The spatial spectrum is obtained by using a lens to 1{X ;&y
do Fourier transform and the far-field spectrum is recorded 0V:PRq;v0
by a CCD camera positioned in its focal plane. sv?Lk4_
First, we summarize our results of on-axis excitation of a |nj,]pA
single 2D gap soliton in Fig. 1. Different from previous onAC;< w
experimental observations in which either the probe beam okZDxg`6
was launched off-axis to match the edge of the first BZ [6] 9i+SU|;j
or its input phase or spectrum was engineered [11], we _!*??B6u
demonstrate on-axis excitation of a 2D gap soliton without mC(q8%/;
a priori phase or spectral engineering. In fact, we show 4#y
