Far-infrared laser calorimetry was used to measure the absorptivity, and thus the emissivity, of aluminum-coated silicon carbide mirror samples produced during the coating qualification run of the Herschel Space Observatory telescope to be launched by the European Space Agency in 2007. The samples were measured at 77 K to simulate the operating temperature of the telescope in its planned orbit about the second Lagrangian point, L 2 , of the Earth-Sun system. Together, the telescope's equilibrium temperature in space and the emissivity of the mirror surfaces will determine the far-infraredsubmillimeter background and thus the sensitivity of two of the three astronomical instruments aboard the observatory if stray-light levels can be kept low relative to the mirror emission. Absorptivities of both clean and dust-contaminated samples were measured at 70, 118, 184, and 496 m. Theoretical fits to the data predict absorptivities of 0.2-0.4% for the clean sample and 0.2-0.8% for the dusty sample, over the spectral range of the Herschel Space Observatory instruments.
A direct excite-probe semiconductor lifethe determination in the picosecond regime h a s been made for the first time in the far infrared. We have used an nF-linac-pumped free-electron laser to determine the relaxation rate associated with intersubband absorption in GaAdAIGaAs quantum wells having a subband separation smaller than the optical phonon energy. The measurement yielas a relaxation lifethe of 40 I 5 ps. This :s compared with a variety of other resulis obtained with less direct techniques.
Detection peculiarities of an un-cooled (room temperature) 8×8 pixel array designed to image broadband THz radiation were investigated. Each pixel consists of a thin conductive film absorber on a dielectric membrane with thermopile temperature readout. It was designed and tested for four combinations of two different types of absorber and thermopile materials. The photo-response profile, determined by scanning the pixels through the focus of a THz laser beam, was wider than expected from a 2-D convolution of the Gaussian beam and the absorber surface. Also the time response did depend on the position of the beam relative to the pixel. Simulations show that those properties are due to the fact that also the thermopiles absorb THz radiation. For the best composition of absorber and thermopile, the responsivity, the noise equivalent power, and the bandwidth were estimated to be of 28 V/W, 5×10 -9 W/Hz 1/2 and 50 Hz, respectively.
The results of the planar diodes based on semiconductor quantum superlattice (SL) applications for direct and coherent detection, harmonics generation in terahertz frequency range is presented.The study used planar diodes with small active area size 1-2 jlm2.To fabricate the diodes were grown by molecular beam epitaxy structure heavily doped superlattices with miniband width 24meV.The experimental dependence of Volt -Watt sensitivity unbiased or biased planar SL diodes in frequency range 1-4.5THz is shown. Coherent detection of of the radiation from BWO and quantum cascade laser (QCL) by using unbiased SL planar diodes with supplementary low frequency (10-200GHz) pump source is demonstrated. The power spectrum of output signal frequency multiplier with the input pump of 140-160GHz is measured in frequency range 0.4-S.1THz.
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