In this work, we discovered the possibility of greatly relaxing requirements to the speed and dynamic range of pump power variation and, thus, of reducing synchronous pumping of ytterbium (Yb)-based fiber lasers to a very simple pump modulation yielding a mode-locked pulsed output. We show that even slow (microsecond-scale) low-index ($\le\! {0.5}$) sine-wave synchronous modulation of the pump power can result in shaping of a regular train of nanosecond laser pulses. It is revealed that the energy-conservative process of laser pulse shortening against the pump modulation period can take place in the quasi–two-level laser active medium owing to mistiming-induced gain discrimination of the temporal laser pulse profile. Thus, nanosecond pulses with energy up to 50 nJ were obtained in our experimental all-fiber Yb-based laser configuration. Our theoretical modeling reveals routes to much stronger pulse shortening through tunable pump modulation parameters. This discovery allows the establishment of more reliable and easy-to-implement high-efficiency alternatives to other types of high-energy ultralong mode-locked fiber lasers.

中文翻译：

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通过同步正弦波泵浦调制对fiber光纤激光器中的纳秒脉冲进行整形

在这项工作中，我们发现了极大地放松对泵浦功率变化的速度和动态范围的要求的可能性，从而将基于（（Yb）的光纤激光器的同步泵浦降低为一个非常简单的泵浦调制，从而产生锁模脉冲输出。我们表明，即使是慢速（微秒级）的低索引（$ \ le \！{0.5} $）泵浦功率的正弦波同步调制可导致形成规则的纳秒级激光脉冲序列。结果表明，由于雾化引起的时间激光脉冲轮廓的增益判别，准脉冲的准二级激光活性介质中可能发生缩短激光脉冲相对于泵浦调制周期的节能过程。因此，在我们的实验性全光纤Yb基激光器配置中，获得了能量高达50 nJ的纳秒脉冲。我们的理论模型揭示了通过可调泵浦调制参数实现更强脉冲缩短的途径。这一发现可以为其他类型的高能超长锁模光纤激光器建立更可靠，易于实现的高效替代方案。