3‐photon microscopy (3PM) excited at the 1700 nm window enables deep‐tissue imaging in vivo, especially in brain. PC rod soliton source has previously been exclusively used as the excitation source, which is rather costly and difficult to align. Here we demonstrate a novel nonlinear optical technique to build femtosecond laser source at the 1700 nm window, based on self‐phase modulation (SPM) in a short span of large‐mode‐area fiber. The spectral broadening experienced by the pump pulse leads to the generation of a red‐shifted sidelobe at 1603 nm. After spectral filtering, this sidelobe corresponds to 170‐fs, 167‐nJ pulses at 1603 nm. Using this SPM source, we further demonstrate deep‐brain 3 PM to a depth of 1500 μm below the mouse brain surface in vivo. Our SPM femtosecond laser source thus provides a cost effective and easy‐to‐align alternative excitation source to the PC rod soliton source.

中文翻译：

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1603 nm的自相位调制飞秒激光源及其在体内深脑3光子显微镜中的应用

在1700 nm窗口处激发的3光子显微镜（3PM）可以在体内，尤其是在大脑中进行深层组织成像。以前，PC棒孤子源一直被专门用作激励源，它相当昂贵且难以对准。在这里，我们展示了一种新颖的非线性光学技术，该技术可以在短距离的大模式区域光纤中基于自相位调制（SPM），在1700 nm窗口内建立飞秒激光源。泵浦脉冲经历的光谱展宽导致在1603 nm处产生红移旁瓣。经过频谱滤波后，此旁瓣对应于1603 nm处的170-fs，167-nJ脉冲。使用此SPM来源，我们进一步在体内演示了深3PM到小鼠大脑表面以下1500μm的深度。