A new design method for a refractive beam shaping optical system operating in mid-infrared band

Abstract

Jamming code development set-ups are generally employed for evaluating the jamming code effectiveness of Directed Infrared Countermeasure (DIRCM) Systems on seeker heads in laboratory conditions. In these set-ups, usually, the output beam of a mid-infrared (mid-IR) laser having similar properties with the DIRCM laser is expanded and collimated before directing it to the seeker head so that a beam with an almost-homogeneous intensity distribution is obtained at the seeker aperture. This simulates what would be expected in a real long distance engagement scenario where an infrared heat seeking missile is attacked by a countermeasure laser and the laser beam diverges to create an almost-homogenous intensity profile at the seeker aperture provided that the effect of atmospheric turbulence is neglected. Large aperture off-axis parabolic mirrors are often employed for the purpose of expanding and collimating the laser beam in these set-ups. However, instead, it is also possible to employ refractive beam shaping optical systems that are much smaller in size compared to these large collimating mirrors in an effort to reduce the laser power loss, required space, and cost for obtaining such uniform laser beam profiles. In this paper, we propose a simple design method for a Galilean beam shaping optical system that transforms a laser beam with a Gaussian intensity distribution into flattop, Super Gaussian, or Fermi-Dirac intensity distributions, hence facilitates obtaining an almost-homogenous intensity distribution for the purpose of future use in a jamming code development setup to be operating in mid-IR band. Similar to Galilean or Keplerian type conventional beam shaping optical systems, the method depends on using two aspheric lenses whose active and opposing surfaces shape the beam by refraction. The first surface redistribute the beam intensity distribution and the second surface collimates the beam. However, contrary to these conventional methods, we employ a simple numerical algorithm to generate the surface equations of the two aspheric lenses. Using our method, we present examples of optical system designs for chosen wavelengths in the mid-IR band. We use ZEMAX’s Physical Optics Propagation package to verify that our design method works.