Bolometers are used for the measurement of

Bolometers are used for the measurement of

Right Answer is:

Any of the above

SOLUTION

  • A bolometer is a very sensitive electrical resistance thermometer that is used to detect and measure weak thermal radiation.
  • Consequently, it is especially well suited as an IR detector.
  • They measure the temperature changes caused by the power changes in the incident optical radiation.
  • A bolometer converts the temperature changes into electrical signal- changes that can be measured.
  • The bolometer used in older instruments consisted of a thin metal conductor, such as the platinum wire.
  • Incident IR radiation heats up this conductor, which causes its electrical resistance to change.
  • The degree of change of the conductor’s resistance is a measure of the amount of radiation that has fallen on the detector.
  • In the case of platinum, the resistance change is 0.4% per °C.
  • The change in temperature depends on the intensity of incident radiation and on the thermal capacity of the detector.
  • It is important to use a small detector and to focus the radiation on it.
  • The rate at which the detector heats up or cools down determines how fast the detector responds to a change in radiation intensity as experienced when an absorption band is recorded.
  • This constitutes the response time of the detector.
  • For these older types of bolometers, the response time is long, on the order of seconds.
  • Consequently, a complete mid-IR scan using a dispersive instrument and halometer could take 20 min.
  • The modern bolometer is micro-machined from silicon.
  • This type of halometer is only a few micrometers in diameter and is usually placed in one arm of a Wheatstone bridge for measurements.
  • The modern micro-bolometer has a fast response time and is particularly useful for detecting far-IR radiation (600-20 cm−1).
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