Femtosecond laser writing can be used to generate a spatially varying refractive index profile within a material, which results in the creation of a gradient-index (GRIN) lens. Creating GRIN lenses in hydrogels via femtosecond laser writing can enable visual correction applications in contact lenses and in intraocular lenses (IOLs) that are currently impossible or impractical to achieve. These potential applications include the creation of visual correctors with higher-order corrections, the imprinting of the wavefront correction in an already implanted IOL, and the ability to further customize a lens already having a femtosecond laser-written correction written in it, among several others.
To further advance the field of femtosecond laser writing of visual correctors, this thesis concerns itself with demonstrating the ability of femtosecond laser writing to create high-quality vision correctors in ophthalmic hydrogels. To do so, first we present an interferometric technique that measures the "calibration function", which is the phase induced in the wavefront when passing through a femtosecond laser-written region as a function of the exposure parameters applied when writing such region. Knowledge of the calibration function allows for the writing of the desired wavefront, as we demonstrated by the creation of arbitrary freeform structures with diameters of 150 μm in commercially available contact lenses.
The writing of lenses of clinically relevant size in plano hydrogels made of an ophthalmic material was achieved by writing different sections of the lens separately and stitching them together. Metrology on the stitched lenses indicates good optical and imaging performance. However, diffraction streaks created by the stitching grid were observed, as well as some unintended multifocality, which was attributed to the induced phase evolving in time after the writing. Furthermore, the visual performance of participants looking through one of the stitched GRIN lenses was measured to be quite good.
Moreover, for the desired correction to be written quickly, it is necessary to use a writing material in which large phase shifts can be induced at large scanning speeds and with the available laser power. In this thesis, we measured the induced phase on several materials and under several writing conditions, and we report the finding of chemical compositions that yielded multiple waves of phase change (at the center of the visible spectrum) at a writing speed of 100 mm/s. Raman spectroscopy measurements of the written areas in the sample indicate that they have a higher water concentration than the surrounding unwritten areas.
This work demonstrates the capability of femtosecond laser writing to produce high quality visual correctors, as well as introducing chemical compositions of ophthalmic materials that can be used for a faster writing process.
|Advisor:||Knox, Wayne H.|
|Commitee:||Ellis, Jonathan D., Fienup, James R., Yoon, Geunyoung|
|School:||University of Rochester|
|Department:||Engineering and Applied Sciences|
|School Location:||United States -- New York|
|Source:||DAI-B 80/09(E), Dissertation Abstracts International|
|Keywords:||Femtosecond phenomena, Gradient-index lenses, Ophthalmic appliances, Polymers|
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