Cascade lasing of molecular HBr in the four-micron region pumped by a Nd:YAG laser

Due to a narrow window of high atmospheric transmission near 4 microns, there is a great deal of interest for a scalable laser energy source in this spectral region. We propose a concept that combines the advantages of solid-state and gas laser technology. A Nd:YAG laser is tuned to 1.3391 microns by inserting an intracavity etalon and raising the operating temperature of the laser rod to 85 degree(s)C. This allows us to excite the v (0 →3), J (4 → 5) vibrational-rotational transition of HBr. To stabilize the frequency, a diode laser locked to this HBr transition seeds the Nd:YAG laser. Once excited, HBr can potentially lase in three subsequent steps to the ground state, emitting three photons in the 4-micron region. We present theoretical and experimental results demonstrating the operational principle of this laser system.