Femtosecond Titanium Sapphire Laser

超快光谱学使得能够研究激发态的动力学以及详细分析光诱导反应的反应机理。由于分子内电子转移过程发生的时间尺度小到fs范围（10^（-15）s），飞秒激光系统是进行这种超快研究必不可少的。为此，需要一个基本系统，包括一个二极管泵浦的免维护钛宝石种子激光器，一个二极管泵浦的Nd：YLF泵浦激光器，一个温度稳定的再生放大器和一个温度稳定的拉伸器和压缩器单元，以及光学参量放大器（OPA）系统。利用该设置获得的具有<60 fs的脉冲宽度的800 nm的激光脉冲具有足够的时间分辨率来表征例如泵浦-探测实验中的上述过程。在上述方法中，首先用光谱定义的激发脉冲对样品进行光学激发，然后在选定的延迟时间Δt之后用宽带白色光脉冲进行检查。对于我们的光活性样品的分析，必须提供不同的激发波长。由于这些原因，必须使用非共线光学参量放大器（OPA）将飞秒激光的原始波长从800 nm ± 5 nm扩展到290-2600 nm，以便随后可以在尽可能宽的范围内进行激发（取决于物质和科学问题）。为了能够在如此宽的范围内使用OPA，并且在最后每个脉冲具有至少1微J的必要能量，在800 nm处> 5 mJ的输出功率是至关重要的。通过这种方式，可以获得具有所需的高时间分辨率和良好信噪比的瞬态吸收光谱。这里描述的仪器参数最终能够对各种不同的样品和复合物进行研究，这在参与小组和合作伙伴的研究中发挥着重要作用。因此，基本问题，如：“什么是光诱导反应的中间步骤，它们的时间常数是什么？是单重态还是三重态？或“是否涉及分子内电荷转移过程？电荷分离和复合过程发生在什么时间尺度上？”可以回答。

Ultrafast spectroscopy enables the investigation of the dynamics of excited states as well as the detailed analysis of reaction mechanisms of light-induced reactions. As intramolecular electron transfer processes take place on time scales down to the fs range (10^(-15) s), a femtosecond laser system is indispensable for performing such ultrafast studies. For this purpose, a basic system consisting of a diode-pumped maintenance-free Ti:sapphire seed laser, a diode-pumped Nd:YLF pump laser, a temperature-stabilized regenerative amplifier and a temperature-stabilized stretcher and compressor unit as well as an optical parametric amplifier (OPA) system is required. The laser pulses of 800 nm with pulse widths of <60 fs obtained with this setup possess a sufficient temporal resolution to characterize the processes described above in e.g. pump-probe experiments. In the aforementioned method, the sample is first optically excited with a spectrally defined excitation pulse and then examined with a broadband white light pulse after a selected delay time Δt. For the analysis of our photoactive samples it is essential that different excitation wavelengths are available. For these reason, a non-collinear optical parametric amplifier (OPA) must be used to extend the original wavelength of the femtosecond laser from 800 nm plus/minus 5 nm to 290-2600 nm so that excitation can subsequently be performed in a broad range as wide as possible (depending on the substance and scientific question). To be able to use the OPA in this broad range and to have the necessary energies of at least 1microJ per pulse at the end, an output power of > 5 mJ at 800 nm is crucial. In this way, transient absorption spectra can be obtained with the required high temporal resolution and good signal-to-noise ratio. The instrument parameters described here ultimately enable the investigation of large variety of different samples and complexes, which play an important role in the research of the participating groups and cooperation partners. As a result, elementary questions such as: "What are the intermediate steps of light-induced reactions and what are their time constants? Is it a singlet or triplet state?" or "Are intramolecular charge transfer processes involved? On which time scales do charge separation and recombination processes occur?" can be answered.