Continuous-wave mode-locked solid-state lasers with enhanced spatial hole burning
Continuous-wave mode-locked solid-state lasers with enhanced spatial hole burning
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DOI：
10.1007/bf01081271
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发表时间：
1995-11
期刊：
影响因子：
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通讯作者：
B. Braun;K. Weingarten;F. X. Kärtner;U. Keller
中科院分区：
文献类型：
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作者：
B. Braun;K. Weingarten;F. X. Kärtner;U. Keller
本文以Nd：YLF激光器为例，系统地研究了具有末端增益（GE）和中间增益（GM）的主动锁模激光器和被动锁模激光器之间的差异。GE激光器产生的脉冲宽度大约比可比较的GM腔短三倍。这是由于增强的空间烧孔（SHB），其有效地消除了饱和增益，并且与GM腔相比允许更大的激射带宽。我们首先调查增强SHB通过测量CW模式光谱，我们已经观察到，在GE腔的模式间距主要取决于晶体长度。这也证实了Nd：LSB晶体，其中泵浦吸收长度明显短于晶体长度。在锁模操作，脉冲宽度为4 ps的被动锁模和5 ps的主动锁模与GE腔，相比，11 ps的被动锁模和17 ps的主动锁模与GM腔。此外，GE腔的时间带宽积大约是sech2脉冲形状的理想积的两倍，并且不能单独通过色散补偿来改善，而GM腔具有接近理想的时间带宽限制性能。GM腔的结果与现有的理论相比较，考虑到泵浦功率相关的增益带宽的附加效应，该增益带宽将Nd：YLF的带宽从360 GHz增加到> 500 GHz。在下面的论文[1]（称为第二部分）中，将提出对SHB效应的严格理论处理。
We systematically investigate the difference between both actively and passively mode-locked lasers with Gain-at-the-End (GE) and Gain-in-the-Middle (GM) at the example of Nd:YLF lasers. The GE laser generates pulse widths approximately three times shorter than a comparable GM cavity. This is due to enhanced Spatial Hole Burning (SHB) which effectively flattens the saturated gain and allows for a larger lasing bandwidth compared to a GM cavity. We first investigate enhanced SHB by measuring the cw mode spectrum, where we have observed that the mode spacing in GE cavities depends primarily on the crystal length. This was also confirmed for a Nd:LSB crystal, where the pump absorption length was significantly shorter than the crystal length. In mode-locked operation, pulse widths of 4 ps for passive mode locking and 5 ps for active mode locking are demonstrated with GE cavities, compared to 11 ps for passive and 17 ps for active mode locking with GM cavities. Additionally, the time-bandwidth product for the GE cavity is approximately twice the ideal product for a sech2pulse shape and cannot be improved by dispersion compensation alone, while the GM cavity has nearly ideal time-bandwidth-limited performance. The results for the GM cavity compare well to existing theories taking into account the added effect of pump-power-dependent gain bandwidth which increases the bandwidth of Nd: YLF from 360 to > 500 GHz. In a following paper [1] (called Part II) a rigorous theoretical treatment of the effects due to SHB will be presented.