A bolometer is a highly sensitive instrument used for detecting heat or electromagnetic radiation. This instrument was invented by Samuel Pierpont Langley, an American astronomer, in 1878. A bolometer was initially used in combination with a telescope to quantify infrared radiation.
The first bolometer used by Langley consisted of two lampblack-coated platinum strips that essentially formed two branches of a Wheatstone bridge connected to a galvanometer and battery. One strip was exposed to radiation and the other was shielded from radiation.
Electromagnetic radiation falling on the exposed strip would heat it and change its resistance. However, a modified version of Langley's bolometer was introduced in 1880, and it was proved to detect thermal radiation.
Working of Bolometers
A bolometer consists of an absorptive element made up of a thin metal layer. The absorptive element is connected to a thermal reservoir via a thermal link. When a radiation strikes the absorptive element, its temperature is increased above the reservoir’s temperature due to the absorption of radiation by the absorptive element.
The intrinsic thermal time constant is equal to the ratio of heat capacity between the reservoir and the absorptive element. Thus, the change in temperature can be directly measured using a resistive thermometer attached to the absorptive element. In some cases, the resistance of the absorptive element itself is used to measure the temperature change.
Benefits of Bolometers
The key benefits of bolometers include the following:
- They are extremely efficient in terms of sensitivity and energy resolution when compared to other conventional particle detectors.
- They operate at room temperature and hence do not require cooling.
- They can also measure non-ionizing particles in addition to ionizing particles and photons.
Applications of Bolometers
Some of the major applications of bolometers are listed below:
- In thermal cameras
- In particle detectors
- Detection of concealed weapons
- In fingerprint scanners
- Air surveillance
- Detection of forest fire
- Astronomical applications.