Interaction of extreme ultraviolet (EUV) pulses of high intensity with gases results in the creation of non-thermalized plasmas. Energies of the driving photons and photoelectrons are sufficient for creation of excited states, followed by emission of the EUV photons. In most cases, decay times of these states are short comparing to the driving EUV pulse. It means that just after stopping of the driving pulse, the EUV emission corresponding to the excited states should also stop. From our earlier measurements in the optical range, however, it can be concluded that lifetimes of such plasmas exceed a time duration of the driving pulse even two orders of magnitude. Hence, it can be expected that the time duration of the EUV emission can be also significantly longer than the irradiation time. In this work, EUV-induced, low-temperature helium (He), krypton, and xenon plasmas were investigated. EUV emission from these plasmas was studied, using a specially prepared detection system, allowing for time-resolved measurements, in selected spectral ranges. The detection system was based on a paraboloidal collector and a semiconductor photodiode, sensitive for the EUV photons. For spectral selection, the corresponding filters or multilayer mirrors were employed. In most cases, the time duration of the EUV emission was significantly longer than the driving EUV pulse. In case of He plasmas, the emission corresponding to excited atoms was detected even hundreds of nanoseconds after the irradiation. It was also shown that the corresponding time profiles depended on densities of gases to be ionized.

中文翻译：

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低温EUV诱导等离子体的时间分辨研究：选定光谱范围内的EUV发射

高强度的极紫外（EUV）脉冲与气体的相互作用会导致产生非热等离子体。驱动光子和光电子的能量足以产生激发态，然后发射EUV光子。在大多数情况下，与驱动EUV脉冲相比，这些状态的衰减时间短。这意味着在驱动脉冲停止之后，与激发态相对应的EUV发射也应停止。然而，从我们先前在光学范围内的测量结果可以得出结论，这种等离子体的寿命甚至超过了驱动脉冲的持续时间，甚至超过了两个数量级。因此，可以预期，EUV发射的持续时间也可以明显长于照射时间。在这项工作中，EUV诱发的低温氦（He），对和氙等离子体进行了研究。使用专门准备的检测系统研究了这些等离子体的EUV发射，可以在选定的光谱范围内进行时间分辨的测量。该检测系统基于抛物面收集器和对EUV光子敏感的半导体光电二极管。为了进行光谱选择，采用了相应的滤光片或多层反射镜。在大多数情况下，EUV发射的持续时间明显长于驱动EUV脉冲。在氦等离子体的情况下，甚至在辐射后几百纳秒内也检测到了与激发原子相对应的发射。还表明，相应的时间曲线取决于要电离的气体的密度。使用专门准备的检测系统，可以在选定的光谱范围内进行时间分辨的测量。该检测系统基于抛物面收集器和对EUV光子敏感的半导体光电二极管。为了进行光谱选择，采用了相应的滤光片或多层反射镜。在大多数情况下，EUV发射的持续时间明显长于驱动EUV脉冲。在氦等离子体的情况下，甚至在辐射后几百纳秒内也检测到了与激发原子相对应的发射。还表明，相应的时间曲线取决于要电离的气体的密度。使用专门准备的检测系统，可以在选定的光谱范围内进行时间分辨的测量。该检测系统基于抛物面收集器和对EUV光子敏感的半导体光电二极管。为了进行光谱选择，采用了相应的滤光片或多层反射镜。在大多数情况下，EUV发射的持续时间明显长于驱动EUV脉冲。在氦等离子体的情况下，甚至在辐射后几百纳秒内也检测到了与激发原子相对应的发射。还表明，相应的时间曲线取决于要电离的气体的密度。对EUV光子敏感。为了进行光谱选择，采用了相应的滤光片或多层反射镜。在大多数情况下，EUV发射的持续时间明显长于驱动EUV脉冲。在氦等离子体的情况下，甚至在辐射后几百纳秒内也检测到了与激发原子相对应的发射。还表明，相应的时间曲线取决于要电离的气体的密度。对EUV光子敏感。为了进行光谱选择，采用了相应的滤光片或多层反射镜。在大多数情况下，EUV发射的持续时间明显长于驱动EUV脉冲。在氦等离子体的情况下，甚至在辐射后几百纳秒内也检测到了与激发原子相对应的发射。还表明，相应的时间曲线取决于要电离的气体的密度。