Our HA50 series and HA120Z 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.
The 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.
With our 6-axis CGH positioner, a CGH can be aligned to a spherical test beam while also centering and orienting the CGH in your interferometer’s field of view.
| Easy Optical Alignment | |
|---|---|
| Step 1: | Mount Alignment CGH facing interferometer and with the transmission sphere focus near prescribed CGH coordinates (x,y,z). |
| Step 2: | Adjust decenter (or tilt-tip) and focus to acquire and null alignment fringes. |
| Step 3: | Replace Alignment CGH with custom CGH null. |
For off-axis CGHs, one must choose between tilting or decentering. Tilting leaves the CGH centered in the field of view, but results in a test axis which is not parallel to the interferometer axis. Decentering keeps the test axis parallel to the interferometer (and radius slide) axis, but may require a faster transmission sphere to fill the decentered test pupil.
We offer four standard HA50 Series Alignment CGHs for use with our small frame CGH Nulls and your 633 nm wavelength interferometer. Our popular Model HA50D0 provides 12 on-axis foci and is sufficient for most users. Models HA50D1 and HA50D3 offer the same focal distances, but with 1 and 3 mm decenter between interferometer and CGH axes. Model HA50T1 offers 1 degree tilt (or equivalent decenter) between interferometer and CGH axes.
We offer the HA120Z Alignment CGH for use with our large frame CGH nulls. The HA120Z provides 16 on-axis foci.
The tables below give CGH coordinates (x,y,z) of the several transmission sphere focus locations. Grating patterns are “spherical” to about 1 fringe. Diffraction efficiency is approximately 1 percent in 3rd order.
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| HA120Z Alignment CGH | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Focal Distances (mm) | Price* | Export* | ||||||||
| Z= | ±36 | ±84 | ±144 | ±200 | ±250 | ±310 | ±439 | ±660 | ||
| X= Y= |
0.000 0.000 |
0.000 0.000 |
0.000 0.000 |
0.000 0.000 |
0.000 0.000 |
0.000 0.000 |
0.000 0.000 |
0.000 0.000 |
$5500 | $6050 |
We often incorporate retroreflection and autocollimation alignment features into custom CGH nulls. Please allow us the opportunity to address your aspheric testing requirements.
