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Gustavo Gandara-Montano, Len Zheleznyak, Wayne H Knox; Optical bench testing of gradient-index Fresnel lenses written with femtosecond laser induced refractive index change. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1275.
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Femtosecond (fs) laser induced refractive-index change has previously been used to write 150um diameter hydrogel microlenses (Gandara-Montano et al., 2015). The purpose of this study was to investigate the optical quality of large refractive corrective devices (6mm diameter) created with this technology.
Seven Fresnel lenses (sphere: -3 to +10D, cylinder: -1.5D) were created with a 6mm diameter optical zone. Each lens was produced within a plano hydrogel by focusing a 400nm fs-laser and a galvo-scanning system (field of view: 245x88um). The lenses were comprised of a stitched mosaic with ~1400 individual rectangles. Optical quality was assessed over a 5.8mm diameter pupil with a custom-built Shack-Hartmann wavefront sensor and an optical bench for imaging the monochromatic point-spread function (543nm, design wavelength), from which the normalized area under the Modulation Transfer Function (aMTF, from 0 to 60cyc/deg) was computed.
The measured writing error was 0.01±0.25D of the desired target. Induced higher order RMS was 0.15±0.04um. The spherical lenses had an average aMTF of 0.70±0.23 (range: 0.31 to 0.97). A correlation between aMTF and induced diopters was observed (R-squared = 0.71) where higher powers had lower aMTF.
The ability to create high-quality ophthalmic devices with fs-laser processing was demonstrated over a large optical zone. Despite stitching-induced scatter, the wavefront data of the lenses showed a strong agreement between the desired and obtained structures. Increasing scanning system field of view to reduce tiling will be the basis of future work.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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