Laser interferometers are the state of the art for characterizing large telescope optics, manufacturing custom optics, aspheres, freeform optics, and for semiconductor wafer characterization. For test optics with large surface errors, a reference optic and/or a custom computer-generated hologram (CGH) can be used to bring the errors within the interferometer’s range.
However, many situations result in large departures from reference optics. Thermal & gravity sag effects in large optics can cause significant deviations, only some of which may be predictable. Test optics in semiconductor manufacturing may include sharp, irregular steps of many waves. In the early stages of optics polishing, departures from reference can be extreme. Custom optics, including asphere and freeform, can deviate hugely from spherical, and for these a custom CGH (with a typical lead time of 6 months and cost of $10k) is not always economical.
We propose to extend the range of an interferometer by providing > 50 waves of programmable phase control using a Spatial Light Modulator (SLM). In addition to extending the range of phase errors that can be characterized, the SLM interferometer can apply additional arbitrary phase.
In Phase I we will upgrade a prototype SLM interferometer that we previously used to demonstrate nulling and programmable phase control. Phase I will focus on improving interferometer speed, calibration, and stability, and quantifying performance through the following technical objectives:
In Phase II BNS will incorporate an upgraded 1536x1536 pixel MacroSLM into a commercial interferometer and demonstrate its performance in typical use cases.
The SLM interferometer can save optics manufacturers, especially free-form optics, time and money during manufacturing, since a greater interferometer range will mean optics can be characterized earlier in the fabrication process when their deviations from reference can be large. It can also allow spherical references or existing CGHs to be used for a wider range of optic designs.