Sharp nose lens design using refractive index gradient

Abstract

For infrared sensors located at the nose of a missile or a projectile, an age-old problem occurs. A conflict between optical quality and aerodynamic drag exists. A new approach for solving this problem is being developed using gradient refractive index, GRIN, for lens design. The equations for lens design incorporating GRIN are formulated for the special case of spherically symmetrical GRIN. A computer code for designing a GRIN lens and for determining aberrations has been developed. A different program (LENS) calculates lens design and lens performance for the case of homogeneous refractive index. Results of this program provide a check on the more complex program which includes GRIN. The computed program calculates the spot diagram for both meridianal and skew rays. The spot diagram, which is the intersection of rays with the focal plane, is plotted, and the Oj-j^g and centroid location of the spot diagram are calculated. Also a cumulative energy diagram is obtained from the program. The computer code has been organized to calculate the items enumerated above for either a circular cone for the inside or outside surface of the pointed lens. For homogeneous refractive index, both cases are included in the program discussed in this report. However, for the GRIN case, only the complete program for a lens with a conical surface on the outside is reported here. The alternate case is being developed by a thesis student. Features of the computer program include the following: use of many subroutines for clarity and for easy modification, and use of program structure for easy integration into an optimization code. Sample lens designs and lens performance are presented. The computer code provides the tools for lens design. Considerables additional work is needed for selecting the best lens design.