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1 2001

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Focusing large-aperture beams generated by high-peak-power lasers

Jabłoński S., Badziak J.

Optica Applicata

2001

Vol. 31, nr 3

625-634

The properties of focusing large-aperture fight beams of parameters typical of the beams produced by picosecond terawatt lasers are analysed numerically with the use of 3-D computer code based on Fresnel-Kirchhoff integral formula. It is shown that, contrary to the case of small-aperture Gaussian-like beams, a peak intensity of light in the focus is a non-monotonic function of f/D with a local maximum at moderate f/D values (5 [left angle bracket]or= f/D [left angle bracket]or= 10), where f is the focal length and D is the aperture of a focusing system. For low f/D values (f/D [left angle bracket] 3) more than 80% of laser energy is scattered after focusing in a low-intensity large-dimension aureole round the central peak of focal intensity distribution. The amount of the scattered energy can be significantly decreased by an increase of f/D, and, as a result, the moderate values of this ratio seem to be optimum for most laser-target experiments. The above features appear for both spherical and aspherical focusing systems.