Polarization and spectral differential imager using channeled spectrum

摘要

The light from an exoplanet is expected to be different from that of its parent star in regard to polarization and spectral features. Thus, polarization or spectral differential technique will be a powerful tool for direct detection of exoplanets. We propose a novel technique that enables to detect both polarization and spectral differential images. This technique will be used in combination with the other high-contrast imagers to enhance the performance. This approach uses two Wollaston prisms (WPs) and a thick retarder (TR) inserted between the WPs. Two WPs generate four images and make it possible to obtain polarization differential images. Spectra of these four images have sinusoidal patterns (channeled spectra) due to the WP-TR-WP system. By inserting an interference filter, this system works as bandpass filters whose center wavelengths are different between the images. Therefore, both polarization and spectral differential images can be obtained. Furthermore, we propose to use two variable retarders (VRs) to remove differential aberrations caused by different optical paths of these four images. One VR is inserted in front of WP-TR-WP system to modulate the polarized light beams, and the other one is inserted between WPs to modulate the channeled spectra. By modulating the retardations of the VRs, it becomes possible to remove the differential aberrations. We present the principle of this method. Currently, we are conducting the preliminary laboratory experiment. The results of the laboratory demonstrations will be also reported.