BackgroundPrevious work indicated that an ultrashort pulse (USP) 425 nm laser is capable of inactivating murine norovirus (MNV: Virol. J. 11:20), perhaps via an impulsive stimulated Raman scattering (ISRS) mechanism, and does not substantially damage human plasma proteins (PLOS One 9:11). Here, further investigation of virus inactivation by laser light is performed.MethodsIn this study, we evaluate whether inactivation of MNV is specific to the USP wavelength of 425 nm, or if it occurs at other visible wavelengths, using a tunable mode-locked Ti-Sapphire laser that has been frequency doubled to generate femtosecond pulses at wavelengths of 400, 408, 425, 450, 465, and 510 nm. Continuous Wave (CW) lasers are also applied. Singlet oxygen enhancers are used to evaluate the sensitivity of MNV to singlet oxygen and oxygen quenchers are used to evaluate effects on virus inactivation as compared to untreated controls.Results> 3 log10 inactivation of MNV pfu occurs after irradiation with an average power of 150 mW at wavelengths of 408, 425 or 450 nm femtosecond-pulsed light for 3 h. Thus results suggest that the mechanism by which a laser inactivates the virus is not wavelength-specific. Furthermore, we also show that irradiation using a continuous wave (CW) laser of similar power at 408 nm also yields substantial MNV inactivation indicating that inactivation does not require a USP. Use of photosensitizers, riboflavin, rose bengal and methylene blue that generate singlet oxygen substantially improves the efficiency of the inactivation. The results indicate a photochemical mechanism of the laser-induced inactivation where the action of relatively low power blue laser light generates singlet oxygen.ConclusionResults suggest formation of short-lived reactive oxygen species such as singlet oxygen by visible laser light as the cause of virus inactivation rather than via an ISRS mechanism which induces resonant vibrations.

Thermally managed Z-scan using a modified chopper was compared to the utilization of a pulse picker with the common calibration material carbon disulfide and then extended to graphene oxide (GO) in different solvents at λ 800 nm. GO in distilled water using femtosecond laser excitation yielded a value of −2.7 :4 × 10 −15 cm 2 ∕W for nanometer particles and −1.6 :6 × 10 −15 cm 2 ∕W for micrometer-sized particles. Openaperture Z-scan results using the modified chopper showed no experimental difference.

The third-order nonlinear optical properties of Nitrogen-enriched TiO2 films deposited by Atomic Layer Deposition (ALD) at a temperature between 100-300°C on quartz substrates were studied using thermally managed Z-scan technique. TiO2 oxide films prepared by Physical Vapor Deposition (PVD) at room temperature were used as control samples. The as-grown ALD films deposited at 150-300°C exhibited values for the nonlinear index of refraction, n2, between 0.6x10-11 and 1x10-9 cm 2 /W, which is 4-6 order larger than previously reported. Annealing the films, for 3 hours at 450°C in air, reduced the nonlinearities below the detection limit of the experimental setup. Similarly, as-grown 100°C ALD and PVD films did not produce a discernible Zscan trace. Composition analysis performed by x-ray photoelectrons spectroscopy (XPS) reveals the presence of Ti-ON metallic bonds in the films that showed high nonlinear optical response. The presence of the metallic bonding gives the films deposited on Si (100) a golden color. These results demonstrate the possibility of a new class of thin-film nonlinear materials that their properties can be tailored by controlling the film composition.

Thermally managed Z-scan performed on ALD grown TiO2 films demonstrated n2 values of 1.7x10-11 and 1.94 x10-10 cm 2 /W for films grown at 100°C and 250°C, respectivelygreater than 1000X that of other growth methods. OCIS codes: (190.0190) Nonlinear optics; (320.0320) Ultrafast optics Development of next-generation high-speed photonics devices, such as ultrafast integrated modulators, require novel materials will large optical nonlinearities [1]-[2]. Established nonlinear materials cut from bulk crystals or liquids are not suitable for integration with CMOS technology. In addition to all-optical on-a-chip device applications, materials that exhibit high nonlinear absorption and a fast response time are useful in optical limiting applications [3] for the protection of optical sensors and the human eye from high intensity light such as lasers [4]. Typical materials proposed in the past for optical limiting have been semiconductors, fullerenes, carbon nanotubes, nanostructured materials such as nanoparticles, graphene, nonlinear absorbers doped in xerogels and sol gel films, glasses, filters, organic/inorganic clusters, as well as 2D atomic crystals and organic dye molecules. For most of these materials, there is a tradeoff between their optical limiting ability and damage thresholds, and response time. The vast majority of these materials are not suitable for covering large-scale areas with consistent reproducibly required for sensitive applications such as infrared counter measures sensors. Therefore, there is a need for CMOScompatible materials with sizable nonlinear optical properties. Thin-films and nanolaminates, grown using atomic layer deposition (ALD), have the potential to meet this need.

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