The spatial spectrum is obtained by using a lens to 9u wL{P&
do Fourier transform and the far-field spectrum is recorded [V@yRWI
by a CCD camera positioned in its focal plane. xKp0r1}
First, we summarize our results of on-axis excitation of a F ,G, b
single 2D gap soliton in Fig. 1. Different from previous M@?"t_e 1
experimental observations in which either the probe beam ^{[`=P'/
was launched off-axis to match the edge of the first BZ [6] lVeH+"M?
or its input phase or spectrum was engineered [11], we =sQ(iso%f
demonstrate on-axis excitation of a 2D gap soliton without {e]NU<G ,
a priori phase or spectral engineering. In fact, we show gw Qvao
