The spatial spectrum is obtained by using a lens to ^M`>YOU2+
do Fourier transform and the far-field spectrum is recorded Ur'9bl{5
by a CCD camera positioned in its focal plane. 42rj6m\
First, we summarize our results of on-axis excitation of a 9W{,=.%MX$
single 2D gap soliton in Fig. 1. Different from previous Qg'c?[~W@
experimental observations in which either the probe beam ZYE' C
was launched off-axis to match the edge of the first BZ [6] oLgg
or its input phase or spectrum was engineered [11], we b#D9eJhS
demonstrate on-axis excitation of a 2D gap soliton without yGb a
a priori phase or spectral engineering. In fact, we show zKIGWH=qqm