Measuring velocity by doppler shift of laser radiation

摘要

A laser doppler velocity measuring system in which a CO2 laser 4 illuminates a volume 2 of interest in the atmosphere, and laser radiation reflected off particles in this volume 2 is mixed on a detector 11 with a local oscillator signal direct from the laser 4, is characterised in that the laser frequency is locked to a desired frequency, e.g. the P20 line, by a feedback signal derived via a highly selective etalon filter 14, whereby the laser cavity is adjusted to give maximum local oscillator signal on the detector 11, which corresponds to the wanted frequency.