One way to visualize this integration process is to observe the effects of coherent summing of one ray at a time. This can be accomplished with a coherent detector in the Non-Sequential Components feature of ZEMAX. The sample file used here is HPSF_Integration.ZMX, and this file is included in the ZIP file that may be downloaded at the end of this article.

This file consists of an elliptical source, a singlet lens, and a detector rectangle object. The source generates random rays over a circular region. All the rays exit parallel to the local Z axis. This source models a collimated source or distant point source. Note the number of layout rays is set to 20, while the number of analysis rays is set to 1. This latter setting will allow one ray at a time to be traced as will be discussed shortly. The lens is a simple singlet, placed to bring the collimated rays to a good focus on the detector. The detector is defined to be an absorber, with 120 x 120 pixels.

Note the detector object Parameter 11, the “PSF Wave #”, is set to 1:

This special mode allows the detector to perform the coherent Huygens PSF integration. Every ray that strikes the detector is converted into a local plane wave that illuminates every pixel on the detector, and the coherent amplitude of the plane wave at every the pixel is added to the coherent amplitude already detected. This allows one ray at a time to be traced, if desired, so the effects of summing individual rays can be seen.