A Bolometers is an element which Senses optical input and delivers thermal output.
Bolometers are radiation detectors that operate based on the principle of measuring the change in a measurable quantity resulting from the absorption of radiation.
The most common type of bolometer is the resistive bolometer, which measures the change in resistance induced by the absorption of radiation and then measures the resulting current/voltage change.
This change in current/voltage is proportional to the absorbed power.
The absorbed radiation causes a resultant temperature rise in the bolometer, which is detected by measuring the change in bolometer resistance by means of an auxiliary bridge circuit.
The bridge circuit is used to nullify the resistance change, and the resulting voltage difference in the bridge circuit is proportional to the change in resistance, which in turn is proportional to the absorbed power.