Efficient tunable infrared lasers for isotope separation

The cost of photons is a major determinant for the economical success of laser enrichment processes. The molecular laser isotope separation (MLIS) using infrared lasers is advantageous in this aspect, because infrared lasers with potentiality for high efficiency and high-power operation is usable. The present efficiency of the MLIS laser system is, however, still unsatisfactory from the economical viewpoint. The aim of current research of laser development at RIKEN is to increase laser efficiency by introducing new technologies for MLIS lasers. Under a name of Breakthrough Studies project, efforts are concentrated on the development of p-H2 Raman lasers, which can overcome the efficiency barrier imposed under the conventional concept of the MLIS laser. For the laser breakthrough studies, two new types of the 16mm Raman laser are now under study. One is the intracavity Raman laser that requires no longer lenghthy oscillator-amplifier chains of TEA-CO2 lasers and large multiple pass Raman cells. A coupled cavity for TEA-CO2 laser and Raman laser is constructed withy a dichroic mirror, and is designed to oscillate in circulary polarization. The laser beam is focused in the Raman cell, while it is expanded in the TEA-CO2 discharge section. In order to design such a pump-Stokes combined cavity, growth of Stokes pulses was analyzed with simulation regarding the threshold powers and pulse durations inside the cavity. The oscillation of CO2 pulses with circular polarization was rea;lized by combination with circularly polarized external CO2 seeder and the careful isotropic arrangement of optics around the optical axis. The success of oscillation recently achieved suggests effectiveness of the intracavity infrared Raman conversion and the possibility of high-efficiency energy extraction. The other is the automatically tuned 16mn laser to the absorption band of UF6. This makes it possible to eliminate the use of highly-pressurized TE-CO2 lasers. We have demonstrated high-power generation of the 16mn pulses of second Stokes waves by simulated rotational Raman scattering in ortho-deuterium. In this scheme, an annular pump beam from the unstable resonator of a C02 power oscillator was converted in a multiple pas cell. We expect that the above studies will lead to the super Raman laser system, which will be more cost and size effective compared the conventional p-H2 laser systems. The outcomes of such research initiatives for the technology achievement will be evaluated by the Atomic Energy Commission at around the year of 2000. (author)