The spatial spectrum is obtained by using a lens to Ox%.We 5
do Fourier transform and the far-field spectrum is recorded C j5=UUnO
by a CCD camera positioned in its focal plane. aH'=k?Of;
First, we summarize our results of on-axis excitation of a &6O0h0V y
single 2D gap soliton in Fig. 1. Different from previous ^ 3O `8o
experimental observations in which either the probe beam 4?',E ddo
was launched off-axis to match the edge of the first BZ [6] [~5<[ 'G
or its input phase or spectrum was engineered [11], we q /eod
demonstrate on-axis excitation of a 2D gap soliton without kE[H q-J=N
a priori phase or spectral engineering. In fact, we show L|y 9T {s
