The spatial spectrum is obtained by using a lens to c!hwmy;
do Fourier transform and the far-field spectrum is recorded ms_ VM>l
by a CCD camera positioned in its focal plane. Bk}><H
First, we summarize our results of on-axis excitation of a }P3tn
single 2D gap soliton in Fig. 1. Different from previous c>1RP5vx
experimental observations in which either the probe beam GdVhK:<>
was launched off-axis to match the edge of the first BZ [6] KvQ,;A
or its input phase or spectrum was engineered [11], we W-
$a
Y2
demonstrate on-axis excitation of a 2D gap soliton without Jd,)a#<j
a priori phase or spectral engineering. In fact, we show @h?shW=^
