The intricate spectrally resolved optical nonlinearities resulting from a spectrally broad femtosecond Gaussian laser pulse have been unraveled using a single-scan and spectrometer-based nonlinear optical probing technique. The interaction of the broad femtosecond laser pulse with a strongly absorbing organic dye has unveiled a remarkably distinct nonlinear absorption behavior across the broad spectral window. The nonlinear absorption behavior unveils an unusual transition from the reverse saturation absorption (RSA) to the saturation absorption (SA) as we sweep the wavelength on both sides of the central wavelength of the excitation laser pulse. A competition between the band-filling and excited-state absorption results in such a dramatic switch-over from the RSA to the SA due to the variation of the intensity distribution across the Gaussian pulse spectrum. On the other hand, the nonlinear refraction studies dictate more over the constant Kerr-type positive nonlinear refractive indices across the entire laser pulse, with a pronounced contribution from the nonlinear absorption phase dominating at the center of the pulse. The presented technique establishes a robust and simple spectrometer-based technique that offers new, to the best of our knowledge, avenues for estimating optical nonlinearities for rapid nonlinear optical measurements.

中文翻译：

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单扫描和基于光谱仪的非线性光学探测中激光脉冲内的光谱解析非线性

使用单扫描和基于光谱仪的非线性光学探测技术，已经阐明了由光谱宽的飞秒高斯激光脉冲产生的复杂的光谱解析光学非线性。宽飞秒激光脉冲与强吸收有机染料的相互作用揭示了跨宽光谱窗口的非常独特的非线性吸收行为。当我们扫描激发激光脉冲中心波长两侧的波长时，非线性吸收行为揭示了从反向饱和吸收（RSA）到饱和吸收（SA）的不寻常转变。由于高斯脉冲光谱上强度分布的变化，带填充和激发态吸收之间的竞争导致从 RSA 到 SA 的剧烈切换。另一方面，非线性折射研究更多地规定了整个激光脉冲中恒定的克尔型正非线性折射率，其中在脉冲中心占主导地位的非线性吸收相位有显着的贡献。所提出的技术建立了一种强大而简单的基于光谱仪的技术，据我们所知，该技术为快速非线性光学测量的光学非线性估计提供了新的途径。