Frequency Doubler for CO2 Laser ITER Diagnostics

In order to meet the objectives of the U.S. contribution toward diagnostics on the ITER fusion reactor, which is being built by an international team, the CO2 laser frequency doubler must achieve a significantly higher conversion efficiency, in order to enable very low noise operation of the sensing interferometer. This project will develop nonlinear optical (NLO) orientation-patterned gallium arsenide (OP-GaAs) crystals for high-efficiency doubling of CO2 lasers. Phase I successfully fabricated OP-GaAs crystals of very high transparency in the long-wave IR and demonstrated the potential for scale-up to larger sizes with higher efficiencies for CO2 laser second harmonic generation (SHG). The concept was demonstrated by converting a 1 W CO2 laser beam from ¿ ~10.6 µm to the second harmonic at ¿ ~5.3 µm. Phase II will scale-up NLO OP-GaAs crystals and demonstrate SHG conversion efficiency (¿) for a 50 W laser. The objective is to attain ¿ >2%, which would be a one-hundred-fold improvement over existing frequency doublers. Then, an optical interferometer instrument system will be designed and constructed, including the OP-GaAs, and the instrument will be tested in a DIII-D fusion reactor. Commercial Applications and other Benefits as described by the awardee: NLO OP-GaAs components should find use in markets for frequency-converter optical devices, including those with second harmonic generation, optical parametric generation, and similar functionality. NLO OP-GaAs for laser conversion also should see market demand within optical systems for DOD applications and for DOE applications such as diagnostic tools for plasma fusion reactors