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Beam Filamentation |
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| We investigate the effects of beam ellipticity on the dynamics of multiple filamentation. We find that increasing the ellipticity of the initial beam decreases the power required for multiple filamentation. At lower input ellipticities, the beam breaks into filaments along its widest dimension, whereas for higher ellipticities the pulse breaks into bands and then into filaments as the power is increased. The breakup patterns of the beam along the wider dimension are consistent with the modulational instability, and these patterns are independent of polarization and noise. Numerical simulations are in qualitative agreement with these features of multiple filamentation breakup. |
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CCD camera images of beam after passing through 30cm sample of BK7 glass for various input pulse powers. Ellipticity (e) increases from top to bottom. Image area is 2 x 1.2mm.
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T. D. Grow and A. L. Gaeta, "Dependence of multiple filamentation on beam ellipticity," Opt. Express 13, 4594-4599 (2005). PDF
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| Self-Similar Collapse |
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| Analyses of many different types of nonlinear wave equations indicate that a collapsing wave will transform into a universal blowup profile regardless of its initial shape; that is, the amplitude of the wave increases as the spatial extent decreases in a self-similar fashion. We show experimentally that the spatial profile of a collapsing optical wave evolves to a specific circularly symmetric shape, known as the Townes profile, for elliptically shaped or randomly distorted input beams. These results represent the first experimental confirmation of this universal collapsing behavior and provide deeper insight into the high-power filamentation of femtosecond laser pulses in air. |
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The propagation of an elliptically shaped input beam (a) is simulated. As the beam propagates (b), it self-focuses, and a circularly symmetric Townes profile is formed on axis (c) as the beam collapses. Part (c) has been magnified four times to show more detail. Lineouts (d) along both axes through the center of the collapsing beam show that the beam attains the numerically calculated Townes profile and is circularly symmetric on axis.
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K. D. Moll, A. L. Gaeta, and G. Fibich, "Self-similar optical wave collapse: observation of the Townes profile," Phys. Rev. Lett. 90, 203902 (2003). PDF
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| 159 Clark Hall |
| Cornell University |
| Ithaca, NY 14853 |
| (607) 255-0657 Lab |
| a.gaeta@cornell.edu |
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