ABSORPTION OF SUBPICOSECOND ULTRAVIOLET-LASER PULSES IN HIGH-DENSITY PLASMA
ABSORPTION OF SUBPICOSECOND ULTRAVIOLET-LASER PULSES IN HIGH-DENSITY PLASMA
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DOI：
10.1007/bf00331903
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发表时间：
1990-02-01
期刊：
影响因子：
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通讯作者：
SCHAFER, FP
中科院分区：
文献类型：
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作者：
FEDOSEJEVS, R;OTTMANN, R;SCHAFER, FP
入射在铝、铜和金固体靶材上的 250 fs KrF 激光脉冲的吸收率在垂直入射时被测量为 1012–1014W cm−2 范围内的激光强度的函数，以及在 1014−2.5×1015W cm−2 的强度范围内作为偏振和入射角的函数。随着强度从 1012W cm−2 增加，法向入射时的反射率从低强度镜面反射率值变为 1014W cm−2 时的 0.5–0.61 范围内的值。对于这种强度，在 54°–57° 范围内的入射角下观察到 p 偏振辐射的最大吸收为 63–80%，随着原子序数的增加而增加。将结果与具有 Drude 模型给出的折射率的尖锐真空-等离子体界面的预期菲涅耳反射率进行比较，并且还与各种尺度长度密度分布的反射率的数值计算进行比较。与 Fresnel/Drude 模型发现了定性一致性，并且与临界密度下归一化碰撞频率 v/ω（在 0.13–0.15 范围内）和归一化密度梯度尺度长度（L/λ0（在 0.018–0.053 范围内，激光强度为 1014W cm−2）的陡峭密度剖面上的吸收数值计算得出了定量一致性。在 2.5×1015W 时） cm−2a 存在少量前等离子体，并且在 45°–50° 范围内的入射角下观察到 p 偏振辐射的最大吸收为 64–76%。
The absorption of 250 fs KrF laser pulses incident on solid targets of aluminum, copper and gold has been measured for normal incidence as a function of laser intensity in the range of 1012–1014W cm−2and as a function of polarization and angle of incidence for the intensity range of 1014−2.5×1015W cm−2. As the intensity increases from 1012W cm−2the reflectivity at normal incidence changes from the low-intensity mirror reflectivity value to values in the range of 0.5–0.61 at 1014W cm−2. For this intensity maximum absorption of 63–80% has been observed for p-polarized radiation at angles of incidence in the range of 54°–57°, increasing with atomic number. The results are compared with the expected Fresnel reflectivity from a sharp vacuum-plasma interface with the refractive index given by the Drude model and also to numerical calculations of reflectivity for various scale length density profiles. Qualitative agreement is found with the Fresnel/Drude model and quantitative agreement is noticed with the numerical calculations of absorption on a steep density profile with normalized collision frequencies,v/ω, in the range of 0.13–0.15 at critical density and normalized density gradient scale lengths,L/λ0, in the range of 0.018–0.053 for a laser intensity of 1014W cm−2.At 2.5×1015W cm−2a small amount of preplasma is present and maximum absorption of 64–76% has been observed for p-polarized radiation at angles of incidence in the range of 45°–50°.