Computer Generated Holograms (CGHs)

The hologram patterns are custom designed and built into standard configurations for rapid turnaround and ease of use. Standard features enable accurate, traceable measurements of reflective surfaces. Optional features allow measurement of bare glass surfaces and make alignment easy.

Standard Sizes

  • 6″ x 6″ x ¼”
  • 6″ x 3″ x ¼”
  • 3″ x 3″ x ¼”
  • 2″ x 2″ x ¼”

Standard Types

  • Chrome Pattern CGH for measuring reflective surfaces
  • Enhanced Efficiency Phase Etched CGH for measuring bare glass surfaces
  • Multiplexed CGH for specialized applications

Standard Features

  • Custom optimized hologram, written onto a select silica substrate.
  • EasyAlign retro pattern for aligning CGH to interferometer
  • Projected fiducial pattern for coarse alignment of test optic
  • Antireflection coating to eliminate ghosts
  • Precision bonded into EasyNull frame
  • Substrate calibration map
  • Engineering and fabrication reports, with tolerance analysis and as-built data
  • Certificate of Accuracy

Optional Features

  • 6DoF fine adjustment positioner with interfaces to the CGH EasyNull frame
  • Mechanical datum features attached to the CGH, measured with a CMM to micron-level accuracy
    • ¼” diameter tooling balls
    • ½” seats for balls or Sphere Mounted Retroreflectors (SMR)
  • Projected references to user defined locations near optic under test
  • Data and software for correcting for mapping distortion
  • Additional engineering to accommodate specific system requirements

CGHs for Measuring
Cylindrical Surfaces

Concave and convex cylindrical surfaces are accurately measured with interferometry + CGH null correctors. The simple shape allows a single CGH to test a wide range of cylinders.

Standard Cylinder CGH Information

Model No. Substrate SizePattern Diameter (mm)Pattern ShapeCylinder F/#Distance to Focus (mm)

Not seeing a feasible option in our Standard Cylinder CGH table?  We create custom Cylinder Nulls too!  Just click the button below to request a quote for a custom Cylinder CGH.

Mechanics for Alignment

Hardware for mounting and aligning the CGH test.

Alignment Stages

AOM Fine Positioner Mounts allow quick and easy setup and operation of the CGH.

  • Easy “click-in” magnetic coupling for AOM CGHs
  • Fine position control for all 6 degrees of freedom

FP6: Fine Positioner Mount for 6″ CGH frames

Height options:

  • B600 standard base with optical axis 6” above mounting interface
  • B425 Mounting bracket with optical axis 4.25″ above the mounting surface

CGH frame options:

  • 6″ CGH frame
  • 3″ CGH frame

(AOM 6” EasyNull mounts and frames are compatible with Diffraction International hardware).

FP3: Fine Positioner Mount for 3” CGH frames

Height options:

  • B600 standard base with optical axis 6” above mounting interface
  • B425 Mounting bracket with optical axis 4.25″ above the mounting surface

CGH frame options:

  • 3″ CGH frame
  • 2″ CGH frame

Alignment References

AOM provides references for aligning the CGH and the Unit Under Test (UUT).  The details depend on customer requirements of datum references and alignment procedures.  Some examples of mechanical alignment product offerings are illustrated below.


Opto-Mechanical References Attached to the CGH

Standard fittings can be attached to the CGH to support tooling balls or optical references to enable quick and accurate assembly and alignment. The position of these features can be controlled to 1 micron accuracy at user specified locations.

Opto-Mechanical References (SMRs) Attached to the Unit Under Test

Use Line Focus References from the CGH to align Sphere Mounted Retroreflectors (SMRs) that are registered to datum features on the unit under test.

Metrology Platform

The metrology platform is a solution for quick and repeatable measurements of batches of optics using a CGH.  The platform is coupled to CGH in a one-time alignment step, providing a kinematic interface to the Unit Under Test (UUT).

ZBR Stitching Software

ZBR software uses a powerful algorithm to combine data for subaperture stitching and calibration.