The spatial spectrum is obtained by using a lens to yT&x`3f"i
do Fourier transform and the far-field spectrum is recorded ]2LXUYB
by a CCD camera positioned in its focal plane. @kz!{g]Sn
First, we summarize our results of on-axis excitation of a PaxK^*
single 2D gap soliton in Fig. 1. Different from previous Pu-p7:99;'
experimental observations in which either the probe beam P6:;Y5e0
was launched off-axis to match the edge of the first BZ [6] 0s )cVYppe
or its input phase or spectrum was engineered [11], we l:q8Pg)
demonstrate on-axis excitation of a 2D gap soliton without q[Vi[b^F
a priori phase or spectral engineering. In fact, we show >6 I Xuq
