Bolometer

Source: Wikipedia, the free encyclopedia.

cosmic microwave background radiation. Image credit: NASA/JPL-Caltech
.

A bolometer is a device for measuring

Samuel Pierpont Langley
.

Principle of operation

thermal conductance
, G. The temperature increase is ΔT = P/G and is measured with a resistive thermometer, allowing the determination of P. The intrinsic thermal time constant is τ = C/G.

A bolometer consists of an absorptive element, such as a thin layer of metal, connected to a thermal reservoir (a body of constant temperature) through a thermal link. The result is that any radiation impinging on the absorptive element raises its temperature above that of the reservoir – the greater the absorbed power, the higher the temperature. The intrinsic thermal time constant, which sets the speed of the detector, is equal to the ratio of the

cryogenic
temperatures, enabling significantly greater sensitivity.

Bolometers are directly sensitive to the energy left inside the absorber. For this reason they can be used not only for ionizing particles and photons, but also for non-ionizing particles, any sort of radiation, and even to search for unknown forms of mass or energy (like dark matter); this lack of discrimination can also be a shortcoming. The most sensitive bolometers are very slow to reset (i.e., return to thermal equilibrium with the environment). On the other hand, compared to more conventional particle detectors, they are extremely efficient in energy resolution and in sensitivity. They are also known as thermal detectors.

Langley's bolometer

The first bolometers made by Langley consisted of two

Fraunhofer lines. He also discovered new atomic and molecular absorption lines in the invisible infrared portion of the electromagnetic spectrum. Nikola Tesla personally asked Dr. Langley whether he could use his bolometer for his power transmission experiments in 1892. Thanks to that first use, he succeeded in making the first demonstration between West Point and his laboratory on Houston Street.[8]

Applications in astronomy

While bolometers can be used to measure radiation of any frequency, for most

mK[9]). Notable examples of bolometers employed in submillimeter astronomy include the Herschel Space Observatory, the James Clerk Maxwell Telescope, and the Stratospheric Observatory for Infrared Astronomy (SOFIA). Recent examples of bolometers employed in millimeter-wavelength astronomy are AdvACT, BICEP array, SPT-3G and the HFI camera on the Planck satellite, as well as the planned Simons Observatory, CMB-S4 experiment,[10] and LiteBIRD
satellite.

Applications in particle physics

The term bolometer is also used in particle physics to designate an unconventional particle detector. They use the same principle described above. The bolometers are sensitive not only to light but to every form of energy. The operating principle is similar to that of a

cryogenic temperature
. They can still be considered to be at the developmental stage.

Applications in plasma physics

Bolometers play a pivotal role in monitoring radiation in fusion plasmas. The

electron cyclotron resonance heating (ECRH). In terms of hardware, the W7-X bolometers are equipped with metal-resistive detectors. These are distinguished by a 5 μm thick gold absorber, sized 1.3 mm in the poloidal direction and 3.8 mm toroidally, mounted on a ceramic (silicon nitride Si3N4) substrate. The inclusion of a 50 nm carbon layer is strategic, enhancing the detection efficiency for low-energy photons. These detectors are notably attuned to impurity line radiation, covering a spectrum from the very ultraviolet (VUV) to soft x-rays (SXR). Given their resilience and innovative design, they are being considered as prototypes for the upcoming ITER bolometer detectors.[11][12]

Microbolometers

Main article: Microbolometer

A

electrical resistance. This resistance change is measured and processed into temperatures which can be represented graphically. The microbolometer grid is commonly found in three sizes, a 640×480 array, a 320×240 array (384×288 amorphous silicon) or less expensive 160×120 array. Different arrays provide the same resolution with larger array providing a wider field of view.[citation needed
] Larger, 1024×768 arrays were announced in 2008.

Hot electron bolometer

The hot electron bolometer (HEB) operates at

thermal conductance
is the electron-phonon thermal conductance.

If the

superconducting materials at low temperature. If the absorbing element does not have a temperature-dependent resistance, as is typical of normal (non-superconducting) metals at very low temperature, then an attached resistive thermometer can be used to measure the electron temperature.[3]

Microwave measurement

A bolometer can be used to measure power at microwave frequencies. In this application, a resistive element is exposed to microwave power. A dc bias current is applied to the resistor to raise its temperature via Joule heating, such that the resistance is matched to the waveguide characteristic impedance. After applying microwave power, the bias current is reduced to return the bolometer to its resistance in the absence of microwave power. The change in the dc power is then equal to the absorbed microwave power. To reject the effect of ambient temperature changes, the active (measuring) element is in a bridge circuit with an identical element not exposed to microwaves; variations in temperature common to both elements do not affect the accuracy of the reading. The average response time of the bolometer allows convenient measurement of the power of a pulsed source.[14]

In 2020, two groups reported microwave bolometers based on graphene-based materials capable of microwave detection at the single-photon level.[15][16][17]

See also

References

  1. ^ "Langley's Bolometer, 1880-1890". Science Museum Group. Retrieved 20 March 2022.
  2. ^ See, for example, bolometers – Definition from the Merriam-Webster Online Dictionary
  3. ^
    doi:10.1063/1.357128
    .
  4. ^ Langley, S. P. (23 December 1880). The "Bolometer". American Metrological Society. p. 1–7.
  5. JSTOR 25138616
    .
  6. ^ Samuel P. Langley Biography (Archived 2009-11-06 at the Wayback Machine). High Altitude Observatory, University Corporation for Atmospheric Research.
  7. ^ "Samuel Pierpont Langley". earthobservatory.nasa.gov. 3 May 2000.
  8. ^ Tesla, Nikola (1992). "section 4". NIKOLA TESLA ON HIS WORK WITH ALTERNATING CURRENTS and Their Application to Wireless Telegraphy, Telephony and Transmission of Power : An Extended Interview. Leland I. Anderson.
    ISBN 978-1-893817-01-2
    . I suppose I had hundreds of devices, but the first device that I used, and it was very successful, was an improvement on the bolometer. I met Professor Langley in 1892 at the Royal Institution. He said to me, after I had delivered a lecture, that they were all proud of me. I spoke to him of the bolometer, and remarked that it was a beautiful instrument. I then said, "Professor Langley, I have a suggestion for making an improvement in the bolometer, if you will embody it in the principle." I explained to him how the bolometer could be improved. Professor Langley was very much interested and wrote in his notebook what I suggested. I used what I have termed a small-mass resistance, but of much smaller mass than in the bolometer of Langley, and of much smaller mass than that of any of the devices which have been recorded in patents issued since. Those are clumsy things. I used masses that were not a millionth of the smallest mass described in any of the patents, or in the publications. With such an instrument, I operated, for instance, in West Point—I received signals from my laboratory on Houston Street in West Point.
  9. ISBN 9781644900741
    .
  10. ^ "CMB-S4 – CMB-S4 Next Generation CMB Experiment". cmb-s4.org.
  11. S2CID 3856215
    .
  12. S2CID 238641528
    .
  13. PMID 10011570
    .
  14. ISBN 0-471-27053-9
    pages 2736–2739
  15. S2CID 202565642. Archived
    from the original on 5 October 2020.
  16. S2CID 221095927. Archived
    from the original on 5 October 2020.
  17. ^ Johnston, Hamish (5 October 2020). "New microwave bolometers could boost quantum computers". Archived from the original on 8 October 2020.

External links

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