Снижение вероятности оптического пробоя благодаря самофильтрации пучка в компрессорах фемтосекундных импульсов

The primary cause of optical breakdown in high-power femtosecond lasers is spatial noise, which inevitably arises when laser pulses are reflected from imperfect surfaces, leading to fluctuations in the beam fluence (energy density). It has previously been shown that femtosecond pulse compressors, based on various diffraction-grating configurations, can filter noise in the transmitted beam, thereby reducing the breakdown probability, and have different efficiencies of such filtering. In this paper, using an analytical and two independent numerical models, we estimate the probability of exceeding the fluence threshold at the laser beam output for an arbitrary linear optical system in the presence of random spatial noise at the beam input. It is found that the complex dynamics of noise with spatiotemporal mixing is determined by the equivalent number of noise modes and the ratio of the root-mean-square deviation to the difference between the threshold and average values. Detailed calculations that account for various beam profiles and noise spectral scales are performed for three types of compressors of greatest practical interest.