CHARIS Polarization Differential Imaging (PDI)

The near-IR WFS pickoff dichroics affect instrument polarization (see measured YJH50 dichroic instrumental polarization).

Recalibration of polarization efficiency and instrument polarization are required. Contact SCExAO team prior to PDI+nearIRWFS proposal submission.

Spectro-Polarimetric Imaging is enabled by a Wollaston prism, field stop, and half-waveplate (HWP) rotation for slow modulation. This mode is refered to as CHARIS-PDI (Polarization Differential Imaging).

CHARIS-PDI datacube scanning wavelength. Coronagraph blocks central PSF. Astrogrid calibration speckles enabled.

Throughput

Spectro-Polarimetric Imaging Throughput (relative to non-PDI observations)
Band	HWP	Wollaston	total
J (1.24um)	96.1%	93.2%	89.6%
H (1.63um)	94.3%	95.7%	90.2%
K (2.14um)	92.2%	92.2%	85.0%

PDI Calibration: derotator and HWP crosstalk

Polarimetric efficiency and crosstalk are posted on this webpage for observers using CHARIS-PDI mode, allowing users to calibrate CHARIS-PDI data.

SCExAO/CHARIS PDI derotator and HWP crosstalk report

Observers should consult the SCExAO/CHARIS PDI derotator and HWP crosstalk report for CHARIS-PDI observation planning and data calibration
[pdf]
[pptx (includes animations)]

Credit: Jasper Ruigrok, Steven Bos, Rob van Holstein, Frans Snik + SCExAO team).

Polarimetric efficiency over derotator angle. Credit: Jasper Ruigrok, Steven Bos, Rob van Holstein, Frans Snik + SCExAO team
Angle of linear polarization offset over derotator angle. Credit: Jasper Ruigrok, Steven Bos, Rob van Holstein, Frans Snik + SCExAO team