Controllable beam break-up, spectral broadening, and coherent beam recombination using arrays of singular beams.

The ever-increasing energy/power of modern laser sources is inevitably leading to new challenges and opportunities. One of them is the problem of spectral broadening of high-energy femtosecond pulses and their subsequent compression in time in, e.g., filaments. At high beam/pulse intensities, these tend to become unstable. One way to avoid such instabilities could be the controllable splitting of the beam into sub-beams. This, however, only makes sense if there is a reliable way to coherently recombine them. In this work, by using phase plates with etched arrays of optical vortices, we show an experimental realization of controllable femtosecond beam splitting, followed by nonlinear spectral broadening and a final coherent beam recombination. The results in ambient air and in a glass substrate confirm the feasibility of the proposed technique. Compression of the spectrally broadened pulses in glass down to the Fourier transform limit is demonstrated. All this provides a reasonable motivation for further optimization.