Phase control requirements of high intensity laser beam combining

Abstract

Aiming at getting the general requirements of the beam combine for ignition scale laser facilities, the analytical expressions including the factors affecting the combine results are derived. The physical meanings of every part are illustrated. Based on these expressions, the effects of the factors, including the beam configuration, piston error, and tip/tilt error, are studied analytically and numerically. The results show that the beam configuration cannot affect the Strehl ratio (SR) of the combined beam, but it influences the FWHM of the main peak and the ratio of the main peak and the side peak. The beam separation should be no more than 1.24 times the individual beam width for the multibeam combine, and be close to the individual beam width for the two-beam combine as much as possible. The piston error can change the characteristics of the combine beam focus, including the peak intensity, the focal spot morphology, the fractional energy contained within a certain area, and the center of mass. For the two-beam combine, a piston error less than 2π/5 rad is suitable, and for the multibeam combine, the standard deviation of the piston error should be no more than 2π/10 rad. The tip/tilt error has a great influence on the combined results. It affects the superposition degree of the focal spots of the combined elements directly. A requirement of 0.5~1 μrad for the standard deviation of the tip/tilt error is adequate.

Stability improvement of multi-beam picosecond–petawatt laser system for ultrahigh peak-power applications

“…This is a challenging task and has never been reported for a highpower laser system. It has been demonstrated in simulations that the tip/tilt error should be no more than 0.5 μrad for two-beam additions to obtain the Strehl ratio (SR) >0.8 [16]. This study meets this requirement in a high-power laser system, paving the way for the application of coherent addition in CPA-configured picosecond-petawatt laser systems.…”

“…Through these efforts, beam-pointing fluctuations can be reduced to 7 μrad or less, which is sufficiently stable for a nanosecond laser system. Although pointing fluctuations of approximately 5-7 μrad are acceptable, the application of picosecond-petawatt laser systems is limited; incoherent and coherent addition in an ultrahigh-intensity laser system require precise spot overlapping [3,4,[16][17][18].…”

A full-path phasing technique based on the far-field interference fringe for tiled-aperture coherent beam combining

“…Yang et al introduced a statistical method to further study the influence of phase difference on the combined far-field patterns [18]. Gao et al extended the analytical expressions and put forward the general phase control requirements of CBC for ignition-scale facilities [19]. These works mainly focus on the influence of relative phase error on coherent efficiency, but there is no direct expression on the relationship between far-field distribution and phase errors to the best of our knowledge.…”

“…Phase errors between different beams influence the combining efficiency significantly [17][18][19]24]. We want to know whether the relation between the far-field distributions and phase errors can be quantitatively described.…”

Four-Beam Tiled-Aperture Coherent Beam Combining of High-Power Femtosecond Laser With Two Compressors

“…To improve the feasibility of this technique for ultra-intense ultra-short laser devices, both theoretical and experimental studies have been carried out in high-power laser fields [17][18][19][20][21][22]. However, these studies were mostly based on two sub-beams, with only one article reporting a phasing method of tiledaperture CBC based on three sub-beams.…”