Guesmi Mariem, Veselá Petra, Žídek Karel
Regional Center for Special Optics and Optoelectronic Systems (TOPTEC), Institute of Plasma Physics, Czech Academy of Science V.V.I., Za Slovankou 1782/3, 182 00, Prague 8, Czech Republic.
Sci Rep. 2022 Mar 9;12(1):3827. doi: 10.1038/s41598-022-07875-0.
A targeted shaping of complex femtosecond pulse waveforms and their characterization is essential for many spectroscopic applications. A 4f pulse shaper combined with an advanced pulse characterization technique should, in the idealized case, serve this purpose for an arbitrary pulse shape. This is, however, violated in the real experiment by many imperfections and limitations. Although the complex waveform generation has been studied in-depth, the comparison of the effects of various experimental factors on the actual pulse shape has stayed out of focus so far. In this paper, we present an experimental study on the targeted generation and retrieval of complex pulses by using two commonly-used techniques: spatial-light-modulator (SLM)-based 4f pulse shaper and second-harmonic generation frequency-resolved optical gating (FROG) and cross-correlation FROG (XFROG). By combining FROG and XFROG traces, we analyze the pulses with SLM-adjusted complex random phases ranging from simple to very complex waveforms. We demonstrate that the combination of FROG and XFROG ensures highly consistent pulse retrieval, irrespective of the used retrieval algorithm. This enabled us to evaluate the role of various experimental factors on the agreement between the simulated and actual pulse shape. The factors included the SLM pixelation, SLM pixel crosstalk, finite laser focal spot in the pulse shaper, or interference fringes induced by the SLM. In particular, we observe that including the SLM pixelation and crosstalk effect significantly improved the pulse shaping simulation. We demonstrate that the complete simulation can faithfully reproduce the pulse shape. Nevertheless, even in this case, the intensity of individual peaks differs between the retrieved and simulated pulses, typically by 10-20% of the peak value, with the mean standard deviation of 5-9% of the maximum pulse intensity. We discuss the potential sources of remaining discrepancies between the theoretically expected and experimentally retrieved pulse.
对复杂飞秒脉冲波形进行有针对性的整形及其表征对于许多光谱应用至关重要。在理想情况下，结合先进脉冲表征技术的4f脉冲整形器应能适用于任意脉冲形状。然而，在实际实验中，这受到许多缺陷和限制的影响。尽管对复杂波形生成已进行了深入研究，但各种实验因素对实际脉冲形状的影响比较至今仍未受到关注。在本文中，我们通过使用两种常用技术：基于空间光调制器（SLM）的4f脉冲整形器以及二次谐波产生频率分辨光学门控（FROG）和互相关FROG（XFROG），对复杂脉冲的有针对性生成和恢复进行了实验研究。通过结合FROG和XFROG轨迹，我们分析了具有SLM调整的从简单到非常复杂波形的复随机相位的脉冲。我们证明，无论使用何种恢复算法，FROG和XFROG的组合都能确保高度一致的脉冲恢复。这使我们能够评估各种实验因素对模拟脉冲形状与实际脉冲形状之间一致性的作用。这些因素包括SLM像素化、SLM像素串扰、脉冲整形器中的有限激光焦斑或由SLM引起的干涉条纹。特别是，我们观察到考虑SLM像素化和串扰效应显著改善了脉冲整形模拟。我们证明完整的模拟可以忠实地再现脉冲形状。然而，即使在这种情况下，恢复脉冲与模拟脉冲之间各个峰值的强度仍存在差异，通常为峰值的10 - 20%，最大脉冲强度的平均标准差为5 - 9%。我们讨论了理论预期脉冲与实验恢复脉冲之间剩余差异的潜在来源。
