Tomaszewska-Rolla Dorota, Lindberg Robert, Pasiskevicius Valdas, Laurell Fredrik, Soboń Grzegorz
Laser and Fiber Electronics Group, Faculty of Electronics, Photonics and Microsystems, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370, Wrocław, Poland.
Department of Applied Physics, Royal Institute of Technology, Hannes Alfvéns Väg 11, 106 91, Stockholm, Sweden.
Sci Rep. 2022 Jan 10;12(1):404. doi: 10.1038/s41598-021-04420-3.
In this work, we show that the nonlinear evolution of femtosecond seed pulses with different parameters (temporal and spectral shapes, repetition rate, pulse energy) in an Yb-fiber amplifier leads to gain-managed nonlinear amplification, enabling robust generation of high-peak-power and nearly transform-limited pulses after external compression. We demonstrate a compressed pulse duration of 33 fs with an energy of 80.5 nJ and a peak power of 2.29 MW for a source with a repetition rate of 30 MHz. For a second seed source with a repetition rate of 125 MHz, we obtained a pulse duration of 51 fs with an energy of 22.8 nJ and a peak power of 420 kW. Numerical simulations incorporating rate equations and nonlinear propagation in the amplifier provide evolutions that agree well with the experimental results. The discrepancies in the amplifier's absorption edge appearing at low repetition rates and higher pump powers are attributed to the temperature dependence of the amplifier's gain cross-sections. Here, we experimentally verify this attribution and thus underline the importance of accounting for the fiber core temperature for precise modelling of the short-wavelength spectral edge of the output pulses in nonlinear Yb-fiber amplifiers. We also measure, for the first time, the relative intensity noise of an amplifier operating in the gain-managed nonlinear regime. The measurements reveal a significant contribution of the amplification process to the overall output noise of the system.
在这项工作中，我们表明，不同参数（时间和光谱形状、重复频率、脉冲能量）的飞秒种子脉冲在掺镱光纤放大器中的非线性演化会导致增益控制的非线性放大，从而在外部压缩后能够稳健地产生高峰值功率且近乎变换极限的脉冲。对于重复频率为30 MHz的光源，我们展示了压缩脉冲持续时间为33 fs，能量为80.5 nJ，峰值功率为2.29 MW。对于重复频率为125 MHz的第二个种子光源，我们获得了脉冲持续时间为51 fs，能量为22.8 nJ，峰值功率为420 kW的结果。结合放大器中的速率方程和非线性传播的数值模拟提供了与实验结果吻合良好的演化情况。在低重复频率和较高泵浦功率下放大器吸收边缘出现的差异归因于放大器增益截面的温度依赖性。在此，我们通过实验验证了这一归因，从而强调了在对非线性掺镱光纤放大器中输出脉冲的短波长光谱边缘进行精确建模时考虑光纤纤芯温度的重要性。我们还首次测量了在增益控制非线性 regime下工作的放大器的相对强度噪声。测量结果揭示了放大过程对系统整体输出噪声的重大贡献。
