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Characterization of noise and transition shapes in superconducting transition-edge sensors using a pulsed laser diode Dan Swetz Quantum Sensors Group NIST Boulder, CO Joel Ullom Doug Bennett Randy Doriese Gene Hilton Kent Irwin Carl Reintsema Dan Schmidt
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How to Characterize TESs?
Parameters: RSh RN n TC GTES CTES α β ΔE IV vs Tbath Power Law Fits Complex Z Pulses Noise Measurements: Models: 1-Body Model 2-Body Model New Parameters: M G2-Body C2-Body Goal: Develop a systematic way to combine TES measurements and optimally constrain TES models Only when we understand out detectors can we predict their behavior and optimize their performance
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The Diode Laser: A new tool for X-ray TES characterization
Vacuum Jacket Laser 1550 nm laser: 0.8 eV/photon (1 keV pulse = 1,200 photons) Computer controlled Variable Attenuator 3K Cold Attenuator Fiber Ferrule Flange Detector 50 mK box Collimator
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New Capabilities using Laser Pulses
Pulse Response above TC Pulses on demand Many trigger options Large range of possible energies Reliable low energy pulses 10,000 averaged pulses -8 -10 Log Detector Response (V) -12 -14 Time (ms) Detector Response vs Pulse Energy Detector Linearity 30 40 30 20 Detector Response (mV) Pulse Peak (mV) 20 10 10 Time (ms) Pulse Energy (keV)
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Goal: An optimized TES for materials analysis at 7 keV*
The Test Detector 600 mm 350 μm square Mo/Cu bilayer 0.1 μm-thick Mo 0.2 μm-thick Cu 7 interdigitated normal Cu bars 0.5 μm thick 90% TES length bismuth film absorber 1.5 μm thick 600 μm SiN frame Overlapping perforations in SiN membrane to control GTES 350 mm Current Goal: An optimized TES for materials analysis at 7 keV* perforations Interdigitated normal bars * Doriese 1EX07
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TES Modeling and Characterization
Simple TES Hypothesis: SiN is adding a dangling 2nd body Estimate from geometry*: Cdangling ~ 0.1 pJ/K, ~ 5% of CTES Questions: Are TESs 1-body (simple) or 2-body (dangling) ? What are the effects on parameters? Can the dangling body explain (part of) the unexplained excess high-frequency noise? Dangling TES * K. Rostem, et. al, Proc. SPIE, 7020, 70200L (2008)
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Parameter Extraction Methodology
RSh RN SC Noise IV vs Tbath Power Law Fits Pulses above Tc n TC RSh 260 uΩ RN 10.7 mΩ n 3.3 TC 109 mK GTES 118 pW/K CTES 1.7 pJ/K GTES CTES β Cdangling Gdangling α M ΔE
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Parameter Extraction Methodology
RSh RN SC Noise IV vs Tbath Power Law Fits Pulses above Tc n TC RSh 260 uΩ RN 10.7 mΩ n 3.3 TC 109 mK GTES 118 pW/K CTES 1.7 pJ/K GTES Measurements at 10—80 % bias of Rnormal in steps of 10% CTES Complex Z β Pulses Noise β Cdangling Gdangling α M ΔE
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Parameter Extraction Methodology
RSh RN SC Noise IV vs Tbath Power Law Fits Pulses above Tc n TC RSh 260 uΩ RN 10.7 mΩ n 3.3 TC 109 mK GTES 118 pW/K CTES 1.7 pJ/K GTES Measurements at 10—80 % bias of Rnormal in steps of 10% CTES Complex Za β Pulsesb β Cdangling Gdangling Cdangling GoF CZ αCZ αpulse GoF pulse Dangling Model Gdangling F α Goodness of Fit Phase Space M ΔE a) Bennett et. al., Proc. AIP, vol pp , (2009) b) Bennett et. al., APL submitted (2010)
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Parameter Extraction Methodology
RSh RN SC Noise IV vs Tbath Power Law Fits Pulses above Tc n TC RSh 260 uΩ RN 10.7 mΩ n 3.3 TC 109 mK GTES 118 pW/K CTES 1.7 pJ/K GTES Measurements at 10—80 % bias of Rnormal in steps of 10% CTES Complex Za β Pulsesb β Cdangling Gdangling Cdangling GoF CZ αCZ αpulse GoF pulse Dangling Model Gdangling α Noise Goodness of Fit Phase Space F M M GoF noise ΔE a) Bennett et. al., Proc. AIP, vol pp , (2009) b) Bennett et. al., APL submitted (2010)
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Parameter Extraction Methodology
RSh RN SC Noise IV vs Tbath Power Law Fits Pulses above Tc n TC RSh 260 uΩ RN 10.7 mΩ n 3.3 TC 109 mK GTES 118 pW/K CTES 1.7 pJ/K GTES Measurements at 10—80 % bias of Rnormal in steps of 10% CTES Complex Za β Pulsesb β Cdangling Gdangling Cdangling GoF CZ αCZ αpulse GoF pulse Dangling Model Gdangling α Noise Goodness of Fit Phase Space M ΔE M GoF noise ΔE a) Bennett et. al., Proc. AIP, vol pp , (2009) b) Bennett et. al., APL submitted (2010)
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Departure from simple model at 1.5 ms
Pulse Fits Good Fit Why 2d GoF phase space? Exclude local minima Poor estimate of error on data Simple model GoF = 1.58 Dangling model achieves GoF = 14 High Cdang, Gdang excluded Bad Fit Departure from simple model at 1.5 ms
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Goodness of Fit: CZ and Noise
Good Fit Good Fit Bad Fit Bad Fit Simple model CZ GoF = 4.5 Dangling model achieves GoF = 6.4 Simple model noise GoF = 11.3 Dangling model achieves GoF =24 Large parameter space excluded, particularly high Cdang, Gdang regions. Reasonable constraints on both Cdangling and Gdangling 13
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α and M are largely unaffected by dangling parameters
Nearly identical values from CZ fits 1-body model predicts αpulse = 310, αCZ = 314 and M = 1.52 Conclusion: Can estimate using simple model
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Dangling Body Affects Noise and Energy Resolution
bad fit region M-noise 2.28 eV = Simple model energy resolution 2.34 eV = Simple model with CTES + Cdangling 2.5—3.1eV = Dangling model energy resolution Dangling noise explains increased mid-frequency noise at ~ Hz Dangling noise degrades resolution by ~ %
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Conclusions and Future Plans
Diode laser is a useful tool for device characterization Device is described by a dangling two-body model Dangling parameters have minimal affect on alpha and excess noise Dangling body significantly degrades energy resolution Repeat analysis on more devices Very preliminary spectrum of Mn Kα Similar 9-bar device ΔEFWHM = 3.64 eV
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Fin
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Energy Resolution vs Gdangling
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Pulse Fits Evidence for dangling models
Dangling model fits data well Requires High S/N – 4000 pulses averaged Simple model: overshoots data at early times undershoots data at late times
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