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Variation of iron species in the UV-irradiated aqueous solution was examined in the presence of various dissolved organic matter (DOM). Under the irradiation at constant light intensity, a regular oscillation in the ratio of Fe(II) to total iron, Fe(II)/Fe(t), was observed when DOM was periodically added into the solution. In each cycle, the Fe(II)/Fe(t) ratio increased initially and then decreased with concomitant degradation of DOM. The Fe(II)/Fe(t) ratio approached a constant value after the DOM was completely mineralized. The period and amplitude of the oscillation were dependent on DOM structure and its initial concentration, but the ultimate photosteady state was not affected by DOM. It was revealed that both DOM and photoreactive Fe(III) species were indispensable for the fluctuation in Fe(II)/Fe(t) ratio. The ultimate photosteady state originated from the equilibrium between Fe(III) photoreduction and aerobic Fe(II) photooxidation induced simultaneously by UV irradiation. It was the DOM that disturbed these two opposite processes, leading to the oscillation in Fe(II)/ Fe(t) ratio under UV irradiation.

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We report the fabrication of a novel high nonlinear fiber made of Ge-Sb-Se chalcogenide glasses with high numerical aperture (∼1.0), where the core and the cladding glasses consist of Ge₁₅Sb₂₅Se₆₀ and Ge₁₅Sb₂₀Se₆₅ (mol. %), respectively. The nonlinear refractive index (n₂) of the core glass is 19×10^-18 m²/W at 1.55 μm, and its laser-induced damage threshold under irradiation of 3.0 μm fs laser is approximately 3674  GW/cm². By pumping a 20-cm-long fiber with a core diameter of 23 μm using 150 fs pulses at 6.0 μm, supercontinuum spanning from ∼1.8 to ∼14  μm was generated.

Silicon photonics has great potential for mid-wave-infrared applications. The dispersion of waveguide can be manipulated by waveguide dimension and cladding materials. Simulation shows that <3 μm wide conversion can be achieved by tuning the pump wavelength.

Dispersive Fourier transform imaging is a powerful technique in achieving ultrafast imaging of wide areas. However, system power efficiency is often limited by dispersive components. Here, we demonstrate that a gap-plasmon metasurface (GPM) based blazed grating can be used in dispersive imaging applications to achieve higher power efficiency than conventional gratings. A sub-wavelength GPM-based grating at telecommunication wavelengths has been designed and fabricated. 75.6% power efficiency with ∼0.4°/10 nm spatial dispersion has been measured for TE polarized waves at normal incidence. The fabricated device has been tested in a wide area real-time dispersive imaging system and &lt;300 μm spatial resolution has been demonstrated experimentally.

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