Two-photon microscopy depends extensively on the two-photon absorption cross sections of biologically relevant chromophores. High repetition rate (HRR) lasers are essential in multiphoton microscopy for generating satisfactory signal to noise at low average powers. However, HRR lasers generate thermal distortions in samples even with the slightest single photon absorption. We use an optical chopper with HRR lasers to intermittently ‘blank’ irradiation and effectively minimize thermal effects to result in a femtosecond z-scan setup that precisely measures the two-photon absorption (TPA) cross-sections of chromophores. Though several experimental factors impact such TPA measurements, a systematic effort to modulate and influence TPA characteristics is yet to evolve. Here, we present the effect of several control parameters on the TPA process that are independent of chromophore characteristics for femtosecond laser pulse based measurements; and demonstrate how the femtosecond laser pulse repetition rate, chromophore environment and incident laser polarization can become effective control parameters for such nonlinear optical properties.

We demonstrate how, irrespective of chromophore characteristics, the femtosecond laser pulse repetition rate, chromophore environment and incident laser polarization are effective control parameters for nonlinear optical properties arising from two-photon processes.

中文翻译：

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探索溶液中两个光子过程的控制参数。


双光子显微镜很大程度上取决于生物相关发色团的双光子吸收截面。高重复率 (HRR) 激光器对于多光子显微镜至关重要，可以在低平均功率下产生令人满意的信噪比。然而，即使只有最轻微的单光子吸收，HRR 激光器也会在样品中产生热变形。我们使用带有 HRR 激光器的光学斩波器来间歇性“空白”照射，并有效地最小化热效应，从而形成飞秒 z 扫描装置，可精确测量发色团的双光子吸收 (TPA) 横截面。尽管有几个实验因素会影响此类 TPA 测量，但调制和影响 TPA 特性的系统性努力尚未发展。在这里，我们介绍了几个控制参数对 TPA 过程的影响，这些参数与基于飞秒激光脉冲的测量的发色团特性无关；并演示飞秒激光脉冲重复率、发色团环境和入射激光偏振如何成为此类非线性光学特性的有效控制参数。

我们证明了，无论发色团特性如何，飞秒激光脉冲重复率、发色团环境和入射激光偏振如何成为双光子过程产生的非线性光学特性的有效控制参数。