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Current interferometric gravitational wave detectors use the combination of quasimonochromatic, continuous-wave laser light at 1064 nm and fused silica test masses at room temperature. Detectors of the third generation, such as the Einstein-Telescope, will involve a considerable sensitivity increase. The combination of 1550 nm laser radiation and crystalline silicon test masses at low temperatures might be important ingredients in order to achieve the sensitivity goal. Here we compare some properties of the fused silica and silicon test mass materials relevant for decreasing the thermal noise in future detectors as well as the recent technology achievements in the preparation of laser radiation at 1064 nm and 1550 nm relevant for decreasing the quantum noise. We conclude that silicon test masses and 1550 nm laser light have the potential to form the future building blocks of gravitational wave detection.

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This letter reports the observation of intersubband electroluminescence from a single-period resonant tunneling structure. Intersubband emission (λ≈8.4 μm), with a full width at half maximum of 7 meV, was observed from a GaAs/AlGaAs triple barrier structure with quantum well widths of 66 and 33 Å. The emission was coupled out of the sample by a metallic grating with a period of 5 μm deposited on the surface. The intensity of emission follows the resonance behavior in the I–V characteristics. As the temperature increases from 10 to 200 K, the emission intensity decreases monotonically by a factor of ∼2 and the emission energy shifts down slightly (ΔE≈2.7 meV). The temperature dependence of the emission energy is explained by a combination of thermal broadening of the electron distribution and the nonparabolicity of the conduction bands.