An area of active research in lasers is to identify new schemes that leverage the advantages of both gas and solid state concepts. The goal of these hybrid laser systems is to efficiently produce high output power light with good beam quality. The authors of this Optics Letter have developed a new hybrid system that has the potential of reaching this goal.

Researchers at Emory University successfully demonstrated an optically pumped laser using noble gas metastables for the gain medium. Traditionally, gas lasers such as the HeNe laser have used a discharge to produce metastable species. Energy from this excited atom is transferred to the lasing species through collisions. Unfortunately such lasing mechanisms are not very efficient. For this novel approach, a discharge is used to produce the metastable, but instead of relying on collisional transfer, the metastable itself is optically pumped to produce lasing. The pumping and lasing mechanism is analogous to that of the diode pumped alkali laser (DPAL), which is a three level laser. The “optically pumped metastable rare gas atom” laser appears to have some advantages over the DPAL. This new laser concept only contains noble gases; therefore it does not require the use of alkali metals or hydrocarbons. The alkalis are highly reactive possibly causing window damage and the hydrocarbons are known to photochemically react producing carbonaceous deposits.

Han and Heaven concisely outline the experimental setup and parameter space that was explored. They ingeniously use an excimer laser without the halogen in order to produce the metastables for the proof-of-principle experiments. Although direct diode pumping is preferred from an efficiency point of view, the use of a tunable optical parametric oscillator allowed a greater number of experiments to be performed. In that regard, they have measured small signal gain for argon, krypton, and xenon. Lasing experiments were conducted with an optical efficiency of ~7% being observed. While this is low, it should be remembered that this is the first demonstration of such a system and many of the operating parameters may be far from optimal.

Finally the authors conclude with a few remarks as to the power requirements for producing enough metastables for a higher power continuous wave laser. Using conservative estimations for both the effective lifetime of lasing specie and the obtainable discharge efficiency, they believe less than 2 kW would be required. This letter has opened a new door in laser research and may lead to several future demonstrations with improved performance as well as validation of the metastable production power requirements.

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