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Tol, J. van; Brunel, L.-C.; Wylde, R. J. |
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A quasioptical transient electron spin resonance spectrometer operating at 120 and 240 GHz |
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Journal Article |
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2005 |
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Rev. Sci. Instrum. |
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Rev. Sci. Instrum. |
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76 |
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7 |
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074101 (1 to 8) |
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Keywords |
Schottky, noise temperature |
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Abstract |
A new multifrequency quasioptical electron paramagnetic resonance (EPR) spectrometer is described. The superheterodyne design with Schottky diode mixer/detectors enables fast detection with subnanosecond time resolution. Optical access makes it suitable for transient EPR (TR-EPR) at 120 and 240 GHz. These high frequencies allow for an accurate determination of small g-tensor anisotropies as are encountered in excited triplet states of organic molecules like porphyrins and fullerenes. The measured concentration sensitivity for continuous-wave (cw) EPR at 240 GHz and at room temperature without cavity is 1013 spins/cm3 (15 nM) for a 1 mT linewidth and a 1 Hz bandwidth. With a Fabry-Perot cavity and a sample volume of 30 nl, the sensitivity at 240 GHz corresponds to [approximate]3×109 spins for a 1 mT linewidth. The spectrometer's performance is illustrated with applications of transient EPR of excited triplet states of organic molecules, as well as cw EPR of nitroxide reference systems and a thin film of a colossal magnetoresistance material. |
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Actually, noise spectral density is given (3e-19 W/Hz) |
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588 |
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Author |
Galeazzi, Massimiliano |
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Title |
Fundamental noise processes in TES devices |
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Journal Article |
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Year |
2011 |
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IEEE Trans. Appl. Supercond. |
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IEEE Trans. Appl. Supercond. |
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21 |
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3 |
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267-271 |
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TES, Johnson noise, phonon noise, excess noise, flux-flow noise, thermal fluctuation noise |
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Microcalorimeters and bolometers are noise-limited devices, therefore, a proper understanding of all noise sources is essential to predict and interpret their performance. In this paper, I review the fundamental noise processes contributing to Transition Edge Sensor (TES) microcalorimeters and bolometers and their effect on device performance. In particular, I will start with a simple, monolithic device model, moving to a more complex one involving discrete components, to finally move to today's more realistic, comprehensive model. In addition to the basic noise contribution (equilibrium Johnson noise and phonon noise), TES are significantly affected by extra noise, which is commonly referred to as excess noise. Different fundamental processes have been proposed and investigated to explain the origin of this excess noise, in particular near equilibrium non-linear Johnson noise, flux-flow noise, and internal thermal fluctuation noise. Experimental evidence shows that all three processes are real and contribute, at different levels, to the TES noise, although different processes become important at different regimes. It is therefore time to discard the term “excess noise” and consider these terms part of the “fundamental noise processes” instead. |
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Recommended by Klapwijk |
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914 |
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