The 10 kJ Eight-Beam CO₂ Laser Fusion System, currently under construction at Los Alamos Scientific Laboratory (LASL), has approximately 100 optical elements per beam. The nominal system is diffraction limited and degradations in performance are caused primarily by imperfect components and alignment errors. Consequently, analysis and predictions for the system are very much dependent on the proper description of the imperfect components.

The approach taken at LASL has been to characterize the components interferometrically. Briefly, interferograms of the various components are made at the 633-nm helium-neon wavelength. These are digitized, after visual examination, at appropriate sampling points along the fringes. Zernike coefficients characterize the optical path difference (OPD) at each manufactured surface, the laser beam is propagated through the entire system, and various parameters of interest such as the Strehl ratio, intensity, and encircled energy distributions are computed at stations of interest throughout the system.

An example of this procedure, using an actual interferogram of a manufactured component, will be presented and the various limitations will be discussed.

Analysis of the total system, based on the expected component quality, has shown that spatial filters are very effective in removing aberrations and that only components after the final spatial filter are crucial to achieving near-diffraction-limited performance. Further analysis of these components has already shown the need to improve the optical quality of the large 16-in.-diameter salt windows in the system.

The approach of defining and characterizing the various manufactured optical components interferometrically appears to be a powerful tool in the analysis and optimization of the optical parameters in the laser fusion system. Detailed results of the analysis for one complete leg of the eight-beam system will be presented.