The spatial spectrum is obtained by using a lens to .` & ($W
do Fourier transform and the far-field spectrum is recorded QWv +J a
by a CCD camera positioned in its focal plane. [op!:K0
First, we summarize our results of on-axis excitation of a x):cirwkl
single 2D gap soliton in Fig. 1. Different from previous r k;k:<c
experimental observations in which either the probe beam D ::),,
was launched off-axis to match the edge of the first BZ [6] Juj"cjob
or its input phase or spectrum was engineered [11], we `;4P?!WG
demonstrate on-axis excitation of a 2D gap soliton without abkl)X>k
a priori phase or spectral engineering. In fact, we show e.jrX;;$!&
