First order distributed feedback optofluidic dye lasers embedded in a 350 mu m thick TOPAS (R) foil are demonstrated. They are designed in order to give high output pulse energies. Microfluidic channels and first order distributed feedback gratings are fabricated in parallel by thermal nanoimprint into a 100 mu m foil. The channels are closed by thermal bonding with a 250 mu m thick foil and filled with 5.10(-3) mol/l Pyrromethene 597 in benzyl alcohol. The fluid forms a liquid core single mode slab waveguide of 1.6 mu m height on a nanostructured grating area of 0.5 x 0.5 mm(2). This results in a large gain volume. Two grating periods of 185 nm and 190 nm yield single mode laser light emission at 566 nm and 581 nm respectively. High emitted pulse energies of more than 1 mu J are reported. Stable operation for more than 25 min at 10 Hz pulse repetition rate is achieved.