Feature of Physical Optics Propagation
Physical Optics Propagation (POP) in Zemax is a tool for simulating and analyzing the behavior of light as it propagates through optical systems. Unlike ray tracing, which assumes idealized geometric rays, POP accounts for the wave nature of light, including diffraction and interference. This makes it valuable for designing and analyzing high-precision optical systems like microscopes, lasers, and other systems requiring detailed wavefront analysis.
The POP module provides detailed information about the behavior of light as a wave, including how its amplitude, phase, polarization, and intensity change as it propagates through an optical system. The key information includes intensity distribution and phase profile. The former shows spatial distribution of light intensity at various points along the propagation path. It helps identify hot spots, energy losses, and beam profile shapes at different stages in the optical system. The latter shows spatial phase distribution of the optical field, which allows for analysis of phase distortions introduced by optical elements or misalignments, which is critical in interferometry and wavefront-sensitive systems.
Beam Propagation Demonstration in POP
Here we use an optical beam propagation model to demonstrate POP process and the information it provides. The model below sets a source (object 0) and 13 steps of propagation locations, which are distributed around the source location, as shown in the Lens Data below.
With some surface overlaps, such as surface 3 and surface 5, overall, 7 surfaces are shown in the structure. Light propagation is tracked in sequential manner towards to right, then backward to negative distance to the source, and back to the source lastly.
In the Physical Optics Propagation window, all the beam profiles at the 13 locations are saved with irradiance, in “Along Beam” manner. This option locates saved beam file in a sequential manner that all surfaces are defined. The beam files, in the format of .ZBF can retrieved at the folder “Documents\Zemax\POP\BEAMFILES”.
Beam Information Through ZBF File
ZBF files contain detailed information about the optical field, including amplitude, phase, beam size and shape. Take the surface #4 as an example below, when the displayed width is listed (6.31 mm), the irradiance distribution is marked and matched with the color bar, with unit of watt/mm^2. The numbers also reveal the beam size is 3.16e-1 mm in radius at this propagation position.
The affiliated text below reveals light profile in more details at surface #4, with nx and ny points in the beam file, and point space decided by the image size and point number in such a view.
The phase distribution can be displayed with contour format. Beyond the basic dimension information, phases relative to the spot margin are shown below. The center phase difference is 1.24 radians.
From the X-cross section view, the maximum phase and their location are clearly displayed.
This phase analysis examines the phase of the optical field, which describes how the peaks and troughs of the electromagnetic wave align spatially across the beam profile. This is useful information for assessing optical aberrations and evaluating beam focus and quality. For example, the planar phase i.e. flat wavefront indicates ideal propagation, typically seen in collimated beams. Spherical phase, i.e. curved wavefront represents focused or diverging beams.
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