Low-noise quantum cascade lasers and optical antenna probe for near-field Raman spectroscopy

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The influence of external feedback on the relative intensity noise of a mid-infrared InGaAs/InAlAs distributed-feedback-quantum cascade lasers was quantitatively clarified for the first time. Next, towards the development of optical antenna probes, mid-infrared optical antennas were fabricated on a Si substrate. The FDTD method can calculate the electric field around an optical antenna, but it is not easy to experimentally discern its distribution normal to the antenna surface. So, a thin Al2O3 layer was deposited on a Si substrate through atomic layer deposition, and dumbbell-shaped slot antennas were made on this substrate. It was possible to grow a layer with the thickness being controlled to an accuracy of ~1 nm. By observing the change in the restrahlen reflection spectras, an understanding of the vertical field distribution could be gained. Obtained results are effective in achieving photo-detectors satisfying both high-sensitivity and high-speed in the mid-infrared range.