Tina M. Valente

Interference fit equations for lens cell design using elastomeric lens mountings

Optical designs often consist of lenses that are mounted in a common lens barrel. For lenses having diameters greater than 20 cm and subject to large temperature differentials and/or shock loading, standard metal retainer ring mountings may not be acceptable. An alternate method for mounting these lenses is to mount each individual lens in its own subcell using an adhesive and then to use an interference or press fit to mount these subcells in the lens barrel. When mounting lenses in this manner, it is necessary to evaluate the stress induced in the glass and the residual difference in the optical path. A closed-form analytical derivation was made for a simple lens mount that relates the allowable magnitude of the interference fit to the stress in the glass. This theoretcal expression was then modified using finite element models for use with complex lens designs. Moreover, since lens mountings may require the use of relatively thick layers of flexible elastomer to mount the lenses in their individual cells to prevent large thermal and/or mechanical stresses, the equation for determining the decentration of lenses mounted in circumferential flexible elastomers is also derived. The theoretical expression was used to verify finite element models that then may be used for more complex mounts.

A Comparison Of The Merits Of Open-Back, Symmetric Sandwich, And Contoured Back Mirrors As Light-Weighted Optics.

There is a need for reliable mirrors which are both light-weight and stiff. However very little documentation exists that compare different types of light weight mirrors. This lead to this parametric study to compare different mirror types, namely, contoured back mirrors, symmetric sandwich mirrors, and open back mirrors. This paper examines each mirror type as compared in each of several categories: 1) Self weight induced deflection, which is a product of stiffness and weight, for mirrors mounted on their backs and of equivalent thickness. 2) Efficiency of mirrors which are of equivalent weight, where efficiency is a function of self weight induced deflection and mirror thickness. 3) Fabrication constraints including ease of manufacture, ease of mounting, mirror thickness, and quilting or print-through of the mirror face plate. The results obtained in these categories can be used to design light-weight mirrors with greater confidence in preferred mirror type.

Analysis of elastomer lens mountings

The equation for determining the decentering of lenses mounted in a circumferential flexible elastomer is derived. A closed form analytical solution was derived for a circular lens mounted in an elastomer to describe this deflection. The theoretical expression was used to verify finite element models which then may be used for more complex mounts. Proper modeling such as element type and aspect ratios are addressed as well as applications of the method for various mounting applications.

Design and construction of a metal matrix composite ultra-lightweight optical system

Significant reduction in weight of optomechanical systems is possible through the use of three new technologies: metal matrix composite materials, Meinel type telescope structures, and shape optimization of mirror substrates. These technologies are successfully employed in a 400 mm aperture f/1.5 dual channel visible/infrared catadioptric telescope system designed and built at the Optical Science Center, University of Arizona. This system is designed for remote control and is operated in an environment characterized by wide temperature shifts as well as severe mechanical vibration. The telescope is a 400 mm aperture f/5 Ritchey-Chretien, with a 1 degree field of view. A Meinel type telescope structure is employed in combination with a single arch sandwich mirror to reduce telescope weight to about 7 kg. An aluminum reinforced with silicon carbide metal matrix composite is used thorughout the telescope, with a metal matrix composite foam as the shear core of the sandwich primary mirror. The dual channel optical bench employs a high performance focal reducer and is constructed of the same type of metal matrix composite used in the telescope. A passive athermalization scheme provides optical aberration correction over a wide range of temperatures, and is combined with a motorized internal focus to avoid moving the telescope secondary. Design and construction of the telescope was facilitated by a process of interactive optical design, computer aided mechanical layout, and finite element analysis. System performance was successfully simulated prior to final assembly using results from actual optical tests. The final system displayed good performance and represents a successful first use of a number of technologies, including the foam core single arch metal matrix composite primary mirror.

Numerical Method For Cassegrain Telescope Baffle Design

An efficient method for calculating optimum dimensions of Cassegrain telescope baffles will be dis-cussed. The baffles are designed to prevent light which has bypassed the optical system or which is outside the field of view from reaching the final image plane. It is also desired to minimize the baffle size to maximize the effective aperture. Graphical methods have been used, but they are time consuming and have limited accuracy. Previous analytical techniques have been cumbersome and difficult to implement. The new technique presented here is an iterative algorithm suitable for implementation on a small computer. The authors have written such a program and have found it to give fast, reliable design information.

Design and construction of an optical system for infrared target simulator

The Optical Science Center, University of Arizona, has designed and constructed an optical system for infrared target simulator for Carco Electronics Inc. The system is a f/3.36 three mirror telecentric system with 12 cm aperture. Due to the working environment, finite element analysis was performed to assure the system quality.

Evaluation of a 60-inch sphere using optical testing and analytical methods

A kinematic whiffle tree type mount for a 60 inch Pyrex spherical mirror that is figured on both sides was designed and built at the Optical Sciences Center. Interferometric testing of the optic was performed in two orientations and these results were then compared with the results of finite element analyses. This comparison was facilitated by the use of computer program PCFRINGE and PHASE. The results of the comparison indicates that analytic predictions, based on the methodology presented herein, will accurately predict the performance of kinematic mirror mount configurations.

Interference fit equations for lens cell design

Optical designs often consist of lenses which are mounted in a common lens barrel. One method for mounting these lenses is to mount each individual lens in its own subcell using an adhesive and then use an interference or press fit to mount these subcells in the lens barrel. When mounting lenses in this manner, it is necessary to evaluate the stress induced in the glass and the residual difference in the optical path. A closed form analytical derivation was made for a simple lens mount that relates the allowable magnitude of the interference fit to the stress in the glass. This theoretical expression was modified using finite element models in order that it may be used for complex lens designs. Proper modeling such as element material properties are addressed, as well as applications for various mounting conditions.