We design CGH nulls using OSLO optical design software. Each CGH null is shipped with lens files in OSLO, ZEMAX and CodeV formats, but it is the OSLO lens files that are primary and complete. We have written translators (in OSLO CCL) to convert from OSLO to ZEMAX and CodeV, but these conversions are often incomplete. In particular, special apertures do not convert readily and we don't even try to convert multiple configurations.
OSLO makes it possible to mostly avoid extraneous dummy surfaces since any one surface can be tilted and/or diffractive and/or have special apertures. We have adopted standard surface note labels for several of the frequently occurring surfaces in our OSLO models.
- The asphere surface being tested.
- A model diffractive surface, coincident with a kinoform asphere, that causes retroreflection to occur for rays that are perpendicular to the would be kinoform facets rather than to the base asphere. This is modeled as a separate surface so that the aspheric surface may retain its actual kinoform prescription (set to zero order).
- CGH Phase
- The aspheric portion of the CGH null phase function, usually a symmetric or asymmetric power series.
- CGH Carrier
- An optical hologram (HOE) surface defined by two real or virtual point sources: (hx1,hy1,hz1) and (hx2,hy2,hz2). The former is usually a best fit sphere to the asphere and the latter is always the wavefront from the interferometer.
- CGH Glass OPD
- A rotationally symmetric phase function, centered on point source, that compensates for the CGH being glass and not air.
- CGH Backside
- The non-patterned back surface of the CGH, usually AR coated.
- An HA6025 Alignment CGH.
- An HA50D0 Alignment CGH.
- Cat's Eye
- The focal point of a Fizeau sphere, treated as a point source.
- Exit Pupil
- A spherical surface, concentric with the Cat's Eye focus point, onto which the test asphere is best imaged. Presumably, the interferometer will be focused to image the Exit Pupil onto the camera (with negligible distortion).
- Field Stop
- A small aperture at the best focus of the null wavefront.
- Knife Edge
- An obstructing edge near the best focus of the null wavefront.
- Zeroth surface in single pass model. Zeroth and last surface in afocal model.
OSLO special apertures are (when projected onto the local XY plane) circles, ellipses, rectangles, quadrangles and triangles. Special apertures either transmit or obstruct and may be grouped. To be transmitted, a ray must intersect inside every transmitting aperture and outside every obstruction for some aperture group. It is Diffraction International's practice to fix the layout of all special apertures in the base configuration and to manipulate only their behavior (transmit vs. obstruct) and grouping for alternate configurations.