Direct multiplexing of low order aberration modes in a photopolymer-based holographic element for analog holographic wavefront sensing

The fabrication of an analog holographic wavefront sensor, capable of detecting the low order defocus aberration, was achieved in an acrylamide-based photopolymer. While other implementations of holographic wavefront sensors have been carried out digitally, this process utilises a recording setup consisting only of conventional refractive elements so the cost and complexity of holographic optical element (HOE) production could be much reduced. A pair of diffraction spots, corresponding to a maximum and minimum amount of defocus, were spatially separated in the detector plane by multiplexing two HOEs with different carrier spatial frequencies. For each wavefront with a known aberration that was introduced during playback of the hologram, the resulting intensity ratio was measured in the expected pair of diffracted spots. A number of HOEs were produced with the diffraction efficiency of the multiplexed elements equalized, for a range of diffraction efficiency strengths, some as low as <5%. These HOEs were used to successfully classify four amounts of the defocus aberration through the observed intensity ratio.

Automated summary

The fabrication of an analog holographic wavefront sensor capable of detecting low-order defocus aberration in an acrylamide-based photopolymer was achieved. The use of conventional refractive elements in the recording setup reduces the cost and complexity of holographic optical element (HOE) production. By multiplexing two HOEs with different carrier spatial frequencies, a pair of diffraction spots corresponding to maximum and minimum defocus amounts can be spatially separated in the detector plane.