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).