Measurements of the optical performance of bolometers for SPICA/SAFARI

Audley, M. D.; Lange, Gert de; Gao, J. R.; Khosropanah, P.; Ridder, M.; Ferrari, L.; Laauwen, W. M.; Ranjan, M.; Mauskopf, Philip Daniel; Morozov, D.; Trappe, Neil

doi:10.1117/12.925234

Cited by 6 publications

(5 citation statements)

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“…This density is still high in comparison with the lowest reported values for superconducting qubits and Cooper-pair transistors1718 (less than 0.1 μm −3 ), but inherent to the relatively high microwave powers we need in this type of experiments. The measured limit in optical NEP due to excess quasiparticles is comparable with the lowest observed optical NEP in other detectors for similar wavelengths293031.…”

Section: Discussionsupporting

confidence: 81%

Fluctuations in the electron system of a superconductor exposed to a photon flux

et al. 2014

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In a superconductor, in which electrons are paired, the density of unpaired electrons should become zero when approaching zero temperature. Therefore, radiation detectors based on breaking of pairs promise supreme sensitivity, which we demonstrate using an aluminium superconducting microwave resonator. Here we show that the resonator also enables the study of the response of the electron system of the superconductor to pair-breaking photons, microwave photons and varying temperatures. A large range in radiation power (at 1.54 THz) can be chosen by carefully filtering the radiation from a blackbody source. We identify two regimes. At high radiation power, fluctuations in the electron system caused by the random arrival rate of the photons are resolved, giving a straightforward measure of the optical efficiency (48±8%) and showing an unprecedented detector sensitivity. At low radiation power, fluctuations are dominated by excess quasiparticles, the number of which is measured through their recombination lifetime.

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Section: Discussionsupporting

confidence: 81%

Fluctuations in the electron system of a superconductor exposed to a photon flux

et al. 2014

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“…The sensitivity of a well-designed Transition Edge Sensor (TES) is determined by the thermal fluctuation noise in the weak link to the heat bath 1 . Noise-equivalent powers (NEPs) as low as 0.5 aW Hz −1/2 are now routinely achieved [2][3][4][5][6][7] . Our own ultra-low-noise TESs, developed for the SAFARI instrument on SPICA 8,9 , have four SiN x support legs, 200 nm thick, 2.1 µm wide and 540 µm long, giving a total thermal conductance G of 0.19 pW K −1 and an NEP of 0.42 aW Hz −1/2 .…”

Section: Introductionmentioning

confidence: 99%

Transition edge sensors with few-mode ballistic thermal isolation

Osman¹,

Withington²,

Goldie³

et al. 2014

Journal of Applied Physics

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We have fabricated Transition Edge Sensors (TESs) whose thermal characteristics are completely characterised by few-mode ballistic phonon exchange with the heat bath. These TESs have extremely small amorphous SiN x support legs: 0.2 µm thick, 0.7 to 1.0 µm wide and 1.0 to 4.0 µm long. We show, using classical elastic wave theory, that it is only necessary to know the geometry and bulk elastic constants of the material to calculate the thermal conductance and fluctuation noise. Our devices operate in the few-mode regime, between 5 and 7 modes per leg, and have noise equivalent powers (NEPs) of 1.2 aW Hz −1/2 . The NEP is dominated by the thermal fluctuation noise in the legs, which itself is dominated by phonon shot-noise. Thus TESs have been demonstrated whose thermal characteristics are fully accounted for by an elastic noise-wave model. Our current devices, and second-generation devices based on patterned phononic filters, can be used to produce optically compact, mechanically robust, highly sensitive TES imaging arrays, circumventing many of the problems inherent in conventional long-legged designs.

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“…In a cold electron bolometer, when the absorber is heated by incident optical power, it is this cooling power, associated with the most energetic of charges tunnelling out of the absorber, which removes the heat. Since the cooling (thermal resetting) of the bolometer is carried out directly by electron diffusion (as opposed to the long, weak, thermal links required by many of today's most sensitive bolometers [14][15][16] ), the thermal time constant associated with the cold electron bolometer is governed by the tunnelling time. This can be 17 as low as 10 ns, whereas other types of detector 18 have response times of the order of 1 ms.…”

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confidence: 99%

A strained silicon cold electron bolometer using Schottky contacts

Brien

Barry

Dunscombe

et al. 2014

Applied Physics Letters

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We describe optical characterisation of a Strained Silicon Cold Electron Bolometer (CEB), operating on a 350 mK stage, designed for absorption of millimetre-wave radiation. The silicon Cold Electron Bolometer utilises Schottky contacts between a superconductor and an n ++ doped silicon island to detect changes in the temperature of the charge carriers in the silicon, due to variations in absorbed radiation. By using strained silicon as the absorber, we decrease the electron-phonon coupling in the device and increase the responsivity to incoming power. The strained silicon absorber is coupled to a planar aluminium twin-slot antenna designed to couple to 160 GHz and that serves as the superconducting contacts. From the measured optical responsivity and spectral response, we calculate a maximum optical efficiency of 50 % for radiation coupled into the device by the planar antenna and an overall noise equivalent power (NEP), referred to absorbed optical power, of 1.1 × 10 −16 W Hz −1 /2 when the detector is observing a 300 K source through a 4 K throughput limiting aperture. Even though this optical system is not optimised we measure a system noise equivalent temperature difference (NETD) of 6 mK Hz −1 /2 . We measure the noise of the device using a cross-correlation of time stream data measured simultaneously with two junction field-effect transistor (JFET) amplifiers, with a base correlated noise level of 300 pV Hz −1 /2 and find that the total noise is consistent with a combination of photon noise, current shot noise and electron-phonon thermal noise.

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Measurements of the optical performance of bolometers for SPICA/SAFARI

Cited by 6 publications

References 0 publications

Fluctuations in the electron system of a superconductor exposed to a photon flux

Fluctuations in the electron system of a superconductor exposed to a photon flux

Transition edge sensors with few-mode ballistic thermal isolation

A strained silicon cold electron bolometer using Schottky contacts

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