ORMOCHALCs: organically modified chalcogenide polymers for infrared optics.

A novel method combining elemental sulfur and selenium was developed, yielding crystalline sulfur-selenium compounds. The compounds were melted, and an organic comonomer added. Once the organic comonomer was consumed, the viscous compound was vitrified and allowed to cool yielding organic-inorganic hybrid polymers that are termed Organically Modified Chalcogenide (ORMOCHALC) polymers.

Optimized moth-eye anti-reflective structures for As2S3 chalcogenide optical fibers.

We computationally investigate moth-eye anti-reflective nanostructures imprinted on the endfaces of As2S3 chalcogenide optical fibers. With a goal of maximizing the transmission through the endfaces, we investigate the effect of changing the parameters of the structure, including the height, width, period, shape, and angle-of-incidence. Using these results, we design two different moth-eye structures that can theoretically achieve almost 99.9% average transmisison through an As2S3 surface.

Angle-of-incidence performance of random anti-reflection structures on curved surfaces.

Random anti-reflection structured surfaces (rARSS) have been reported to improve transmittance of optical-grade fused silica planar substrates to values greater than 99%. These textures are fabricated directly on the substrates using reactive-ion etching techniques, and often result in transmitted spectra with no measurable interference effects (fringes) for a wide range of wavelengths. The inductively coupled reactive-ion plasma (ICP-RIE) used in the fabrication process to etch the rARSS is anisotropic and thus well suited for planar components. The improvement in spectral transmission has been found to be independent of optical incidence angles for values from 0° to ±30°. Qualifying and quantifying the rARSS performance on curved substrates, such as convex lenses, is required to optimize the fabrication of the desired AR effect on optical-power elements. In this work, rARSS was fabricated on fused silica plano-convex lenses using a planar-substrate optimized ICP-RIE process to maximize optical transmission in the range from 500 to 1100 nm. Results are presented from optical transmission tests of rARSS lenses for both TE and TM incident polarizations at a wavelength of 633 nm and over a 70° full field of view. These results suggest optimization of the fabrication process to account for anisotropy is not required, mainly due to the wide angle-of-incidence AR tolerance performance of the rARSS lenses.

Calculation of the expected output spectrum for a mid-infrared supercontinuum source based on As 2 S3 chalcogenide photonic crystal fibers.

We computationally investigate supercontinuum generation in an As 2 S3 solid core photonic crystal fiber (PCF) with a hexagonal cladding of air holes. With a goal of obtaining a supercontinuum output spectrum that can predict what might be seen in an experiment, we investigate the spectral and statistical behavior of a mid-infrared supercontinuum source using a large ensemble average of 106 realizations, in which the input pulse duration and energy vary. The output spectrum is sensitive to small changes (0.1%) in these pulse parameters. We show that the spectrum can be divided into three regions with distinct characteristics: a short-wavelength region with high correlation, a middle-wavelength region with minimal correlation, and a long-wavelength region where the behavior is dominated by a few rare large-bandwidth events. We show that statistically significant fluctuations exist in the experimentally expected output spectrum and that we can reproduce an excellent match to that spectrum with a converged shape and bandwidth using 5000 realizations.

Efficient inscription of Bragg gratings in As2S3 fibers using near bandgap light.

Efficient inscription of Fiber Bragg gratings (FBGs) in single-mode, thin cladding As(2)S(3) fibers is demonstrated by using near bandgap light at 532 nm. The FBGs with the reflectivity of over 80% can be induced in only 80-90 s, substantially faster than in previous reports. The dynamics of the grating growth are investigated in the photosensitivity process, showing a fast blue shift of the Bragg wavelength and then a somewhat slower red shift. The aging of the grating after fabrication is also reported, indicating a 37% decay of the grating strength.

Low-temperature deposition of BaCuSF, a visible through mid-infrared p-type transparent conductor.

Barium copper sulfur fluoride (BaCuSF) is a p-type transparent conductor (p-TC) that, when doped with potassium, exhibits exceptionally high conductivity. The results of a detailed optical and electronic characterization of BaCuSF thin films deposited at a substrate temperature of 100 °C are presented. X-ray diffractometry shows the presence of a cubic BaCuSF phase. Spectroscopic measurements demonstrate that the films transmit from the visible through the mid-infrared with a band gap of 1.8 eV. Hall measurements indicate that the material is a degenerate semiconductor. As deposited, the films exhibit conductivity at room temperature of approximately 260 S/cm - among the highest reported room temperature conductivities for p-TCs. After post-deposition treatment in water, their conductivity increases to as high as 800 S/cm, and their band gap is reduced to 1.5 eV. The potential for low temperature deposition of p-type films with high conductivity and optical transmittance makes BaCuSF promising for several applications including flexible electronics and photovoltaics.

Octave spanning supercontinuum in an As2S3 taper using ultralow pump pulse energy.

An octave spanning spectrum is generated in an As2S3 taper via 77 pJ pulses from an ultrafast fiber laser. Using a previously developed tapering method, we construct a 1.3 µm taper that has a zero-dispersion wavelength around 1.4 µm. The low two-photon absorption of sulfide-based chalcogenide fiber allows for higher input powers than previous efforts in selenium-based chalcogenide tapered fibers. This higher power handling capability combined with input pulse chirp compensation allows an octave spanning spectrum to be generated directly from the taper using the unamplified laser output.

Characterization of picosecond pulse nonlinear propagation in chalcogenide As(2)S(3) fiber.

We characterize the nonlinear propagation of picosecond pulses in chalcogenide As(2)S(3) single-mode fiber using a pump-probe technique. The cross-phase modulation (XPM)-induced sideband broadening and stimulated Raman scattering (SRS)-induced sideband amplification are measured in order to map out the Raman gain spectrum of this glass across the C-band. We extract the Raman response function from the Raman gain spectrum and determine the power and polarization dependence of the SRS. In contrast to previous work using As(2)Se(3) fiber, we find that the As(2)S(3) fiber does not suffer from large two-photon absorption (TPA) in the wavelength range of the telecommunications band. We achieved a 20 dB peak Raman gain at a Stokes shift of 350 cm(-1) in a 205 mm length of As(2)S(3) single-mode fiber. The Raman gain coefficient is estimated to be 4.3x10(-12) m/W and the threshold pump peak power is estimated to be 16.2 W for the 205 mm As(2)S(3) fiber. We also demonstrate that we can infer the dispersion of the As(2)S(3) fiber and justify the Raman response function by comparing simulation and experimental results.

High bit rate all-optical signal processing in a fiber photonic wire.

We report the first demonstration of high bit rate signal processing by a fiber-based photonic wire. We achieve 160 Gb/s demultiplexing via four wave mixing in a 1.9 microm diameter photonic wire tapered from As(2)S(3) chalcogenide glass single mode fibre, with very low pump power requirements ( < 20 mW average power, 0.45 W peak power), enabled by a very high nonlinearity (gamma approximately 7850 W(-1) km (-1) ) and greatly reduced dispersion.

Low-frequency electromagnetic field effects on functional groups in human skin keratinocytes cells revealed by IR-SNOM.

Human HaCaT cells, exposed for 24 h to a 1 mT (rms) 50 Hz sinusoidal magnetic field in a temperature-regulated solenoid, suffer detectable changes in their biochemical properties and shapes. By using infrared wavelength-selective scanning near-field optical microscopy, we observed changes in the distribution of the inner chemical functional groups and in the cell morphology with a resolution of 80-100 nm.

Infrared scanning near-field optical microscopy investigates order and clusters in model membranes.

Due to its surface sensitivity and high spatial resolution, scanning near-field optical microscopy (SNOM) has a significant potential to study the lateral organization of membrane domains and clusters. Compared to other techniques, infrared near-field microscopy in the spectroscopic mode has the advantage to be sensitive to specific chemical bonds. In fact, spectroscopic SNOM in the infrared spectral range (IR-SNOM) reveals the chemical content of the sample with a lateral resolution around 100 nm (Cricenti et al., 1998a, 1998b, 2003). Model lipid membranes were studied by IR-SNOM at several wavelengths. Topographical micrographs reveal the presence of islands at the surface and the optical images indicate the formation of locally ordered multiple bilayers - both critically important features for biotechnology and medical applications.

Characterization of mid-infrared single mode fibers as modal filters.

We present a technique for measuring the modal filtering ability of single mode fibers. The ideal modal filter rejects all input field components that have no overlap with the fundamental mode of the filter and does not attenuate the fundamental mode. We define the quality of a nonideal modal filter Q(f) as the ratio of transmittance for the fundamental mode to the transmittance for an input field that has no overlap with the fundamental mode. We demonstrate the technique on a 20 cm long mid-infrared fiber that was produced by the U.S. Naval Research Laboratory. The filter quality Q(f) for this fiber at 10.5 microm wavelength is 1000+/-300. The absorption and scattering losses in the fundamental mode are approximately 8 dB/m. The total transmittance for the fundamental mode, including Fresnel reflections, is 0.428+/-0.002. The application of interest is the search for extrasolar Earthlike planets using nulling interferometry. It requires high rejection ratios to suppress the light of a bright star, so that the faint planet becomes visible. The use of modal filters increases the rejection ratio (or, equivalently, relaxes requirements on the wavefront quality) by reducing the sensitivity to small wavefront errors. We show theoretically that, exclusive of coupling losses, the use of a modal filter leads to the improvement of the rejection ratio in a two-beam interferometer by a factor of Q(f).

Waveguide amplifiers in sputtered films of Er3+-doped gallium lanthanum sulfide glass.

Waveguide amplifiers fabricated in Er3+-doped gallium lanthanum sulfide (GLS) glass are demonstrated. GLS is deposited onto fused silica substrates by RF magnetron sputtering, and waveguides are patterned by use of the lift-off technique. The waveguides exhibit a total internal gain of 6.7 dB (2.8 dB/cm) for a signal with a wavelength of 1.55 mum. This experiment is, to the best of our knowledge, the first demonstration of gain in an Er3+-doped chalcogenide glass waveguide. The fabrication methods we apply, if used with other rare earth dopants, could potentially be employed to produce sources operating in the mid-IR.

Small-core As-Se fiber for Raman amplification.

We have demonstrated Raman small-core As-Se fiber. More than 20-dB of gain was observed in a 1.1-m length of fiber pumped by a nanosecond pulse of approximately 10.8-W peak power at 1.50 microm. The peak of the Raman gain occurred at a shift of approximately 240 cm(-1). The Raman gain coefficient is estimated to be approximately 2.3 x 10(-11) m/W, which is more than 300 times greater than that of silica. The large Raman gain coefficient coupled with the large IR transparency window of these fibers shows promise for development of As-Se Raman fiber lasers and amplifiers in the near-, mid-, and long-IR spectral regions.

Highly nonlinear As-S-Se glasses for all-optical switching.

We have synthesized a series of chalcogenide glasses from the As-S-Se system that is designed to have strong nonlinearities. Measurements reveal that many of these glasses offer optical Kerr nonlinearities greater than 400 times that of fused silica at 1.25 and 1.55mum and figures of merit for all-optical switching greater than 5 at 1.55mum .

Spectroscopic scanning near-field optical microscopy with a free electron laser: CH2 bond imaging in diamond films.

Hydrogen chemistry in thin films and biological systems is one of the most difficult experimental problems in today's science and technology. We successfully tested a novel solution, based on the spectroscopic version of scanning near-field optical microscopy (SNOM). The tunable infrared radiation of the Vanderbilt free electron laser enabled us to reveal clearly hydrogen-decorated grain boundaries on nominally hydrogen-free diamond films. The images were obtained by SNOM detection of reflected 3.5 microm photons, corresponding to the C-H stretch absorption, and reached a lateral resolution of 0.2 microm, well below the lambda/2 (lambda = wavelength) limit of classical microscopy.

Phosphatidylinositol 3-kinase and mTOR mediate lipopolysaccharide-stimulated nitric oxide production in macrophages via interferon-beta.

Bacterial lipopolysaccharide (LPS) elicits responses by macrophages that help the body repel infections. Recent evidence indicates that phosphatidylinositol 3-kinase (PI 3-kinase) may mediate some of these responses. Here, we show that exposing macrophages to LPS rapidly increased membrane-associated PI 3-kinase activity and also elevated p70 S6 kinase activity. Inhibitors of PI 3-kinase or the mammalian target of rapamycin (mTOR) fully blocked p70 S6 kinase activation, implying that this kinase is controlled by PI 3-kinase and mTOR. These inhibitors also substantially reduced LPS-induced nitric oxide (NO) production. This inhibition was, in part, attributable to impaired LPS-stimulated secretion of interferon-beta, an autocrine co-factor for NO production. However, the addition of exogenous interferon-beta did not fully restore NO production, indicating that the NO response was being inhibited by another mechanism as well. Together, these data suggest that PI 3-kinase, mTOR, and possibly p70 S6 kinase mediate LPS-induced NO production by regulating the secretion of interferon-beta and by a second undefined mechanism.

Large Kerr effect in bulk Se-based chalcogenide glasses.

High-speed optical communication requires ultrafast all-optical processing and switching capabilities. The Kerr nonlinearity, an ultrafast optical nonlinearity, is often used as the basic switching mechanism. A practical, small device that can be switched with ~1-pJ energies requires a large Kerr effect with minimal losses (both linear and nonlinear). We have investigated theoretically and experimentally a number of Se-based chalcogenide glasses. We have found a number of compounds with a Kerr nonlinearity hundreds of times larger than silica, making them excellent candidates for ultrafast all-optical devices.

Effect of temperature on the absorption loss of chalcogenide glass fibers.

The change in the absorption loss of IR-transmitting chalcogenide glass fibers in the temperature range of -90 degrees C or= 6 microm the change in loss was mainly due to multiphonon absorption. The change in loss for tellurium-based glass fibers increased significantly at T = 60 degrees C. The increase in the loss at short wavelengths (lambda or= 9 microm, multiphonon absorption dominated the loss spectrum.

In vivo and in vitro assessment of mitogen activated protein kinase involvement during quail secondary palate formation.

Spatiotemporally regulated cell proliferation and differentiation are crucial for the successful completion of morphogenesis of the vertebrate secondary palate. An understanding of the mechanisms by which these cellular phenomena are regulated during palate development involves the identification of the various signal transduction pathways. In the present study, the presence and activation of mitogen-activated protein (MAP) kinases were investigated during the development of quail secondary palate. The palatal shelves were dissected on days 5-9 of incubation, homogenized, and centrifuged, after which the samples were separated by anion exchange fast protein liquid chromatography. The fractions were analyzed for myelin basic protein (MBP) phosphorylation. In addition, primary cultures of quail palate mesenchymal cells (QPMCs) were treated with epidermal growth factor (EGF) and prepared for MBP phosphorylation assays. A temporally regulated pattern of phosphotransferase activity, characterized by a three-fold increase in phosphotransferase activity toward MBP between days 5 and 8 of incubation, was observed during quail palate development. Western blotting, using MAP kinase antibodies, demonstrated the presence of a 42-kDa isoform between days 5 and 9 of incubation, during which the level of protein remained constant. Antityrosine immunoblotting with 4G10 also detected a 42-kDa protein. Phosphotransferase assays, using either a MAP kinase-specific substrate peptide (S5) or a protein kinase C inhibitor (R3), further confirmed the presence of a MAP kinase in the developing palate of quail. Because diverse biological processes occur concurrently during in vivo palate morphogenesis, the involvement of MAP kinase was explored further in primary cell culture. The data showed that EGF stimulated proliferation and activated 42-kDa MAP kinase in QPMCs. It is suggested that MAP kinase cascade may be involved in growth factor-regulated cell proliferation during morphogenesis of quail secondary palate.