钛宝石飞秒激光器中孤子分子的内部动态探测

Internal dynamic detection of soliton molecules in Ti:sapphire femtosecond laser

孤子是自然界中一种基本的非线性波动传递形式,孤子间的相互作用能够映射出复杂非线性系统的多体动力学过程,具有重要的基础研究价值.被动锁模激光器是研究孤子相互作用的理想平台.光孤子之间的吸引、排斥作用能够形成孤子分子,而时间拉伸色散傅里叶变换(TS-DFT)技术使得实时探测孤子分子动力学成为可能.基于TS-DFT技术,本文实验研究了钛宝石飞秒激光器产生的孤子分子的内部动态,通过改变抽运功率,分别观察到了间隔为180 fs的稳定的孤子分子和间隔为105 fs的具有微弱相位振荡的孤子分子,后者的振动幅度仅为0.05 rad.实验发现受到环境影响,稳定态的孤子分子还能够转变为相位滑动状态.这些间隔为百飞秒量级的光学孤子分子对于研究孤子的近程非线性相互作用具有突出的意义.

Soliton is a universal format of nonlinear wave propagation in nature. Soliton can maintain its shape during propagation. This unique property has been widely observed in plasma physics, high energy electromagnetics,hydrodynamics, and nonlinear optics. Soliton interactions can reflect collective dynamic behaviors in complex nonlinear systems, showing significant basic research value. Passive mode-locked laser is an ideal platform for studying soliton interaction. The attraction and repulsion between two optical solitons can form soliton molecules. Their properties have been intensively studied by optical spectral analysis. However, conventional optical spectrum analyzers show low resolution and long average time. Time-stretched dispersive Fourier transformation(TS-DFT) is an emerging-powerful measurement technology, which can map the spectrum of an optical pulse to a temporal waveform under sufficient dispersion. The TS-DFT makes it possible to detect the dynamics of the solitons in real time. Based on TS-DFT, the internal dynamics of the solitons in Ti:sapphire femtosecond laser is studied in experiment. By changing the pump power, the stable soliton molecules with a separation of 180 fs and the weak phase oscillatory soliton molecules with a separation of 105 fs are observed.The amplitude in the weak oscillation state is merely 0.05 rad. We also find that the soliton molecules in stable state can transform into phase sliding state under environmental perturbation. These optical soliton molecules with a binding separation of 100 fs are of great significance for studying the short-range nonlinear interactions of solitons.