Thin-Film Broadband Large Area Imaging System

Our Phase I program has addressed the possibility of applying thin-film diffractive waveplate technology to large aperture space-based telescopes for such applications as exoplanet imaging and spectral analysis. The major benefit that may be achievable with this technology is to make very large aperture, diffraction limited, space-based imaging possible at a small fraction of the cost that would be incurred with alternative methods using conventional optics including a reflective primary mirror. We have developed a point optical design that is predicted to achieve diffraction-limited imaging in the visible wavelength band over a bandwidth of \xb18% of the center wavelength. The geometrical phase modulation introduced by waveplate lenses is wavelength independent - resulting in the broadband nature of these new generation components and feasibility for having near 100% diffractive efficiency over very broad range of wavelengths. Since, however, the diffraction angle depends on wavelength, the bandwidth of a diffraction-limited astronomical telescope with a flat, transmissive primary element may be limited by chromatic aberration. Finding solutions to the problem of chromatic aberrations was an important task during Phase I of our program. Luckily, unlike conventional mirrors and lenses, our novel optical components provide a myriad of opportunities to deal with the problem - we found an opportunity of increasing the diffraction limited bandwidth by near 16,000 times! While alternative diffractive optical techniques for large-aperture space-based imaging, there has been only a small effort devoted to DW lenses and mirrors for this application. In view of the critical potential advantages of this technology over the alternatives, we believe that these techniques merit further investigation for such applications.