光谱扫描滤波法提升飞秒激光信噪比的理论分析

在时间--频率域中,啁啾脉冲被淹没在放大自发辐射等噪声中,且其瞬时频率线性分布,基于此,提出采用光谱扫描滤波的办法来提升高功率飞秒激光系统的信噪比,并以法布里--珀罗干涉仪作为光谱扫描滤波器,对该法提升信噪比的效果进行了详细的理论分析.采用短时傅里叶变换方法,研究了光谱扫描滤波器对自发辐射放大(ASE)的滤波效果,数值分析表明,在时间抖动为-2 ps到2 ps之间、光谱扫描滤波器的通带宽度为0.4 nm条件下,该法能将飞秒激光系统的信噪比提升2个量级,而啁啾信号光以超过90%的透光率通过光谱扫描滤波器;级联光谱扫描滤波方式能进一步提升飞秒激光信噪比.

Theoretical analysis on scanning spectral filter method for signal-noise-ratio improvment in femtosecond laser system

A scanning spectral filter method to improve the signal-noise-ratio in the femtosecond chains is proposed by using the characteristic that the instantaneous frequency varies with the time approximately linearly for the chirped pulse in the time-frequency domain. The scanning spectral filtering for reduing the amplification of spontaneous emission (ASE) intensity is analyzed in the time-frequency domain by using the Short-Time Fourier Transform method. The results show that the pulse contrast can be improved by two orders, and the transmission efficiency of the chirped pulse can exceed 90% when the synchronizing time jitter ranges from -2ps to 2ps and the chirp rate p from 0.9C/T² to 1.10C/T². Adopting the cascaded scanning filter to improve the pulse contrast is investigated too, which can improve the pulse contrast effectively. The great advantage of this novel nonlinear spectral filter technology is high energy and high peak intensity femtosecond chains for it filters out the ASE in the near field in temporal domain.