Bolometer

A bolometer also bolometric detector (Greek symbols " throw ", " beam " ), is a radiation sensor for the measurement over the entire wavelength range. The measuring principle is absorption and heating.

Inventor was the American astronomer Samuel Pierpont Langley in 1878.

For absorption serve blackened surfaces. For the measurement of the temperature rise of power pulses is evaluated. For the continuous measurement of the radiation power, the heat must be dissipated. These are defined thermal bridges that exist for the measurement of large benefits from solid metal and are water cooled at the other end. The measured quantity is the heat flow and results from the temperature difference across the thermal bridge divided by its thermal resistance.

The temperature sensors are used due to their simplicity thermistors question. In the imaging microbolometer arrays NTCs are used, since they have a steeper curve, but connected only in a relatively narrow temperature range and in a small design with considerable shot noise.

The alternatives are the thermocouples that measure temperature differences directly. For a higher thermal stress more thermocouples are electrically connected in series, but thermally in parallel. Often, such a thermopile even the entire thermal bridge dar.

This is also true for the most sensitive detectors of only a single thermocouple made ​​of very thin wires or thin film structures. If you can - unlike the pyrgeometers - the focus on the radiation to be measured a contact of the thermocouple, so the need for extra absorber surface, which should be very thin and very good thermal conductivity for short reaction times, eg a gold foil.

The inclusion in a vacuum reduces external interference by heat transfer to air or convection. The temperature of the surrounding parts of the detector must be accurately controlled, gold-plated surfaces emit less heat radiation. The highest sensitivity is achieved with cryogenic bolometers.