Achromatic Optics for Phase Apodization Coronagraphy

Phase Apodization Coronagraphy (PAC) uses a pupil phase pattern to suppress the diffraction halo over some region around a star. Since the halo suppression requires a particular phase pattern be present and phase is inherently wavelength-dependent, PAC suppression is normally chromatic. We discuss the suppression bandwidth of a PAC implemented with a mirror or a single-component apodizing phase plate (APP) transmission optic. We then consider achromatic APP designs made possible by the use of two materials and the expected benefits. We present a design for a high-throughput achromatized APP for the LBT LMIRCam that is optimized for the direct imaging of cool extrasolar giant planets around nearby stars at thermal infrared wavelengths.