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.
Generating multiple local oscillator beams is one challenge to develop large heterodyne receiver arrays (~100 pixels), which allow astronomical instrumentations mapping more area within limited space mission lifetime. Here, We combine a reflective Fourier grating with an unidirectional antenna coupled 3rd-order distributed feedback (DFB) quantum cascade laser (QCL) to generate 81 beams at 3.86 THz. We have measured the beam pattern of the diffracted 81 beams, which agrees well with a simulated result from COMSOL Multiphysics with respect to the angular distribution and power distribution among the 81 beams. The diffraction efficiency of the Fourier grating is derived to be 94±3%, which is very close to the simulated result of 97%. For an array of equal superconducting hot electron bolometer mixers, 64 out of 81 beams can pump the HEB mixers with similar power, resulting in receiver sensitivities within 10%. Such a combination of a Fourier grating and a QCL can create an LO with 100 beams or more, enabling a new generation of large heterodyne arrays for astronomical instrumentation. This paper is essentially a copy of our paper in Optics Express.
GUSTO will be a NASA balloon borne terahertz observatory to be launched from Antarctica in late 2021 for a flight duration of 100-170 days. It aims at reviewing the life cycle of interstellar medium of our galaxy by simultaneously mapping the three brightest interstellar cooling lines: [OI] at 4.7 THz, [CII] at 1.9 THz, and [NII] at 1.4 THz; along the 124 degrees of the galactic plane and through a part of the Large Magellanic Cloud. It will use three arrays of 4x2 mixers based on NbN hot electron bolometers (HEBs), which are currently the most sensitive mixers for high resolution spectroscopic astronomy at these frequencies.
Here we report on the design of a novel 4.7 THz receiver for GUSTO. The receiver consists mainly of two subsystems: a 4×2 HEB quasi-optical mixer array and a 4.7 THz multi-beam LO. We describe the mixer array, which is designed as a compact monolithic unit. We show, for example, 10 potential HEB detectors with the state of the art sensitivity of 720 K measured at 2.5 THz. They have a small variation in sensitivity, being less than 3%, while also meet the LO uniformity requirements. For the multi-beam LO we demonstrate the combination of a phase grating and a single QCL at 4.7 THz, which generates 8 sub-LO beams, where the phase grating shows an efficiency of 75%. A preliminary concept for the integrated LO unit, including QCL, phase grating and beam matching optics is presented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.