High resolution bremsstrahlung and fast electron characterization in ultrafast intense laser–solid interactions
High resolution bremsstrahlung and fast electron characterization in ultrafast intense laser–solid interactions
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超快强激光-固体相互作用中的高分辨率轫致辐射和快速电子表征
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发表时间：
2013
期刊：
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通讯作者：
K. Krushelnick
中科院分区：
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作者：
C. Zulick;B. Hou;F. Dollar;A. Maksimchuk;J. Nees;A. Thomas;Z. Zhao;K. Krushelnick
在100 keV和1 MeV之间的能量范围内，研究了强激光-固体相互作用（1 > ~ 1018 W cm−2）轫致辐射的强度、角度和物质依赖性的标度。这是对相对论性激光-等离子体相互作用产生的轫致辐射光子的首次高分辨率测量（E/ΔE > 200）。采用高纯度锗探测器，在高重复率(500 Hz) λ3激光设备上进行测量。观察到轫致辐射光谱随激光强度和观测角度的不同，具有80（±10）~ 550（±60）keV的两种有效温度能量分布。这两种温度是由不同的加速电子种群产生的。一个群体各向同性，产生较低的有效轫致温度。高能电子束沿激光镜面反射方向从靶体前方射出产生较高的韧致温度，这也是韧致有效温度达到峰值的方向。两种有效轫致温度均与先前在λ3上测得的实验电子温度标度一致。用粒子胞内代码OSIRIS和蒙特卡罗代码MCNPX模拟了电子居群和韧致温度，与实验结果吻合较好。观察到的方向性和强度尺度表明皮秒和飞秒持续脉冲相互作用之间存在显着差异。
The scaling of the intensity, angular and material dependence of bremsstrahlung radiation from an intense (I > 1018 W cm−2) laser–solid interaction has been characterized at energies between 100 keV and 1 MeV. These are the first high resolution (E/ΔE > 200) measurements of bremsstrahlung photons from a relativistic laser–plasma interaction. The measurement was performed using a high purity germanium detector at the high-repetition rate (500 Hz) λ3 laser facility. The bremsstrahlung spectra were observed to have a two effective temperature energy distribution which ranged between 80 (± 10) and 550 (± 60) keV depending on laser intensity and observation angle. The two temperatures were determined to result from separate populations of accelerated electrons. One population was isotropic and produced the lower effective bremsstrahlung temperature. The higher bremsstrahlung temperature was produced by an energetic electron beam directed out of the front of the target in the direction of the specular laser reflection, which was also the direction the bremsstrahlung effective temperature peaked. Both effective bremsstrahlung temperatures scaled consistently with a previously measured experimental electron temperature scaling on λ3. The electron populations and bremsstrahlung temperatures were modeled in the particle-in-cell code OSIRIS and the Monte Carlo code MCNPX and were in good agreement with the experimental results. The observed directionality and intensity scaling suggest a significant difference between picosecond and femtosecond duration pulse interactions.