The spectral window around 1700 nm is interesting for in-depth multiphoton microscopy of intact tissues due to reduced scattering and absorption in this wavelength range. However, wide adoption of this excitation range will rely on the availability of robust and cost-effective high peak power pulsed lasers operating at these wavelengths. Here, we report on a fiber-based femtosecond laser providing up to 95 nJ, 85 fs pulses at 1800 nm. The laser system makes use of a fiber-based chirped pulse amplifier emitting at 1560 nm followed by an in-house fabricated very large mode area antiresonant fiber for soliton self-frequency shift. Megawatt-peak power pulses at the repetition rate of 1 MHz are available directly at the output of the flexible fiber. We illustrate the potential of the source for biological microscopy by recording three-photon-excited fluorescence images of mouse nervous tissue. The flexible fiber tailored to propagate megawatt solitons in the biologically relevant window around 1700 nm opens the way to deep brain imaging of freely moving animals via miniaturized endomicroscopes.

由于该波长范围内的散射和吸收减少，因此 1700 nm 附近的光谱窗口对于完整组织的深度多光子显微术很有趣。然而，这种激发范围的广泛采用将依赖于在这些波长下工作的稳健且具有成本效益的高峰值功率脉冲激光器的可用性。在这里，我们报告了一种基于光纤的飞秒激光器，可在 1800 nm 处提供高达 95 nJ、85 fs 的脉冲。激光系统使用基于光纤的啁啾脉冲放大器，发射波长为 1560 nm，然后是内部制造的非常大模式面积的反谐振光纤，用于孤子自频移。可直接在柔性光纤的输出端获得重复率为 1 MHz 的兆瓦峰值功率脉冲。我们通过记录小鼠神经组织的三光子激发荧光图像来说明生物显微镜来源的潜力。专为在 1700 nm 左右的生物相关窗口中传播兆瓦孤子而定制的柔性光纤，为通过微型内窥镜对自由移动的动物进行深部脑成像开辟了道路。