕ, we found boundary states lying within the gaps localized either on the left or on the right boundary of the system, characterizing the so-called topological states.

The warm white light emission from the MOS capacitor containing the Zr-doped HfO2 high-k thin film on a p-type Si wafer under various post deposition annealing temperatures has been investigated. The light intensity is affected by the annealing temperature and the magnitude of the stress voltage. The annealing temperature changes the defect density and the physical thickness of the high-k stack. The high stress voltage induces the strong light emission because of the passage of a large current through the conductive path. The broad band emission spectrum covers the visible and near IR wavelength range with a large color rendering index. This new light emission device has a very long lifetime of > 1,000 hours at the atmosphere without a protection layer. The device is made of the IC compatible material and fabrication process, which favors the application over a wide range of products.

The use of organic nonlinear optical (ONLO) materials in electro-optic (EO) modulators requires that the active molecular components (chromophores) be acentrically oriented. The fundamental molecular constituents are in a condensed, glassy phase. Molecular orientation in such systems is typically achieved by applying a DC poling field to the glassy material. We are developing efficient coarse-grained classical Monte Carlo (MC) methods to simulate the order of such systems. The most challenging aspects of these simulations are convergence to an experimentally relevant equilibrium ensemble and verification of simulation accuracy. We use a variety of molecular descriptions and a variety of MC methods to achieve proper order in the shortest number of computational cycles possible. Herein, we illustrate a few examples of the types of calculations and compare with experimental results with representative amorphous organic materials, including electro-optic chromophores.

We studied the effect of a cross-conjugated bridging group (χC) on charge-transfer in a push-pull chromophore system. The hyperpolarizability of such molecules was found to be comparable to that of a fully π-conjugated molecule (πC) with the same donor and acceptor. The cross-conjugated moiety was then applied as a pendant to a fully π-conjugated chromophore containing a tricyanopyrroline acceptor (TCP). The addition of a χC moiety did not alter the intrinsic hyperpolarizability and provides an avenue for extending and aiding πC systems. The molecules were examined by X-ray diffraction (XRD), hyper-Raleigh scattering (HRS) and UV-visible (UV-vis) spectroscopy. Experimental results were compared with the predictions of density functional theory (DFT). Cross-conjugated molecules have comparable β values, relative to πC molecules, due to reduced spatial overlap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). Thus, the χC architecture could facilitate independent modification of donor and acceptor strengths while minimizing unfavorable effects on electronic transitions and dipole moments.