We demonstrate a gain-switched singly Ho³⁺-doped ZBLAN fiber laser for the first time in the wavelength region around 2.94 μm which circumvents the strong water vapor lines. Four switchable gain-switched temporal states with 1/n (n = 4,3,2,1) pump repetition rates are first observed. The influences of pump power (pulse energy), repetition rate, duty cycle (pulse duration), and laser wavelength on their characteristics are studied, respectively. The results indicate that high pump repetition rate, large pump duty cycle, and short laser wavelength are beneficial for obtaining more gain-switched temporal states. For the case (n = 1), the increased pump repetition rate contributes to the increased pulse duration while decreased pulse energy and peak power. While μs-level pump pulse duration variation has an almost negligible effect on them. By introducing a plane ruled grating, the wavelength tuning was performed yielding a tuning range of 105 nm from 2895.5 nm to 3000.5 nm which just overlays the peak region of liquid water absorption. Finally, further optimizing of laser performances is discussed as well. This demonstration is helpful for preliminarily designing, prior to constructing a mid-infrared gain-switched laser which can find direct applications in laser surgery.

中文翻译：

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在2.94μm左右的波长区域中的状态可切换和波长可调的增益切换中红外光纤激光器

我们演示了一个增益切换的Ho ³⁺掺杂的ZBLAN光纤激光器首次出现在2.94μm左右的波长范围内，这绕过了强水蒸气线。首先观察到具有1 / n（n = 4,3,2,1）泵重复率的四个可切换的增益切换时间状态。分别研究了泵浦功率（脉冲能量），重复频率，占空比（脉冲持续时间）和激光波长对其特性的影响。结果表明，较高的泵浦重复率，较大的泵浦占空比和较短的激光波长有利于获得更多的增益切换时间状态。对于这种情况（n = 1），增加的泵重复频率有助于增加脉冲持续时间，同时减少脉冲能量和峰值功率。尽管μs级泵脉冲持续时间的变化对它们的影响几乎可以忽略不计。通过引入平面直纹光栅，进行波长调谐得到从2895.5 nm到3000.5 nm的105 nm调谐范围，该范围正好覆盖了液体吸水的峰值区域。最后，还讨论了激光性能的进一步优化。该演示有助于在构造可以在激光手术中找到直接应用的中红外增益切换激光器之前进行初步设计。