摘要
利用基于自由电子激光经典理论的一维模型的两个程序(MFEL1和FEL0),数值模拟了1.06μm自由电子激光振荡器的各物理参数的演化。MFEL1是考虑了Slippage效应的短脉冲多模计算程序,FEL0是没考虑Slippage效应的长脉冲单模计算程序。前者更能反映实际情况,后者能更细致地模拟光场与电子束在一次放大过程中的演化。计算表明,在短脉冲情况下,激光强度、品质、增益和能量抽取效率强烈依赖于电子束流强度,对一定范围的能散变化却不敏感;但在长脉冲情况下,上述物理量对能散在同样范围内的变化较为敏感。光强度的增益谱清楚地再现了小信号放大的Madey定理。在信号接近饱和时,增益谱的非零部分出现在远离共振频率的区域,这正是FEL中的边带不稳定性。
Evolutions of electron beam and optical field in an oscillator are simulated numerically with MFEL 1 and FEL 0 codes, based on 1 -D free electron laser theory. The code MFEL 1 is applied for short pulse case of, for example, rf linac FELs, FELO is for single mode simulation which can describe the motion in phase space of electrons with energy spread and give some interesting results in short computer running time.
In the short pulse case, the calculations show that the power of the laser does not reach saturation in macro-pulse duration because the current of beam is too small. Frequency spectra and pulse profile of optical field are strongly dependent on the beam current, but rather insensitive to the energy spread in the region under consideration. The duration of optical pulse is only one tenth of that of the electron beam.
Small signal's gain-spectrum calculations almost reproduce the Madey's theorem with the optimum detune at △λ =0.098μm, while △λ=0.088μm from Madey's theorem. When strength of optical field is approaching saturation, the gain-spectrum is completely different from that of small signal and the non-zero gains appear in the region far from the resonant frequency and optimum detune. This means that the instability of sidebands occur which has been observed by the Los Alamas oscillator experiments.
出处
《强激光与粒子束》
EI
CAS
CSCD
1990年第4期442-454,共13页
High Power Laser and Particle Beams
关键词
振荡器
能散
增益谱
模拟
计算
oscillator, energy spread, gain spectrum.
