A five element zoomable anamorphic beam expander is designed and fabricated for a laser illumination system used in the manufacture of patterned micro-circuit substrates. The beam expander is the front end of a Gaussian to top-hat beam shaping illuminator. The tightly toleranced optical system downstream of the beam expander should not be readjusted with changes to the input beam. The job of the beam expander is to maintain, independent of the input beam, a constant diffraction limited output beam size as well as a specific waist location. A high power quasi-CW laser at 355 nm is employed for high throughput. The specifications of the laser allow for a range of x,y-beam diameters (ellipticity), x,y-waist locations (astigmatism), and x,y-divergence. As the laser’s frequency tripling crystal is exposed to high fluence over time, the beam parameters will change. At some point the laser is exchanged for a new one, and a new set of beam parameters is presented to the beam expander. Movable cylindrical lenses enable the independent adjustment of x- and y-beam parameters. The mounting cells are motorized to enable adjustments remotely. We present the optical design approach using Gaussian beam ray tracing and discuss the mechanical implementation.
We introduce a novel application of reflective axicon surfaces to high performance image-forming objectives. The
reflective surfaces are arranged such that the optical and mechanical axes are collinear, yet have the potential to provide unobscured transmission. Offering the ability to compete with the performance of traditional diffraction-limited unobscured optical systems provides a design and fabrication alternative where demanding optical requirements must be met. There are four possible arrangements for construction, with the two outer reflectors always being concave and the two inner reflectors being either concave or convex. Multitudes of novel design forms are explored. We describe monolithic and two-piece solid, two- and three-piece reflective, and two-piece hollow-solid hybrids. We analyze the performance of such designs and compare to the performance of both refractive and reflective systems.
Changes in the shape of large lens elements due to the influences of gravity are important to consider in the fabrication,
testing and assembly of optical systems. Tried and proven methods used for mounting large mirrors to minimize the
effects of gravity are typically not applicable to large transmissive lens elements, due to the simple requirement that the
clear aperture of a lens must remain free of mechanical obstructions. Precautions must be taken to ensure that an
element's surfaces are correctly fabricated and then maintained when assembled into the final system. The amount of
distortion caused by the weight of a particular lens element is dependent on a number of factors including: size, aspect
ratio, shape, material, and the support on which it rests. Examples of the effects of these factors are modeled using
Finite Element Analysis and demonstrated through interferometric testing. Attention is given to the mounting of lens
elements within a system and simulating "real-world" conditions. These "real-world" conditions can produce results that
are different from what was expected if only ideal cases have been considered. The work presented will aid the
designer, fabricator, and metrologist to identify what optical elements and mounting conditions may be problematic and
to minimize their effects.
Techniques and formulas will be presented that demonstrate an effective means of characterizing the rigid body motions of optical elements from their nominal positions as caused by manufacturing tolerances and thermal effects. These techniques allow accurate prediction of the final position of a mechanically held lens element to be determined relative to mechanical datums. Even a single lens element with entirely nominal dimensions often needs to be positioned relative to a mechanical reference; the effects of any inherent inaccuracy of the mounting process can be over-looked and/or over-simplified. Tolerances on lens seats, element radii, bore diameters as well as thermal effects need to be accounted for in a design in order to accurately predict the final optical performance of a system in an "as built" condition. The differences in accounting for the mounting tolerances of edge mounted, cell mounted, and surface-centered elements are discussed. The work presented will aid in linking the tools available to the optical engineer in the form of optical design software, with the data available to the mechanical engineer in the form of manufacturing and fabrication tolerances.