4 × 2 Hot electron bolometer mixer arrays for detection at 1.4, 1.9, and 4.7 THz for the balloon-borne terahertz observatory GUSTO

We have successfully demonstrated three 4×2 hot electron bolometer (HEB) mixer arrays, designed to operate between 4.2 and 5.5 K, with local oscillator (LO) frequencies of 1.4, 1.9, and 4.7 THz, respectively. These arrays consist of spiral antenna coupled NbN HEB mixers combined with elliptical lenses. These are to date the highest pixel count arrays using a quasi-optical coupling scheme at supra-THz frequencies. At 1.4 THz, we obtained an average double sideband mixer noise temperature of 330 K, a mixer conversion loss of 5.2 dB, and an optimum LO power of 210 nW. The array at 1.9 THz has an average mixer noise temperature of 425 K, a mixer conversion loss of 6.4 dB, and an optimum LO power of 190 nW. For the array at 4.7 THz, we obtained an average mixer noise temperature of 715 K, a mixer conversion loss of 8.9 dB, and an optimum LO power of 240 nW. We found the arrays to be uniform regarding the mixer noise temperature with a standard deviation of 3% to 4%, the conversion loss with a standard deviation of 8% to 11%, and optimum LO power with a standard deviation of 5% to 6%. The noise bandwidth was also measured, being 3.5 GHz for the three arrays. These performances are comparable to previously reported values in the literature for single pixels and also other detector arrays at similar frequencies. Our arrays met the instrument requirements and were employed in the Galactic/Extra-Galactic ULDB Spectroscopic Terahertz Observatory (GUSTO), a NASA balloon-borne observatory. GUSTO launched from Antarctica on the 31st of December 2023 having a successful flight of 57 days, the longest ever recorded by NASA for such a mission profile.