We measured the double sideband (DSB) receiver noise temperature (TrecDSB) of an NbN hot electron bolometer (HEB) mixer at three local oscillator frequencies of 1.6, 2.5, and 5.3 THz. The HEB has cleaned contact interfaces with a 200 nm thick Au layer. The measuredTrecDSB values are 530 ± 11 K, 640 ±18 K, and 2190 ±150 K at 1.6, 2.5, and 5.3 THz, respectively, using an air setup with total optical losses of 2.60 ± 0.04, 2.63 ± 0.16, and 4.70 ± 0.24 dB, respectively. We derived low mixer noise temperatures (TmixerDSB) of 240 ± 6 K at 1.6 THz and 290 ± 13 K at 2.5 THz, achieving over 30% improvement compared to published NbN HEB mixers. This enhancement can reduce the integration time of a heterodyne instrument by roughly a factor of 2. At 5.3 THz,TmixerDSB is 620 ± 55 K, showing limited improvement due to non-optimized antenna geometry. These results also contribute to understanding the device physics of a wide HEB (4 μm) at high frequencies.

Enabled by planarized phase engineering, metalenses based on metasurfaces offer compact and scalable solutions for applications such as sensing, imaging, and virtual reality. They are particularly attractive for multi-pixel, large-scale heterodyne focal plane arrays in space observatories, where a flat metalens array on a silicon wafer can replace individual lenses, greatly simplifying system integration and beam alignment. In this work, we demonstrate a superconducting niobium nitride (NbN) hot electron bolometer (HEB) mixer coupled to a silicon-based metalens operating at terahertz frequencies. The metalens phase profile was derived from a finite-size Gaussian beam source using the Rayleigh–Sommerfeld diffraction integral, and its focusing behavior was validated through 2D simulation. Experimentally, the metalens-coupled NbN HEB receiver exhibited a noise temperature of 1800K at 1.63THz. The power coupling efficiency from free space to the mixer via the metalens was measured to be 25%. Measured far-field beam profiles are Gaussian-like with sidelobes below −14dB. These results demonstrate the feasibility of integrating metalenses with HEB mixers for THz detection, offering a scalable path for compact focal plane arrays in space-based THz instrumentation.

We propose a novel approach to multiplex a single Gaussian beam from a THz source into seven beams arranged in a hexagonal configuration, matching an array of Hot Electron Bolometer (HEB) mixers. This configuration is necessary for the High-Resolution Receiver (HiRX) instrument on the proposed NASA Single Aperture Large Telescope for Universe Studies (SALTUS) space mission. The beam splitter relies on a reflector that introduces a phase shift to the incident Gaussian beam; after propagation, the desired amplitude distribution is achieved at the mixer array plane. Unlike existing THz multiplexers, our method does not use a phase grating based on the repetition of a unit cell. Instead, we employ an iterative phase reconstruction (Gerchberg- Saxton) algorithm to retrieve the required phase shift. This paper discusses the scientific motivation, current state of the art, design methodology, simulation outcomes, and experimental validation of the reflector. [...]

Achieving both high redox activity and rapid ion transport is a critical and pervasive challenge in electrochemical energy storage applications. This challenge is significantly magnified when using large-sized charge carriers, such as the sustainable ammonium ion (NH₄⁺). A self-assembled MXene/n-type conjugated polyelectrolyte (CPE) superlattice-like heterostructure that enables redox-active, fast, and reversible ammonium storage is reported. The superlattice-like structure persists as the CPE:MXene ratio increases, accompanied by a linear increase in the interlayer spacing of MXene flakes and a greater overlap of CPEs. Concurrently, the redox activity per unit of CPE unexpectedly intensifies, a phenomenon that can be explained by the enhanced de-solvation of ammonium due to the increased volume of 3 Å-sized pores, as indicated by molecular dynamic simulations. At the maximum CPE mass loading (MXene:CPE ratio = 2:1), the heterostructure demonstrates the strongest polymeric redox activity with a high ammonium storage capacity of 126.1 C g⁻¹ and a superior rate capability at 10 A g⁻¹. This work unveils an effective strategy for designing tunable superlattice-like heterostructures to enhance redox activity and achieve rapid charge transfer for ions beyond lithium.