4.7 THz local oscillator multiplexer for GUSTO

GUSTO (Galactic/ Extragalactic ULDB Spectroscopic Terahertz Observatory) equipped with three 8-pixel detection channels at 1.4, 1.9, and 4.7 THz will perform the largest single-flight mapping of the important lines of nitrogen [NII], carbon [CII], oxygen [OI] respectively, within the Milky Way and Large Magellanic Cloud.. Whilst the cutting edge technologies are applied in the mixer and local oscillator (LO) components, their proper coupling is crucial. Here we present the design, manufacturing and measurement results of a phase grating for multiplexing a single beam from a quantum cascade laser to 8 beams as the LO at 4.7 THz. We experimentally confirmed that the grating meets all the requirements. This is the first time that such a complete characterization of a THz phase grating is being reported. This accomplishment paves the way for future larger array receivers to apply this component for such a critical function.