Abstract

Channeling of laser energy is expected when a high-intensity pulse is focused in a plasma^1,2 At high intensities (10¹⁹ W/cm²) the electron motion becomes relativistic, Additionally, intense laser radiation drives electrons out of the focal region because of spatial intensity gradients near the laser focus (ponderomotive forces). Both effects act to reduce the plasma frequency and thus increase the refractive index where the laser is most intense. The positive lens thus formed can balance diffraction of the focused radiation and result in collimation over lengths longer than the Rayleigh range. Channeling is limited by two effects: erosion of pulse energy by diffraction of the low-intensity (below threshold) leading edge of the pulse and depletion of the trailing edge by nonlinear scattering processes.¹

© 1993 Optical Society of America