Modern reforms and diagnostics of the dc-discharged high-speed axial-flow CO laser

Applying new techniques such as fast gas-circulation, gas dynamics and RF (or microwave) discharge to high gain gas laser media, i.e., CO 2 and CO and so on, the output power has been extremely enhanced, thereby making their availability wider than ever expected. In particular, a high power CO laser has been extensively expected for machinery, welding, and material processing, because of one-half wavelength of the CO 2 laser which offers various advantages such as beam- focusing efficiency, high absorption coefficient to metallic materials, and convertibility to optical elements. Among various schemes of CO laser, a DC discharged fast-axial flow (FAF) system has been still attracted for the aforementioned purposes due to superiority in beam quality and stability of the discharge. Thus, the authors have developed a prototype of compact DC discharged FAF CO laser system and demonstrated 385 W/m and 165 W/m, respectively, at subroom and room temperature operations. Then, the output power tends to usually decrease with turning on the discharge and to be eventually stable under thermal equilibrium. These transient output-reduction are quite sensitive to the gas temperature which also depends on the gas-flow velocity (upsilon) and the discharge current I dis in the experiments. In the present paper we shall review our recent works on the DC discharge type FAF CO laser developed, especially focusing on the transient properties of the output power obtained experimentally, in comparison with theoretical analysis. Then, we shall also attempt to improve this transient output-reduction at room-temperature operation by inserting molecular sieve within a gas-circulation path, together with is theoretical interpretation.