Vol. 16, issue 10, article # 6

Zemlyanov A. A., Geints Yu. E. Internal and external focusing of the optical field of a femtosecond pulse at its diffraction on a spherical particle . // Atmospheric and oceanic optics. 2003. V. 16. No. 10. P. 822-825. PDF
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The effect of internal and external focusing of an ultrashort laser pulse on micron-sized spherical particles is investigated numerically. Peculiarities have been found in the dynamics of formation of the spatial intensity distribution of spectrally limited light pulses scattered on particles at different pulse duration, particle size, and absorption coefficient of the particulate matter. It is shown that in the zone of the geometrical focus (behind the particle) the maximum achievable intensity of the total field may be tenfold higher than that inside the particle independent of the duration of the initial laser pulse, copying its profile. In the zone of internal focusing of the optical field at laser pulse shortening, the absolute peak of the field intensity decreases, in general, as compared to its stationary value, which is higher for larger particles. However, this decrease becomes significant only at resonance excitation of the particle internal field. The increase of the absorption coefficient of the particulate matter leads to a decrease in the maxima of the optical field intensity in the zones of its external and internal focusing, but still keeps the ratio between them.