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Abstract

A laser radar system capable of measuring windspeed to within 1 m/s at distances in the range of 10 km. The system comprises two fast atomic line filter-detectors, a first filter-detector and a second filter-detector, in which a metal vapor is excited by signal light and further excited to a Rydberg level by a pump laser beam. An electric field is applied to the filters which ionizes the atoms. The filter-detectors operate at one of the resonance absorption peaks of the metal vapor. The second filter-detector is also subject to a magnetic field which splits the absorption peak of the vapor into two absorption peaks leaving a valley in the position of the original absorption peak. A preferred lasing frequency range is a frequency range covering a portion of one of the slopes of the peak of the first filter and a portion of one of the opposite direction slopes of one of the peaks of the second filter. Within this range an increase in the frequency of signal light will result in a greater fraction of the light detected by one filter-detector and a smaller fraction detected by the other filter-detector and a decrease in the frequency of the signal light will have the opposite effect. In a preferred embodiment of this invention laser pulses from a laser operating near the midpoint of the preferred frequency range are beamed at a target which could be a windy portion of the atmosphere. Backscattered doppler shifted light from aerosols and particles in the atmosphere are collected by a telescope split into two parts, one part being directed to each filter-detector. The intensities of the light detected by the filter-detector are compared and the relative magnitudes are used to determine the windspeed in the direction of the laser beam. Pulses can be made very short and the travel time of the light is used to determine the range so that a map of windspeed as a function of range is provided in the direction of the laser beam.

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First Claim