Photon Sieve Bandwidth Broadening by Reduction of Chromatic Aberration Effects Using Second-Stage Diffractive Optics
AIR FORCE INSTITUTE OF TECHNOLOGY WRIGHT-PATTERSON AFB OH GRADUATE SCHOOL OF ENGINEERING AND MANAGEMENT
Pagination or Media Count:
A photon sieve is a lightweight diffractive optic which can be useful for space-based imaging applications. It is limited by chromatic aberration and a narrow bandwidth. A Fresnel zone plate is used to counteract this effect in a manner similar to that accomplished with a traditional holographic corrector. First, a radiometric analysis established a target for bandwidth improvement. Next, a sieve was designed, fabricated, and characterized. Third, the bandwidth-broadening correction scheme was developed to correct primary chromatic aberration. Finally, a zone plate was designed, fabricated, and tested. Performance of the corrected system was measured over the target bandwidth. The corrected system resolved the 3-1 group of a resolution target at the primary wavelength and across an 8-nm bandwidth. The uncorrected system resolved the smaller 6-5 group at the primary wavelength but resolved the 3-1 group over only a 2-nm range. The lower resolution of the corrected system at the primary wavelength is suspected to be a result of corrector design flaws which allowed only the central 2-4 mm to be used. When accounting for this reduced diameter, resolving the 3-1 group does indicate nearly diffraction-limited performance over a bandwidth four times greater than the uncorrected system at the same resolution. This result suggests correction is occurring. A redesign of the corrector may increase performance.