Fast bolometric detection

With the advent of heat pulse measurements in solids and helium there is a need for fast bolometers. For if the detector time constant is < approximately 1/3fsub(max) where fsub(max) is the highest frequency component of the time varying signal, the detector output follows the incident flux. Although in principle the same information can be obtained from a slow detector the information cannot be directly assimilated but needs deconvolution. It is described how the much used graphite film bolometers can be constructed so that they have a time constant of a few microseconds. In essence the graphite film bolometer is made by painting or spraying a colloidal suspension of graphite onto an insulating substrate. The resistance of the thin film is measured by having a constant standing current and monitoring the voltage. It operates by the incident energy flux warming the graphite which lowers its resistance and changes the voltage across it. Besides its simplicity, graphite has the property of responding to all phonon frequencies and hence is a total energy detector. (Auth.)