Optically-pumped mid-infrared vibrational-rotational transition gas lasers and amplifiers with improved efficiency and practicality. Inventive laser and amplifier devices include: laser active media comprising a mixture of alkali vapor, selected hetero-nuclear molecular gas, and one or more buffer gases; conventional semiconductor laser diode pump sources with nanometer scale spectral bandwidths; and preferential laser emission in ro-vibrational transitions among relatively low-lying vibrational levels.