The spatial spectrum is obtained by using a lens to gPA),
NrN
do Fourier transform and the far-field spectrum is recorded :SUU)jLq
by a CCD camera positioned in its focal plane. '7j!B1K-
First, we summarize our results of on-axis excitation of a ) ]W|i9
single 2D gap soliton in Fig. 1. Different from previous \_#Z~I{
experimental observations in which either the probe beam Qgel^"t]i
was launched off-axis to match the edge of the first BZ [6] }2 X"
or its input phase or spectrum was engineered [11], we =g hN)[AZV
demonstrate on-axis excitation of a 2D gap soliton without lY,dyNFHV
a priori phase or spectral engineering. In fact, we show # $dk
