Abstract

For more than 20 years lidar systems have been used to study the chemistry and dynamics of the upper atmosphere above 70 km altitude. A variety of important minor atmospheric constituents have resonance lines in the near IR to near UV region of the optical spectrum which can be probed with exceptional sensitivity and resolution using resonance fluorescence lidar techniques. The most widely studied have been atomic Na, Fe, Li, K, Ca, and Ca+. Sodium is especially important because the fine structure of the D2 resonance line can now be probed with sufficient spectral resolution to deduce temperature and Doppler winds. To be most useful for studies related to global change issues, measurements of these constituents and parameters must be obtained with high resolution and accuracy. Measurement resolution ~100 s and ~100 m and accuracies ~1 K, ~0.5 m/s, and ~1% in density are needed. This performance can be achieved with laser power levels ~10 W, linewidths <100 MHz, and frequency stability better than 1 MHz. In the field of astronomy, sodium lidar techniques are now being developed for creating artificial guide stars in the upper atmosphere that can be used with ground based adaptive telescopes to compensate image distortion caused by atmospheric turbulence. To create a laser guide star that is sufficiently small and bright to adaptively compensate a 2 m class telescope, also requires power levels ~10 W. The required pulse rate is ~100 pps, the pulse length is ~50 microsec, the optium bandwidth is ~600 MHz, and the beam divergence can be no larger than a few microrad. The laser requirements for both of these applications present significant challenges to the laser designer. Some of the current designs and their limitations are discussed.

© 1991 Optical Society of America

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