Deposited dielectrics with low mm-submm loss will be of great benefit to on-chip superconducting circuits for mm-submm astronomy. Compared with planar chip designs, multilayer structures with deposited dielectrics allow for more compact circuit elements, and eliminate radiation losses at high frequencies. While recently hydrogenated amorphous silicon carbide has been demonstrated to exhibit low dielectric losses at mm-submm wavelengths, the origin of the mm-submm loss in hydrogenated amorphous silicon carbide remains unknown.
We measured the 270-600 GHz dielectric losses of hydrogenated amorphous silicon carbide in superconducting microstrip lines. Furthermore, we measured the complex dielectric constant of the hydrogenated amorphous silicon carbide in the 3-100 THz range using Fourier transform spectroscopy. We modeled the loss data from 0.27-100 THz using a Maxwell-Helmholtz-Drude dispersion model. Our results demonstrate that phonon modes above 10 THz dominate the mm-submm losses in deposited dielectrics.
We present measurements of a polarization sensitive lens-antenna coupled MKID array at 1.5THz, mounted with an additional 20dB neutral density filter in a wide field camera. This allows full end to end system characterization with room temperature optical sources, but under similar optical loading conditions as expected in a space based polarimeter configuration.
The system is characterized using a wideband polarized photomixer based phase and amplitude beam pattern setup at 1.5THz. Two separate measurements with orthogonal source polarizations enable the co and cross polarization to be extracted, showing the full system low cross-polarization needed for many future polarimetric applications. Such a measurement setup is additionally of potential interest for the characterization of future missions (for example in the Far Infra-Red): to obtain the optical beam quality and verifying the optical interfaces on a component/sub-component level. We present and discuss this setup and the characterization of the lens-antenna coupled MKID camera.
We present the design and cryogenic characterization of highly sensitive 7 THz lens-antenna-coupled MKIDs for future actively cooled far-infrared space telescopes. This is the highest operating frequency ever demonstrated for antenna-coupled MKIDs. The detector is based on a broadband leaky-wave lens-antenna coupled to a hybrid (Al/NbTiN) CPW MKID. Both the antenna and the photosensitive Al section of the MKID lay on a thin dielectric membrane, improving both the antenna efficiency and the detector sensitivity. The high operating frequency requires the definition of sub-micron features with electron-beam lithography, pristine laser-ablated lenses, and very accurate alignments during assembly. We have tested a prototype chip and have obtained a detector noise equivalent power of 3e-20W/sqrt(Hz) with a high coupling efficiency. Additionally, we have measured the antenna beam pattern. With these measurements we demonstrate a detector system suitable for highly-sensitive (imaging) spectrometers.
Future observatories for the far-infrared (FIR), such as envisioned in the NASA Probe announcement, will offer unprecedented sensitivity by using cryogenically cooled optics. Large arrays of lens-absorber coupled Microwave Kinetic Inductance Detectors (MKIDs) are the only candidate to fulfill the requirements for these observatories, requiring unprecedented sensitivity with a noise equivalent power below 10^(-19) W/√Hz while operating up to 12THz. The incoherent coupling mechanism of distributed absorbers leads to a robustness against misalignment, assembly, and fabrication issues at FIR wavelengths. In this contribution, we will present the design and fabrication of large arrays of lens-absorber coupled detectors and evaluate their performance at 7 and 12THz and demonstrate an NEP of 0.7⋅10^(-19) W/√Hz.
Theoretical solar cell efficiency limits increase with optical concentration of sunlight while the usage of expensive absorber material decreases. In practice, the efficiency of concentrator solar cells peaks already at a few hundred Suns and drops sharply thereafter due to a trade-off between shading losses due to the front metal grid and resistive heating losses of the cell. In this work we deposit a transparent polymer layer with V-shaped grooves, imprinted above the cell’s metal fingers, which redirects light away from the metal and onto the absorber material. This renders the contacts effectively transparent and breaks the trade-off, thus allowing for higher concentration ratios and higher efficiency. We will demonstrate how performance of a Si solar cell with 25% front metal grid coverage and an initial short-circuit current density (JSC) of 29.95 mA/cm2 can be improved to a JSC of 39.12 mA/cm2 after adding the patterned polymer, mitigating shading losses almost completely. Furthermore, we investigate the performance of this layer with respect to varying angles of incidence and find that as long as the V-grooves are parallel to the line that describes the motion of the sun across the hemisphere, there is no loss in performance as a function of angle. In fact, based on the electronic and optical angular performance of the designed structure, we obtain an effective shading of 0.6% for a solar cell with 25% front metal grid coverage at 1000 suns, for a realistic concentration geometry. Lastly, we plan on presenting experimental IV-data of highly efficient III-V cells with V-grooves under concentration.
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