2D-smoothing of laser beam fluctuations in optical compressor

Abstract

We propose a modification of the four diffraction gratings Treacy compressor (TC)—a double-smoothing grating compressor (DSGC)—which enables smoothing of spatial fluctuations of a laser beam in two directions. Smoothing along the groves is due to oblique incidence on the gratings or tilted grooves. Smoothing in the direction normal to the grooves is achieved due to the use of nonidentical pairs of gratings. It is shown that the far-field fluence and the focal beam intensity after the DSGC are like those after the TC. Smoothing is a consequence of spatial harmonics lagging behind or overtaking the main pulse in proportion to the transverse wave vector. Analytical expressions are obtained for the spectrum of fluence fluctuations and fluence rms at the DSGC output. The efficiency of suppressing small-scale self-focusing in transmissive optical elements after the DSGC, for example, in the case of post-pulse compression is assessed.

New grating compressor designs for XCELS and SEL-100 PW projects

“…At the same time, they can be easily modified into asymmetric compressors that ensure reduction of fluence fluctuations due to the time delay of high-frequency spatial harmonics [13,15] or spatial dispersion of the output beam [5,12,14]. In asymmetric compressors, grating pairs differ from each other: 𝐿 2 ≠ 𝐿 1 [5,12,14]; 𝑁 2 ≠ 𝑁 1 , 𝛼 2 ≠ 𝛼 1 [13]; 𝛾 2 ≠ 𝛾 1 [15]. Note that 𝛾 2 and 𝛾 1 can have not only different absolute values, but also signs.…”

“…The fill-factor 𝜂 depends on the energy and spectral properties of the spatial noise of the beam, in particular, on rms and effective spatial frequency [11]. Both these parameters can be significantly reduced by using an asymmetric compressor [5,[12][13][14] or a compressor with an out-of-plane geometry [15]. The purpose of this work is to search for the following compressor parameters: angle of incidence on the first grating 𝛼, distance between the gratings along the normal 𝐿, and groove density 𝑁 that allow obtaining the maximum value of 𝑊.…”