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Summary form only given.We observed a new type of laser action from optically pumped dye-molecules in solution filled in air-rods of a two-dimensional (2D) photonic lattice with the lattice constant a of /spl sim/1 /spl mu/m. The original lattice is composed of a parallel array of 1.0-mm-long air-rod cylinders of 0.66 to 0.90 /spl mu/m diameter (d) in a background material of PbO glass. The intersections of the rods with a perpendicular plane form a 2D triangular lattice; the lattice of a quasi-circular bundle with 1.3-1.5 mm size, of many hexagonal arrays, is supported by another PbO glass. The experiments were performed on two samples of such a photonic lattice with the air-rods filled with solution containing sulforhodamine-B dye in DMSO. The sample was optically pumped homogeneously along the rods by using a SHG beam of a pulsed Nd-YAG laser, and the radiation was detected in the lateral direction. We calculated the corresponding photonic band structure. The results reveal that reflecting the small difference of the relevant refractive indices between the PbO glass and the solvent, no significant bandgap is open in any direction, but there are a few special frequencies where the band dispersion is almost flat over the Brillouin zone, indicating that the density of photonic states is high, or the group velocity is very slow. Furthermore, there are many uncoupled bands that cannot couple to the external plane waves for symmetry reason; therefore those bands should have a high Q-value. With the help of the calculated results, we tentatively interpret the mechanisms as follows. The slow group velocity causes the lasers at 610 and 639 nm, while the uncoupled modes are responsible for the laser at 603 nm.