51 research outputs found
Optimizing the Efficiency of Fabry-Perot Interferometers with Silicon-Substrate Mirrors
We present the novel design of microfabricated, silicon-substrate based
mirrors for use in cryogenic Fabry-Perot Interferometers (FPIs) for the mid-IR
to sub-mm/mm wavelength regime. One side of the silicon substrate will have a
double-layer metamaterial anti-reflection coating (ARC) anisotropically etched
into it and the other side will be metalized with a reflective mesh pattern.
The double-layer ARC ensures a reflectance of less than 1% at the surface
substrate over the FPI bandwidth. This low reflectance is required to achieve
broadband capability and to mitigate contaminating resonances from the silicon
surface. Two silicon substrates with their metalized surfaces facing each other
and held parallel with an adjustable separation will compose the FPI. To create
an FPI with nearly uniform finesse over the FPI bandwidth, we use a combination
of inductive and capacitive gold meshes evaporated onto the silicon substrate.
We also consider the use of niobium as a superconducting reflective mesh for
long wavelengths to eliminate ohmic losses at each reflection in the resonating
cavity of the FPI and thereby increase overall transmission. We develop these
silicon-substrate based FPIs for use in ground (e.g. CCAT-prime), air (e.g.
HIRMES), and future space-based telescopes (e.g. the Origins Space Telescope
concept). Such FPIs are well suited for spectroscopic imaging with the upcoming
large IR/sub-mm/mm TES bolometer detector arrays. Here we present the
fabrication and performance of multi-layer, plasma-etched, silicon metamaterial
ARC, as well as models of the mirrors and FPIs.Comment: Presented at SPIE Advances in Optical and Mechanical Technologies for
Telescopes and Instrumentation III, June 14, 201
The Simons Observatory: Magnetic Shielding Measurements for the Universal Multiplexing Module
The Simons Observatory (SO) includes four telescopes that will measure the
temperature and polarization of the cosmic microwave background using over
60,000 highly sensitive transition-edge bolometers (TES). These multichroic TES
bolometers are read out by a microwave RF SQUID multiplexing system with a
multiplexing factor of 910. Given that both TESes and SQUIDs are susceptible to
magnetic field pickup and that it is hard to predict how they will respond to
such fields, it is important to characterize the magnetic response of these
systems empirically. This information can then be used to limit spurious
signals by informing magnetic shielding designs for the detectors and readout.
This paper focuses on measurements of magnetic pickup with different magnetic
shielding configurations for the SO universal multiplexing module (UMM), which
contains the SQUIDs, associated resonators, and TES bias circuit. The magnetic
pickup of a prototype UMM was tested under three shielding configurations: no
shielding (copper packaging), aluminum packaging for the UMM, and a
tin/lead-plated shield surrounding the entire dilution refrigerator 100 mK cold
stage. The measurements show that the aluminum packaging outperforms the copper
packaging by a shielding factor of 8-10, and adding the tin/lead-plated 1K
shield further increases the relative shielding factor in the aluminum
configuration by 1-2 orders of magnitude.Comment: 7 pages, 4 figure, conference proceedings submitted to the Journal of
Low Temperature Physic
Comparing complex impedance and bias step measurements of Simons Observatory transition edge sensors
The Simons Observatory (SO) will perform ground-based observations of the
cosmic microwave background (CMB) with several small and large aperture
telescopes, each outfitted with thousands to tens of thousands of
superconducting aluminum manganese (AlMn) transition-edge sensor bolometers
(TESs). In-situ characterization of TES responsivities and effective time
constants will be required multiple times each observing-day for calibrating
time-streams during CMB map-making. Effective time constants are typically
estimated in the field by briefly applying small amplitude square-waves on top
of the TES DC biases, and fitting exponential decays in the bolometer response.
These so-called "bias step" measurements can be rapidly implemented across
entire arrays and therefore are attractive because they take up little
observing time. However, individual detector complex impedance measurements,
while too slow to implement during observations, can provide a fuller picture
of the TES model and a better understanding of its temporal response. Here, we
present the results of dark TES characterization of many prototype SO
bolometers and compare the effective thermal time constants measured via bias
steps to those derived from complex impedance data.Comment: 10 pages, 6 figures, SPIE Astronomical Telescopes + Instrumentation
2020, Paper Number: 11453-18
In situ Performance of the Low Frequency Arrayfor Advanced ACTPol
The Advanced Atacama Cosmology Telescope Polarimeter (AdvACT) \cite{thornton}
is an upgrade for the Atacama Cosmology Telescope using Transition Edge Sensor
(TES) detector arrays to measure cosmic microwave background (CMB) temperature
and polarization anisotropies in multiple frequencies. The low frequency (LF)
array was deployed early 2020. It consists of 292 TES bolometers observing in
two bands centered at 27 GHz and 39 GHz. At these frequencies, it is sensitive
to synchrotron radiation from our galaxy as well as to the CMB, and complements
the AdvACT arrays operating at 90, 150 and 230 GHz. We present the initial LF
array on-site characterization, including the time constant, optical efficiency
and array sensitivity
The Simons Observatory: Magnetic Sensitivity Measurements of Microwave SQUID Multiplexers
The Simons Observatory (SO) will be a cosmic microwave background (CMB)
survey experiment with three small-aperture telescopes and one large-aperture
telescope, which will observe from the Atacama Desert in Chile. In total, SO
will field 70,000 transition-edge sensor (TES) bolometers in six spectral
bands centered between 27 and 280 GHz in order to achieve the sensitivity
necessary to measure or constrain numerous cosmological quantities. The SO
Universal Focal Plane Modules (UFMs) each contain a 150 mm diameter TES
detector array, horn or lenslet optical coupling, cold readout components, and
magnetic shielding. SO will use a microwave SQUID multiplexing (MUX)
readout at an initial multiplexing factor of 1000; the cold (100 mK)
readout components are packaged in a MUX readout module, which is part of
the UFM, and can also be characterized independently. The 100 mK stage TES
bolometer arrays and microwave SQUIDs are sensitive to magnetic fields, and
their measured response will vary with the degree to which they are
magnetically shielded. We present measurements of the magnetic pickup of test
microwave SQUID multiplexers as a study of various shielding configurations for
the Simons Observatory. We discuss how these measurements motivated the
material choice and design of the UFM magnetic shielding.Comment: 5 pages, 6 figures, conference proceedings submitted to IEEE
Transactions on Applied Superconductivit
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