CIAO's polarimetry has a rotatable and achromatic half wave plate and a wire grid analyzer for measurement of linear polarization at JHK band. Circular polarimetry with a quarter wave plate is also available in a shared-risk mode from S06A. You can download a paper about CIAO polarimetry.

Characteristics of polarization components

  • half wave plate
    the efficiency, namely wave retarder, is 99%.
  • wire grid analyzer
    the efficiency is 90% (J), 93% (H) and 95% (K).
  • instrumental polarization
    less than 1 %.

Calculation of SN

The signal-to-noise ratio (SNRs) per an image with a polarization position angle is calculated by

SNR = sqrt(2) / pacc.

Where pacc is required accuracy of degree of polarization. Generally, Pacc should be 3 times or better than predicted degree of polarization. As an example, we consider 10% of degree of polarization is predicted in our object, the accuracy pacc requires <3.3%. The SN to be required is >43.

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