Abstracts Category : Other

Chromatic properties of index of refraction gradients inglass

by Danette Patrice Ryan-Howard

The chromatic properties of index of refractiongradients have been predicted theoretically and verifiedexperimentally. The use of these materials in the design of colorcorrected optical systems has been investigated and confirmed bythe evaluation of two fabricated lenses. </br>Amodel for the chromatic properties of gradient index materials hasbeen developed. The index of refraction is calculated based on thecomposition of the material. Since the index of refraction and theconventional Abbe number change as a function of the composition ofthe glass, a gradient Abbe number and partial dispersion aredefined. Analysis of combinations of ion exchange pairs and glassesresult in a wide range of gradient Abbe numbers and partialdispersions. The range of Abbe numbers can be further extended byusing glasses which contain more than one exchange ion or by usingmixed salt baths. </br>Measurements of thechromatic properties were made with a multiple wavelength A.C.interferometer. The gradient Abbe numbers and partial dispersionsfor a number of samples were calculated and corrected to remove theerrors due to the lateral color of the imaging lens. Evaluation ofthe samples showed that the index and dispersion data correlatedwell with that predicted by the model. The accuracy of the Abbenumber is highest for dispersive samples and decreases as thesample becomes less dispersive. For the non-dispersive samples, theuncertainty in the value of the lateral color of the imaging ionsis the limiting factor on the measurements. </br>Thin lens formulae for the paraxial axialcolor and secondary spectrum of a radial gradient singlet withcurves indicated that a family of solutions exists for which thesinglet is achromatized and corrected for secondary spectrum. Bycorrect choice of base glass, it was possible to obtain a singletwhich, in addition to its color correction, has no Petzval fieldcurvature. The design of a single element 10x microscope objectiveverified the results. The design of a two element 40x microscopeobjective showed that it is possible to replace a six elementdiffraction limited 40x objective with a two element systemcomposed of one homogeneous lens and one gradient lens withoutsacrificing either monochromatic performance or color correction. </br>The evaluation of a previously fabricatedaxial gradient collimator showed that the lens is corrected forspherical aberration at all wavelengths and thus has greatlyimproved performance over its homogeneous counterpart. Evaluationof the fabricated Wood element showed that a large gradient Abbenumber reduces the paraxial axial color. Correlation of thedirectly measured quantities, paraxial axial color, secondaryspectrum and spherochromatism with the values predicted by themodel verified that the predicted superior performance ofgradient-index lenses can be obtained.