Li Derong, Lv Xiaohua, Bowlan Pamela, Du Rui, Zeng Shaoqun, Luo Qingming
Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics, Huazhong University of Science & Technology, Wuhan, 430074, China.
Opt Express. 2009 Sep 14;17(19):17070-81. doi: 10.1364/OE.17.017070.
The evolution of the frequency chirp of a laser pulse inside a classical pulse compressor is very different for plane waves and Gaussian beams, although after propagating through the last (4th) dispersive element, the two models give the same results. In this paper, we have analyzed the evolution of the frequency chirp of Gaussian pulses and beams using a method which directly obtains the spectral phase acquired by the compressor. We found the spatiotemporal couplings in the phase to be the fundamental reason for the difference in the frequency chirp acquired by a Gaussian beam and a plane wave. When the Gaussian beam propagates, an additional frequency chirp will be introduced if any spatiotemporal couplings (i.e. angular dispersion, spatial chirp or pulse front tilt) are present. However, if there are no couplings present, the chirp of the Gaussian beam is the same as that of a plane wave. When the Gaussian beam is well collimated, the introduced frequency chirp predicted by the plane wave and Gaussian beam models are in closer agreement. This work improves our understanding of pulse compressors and should be helpful for optimizing dispersion compensation schemes in many applications of femtosecond laser pulses.
在经典脉冲压缩器中，平面波和高斯光束内激光脉冲频率啁啾的演化有很大不同，尽管在通过最后一个（第4个）色散元件后，这两种模型给出相同的结果。在本文中，我们使用一种直接获取压缩器所获得光谱相位的方法，分析了高斯脉冲和光束频率啁啾的演化。我们发现相位中的时空耦合是高斯光束和平面波所获得的频率啁啾存在差异的根本原因。当高斯光束传播时，如果存在任何时空耦合（即角色散、空间啁啾或脉冲前沿倾斜），将会引入额外的频率啁啾。然而，如果不存在耦合，高斯光束的啁啾与平面波的啁啾相同。当高斯光束被很好地准直时，平面波和高斯光束模型预测的引入频率啁啾更接近一致。这项工作增进了我们对脉冲压缩器的理解，并且应该有助于在飞秒激光脉冲的许多应用中优化色散补偿方案。
