The spatial spectrum is obtained by using a lens to #;0F-pt
do Fourier transform and the far-field spectrum is recorded l@:&0id4I
by a CCD camera positioned in its focal plane. y9Pw'4R
First, we summarize our results of on-axis excitation of a |mQC-=6t;Y
single 2D gap soliton in Fig. 1. Different from previous sK@]|9ci Q
experimental observations in which either the probe beam ~KYA{^`*
was launched off-axis to match the edge of the first BZ [6] @$fvhEkrT@
or its input phase or spectrum was engineered [11], we uCx6/ n6'
demonstrate on-axis excitation of a 2D gap soliton without ^U9 b) KA
a priori phase or spectral engineering. In fact, we show ;$vVYC
