Study of focusing into closely spaced spots via illuminating a diffractive optical element by a short-pulse laser beam

We perform a comparative numerical study of the formation of closely spaced focal spots in the focal plane with diffraction gratings and binary optical elements matched with the Hermite-Gaussian modes. It is shown that low-index modes provide the generation of good-quality focal spots and relative tolerance to chromatic dispersion. Experiments with pulsed and tunable lasers have shown that phase optical elements matched with TEM(1,0) and TEM(1,1) modes show promise for creation of arrays of closely spaced focal spots.