Ultra-sensitive Transition-Edge Sensors for the Background Limited Infrared/Sub-mm Spectrograph (BLISS)

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We report progress in fabricating ultra-sensitive superconducting transition-edge sensors (TESs) for BLISS. BLISS is a suite of grating spectrometers covering 35–433 μm with R∼700 cooled to 50 mK that is proposed to fly on the Japanese space telescope SPICA. The detector arrays for BLISS are TES bolometers readout with a time domain SQUID multiplexer. The required noise equivalent power (NEP) for BLISS is NEP=10−19 W/Hz1/2 with an ultimate goal of NEP=5×10−20 W/Hz1/2 to achieve background limited noise performance. The required and goal response times are τ=150 ms and τ=50 ms respectively to achieve the NEP at the required and goal optical chop frequency 1–5 Hz. We measured prototype BLISS arrays and have achieved NEP=6×10−18 W/Hz1/2 and τ=1.4 ms with a Ti TES (TC=565 mK) and NEP∼2.5×10−19 W/Hz1/2 and τ∼4.5 ms with an Ir TES (TC=130 mK). Dark power for these tests is estimated at 1–5 fW.