Femtosecond Titanium Sapphire Laser

超快光谱学使研究激发态动力学和光诱导反应机理的详细分析成为可能。由于分子内电子转移过程发生在fs范围（10^(-15)s）的时间尺度上，因此飞秒激光系统对于进行这种超快研究是必不可少的。为此，需要一个由二极管泵浦免维护Ti：蓝宝石籽激光器、二极管泵浦Nd:YLF泵浦激光器、温度稳定的再生放大器、温度稳定的拉伸器和压缩器单元以及光学参量放大器（OPA）系统组成的基本系统。用这种装置获得的800 nm脉冲宽度小于60秒的激光脉冲具有足够的时间分辨率来表征上述过程，例如泵浦探针实验。在上述方法中，样品首先用光谱定义的激发脉冲进行光激发，然后在选定的延迟时间Δt后用宽带白光脉冲进行检测。为了分析我们的光活性样品，必须有不同的激发波长。因此，必须使用非共线光学参量放大器（OPA）将飞秒激光器的原始波长从800 nm±5 nm扩展到290-2600 nm，以便随后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，并在最后获得每个脉冲至少1微j的必要能量，在800 nm处的输出功率为bb50 mJ是至关重要的。通过这种方法，可以获得具有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调查各种不同的样品和配合物，这在参与团体和合作伙伴的研究中发挥重要作用。因此，一些基本问题，比如：“光诱导反应的中间步骤是什么？它们的时间常数是什么？”它是单线态还是三重态？”或“是否涉及分子内电荷转移过程？”电荷分离和复合过程在哪个时间尺度上发生？

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.