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A transition-edge sensor (TES) is a type of
cryogenic
In physics, cryogenics is the production and behaviour of materials at very low temperatures.
The 13th IIR International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of “cryogenics” and “cr ...
energy sensor or
cryogenic particle detector Cryogenic particle detectors operate at very low temperature, typically only a few degrees above absolute zero. These sensors interact with an energetic elementary particle (such as a photon) and deliver a signal that can be related to the type of p ...
that exploits the strongly temperature-dependent
resistance of the
superconducting phase transition.
History
The first demonstrations of the superconducting transition's measurement potential appeared in the 1940s, 30 years after
Onnes Onnes may refer to:
* Onnes (general), one of the generals of the mythological Assyrian king Ninus
* Onnes, alternative spelling of Onnyos, a rural locality in Amginsky District of the Sakha Republic, Russia
See also
* Onne
Onne also known as On ...
's discovery of
superconductivity
Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic flux fields are expelled from the material. Any material exhibiting these properties is a superconductor. Unlike ...
. D. H. Andrews demonstrated the first transition-edge
bolometer
A bolometer is a device for measuring radiant heat by means of a material having a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley.
Principle of operation
A bolometer ...
, a current-biased
tantalum
Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as ''tantalium'', it is named after Tantalus, a villain in Greek mythology. Tantalum is a very hard, ductile, lustrous, blue-gray transition metal that is ...
wire which he used to measure an infrared signal. Subsequently he demonstrated a transition-edge
calorimeter
A calorimeter is an object used for calorimetry, or the process of measuring the heat of chemical reactions or physical changes as well as heat capacity. Differential scanning calorimeters, isothermal micro calorimeters, titration calorimete ...
made of
niobium nitride
Niobium nitride is a compound of niobium and nitrogen (nitride) with the chemical formula NbN. At low temperatures (about 16 K) NbN becomes a superconductor, and is used in detectors for infrared light.
Uses
*Niobium nitride's main use is as a ...
which was used to measure
alpha particles
Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be prod ...
. However, the TES detector did not gain popularity for about 50 years, due primarily to the difficulty in stabilizing the temperature within the narrow superconducting transition region, especially when more than one pixel was operated at the same time, and also due to the difficulty of signal readout from such a low-
impedance system.
Joule heating
Joule heating, also known as resistive, resistance, or Ohmic heating, is the process by which the passage of an electric current through a conductor (material), conductor produces heat.
Joule's first law (also just Joule's law), also known in c ...
in a current-biased TES can lead to thermal runaway that drives the detector into the normal (non-superconducting) state, a phenomenon known as positive
electrothermal feedback In electronics, electrothermal feedback is the interaction of the electric current and the temperature in a device with a temperature-dependent electrical resistance. This interaction arises from Joule heating.
The temperature-dependence of the ...
. The thermal runaway problem was solved in 1995 by K. D. Irwin by voltage-biasing the TES, establishing stable negative
electrothermal feedback In electronics, electrothermal feedback is the interaction of the electric current and the temperature in a device with a temperature-dependent electrical resistance. This interaction arises from Joule heating.
The temperature-dependence of the ...
, and coupling them to superconducting quantum interference devices (
SQUID
True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...
) current amplifiers. This breakthrough has led to widespread adoption of TES detectors.
[K. D. Irwin and G. C. Hilton, "Transition-edge sensors", ''Cryogenic Particle Detection'', ed. C. Enss, Springer (2005), .]
Setup, operation, and readout
The TES is voltage-biased by driving a current source ''I''
bias through a load resistor ''R''
L (see figure). The voltage is chosen to put the TES in its so-called "self-biased region" where the power dissipated in the device is constant with the applied voltage. When a
photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always ...
is absorbed by the TES, this extra power is removed by negative
electrothermal feedback In electronics, electrothermal feedback is the interaction of the electric current and the temperature in a device with a temperature-dependent electrical resistance. This interaction arises from Joule heating.
The temperature-dependence of the ...
: the TES
resistance increases, causing a drop in TES current; the
Joule power
Joule heating, also known as resistive, resistance, or Ohmic heating, is the process by which the passage of an electric current through a conductor produces heat.
Joule's first law (also just Joule's law), also known in countries of former U ...
in turn drops, cooling the device back to its equilibrium state in the self-biased region. In a common
SQUID
True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...
readout system, the TES is operated in series with the input coil ''L'', which is inductively coupled to a SQUID series-array. Thus a change in TES current manifests as a change in the input
flux
Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ph ...
to the SQUID, whose output is further amplified and read by room-temperature electronics.
Functionality
Any
bolometric
A bolometer is a device for measuring radiant heat by means of a material having a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley.
Principle of operation
A bolometer ...
sensor employs three basic components: an
absorber
In Particle physics, high energy physics experiments, an absorber is a block of material used to Absorption (electromagnetic radiation), absorb some of the energy of an incident Elementary particle, particle. Absorbers can be made of a variety of ...
of incident energy, a
thermometer
A thermometer is a device that temperature measurement, measures temperature or a temperature gradient (the degree of hotness or coldness of an object). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a merc ...
for measuring this energy, and a
thermal link to base temperature to dissipate the absorbed energy and cool the detector.
[A. Lita ''et al.'', "Counting near-infrared single-photons with 95% efficiency", ''Optics Express'' 16, 3032 (2008), .]
Absorber
The simplest absorption scheme can be applied to TESs operating in the near-IR, optical, and UV regimes. These devices generally utilize a
tungsten
Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isolat ...
TES as its own absorber, which absorbs up to 20% of the incident radiation.
[A. J. Miller ''et al.'', "Demonstration of a low-noise near-infrared photon counter with multiphoton discrimination", ''Appl. Phys. Lett.'', 83, 791–793. (2003), .] If high-efficiency detection is desired, the TES may be fabricated in a multi-layer
optical cavity An optical cavity, resonating cavity or optical resonator is an arrangement of mirrors or other optical elements that forms a cavity resonator for light waves. Optical cavities are a major component of lasers, surrounding the gain medium and provi ...
tuned to the desired operating wavelength and employing a backside mirror and frontside anti-reflection coating. Such techniques can decrease the transmission and reflection from the detectors to negligibly low values; 95% detection efficiency has been observed.
[ At higher energies, the primary obstacle to absorption is transmission, not reflection, and thus an absorber with high photon stopping power and low heat capacity is desirable; a ]bismuth
Bismuth is a chemical element with the Symbol (chemistry), symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental ...
film is often employed.[ Any absorber should have low ]heat capacity
Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to an object to produce a unit change in its temperature. The SI unit of heat capacity is joule per kelvin (J/K).
Heat capacity i ...
with respect to the TES. Higher heat capacity in the absorber will contribute to noise and decrease the sensitivity of the detector (since a given absorbed energy will not produce as large of a change in TES resistance). For far-IR radiation into the millimeter range, the absorption schemes commonly employ antennas
In radio engineering, an antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver. In transmission, a radio transmitter supplies a ...
or feedhorn
A feed horn (or feedhorn) is a small horn antenna used to couple a waveguide to e.g. a parabolic dish antenna or offset dish antenna for reception or transmission of microwave. A typical application is the use for satellite television recept ...
s.
Thermometer
The TES operates as a thermometer in the following manner: absorbed incident energy increases the resistance of the voltage-biased sensor within its transition region, and the integral of the resulting drop in current is proportional to the energy absorbed by the detector.[ The output signal is proportional to the temperature change of the absorber, and thus for maximal sensitivity, a TES should have low heat capacity and a narrow transition. Important TES properties including not only heat capacity but also thermal conductance are strongly temperature dependent, so the choice of ]transition temperature
Transition temperature is the temperature at which a material changes from one crystal state (allotrope) to another. More formally, it is the temperature at which two crystalline forms of a substance can co-exist in equilibrium. For example, when ...
''T''c is critical to the device design. Furthermore, ''T''c should be chosen to accommodate the available cryogenic system. Tungsten has been a popular choice for elemental TESs as thin-film tungsten displays two phases, one with ''T''c ~15 mK and the other with ''T''c ~1–4 K, which can be combined to finely tune the overall device ''T''c. Bilayer and multilayer TESs are another popular fabrication approach, where thin film
A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many ap ...
s of different materials are combined to achieve the desired ''T''c.
Thermal conductance
Finally, it is necessary to tune the thermal coupling between the TES and the bath of cooling liquid; a low thermal conductance is necessary to ensure that incident energy is seen by the TES rather than being lost directly to the bath. However, the thermal link must not be too weak, as it is necessary to cool the TES back to bath temperature after the energy has been absorbed. Two approaches to control the thermal link are by electron–phonon coupling and by mechanical machining. At cryogenic temperatures, the electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no kn ...
and phonon
In physics, a phonon is a collective excitation in a periodic, Elasticity (physics), elastic arrangement of atoms or molecules in condensed matter physics, condensed matter, specifically in solids and some liquids. A type of quasiparticle, a phon ...
systems in a material can become only weakly coupled. The electron–phonon thermal conductance is strongly temperature-dependent, and hence the thermal conductance can be tuned by adjusting ''T''c. Other devices use mechanical means of controlling the thermal conductance such as building the TES on a sub-micrometre membrane over a hole in the substrate or in the middle of a sparse "spiderweb" structure.[J. Bock ''et al.'', "A novel bolometer for infrared and millimeter-wave astrophysics", ''Space Science Reviews'', 74, 229–235 (1995), .]
Advantages and disadvantages
TES detectors are attractive to the scientific community for a variety of reasons. Among their most striking attributes are an unprecedented high detection efficiency customizable to wavelengths from the millimeter regime to gamma rays and a theoretical negligible background dark count level (less than 1 event in 1000 s from intrinsic thermal fluctuations
In statistical mechanics, thermal fluctuations are random deviations of a system from its average state, that occur in a system at equilibrium.In statistical mechanics they are often simply referred to as fluctuations. All thermal fluctuations b ...
of the device). (In practice, although only a real energy signal will create a current pulse, a nonzero background level may be registered by the counting algorithm or the presence of background light in the experimental setup. Even thermal blackbody radiation
Black-body radiation is the thermal electromagnetic radiation within, or surrounding, a body in thermodynamic equilibrium with its environment, emitted by a black body (an idealized opaque, non-reflective body). It has a specific, continuous spect ...
may be seen by a TES optimized for use in the visible regime.)
TES single-photon detectors suffer nonetheless from a few disadvantages as compared to their avalanche photodiode
An avalanche photodiode (APD) is a highly sensitive semiconductor photodiode detector that exploits the photoelectric effect to convert light into electricity. From a functional standpoint, they can be regarded as the semiconductor analog of pho ...
(APD) counterparts. APDs are manufactured in small modules, which count photons out-of-the-box with a dead time
For detection systems that record discrete events, such as particle and nuclear detectors, the dead time is the time after each event during which the system is not able to record another event.
An everyday life example of this is what happens when ...
of a few nanoseconds and output a pulse corresponding to each photon with a jitter of tens of picoseconds. In contrast, TES detectors must be operated in a cryogenic environment, output a signal that must be further analyzed to identify photons, and have a jitter of approximately 100 ns. Furthermore, a single-photon spike on a TES detector lasts on the order of microseconds.
Applications
TES arrays are becoming increasingly common in physics and astronomy experiments such as SCUBA-2, the HAWC+ instrument on the Stratospheric Observatory for Infrared Astronomy
The Stratospheric Observatory for Infrared Astronomy (SOFIA) was an 80/20 joint project of NASA and the German Aerospace Center (DLR) to construct and maintain an airborne observatory. NASA awarded the contract for the development of the aircraf ...
, the Atacama Cosmology Telescope
The Atacama Cosmology Telescope (ACT) is a cosmological millimeter-wave telescope located on Cerro Toco in the Atacama Desert in the north of Chile. ACT makes high-sensitivity, arcminute resolution, microwave-wavelength surveys of the sky in ord ...
, the Cryogenic Dark Matter Search
The Cryogenic Dark Matter Search (CDMS) is a series of experiments designed to directly detect particle dark matter in the form of Weakly Interacting Massive Particles (or WIMPs). Using an array of semiconductor detectors at millikelvin temperatur ...
, the Cryogenic Rare Event Search with Superconducting Thermometers
The Cryogenic Rare Event Search with Superconducting Thermometers (CRESST) is a collaboration of European experimental particle physics groups involved in the construction of cryogenic detectors for direct dark matter searches. The participating in ...
, the E and B Experiment
The E and B Experiment (EBEX) will measure the cosmic microwave background radiation of a part of the sky during two sub-orbital (high-altitude) balloon flights. It is an experiment to make large, high-fidelity images of the CMB polarization aniso ...
, the South Pole Telescope
The South Pole Telescope (SPT) is a diameter telescope located at the Amundsen–Scott South Pole Station, Antarctica. The telescope is designed for observations in the microwave, millimeter-wave, and submillimeter-wave regions of the electrom ...
, the Spider polarimeter, the X-IFU instrument of the Advanced Telescope for High Energy Astrophysics
Advanced Telescope for High-ENergy Astrophysics (''Athena'') is an X-ray observatory mission selected by European Space Agency (ESA) within its Cosmic Vision program to address the Hot and Energetic Universe scientific theme. ''Athena'' will ...
satellite, the futur
LiteBIRD
Cosmic Microwave Background polarization experiment, the Simons Observatory
The Simons Observatory is located in the high Atacama Desert in Northern Chile inside the Chajnator Science Preserve, at an altitude of 5,200 meters (17,000 ft). The Atacama Cosmology Telescope (ACT) and the Simons Array are located nearby an ...
, and the CMB Stage-IV Experiment.
See also
* Bolometer
A bolometer is a device for measuring radiant heat by means of a material having a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley.
Principle of operation
A bolometer ...
* Cryogenic particle detectors Cryogenic particle detectors operate at very low temperature, typically only a few degrees above absolute zero. These sensors interact with an energetic elementary particle (such as a photon) and deliver a signal that can be related to the type of ...
References
{{reflist
Superconducting detectors
Radiometry
Sensors
Particle detectors