Ulrich Fotheringham

Glass modification techniques for photonic devices

No abstract available.

Design of a tessar lens including a diffractive optical element

To study the quantitative impact of diffractive optical elements on lens design and glass selection, a Zeiss Tessar lens (f/6) with and without a diffractive optical element is optimized with respect to the wavefront performance by a Zemax(R) Hammer routine. Optimization includes the selection of glasses as well as the geometry of the optical elements. In a first run, these are all refractive elements. In a second run, one refractive element is replaced with one diffractive surface. In a third run, the diffractive surface is introduced as an additional feature. It is found that one refractive element can be replaced with a diffractive surface at a moderate loss of lens performance. This holds, however, only for an optimized glass selection, which is found to be particularly important. In the case of four refractive elements plus diffractive surface, an according result is obtained. The diffractive surface will improve the overall system performance if and only if the glass selection is appropriate.

Reshaping at High Viscosities

In the standard model of Tool-Narayanaswamy for the viscoelastic material behavior of glass, the shear modulus of elasticity is assumed to be temperature independent. The motivation is the exponential temperature dependence of the viscosity, which implies an exponential temperature dependence of the characteristic shear stress relaxation times. The usual assumption is that the decrease of the modulus of elasticity slows down significantly with increasing temperature.