Pressure-scanned Fabry-Perot interferometer for nightglow measurements: its construction and operation.

A very flexible system for pressure-scanning a Fabry-Perot interferometer is described. The pressure in the interferometer chamber is altered in small steps, allowing the frequency of transmission to stay fixed during the integration time in contrast to continuously scanning systems, which give a distortion of the line profile for long integration times. The system is highly linear, and the pressure scanning range, the pressure change per step (i.e., the resolution), and the integration time per channel are variable within wide limits.