The spatial spectrum is obtained by using a lens to '6#G$
do Fourier transform and the far-field spectrum is recorded d9#Vq=H /
by a CCD camera positioned in its focal plane. tt zNv>L,
First, we summarize our results of on-axis excitation of a K^shT h8k
single 2D gap soliton in Fig. 1. Different from previous w +t@G `d
experimental observations in which either the probe beam @1JwjtNk
was launched off-axis to match the edge of the first BZ [6] GQqGrUQ*}
or its input phase or spectrum was engineered [11], we \^c4v\s<o#
demonstrate on-axis excitation of a 2D gap soliton without //q(v,D%Q
a priori phase or spectral engineering. In fact, we show EiL#D wx
