Design of an optical beam combiner for dual-frequency observation with ALMA

Abstract

The aim of this work is to improve high-frequency calibration data on longbaseline observations for the ALMA antennas. A dual-frequency atmospheric phase error calibration method is proposedand will be implementedby the simultaneous observation intwo ALMA Bands, specifically 6 and 9, coupledby means external optics in a few baselines. This method is envisioned todemonstrate the advantage of receiving signals simultaneously at different frequencies from the same pointof the sky. Itwill permit an increase of accuracy in determining the phase correction needed to reduce the effects of the atmosphereand,therefore, it will enable higher resolutions when imaging at high frequenciesusing the ALMA interferometer.While maintaining the existing receiver optics, an opticallayout that couples Bands 6 and 9 is proposed. Here we demonstrate that very limited impact on the existing ALMA system is needed. Furthermore, we present in detail the optical layout, made within the formalism of ray optics. The initial results demonstrate the feasibility of the proposed system.