A line-field scanning Fourier-domain optical coherence tomography (OCT) system (LF-FDOCT) that makes high-resolution and large-dynamic-range imaging possible was demonstrated. Unlike the conventional flying-spot OCT system, the x-axis parallel imaging (one B-scan) has a coherent imaging mode. A theoretical simulation of parallel interference imaging was derived, and the anisotropic resolution along two orthogonal directions was achieved. Validated by experimental results, the spatial resolutions along the x and y axis directions were 2.46 and 2.19 μm, and the theoretical resolutions were 1.8 and 1.34 μm, respectively. The field of view (FOV) in the lateral direction was 900 μm ( x ) × 850 μm ( y ) , and the axial resolution and FOV in the experiment were 2.5 and 700 μm, respectively. The maximal axial sensitivity was measured to be 90.5 dB when the sample was a specula. The en face of tomato and the cross-section of multilayer glass were demonstrated based on the LF-FDOCT system. The three-dimensional image of adherend sample including gels and microelectrodes was realized, proving the LF-FDOCT system had the capability of high resolution and high-dynamic-range imaging.
Lead halide perovskites are widely applied in not only photovoltaics, but also on-chip light source, nanolaser, and photon detection. In order to promote the incorporation of perovskite into integrated devices, microscale color patterning flexibility is a very important step. Femtosecond (fs) laser fabrication has shown significant advantages of high spatial resolution, low surround damage, and high processing efficiency over the other laser fabrication. Compared to the state-of-art techniques, the straightforward fs-direct laser writing (fs-DLW) also has advantages of mask-free, simple one step, and contactless. Here, a specially designed formamidinium lead mixed-halide nanoplatelet (FAPb(BrxI1-x)3 NP) with gradient bandgap is fabricated by chemical vapor deposition method. Then, spatially resolved modulation of the fluorescence by fs-DLW is demonstrated on the as-grown NP. The fluorescence color is modulated from red to green under a controlled laser pulse, due to the replacement of iodide ions by bromide ions. Specifically, the as-grown NP (thickness≈800 nm) is with a gradual bromide-iodide composition along the depth, mainly exhibits an emission of 710-nm from the bottom iodine rich phase. After halide substitution induced by fs-DLW, new fluorescence peaks appear in the wavelength range of 540 to 700 nm, which is controlled by the fs-DLW conditions. The fluorescent color is spatially modulated from red to green, enabling microscale resolved multicolor emission, implying the potential applications in micro-encryption, sensors, multicolor displays, lasers, and light-emitting devices.
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