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Transmission of quasi-monochromatic powerful laser beams through materials exhibiting intensity dependence of their refractive index (optical Kerr nonlinearity) frequently results in chaotic breakdown of the propagated beams. This corresponds to recognized instabilities of the solutions of the three-dimensional propagation equation (cubic nonlinear Schrödinger equation). Two -dimensional stable "soliton" solutions were found theoretically by Zakharov and Shabat in 1972 [1]. These solutions describe,for the fundamental order stable self -trapping of single mode, two -dimensional monochromatic beams through homogeneous nonlinear slab. Higher orders solutions consist in periodical narrowings and spreadings of the guided beam. We experimentally demonstrated the existence of the "first order (fundamental) soliton beam" in 1985 [2]. Now we present the first generation of second and third order soliton beams in a planar nonlinear waveguide illuminated by suitably shaped modelocked YAg /Nd laser pulses and their observation by time resolved imaging through the slit of a picosecond streak camera. -SOLITON BEAMSIntense laser beams propagating in a nonlinear Kerr and of the self induced variation of the refractive index. For in an hyperbolic secante spatial distributicin, the induced index to a self-guided propagation : it's the 1s order soliton beam medium suffer the opposite effects of diffraction a beam carrying the fundamental soliton power Ps gradient gives rise, in a two dimensional feature, (Fig. lb). For comparison we show on figure 1(a) the linear behaviour of the same beam. The second order soliton beam corresponds simply to a power fourtimes higher. In this case, preponderant nonlinear effects make the beam to converge until its size becomes sufficiently small so that diffraction dominates in turn and spreads it to its initial pattern. The propagation length above which the optical field recovers its initial distribution is called the soliton period Z ( fig. 1(c)). After that length a b d an other cycle begins.For a nine times higher power (9 Ps), corresponding to a third order soliton beam, the propagation remains periodic with the same periodicity Z but transient structures are more complex (Fig. 1(d)).Note that the beim spatial shape after a propagation over a half soliton period allows to discriminate the order of the observed soliton. Figure 1 3 -1st, 2ndAND 3rd ORDER SOLITON BEAMS OBSERVATION Soliton beams propagations may appear at precise intensity levels and require then a C.W. light source. Nevertheless, in front of the high intensities that were needed, we were obliged to use pulsed laser. So a pulse shaping stage [3] has been employed to obtain 200 ps rectangular shaped pulses from 30 ps laser pulses ( X = 0,53 microns), in order to make a quasi constant illumination. The following step consisted in the conformation of the spatial distribution of the laser beam to the soliton pattern. As soliton solutions exist only in a two dimensional propagation feature we have chosen for the nonlinear medium a CS...

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