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理解大口径光学系统离轴抛物面镜聚焦后超短脉冲时间信噪比(SNR)在焦斑处空间分布的特性有助于更准确地认识超快激光物理实验中的脉冲时空特性。利用空间上菲涅耳近似下的分两步聚焦的坐标变换快速傅里叶变换(FFT)算法,结合时间域的傅里叶积分变换方法,引入了光学系统波前误差,对聚焦过程进行时空仿真。解释了大口径光学系统波前误差造成时间信噪比退化的原因,计算分析随机波前误差参数(误差大小、空间尺度)对聚焦时间信噪比的影响,并针对不同频段的光学系统波前误差控制提出要求。明确大口径光学系统中随机波前误差与时间信噪比之间的关系,为大口径超短脉冲系统的设计指标分配与波前误差控制提供了理论基础。
Understanding the spatial distribution of the signal-to-noise ratio (SNR) at the focal spot after focusing the off-axis parabolic mirror of a large aperture optical system helps to better understand the pulse spatio-temporal characteristics in ultrafast laser physics experiments. In this paper, a Fresnel-like fast Fourier Transform (FFT) algorithm based on Fresnel approximation is introduced, and the wavefront error of the optical system is introduced in combination with the Fourier transform in the time domain. simulation. The reasons for the degradation of time signal-to-noise ratio caused by the wave front error of large-aperture optical system are explained. The effects of random wavefront error parameters (error magnitude and spatial scale) on signal to noise ratio of focusing time are analyzed and analyzed. Error control request. The relationship between the random wavefront error and the time signal to noise ratio in a large aperture optical system is clarified, which provides a theoretical basis for the design index assignment and wavefront error control of a large-aperture ultrashort pulse system.