Jain Ayush, Wang Yejun, Kulatilaka Waruna D
Opt Lett. 2019 Dec 15;44(24):5945-5948. doi: 10.1364/OL.44.005945.
In many recent studies, ultrashort femtosecond (fs) two-photon (2p) laser-induced fluorescence (LIF) of atomic hydrogen (H) has been demonstrated using a 205 nm excitation. However, 205-nm- deep ultraviolet (UV) pulses can be problematic in practical devices containing thick transmissive optics and can also be susceptible to photolytic production at high laser energies. In this Letter, we investigate the three-photon (3p) excitation scheme of H by using red-shifted 307.7 nm fs laser pulses. Efficient 3p excitation resulting from fs laser pulses enable the 3pLIF detection of H, which was previously unattainable in most flame conditions using ns or ps pulses. Measurements are reported in // Bunsen jet flames and premixed / flames and compared to similar 2pLIF schemes with fs pulses. Saturation effects, photolytic interferences, and stimulated emissions effects are studied, as well as the benefits of 3pLIF in diagnostic hardware with thick optical windows.
在许多近期的研究中，已利用205纳米激发展示了超短飞秒（fs）双光子（2p）激光诱导的氢原子（H）荧光（LIF）。然而，在包含厚透射光学器件的实际装置中，205纳米深紫外（UV）脉冲可能会出现问题，并且在高激光能量下也容易受到光解产生的影响。在本信函中，我们通过使用红移至307.7纳米的飞秒激光脉冲来研究氢原子的三光子（3p）激发方案。飞秒激光脉冲产生的高效三光子激发实现了对氢原子的三光子激光诱导荧光检测，这在大多数火焰条件下使用纳秒或皮秒脉冲之前是无法实现的。报告了在本生灯射流火焰和预混火焰中的测量结果，并与使用飞秒脉冲的类似双光子激光诱导荧光方案进行了比较。研究了饱和效应、光解干扰和受激发射效应，以及三光子激光诱导荧光在具有厚光学窗口的诊断硬件中的优势。
