Photo-induced reduction of graphene oxide coating on optical waveguide and consequent optical intermodulation.

Increased absorption of transverse-magnetic (TM)-polarised light by a graphene-oxide (GO) coated polymer waveguide has been observed in the presence of transverse-electric (TE)-polarised light. The GO-coated waveguide exhibits very strong photo-absorption of TE-polarised light--and acts as a TM-pass waveguide polariser. The absorbed TE-polarised light causes a significant temperature increase in the GO film and induces thermal reduction of the GO, resulting in an increase in optical-frequency conductivity and consequently increased optical propagation loss. This behaviour in a GO-coated waveguide gives the action of an inverted optical switch/modulator. By varying the incident TE-polarised light power, a maximum modulation efficiency of 72% was measured, with application of an incident optical power level of 57 mW. The GO-coated waveguide was able to respond clearly to modulated TE-polarised light with a pulse duration of as little as 100 µs. In addition, no wavelength dependence was observed in the response of either the modulation (TE-polarised light) or the signal (TM-polarised light).

Field Emission from Zinc Oxide Nanobelts.

We report here, the in-situ field emission (FE) property measurement on the individual ZnO nanobelts inside a high resolution transmission electron microscope (TEM) using a special scanning tunneling microscopy (STM)-TEM system. The field emission properties were found to be size scale dependent. It was found that the threshold voltage decreases and the field enhancement factor increases with the decrease in the diameter of the tip of the nanobelt and increase in the sharpness of the tip. The field emission parameter was estimated following the Fowler-Nordheim (F-N) theory. The ZnO nanobelt with the sharp agave like tip structure (d = 10 nm) showed the highest value of the field enhancement factor, ß ≈ 4562, and a high field emission current of ~ 502 µA.

Graphene oxide-based waveguide polariser: from thin film to quasi-bulk.

We have demonstrated a broadband waveguide polariser with high extinction ratio on a polymer optical waveguide coated with graphene oxide via the drop-casting method. The highest extinction ratio of nearly 40 dB is measured at 1590 nm, with a variation of 4.5 dB across a wavelength range from 1530 nm to 1630 nm, a ratio that is (to our knowledge) the highest reported for graphene-based waveguide polarisers to date. This result is achieved with a graphene oxide coating length along the propagation direction of only 1.3 mm and a bulk film thickness of 2.0 µm. The underlying principles of the strongly polarisation dependent propagation loss demonstrated have been studied and are attributed to the anisotropic complex dielectric function of graphene oxide bulk film.

In situ observation of size-scale effects on the mechanical properties of ZnO nanowires.

In this investigation, the size-scale in mechanical properties of individual [0001] ZnO nanowires and the correlation with atomic-scale arrangements were explored via in situ high-resolution transmission electron microscopy (TEM) equipped with atomic force microscopy (AFM) and nanoindentation (NI) systems. The Young's modulus was determined to be size-scale-dependent for nanowires with diameter, d, in the range of 40 nm ≤ d ≤ 110 nm, and reached the maximum of ∼ 249 GPa for d = 40 nm. However, this phenomenon was not observed for nanowires in the range of 200 nm ≤ d ≤ 400 nm, where an average constant Young's modulus of ∼ 147.3 GPa was detected, close to the modulus value of bulk ZnO. A size-scale dependence in the failure of nanowires was also observed. The thick ZnO nanowires (d ≥ 200 nm) were brittle, while the thin nanowires (d ≤ 110 nm) were highly flexible. The diameter effect and enhanced Young's modulus observed in thin ZnO nanowires are due to the combined effects of surface relaxation and long-range interactions present in ionic crystals, which leads to much stiffer surfaces than bulk wires. The brittle failure in thicker ZnO wires was initiated from the outermost layer, where the maximum tensile stress operates and propagates along the (0001) planes. After a number of loading and unloading cycles, the highly compressed region of the thinner nanowires was transformed from a crystalline to an amorphous phase, and the region near the neutral zone was converted into a mixture of disordered atomic planes and bent lattice fringes as revealed by high-resolution images.

Enhancement of CsLiB(6)O(10) surface-damage resistance by improved crystallinity and ion-beam etching.

The surface laser-induced damage threshold (LIDT) of CsLiB(6)O(10) (CLBO) crystal was enhanced twofold with improved crystallinity and ion-beam etching. For crystals with high crystal quality (bulk LIDT, 15.0-19.0 GW/cm(2)), the surface LIDT was 1.4-fold higher than for those with conventional crystal quality (bulk LIDT, 9.0-12.0 GW/cm(2)). In addition, removal of residual surface-polishing compounds by means of ion-beam etching can further enhance the surface LIDT by another 1.5-fold. Thus, CLBO crystals with high crystal quality and ion-beam etching are now more reliable for high-power UV light generation.

Complete nucleotide sequence and genome organization of hibiscus chlorotic ringspot virus, a new member of the genus Carmovirus: evidence for the presence and expression of two novel open reading frames.

The complete nucleotide sequence of hibiscus chlorotic ringspot virus (HCRSV) was determined. The genomic RNA (gRNA) is 3,911 nucleotides long and has the potential to encode seven viral proteins in the order of 28 (p28), 23 (p23), 81 (p81), 8 (p8), 9 (p9), 38 (p38), and 25 (p25) kDa. Excluding two unique open reading frames (ORFs) encoding p23 and p25, the ORFs encode proteins with high amino acid similarity to those of carmoviruses. In addition to gRNA, two 3'-coterminated subgenomic RNA (sgRNA) species were identified. Full-length cDNA clones derived from gRNA and sgRNA were constructed under the control of a T7 promoter. Both capped and uncapped transcripts derived from the full-length genomic cDNA clone were infectious. In vitro translation and mutagenesis assays confirmed that all the predicted ORFs except the ORF encoding p8 are translatable, and the two novel ORFs (those encoding p23 and p25) may be functionally indispensable for the viral infection cycle. Based on virion morphology and genome organization, we propose that HCRSV be classified as a new member of the genus Carmovirus in family Tombusviridae.

Alleviation of photoinduced damage in GdxY1-xCa4O(BO3)3 at elevated crystal temperature for noncritically phase-matched 355-nm generation.

We developed a Gd(x)Y(1-x)Ca(4)O(BO(3))(3) (GdYCOB) crystal for control of optical birefringence. GdYCOB crystals were successfully used to generate noncritical phase-matched (NCPM) second and third harmonics of 1064-nm lights. However, we observed degradation of third-harmonic-generation (THG) output power and distortion of the beam pattern as a result of photoinduced damage and thermal dephasing. The photoinduced damage was classified into two types. One was gray-track and the other was photorefractive damage. It seems that these types of damage were similar to the types of damage that occurred with KTiOPO(4) and LiNbO(3) crystals. We tried to circumvent this problem by crystal heating. Photoinduced damage of GdYCOB was overcome by elevation of the crystal temperature, and NCPM THG (355-nm) output power from heated GdYCOB increased to 9 mW (62.5 kHz).

Long-term operation of CsLiB(6)O(10) at elevated crystal temperature.

We have successfully resolved the degradation problem of CsLiB(6)O(10) (CLBO) by means of elevated crystal temperature. CLBO crystals were continuously operated at 160 degrees C in ordinary room humidity. No degradation of performance was observed after more than 1 month. We believe that heating CLBO crystal above 130 degrees C can relieve stresses introduced by crystal hydration, cutting, polishing, and thermal shock owing to laser power absorption. Thus long-term operation of CLBO crystal is achieved for effective application of laser frequency conversion. Output stability from CLBO is also further enhanced at elevated crystal temperature.

Alleviation of thermally induced phase mismatch in CsLiB6O10 crystal by means of temperature-profile compensation.

A new mechanism was found to alleviate the thermally induced phase mismatch of nonlinear optical crystals. By cooling CsLiB>(6)O(10) at an elevated crystal temperature with gas, we improved laser conversion efficiency from green (532 nm) to UV (266 nm) 2.3 times compared with that without cooling. In situ observation of the temperature profile on the output surface revealed that such cooling initiates a negative temperature profile that compensates for the positive profile generated from laser absorption. A 10.6-W UV output with excellent stability was generated. The optimum crystal length was substantially extended.

High-power fourth- and fifth-harmonic generation of a Nd:YAG laser by means of a CsLiB(6)O(10).

High pulse energies of nanosecond-level fourth- and fifth-harmonic (4omega and 5omega) generation of a Nd:YAG laser have been obtained with a CsLiB(6)O(10) (CLBO) nonlinear crystal. 500 mJ of 4omega output with a conversion efficiency of 50% from the second-harmonic input was generated. 5omega output at 213 nm of as high as 230 mJ was obtained by sum-frequency generation of the 266- and 1064-nm beams, corresponding to a 10.4% conversion efficiency of the initial fundamental input energy. The characteristics of the CLBO crystal that permit this effective frequency conversion are discussed.