Mode distortion measurements on the Jefferson lab IR FEL
Mode distortion measurements on the Jefferson lab IR FEL
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Jefferson 实验室 IR FEL 上的模式失真测量
DOI：
10.1016/s0168-9002(02)00357-1
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发表时间：
2002
影响因子：
1.4
通讯作者：
M. Shinn.
中科院分区：
文献类型：
--
作者：
S. Benson;J. Gubeli;M. Shinn.
我们之前曾报道过具有近同心腔的高功率 FEL 中镜面畸变的分析计算。该分析使我们能够估计 FEL 相互作用受到影响的功率水平，尽管目前尚不存在 FEL 功率与失真的确切理论。最近，我们使用中心波长为 5μm 的谐振器直接测量了模式尺寸和光束质量作为功率的函数。谐振器镜是氟化钙。这种特殊材料在给定功率下表现出大量的畸变，但由于折射率与温度的负斜率，几乎不会对激光输出增加光学相位畸变。因此，可以根据谐振器输出处的测量直接计算腔中的模式。角度抖动的存在导致原始测量结果与冷腔预期不一致。消除角度抖动的影响，我们得出与冷腔测量一致的结果。结果表明，当瑞利范围增长 4.3 倍时，IR 演示 FEL 的 FEL 功率受到限制。这对应于每个镜子 0.15λ 的球面像差。
We have previously reported on the analytical calculations of mirror distortion in a high-power FEL with a near-concentric cavity. This analysis allowed us to estimate the power level at which the FEL interaction would be affected, though no exact theory of FEL power vs. distortion exists at this point. Recently we have directly measured the mode size and beam quality as a function of power using a resonator with a center wavelength of 5μm. The resonator mirrors were calcium fluoride. This particular material exhibits a large amount of distortion for a given power but, due to the negative slope of refractive index vs. temperature, adds almost no optical phase distortion on the laser output. The mode in the cavity can thus be directly calculated from the measurements at the resonator output. The presence of angular jitter produced raw measurements inconsistent with cold cavity expectations. Removing the effects of the angular jitter, we derive results in agreement with cold cavity measurements. The resulting indicates that the FEL power is limited for the IR Demo FEL when the Rayleigh range grows by a factor of 4.3. This corresponds to spherical aberration of 0.15λ per mirror.