This paper presents a phenomenological analysis of thermodynamic parameters of a pulsed supersonic gas jet in a conical nozzle. Conditions have been found out for the condensation and formation of large krypton clusters resulting from phase transitions during adiabatic expansion of gas through the nozzle into vacuum. We have identified the phase state of the large clusters (submicron droplets consisting of ∼10⁷ monomers) forming in the jet and obtained a high yield of X-rays from a cluster nanoplasma produced by femtosecond laser pulses of relativistic intensity I. It has been shown that, at I ≈ 3 10¹⁸ W cm⁻², a nanoplasma consisting of large krypton clusters emits a broadband X-ray spectrum in the range 5 – 100 keV. The integrated laser to X-ray energy conversion efficiency achieved is ∼10⁻⁵ (400 nJ), and the efficiency of characteristic Kα line (12.6 keV) generation is ∼1.5 10⁻⁶ (68 nJ), which corresponds to a quantum yield of ∼3 10⁸ photons s⁻¹ (4π)⁻¹, with a contrast of ∼25 relative to bremsstrahlung background.

本文介绍了锥形喷嘴中脉冲超音速气体射流的热力学参数的现象学分析。在气体通过喷嘴进入真空的绝热膨胀过程中，由于相变而导致冷凝和形成大型氪团簇的条件已被发现。我们已经确定了在射流中形成的大簇（由~ ^{10 7 个}单体组成的亚微米液滴）的相态，并从相对论强度I 的飞秒激光脉冲产生的簇纳米等离子体中获得了高产率的 X 射线。已经表明，在I ≈ 3 10 ¹⁸ W cm ^-2，由大型氪星团组成的纳米等离子体发出 5 – 100 keV 范围内的宽带 X 射线光谱。实现的集成激光到 X 射线能量转换效率为 ~10 ^-5 (400 nJ)，特征 K α线 (12.6 keV) 产生效率为 ~1.5 10 ^-6 (68 nJ)，对应于一个量子～3 10 ⁸光子 s ^-1 (4 π ) ^{-1 的}产量，相对于轫致辐射背景的对比度为～25。