Our HA50D0 and HA6025 Alignment CGHs are used to optically align CGHs to your interferometer test beam and radius slide axis. On replacing the Alignment CGH with a Custom CGH Null, the spherical or collimated test beam is diffracted to produce a prescribed aspheric wavefront.
An Alignment CGH is a reflective zone plate which diffracts your spherical test beam back onto itself to create an interferogram. By turning adjustment screws to remove tilt and focus fringes, the CGH coordinate system is optically aligned to the focus of your interferometer’s spherical test beam.
Each alignment CGH has multiple pie-shaped apertures and acts like a multi-radius return sphere. By using plus and minus diffracted orders, the same alignment CGH works for both real and virtual foci. Grating patterns are “spherical” to about 1 fringe. Diffraction efficiency is approximately 1% in 3rd order.
If space permits, we incorporate retro-reflective alignment features into each custom CGH null. Even then, an Alignment CGH makes alignment easier because of its greater brightness and large aperture.
We offer the HA50D0 Alignment CGH for use with our small frame CGH Nulls. It works at 632.8 nm wavelength, providing 12 on-axis foci:
|HA50D0 Alignment CGH|
|Focal Distances from HA50D0 Face (mm)|
For best accuracy in alignment transfer, the HA50D0 and the custom CGH null must be used in the same orientation and the balls which attach to the CGH positioner must be the 3 nearest the notch. Our M506 CGH positioner and M1206R Adapter Plate each include a “key” bolt that can be used to ensure these conditions are met.
We offer the HA6025 Alignment CGH for use with our 6025-format CGH nulls. It works at 632.8 nm wavelength, providing 16 on-axis foci:
|HA6025 Alignment CGH|
|Focal Distances from HA6025 Face (mm)|
|Focal Distances from CGH Null (mm)|
The focal distances from the CGH null face are 6 mm greater than from the HA6025 face. This is because the HA6025 faces the interferometer, whereas our 6025-format CGH nulls invariably face the test optic.
The HA6025 Alignment CGH uses flexure corner mounts for best framing accuracy. CGH nulls designed to be used with an HA6025 should also have flexure corner mounts.