We report on a quasi-nondegenerate pump-probe technique that is based on spectral-filtration of femtosecond laser pulses by a pair of mutually-spectrally-disjunctive interference filters. This cost- and space-efficient approach can be used even in pump-probe microscopy where collinear propagation of pump and probe pulses is dictated by utilization of a microscopic objective. This technique solves the contradictory requirements on an efficient removal of pump photons from the probe beam, to achieve a good signal-to-noise ratio, simultaneously with a needed spectral proximity of the excitation and probing, which is essential for magnetooptical study of many material systems. Importantly, this spectral-filtration of 100 fs long laser pulses does not affect considerably the resulting time-resolution, which remains well below 500 fs. We demonstrate the practical applicability of this technique with close but distinct wavelengths of pump and probe pulses in spatially- and time-resolved spin-sensitive magnetooptical Kerr effect (MOKE) experiment in GaAs/AlGaAs heterostructure, where a high-mobility spin system is formed after optical injection of electrons at wavelengths close to MOKE resonance. In particular, we studied the time- and spatial-evolutions of charge-related (reflectivity) and spin-related (MOKE) signals. We revealed that they evolve in a similar but not exactly the same way which we attributed to interplay of several electron many-body effects in GaAs.

中文翻译：

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基于光谱滤波的 GaAs/AlGaAs 异质结构准非简并泵-探针磁光实验

我们报告了一种准非简并泵浦探针技术，该技术基于飞秒激光脉冲的光谱过滤，通过一对相互光谱分离的干涉滤波器。这种节省成本和空间的方法甚至可以用于泵浦探针显微镜，其中泵浦和探针脉冲的共线传播是由使用显微物镜决定的。该技术解决了从探测光束中有效去除泵浦光子的矛盾要求，以实现良好的信噪比，同时需要激发和探测的光谱接近度，这对于许多材料的磁光研究至关重要系统。重要的是，这种 100 fs 长激光脉冲的光谱过滤不会显着影响由此产生的时间分辨率，它仍然远低于 500 fs。我们在 GaAs/AlGaAs 异质结构中的空间和时间分辨自旋敏感磁光克尔效应 (MOKE) 实验中证明了该技术的实际适用性，泵浦和探测脉冲的波长接近但不同，其中形成了高迁移率自旋系统在接近 MOKE 共振波长的电子光学注入之后。特别是，我们研究了电荷相关（反射率）和自旋相关 (MOKE) 信号的时间和空间演化。我们发现它们以类似但不完全相同的方式演化，我们将其归因于 GaAs 中几种电子多体效应的相互作用。