Light absorption in ultrathin layer of semiconductor has been considerable interests for many years due to its potential
applications in various optical devices. In particular, there have been great efforts to engineer the optical properties of
the film for the control of absorption spectrums. Whereas the isotropic thin films have intrinsic optical properties that are
fixed by materials’ properties, metafilm that are composed by deep subwavelength nano-building blocks provides
significant flexibilities in controlling the optical properties of the designed effective layers. Here, we present the ultrathin
semiconductor metafilm absorbers by arranging germanium (Ge) nanobeams in deep subwavelength scale. Resonant
properties of high index semiconductor nanobeams play a key role in designing effective optical properties of the film.
We demonstrate this in theory and experimental measurements to build a designing rule of efficient, controllable
metafilm absorbers. The proposed strategy of engineering optical properties could open up wide range of applications
from ultrathin photodetection and solar energy harvesting to the diverse flexible optoelectronics.
The inflationary paradigm of the early universe predicts a stochastic background of gravitational waves which would generate a B-mode polarization pattern in the cosmic microwave background (CMB) at degree angular scales. Precise measurement of B-modes is one of the most compelling observational goals in modern cosmology. Since 2011, the Keck Array has deployed over 2500 transition edge sensor (TES) bolometer detectors at 100 and 150 GHz to the South Pole in pursuit of degree-scale B-modes, and Bicep3 will follow in 2015 with 2500 more at 100 GHz. Characterizing the spectral response of these detectors is important for controlling systematic effects that could lead to leakage from the temperature to polarization signal, and for understanding potential coupling to atmospheric and astrophysical emission lines. We present complete spectral characterization of the Keck Array detectors, made with a Martin-Puplett Fourier Transform Spectrometer at the South Pole, and preliminary spectra of Bicep3 detectors taken in lab. We show band centers and effective bandwidths for both Keck Array bands, and use models of the atmosphere at the South Pole to cross check our absolute calibration. Our procedure for obtaining interferograms in the field with automated 4-axis coupling to the focal plane represents an important step towards efficient and complete spectral characterization of next-generation instruments more than 10000 detectors.
We propose and demonstrate a metal-dielectric thin film that delivers low reflection and high absorption over the entire
visible spectrum. This thin black film consists of SiO<sub>2</sub>/Cr/SiO<sub>2</sub>/Al layers deposited on glass substrate. Measured
reflectance and absorptance of the black film are 0.7% and 99.3%, respectively, when averaged over the range 380-780
nm. The total thickness of the black film is only about 220 nm. This thin black film can be used as a thin absorbing layer
for displays that require both broadband anti-reflection and high contrast characteristics.