We report on a laser system that produces near-transform-limited picosecond pulses in the 3–5-µm wavelength range with bandwidths adjustable from values close to the pump bandwidth (∼16 cm-1) to more than fivefold narrower bandwidths (<3 cm-1) and with the pulse energies that exceed 48 µJ at 3 µm and 5 µJ at 5 µm. The system employs difference-frequency mixing in a potassium titanyl arsenate crystal pumped by an amplified Ti:sapphire laser and seeded by a traveling-wave optical parametric generator. The difference-frequency bandwidth narrowing is achieved by equal chirping of the seed and the pump pulses with two pulse stretchers before mixing.